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Splitting stars – for us and for you!

We are experienced amateur astronomers who especially enjoy viewing double stars with long-focus refractors.  This journal is a record of our observations, but we also hope it will serve as a guide to you to help you plan observing sessions and choose double stars you want to observe.  In the column to the left you’ll find a drop down menu listing the doubles in this blog by constellation – and to the right there’s a list of our 10 most recent observations. Finally, you have two other choices:

  • First, you can read  our observations of a double and leave your own observations of that same star as a comment.
  • Second, you can subscribe to this blog so that you get email notifications when we add a star to it. Just check out the links in the right-hand column.

We’d love to hear from you regarding your own observations of the same doubles.

The Double Stars of Collinder 65, Part Two: OΣ 107, OΣ 108, HJ 3274, and HJ 3275

Now on to the last group of double stars in CR 65, which are located in the north part of the cluster.  If you missed part one, you can get to it by clicking on this link.

Here are our charts once again, starting first with a wide view:

Stellarium screen image with labels added, click for a larger view.

Stellarium screen image with labels added, click for a larger view.

And here are the finder views with the distances shown, starting with an erect image view:

This is an erect image chart, which will match the orientation you see in an RACI (right angle,correct image) 8x50 finder. (Stellarium screen image, labels added, click to enlarge).

This is an erect image chart, which will match the orientation you see in an RACI (right angle,correct image) 8×50 finder. (Stellarium screen image, labels added, click to enlarge).

And here’s the mirror-reversed image for use at the eyepiece of a refractor or SCT:

Stellarium screen image, labels added, click to enlarge:

Stellarium screen image, labels added, click to enlarge:

We’ll begin with an Otto Wilhlem von Struve discovery, OΣ 107. If you start at S 478, aka 111 Tauri, which is located near the middle of the west edge of CR 65, you’ll find OΣ 107 located 52’ to the northeast. If you have any influence with the sky guys and/or gals who control the seeing, give ‘em a call on the celestial night line – it’ll make things easier!

OΣ 107 (STT 107)         HIP: 25499    SAO: 94554
RA: 05h 27.2m    Dec: +17° 58’

Identifier  Magnitudes Separation  PA WDS
MCA 19 Aa, Ab:   5.80,  6.80      0.10″    89°  2007
STT 107 AB:   5.39, 10.10     10.30″  306°  1998
STT 107 AC:   5.39, 11.80     10.10″  346°  1998
STT 107 BC: 10.10, 11.80      7.00″    59°  2012

Distance: 549 Light Years (Simbad)
Spectral Classifications: “A” is B5, “B” is F8

On first glance, this scene reminded me of the alignment of Σ 697, which was the last star we looked at in part one. Alluring as the scene is, though, the two stars lined up to the west of the primary are not cataloged as part of OΣ 107.

In fact, you’ll have to look at the inset to see the “B” and “C” companions of the primary.   (East & west are reversed here to match the refractor image, click on the sketch for a better view of the close companions).

In fact, you’ll have to look at the inset to see the “B” and “C” companions of the primary.  Also shown here to the northwest of the primary is TDS 3195 with magnitudes of 10.6 and 10.98, separated by 0.4″ at 62 degrees (WDS 1991) — a bit beyond my reach!   (East & west are reversed here to match the refractor image, click on the sketch for a better view of the close companions).

I had a devil of a time prying both “B” and “C” out of the glare of the primary using the five inch refractor, but persistence finally paid off.  Not surprisingly, “B” popped into view first, and once I had it, patience added to more persistence finally resulted in “C” making an appearance.  The seeing was about average, although it was wavering between II and III on this chart.  The trick was to sit and wait for moments of good seeing and then to be quick with the eye.  It took several glimpses before I was convinced I was looking at “C”, and I went back later with a six inch refractor to confirm I had it.

Click to enlarge.

Click to enlarge.

There hasn’t been much change over the years in the measures of the AB and AC pairs, as can be seen in the excerpt at the right from William Hussey’s book on Otto Struve’s double star discoveries.  The position angle for AB measured in 1842 by Mädler (Ma) is at odds with the other measures, but otherwise, the PA’s average out to about 307°.

As for AC, it’s obvious from Hussey’s narrative the “C” component is difficult to measure (Otto Struve estimated the position angle), which probably is due to the glare caused by the primary. Hussey also found “C” was difficult because of its faintness, even with the twelve inch refractor at Lick Observatory. The most recent position angle in the WDS, 346°, seems to be at odds with the data in Hussey’s list, which probably is a further indication of the difficulty in measuring it.

I checked several photos of STT 107 in hopes I could get a measurement for both AB and AC, but the primary is so bright it blots out the “B” and “C” components.   There’s very little proper motion in the primary, +008 -021 (.008”/yr east, .021”/yr south), which corresponds with the minor change in the AB pair, but there’s no proper motion data on either “B” or “C”.

Now we’ll move on to OΣ 107’s sibling, OΣ 108, which is a short 39′ jaunt northeast from our current location.   Once you have it in view, you’ll find it’s accompanied by HJ 3275 to its northeast. (Here’s the erect image chart again, and the mirror-image chart).

OΣ 108 (STT 108)         HIP: 25702    SAO: 94586
RA: 05h 29.3m   Dec: +18° 22’
Magnitudes: 6.77, 10.42
Separation:  3.2”
Position Angle: 130° (WDS 1994)
Distance: 609 Light Years (Simbad)
Spectral Classification: “A” is A2

This is another tight pair which is made more difficult by a large magnitude difference, in this case a spread of 3.65 magnitudes.   I used the same procedure described above in order to catch a glimpse of the secondary with the five inch Meade, and made a second visit with a six inch refractor in order to confirm it.

This hand-full of scattered starlight includes all three of our remaining stars.   The secondary of OΣ 108 is visible in the upper inset on the right. The inset below, which is included for identification purposes, represents the same magnification as the larger sketch.   (East & west reversed once more, click on the sketch for a much better view).

This hand-full of scattered starlight includes all three of our remaining stars. The secondary of OΣ 108 is visible in the upper inset on the right. The inset below, which is included for identification purposes, represents the same magnification as the larger sketch. (East & west reversed once more, click on the sketch for a much better view).

Click to enlarge.

Click to enlarge.

Hussey’s 1898 observations of OΣ 108 are shown at the right, along with Otto Struve’s 1849 observation and four additional observations Hussey took from Burnham’s 1906 catalog.   Apart from Otto Struve’s 1849 position angles of 137.1° and 139.5°, the measures shown are pretty consistent.  Comparing that data with the 1994 position angle and separation in the WDS, it looks like this pair has moved slightly closer.  At the bottom of that page, I also included three later observations which come from R.G. Aitken’s 1932 New General Catalogue of Double Stars Within 120° of the North Pole, which continue the consistency in position angle and separation.

There isn’t much proper motion in the case of either star, but what stands out in the WDS data is the two stars are moving parallel to each other, with the primary moving at a rate of -015 -005 (.015”/yr west, .005”/yr south) and the secondary at a rate of -013 -004 (.013”/yr west, .004”/yr south).  That would indicate the measurable change in PA and separation should be negligible, or at least less than what the 1994 WDS measures indicate.  It’s possible the close proximity of the two stars, along with the wide magnitude difference, also makes this a tough pair to measure.  At any rate, since the last WDS date of measure is 1994, it looks like this pair could use an update.

Also included on the sketch above are two John Herschel discoveries, one of which was supplemented with additions by S.W. Burnham and Robert G. Aitken.

HJ 3275        HIP: 25745   SAO: 94589
RA: 05h 29.8m   Dec: +18° 25’

Identifier Magnitudes Separation  PA WDS
Bu 891 AB:  7.65, 13.60     10.60″ 128°  2000
HJ 3275 AC:  7.65,  8.22     56.30″   21°  2011
A 2433 CD:  8.22, 11.98      1.40″ 254°  1999

Distance: 567 Light Years (Simbad)
Spectral Classifications: “A” is A0, “C” is F

HJ 3274      No HIP or SAO Number
05h 29.7m   Dec: +18° 19’
Magnitudes: 11.04, 11.23
Separation:   5.3”
Position Angle: 107° (WDS 2000)
No distance or spectral classification in Simbad or WDS

Click to enlarge!

Click to enlarge!

John Herschel’s observations of HJ 3274 and HJ 3275 are shown at the left, but if you look at his data, you’ll see what appear to be estimates for HJ 3274 and no data at all, apart from magnitudes, on HJ 3275, which he describes as a “coarse double star” (probably a reference to their separation).   Also included on that page are his observations of Σ 697 and Σ 730, which were covered in part one of these posts on CR 65 (source).

HJ 3274 is the less impressive of the pair, and it takes an observant eye to catch the two faint stars. I wasn’t aware it of it when I first looked at this field, but as I was studying HJ 3275 I caught a hint of its duplicity out of the corner of my eye. When I gave it more attention, I was able to pry the secondary loose without too much effort.

HJ 3275 is the more interesting of the two, mainly because it’s been expanded from the two obvious components to include two more members, both of which are difficult to catch.

Click to enlarge.

Click to enlarge.

R.G. Aitken first caught sight of the tough CD pair in 1912, which was well beyond my seeing-limited reach on the two nights I looked for it.   I found that observation in his 1932 New General Catalogue, which includes measures for the AB pair (β 891) as well as the AC pair (h 3275), also referred to by Aitken as number 64 in Otto Struve’s appendix catalog. He expands the historical record even further when he refers to A 2433 as having been cataloged as JC 883. The JC refers to W.S. Jacob, whose observation I was unable to locate, although I did find several of his star catalogs. (Here’s more information on Jacob, who was an interesting observer in his own right).

S.W. Burnham was the first person to excavate the 13.60 magnitude “B” component from the 7.65 magnitude glare of the primary, using the 18 ½ inch refractor at Dearborn Observatory in 1879 (that observation is shown above in Aitken’s catalog).

Click to enlarge.

Click to enlarge.

If you compare Burnham and Aitken’s data, you’ll see the position angle of the AB pair meanders from 121.6° (1879) to 126.7° (1891) to 122.2° (1898) to 126.2° (1910) to 128.5° (1917), while the separation remains in the 10.6” range except for Burnham’s 1879 measure. More than likely the glare of the primary also makes this pair difficult to measure.

Burnham’s perceptive eye also detected an increase in separation taking place between “A” and “C”, which is confirmed by looking at the WDS proper motion numbers. This Aladin photo, with the aid of an overlay from Simbad, shows why the distance between the two stars is slowly increasing:

This is an erect image, so east and west are opposite of my sketch above.   Click for a better view.

This is an erect image, so east and west are opposite of my sketch above. Click for a better view.

There’s no proper motion data for the “B” component, but based on the 2000 WDS separation for AB at 10.60”, which is essentially the same as Burnham and Aitken’s data, it appears the two stars may be moving in tandem with each other.
_____________________________

There’s one other aspect of the Collinder 65 cluster worth looking at, which is the relation of the various stars to each other.  Normally an open cluster is a group of stars with similar distances, most of which are moving in the same direction.  For example, here’s a listing of the brighter stars in the Hyades cluster (the distances in black are members of the cluster), which is located fourteen degrees west of CR 65.  (That chart is included at end of this rollickingly informative post).

Compare that chart with this one showing the major luminaries of CR 65 . . . . . . .

Star    Dist (LY)      PM RV (km/s)
S 478          47
110 Tau        407
STT 107        549 +008 -021   +14.9
113 Tau        565 +001 -006   +27.2
HJ 3275        567 +003 -039     +1.0
STT 108        609  -015 -005
117 Tau        613 +017 -045
116 Tau        685
STF 697        874
STF 730      2991
 ———  ———-
122 Tau        158
120 Tau      1552
119 Tau      1791

. . . . . . . and you find the stellar distances are nowhere near as similar as those of the Hyades.   I highlighted three stars in red with similar distances, and another pair in green.   The three in red do in fact have similar proper motions, indicating a possible physical relation.  However, in order to get a three-dimensional view of what’s taking place, I included their radial velocities (RV), which tells us how fast the stars are moving towards us or away from us (in this case, away from us).   Adding that third dimension leads to the opposite conclusion.  As for the two stars in green, the proper motions are all we need to determine they’re unrelated.

I also expanded the boundary of CR 65 a bit to take in the last three stars at the bottom of the list, just to see if any of them might have distances similar to a few of those within the boundaries of the cluster – and it’s obvious they don’t.

So whatever criteria Collinder used for grouping this scattering of stars into a cluster, it apparently had nothing to do with their being physically related.  One more stellar mystery for the books!

Next tour will take us north of the Hyades to a small (non-clustered) group of four stars, two of which deserve to be better known than they presently are.

Clear Skies!  :cool:

The Double Stars of Collinder 65, Part One: Σ 730, S 478, and Σ 697

Located north of the head of Orion and south of the horns of Taurus is a large open cluster known as Collinder 65 (CR 65), which is unlabeled on some star charts. You’ll find it about five degrees north of Lambda (λ) Orionis, stretched out across the Orion-Taurus border. (Lambda (λ) Orionis, a beautiful multiple star better known as Meissa, is at the center of another Collinder open cluster, CR 69).

Stellarium screen image with labels added, click to enlarge.

Stellarium screen image with labels added, click to enlarge.

The diameter of CR 65 varies, ranging from 140’ (2.3°) to 220’ (3.7°), depending on which source you consult. At any rate, it’s noticeably larger than its Orion relative, CR 69.

Stellarium screen image with labels added, click for a larger view.

Stellarium screen image with labels added, click for a larger view.

Both clusters are enticing binocular objects and rival one another in aesthetic appeal. Whereas CR 69 is dominated by the beautiful cream-colored white light of Meissa, CR 65 is illuminated by a handful of fifth and sixth magnitude Flamsteed-numbered stars. Scattered within that steady starlight are half a dozen multiple stars beckoning to the yearning eyes of a double star connoisseur.

The six double stars we’re going to look at are identified here in tantalizing turquoise. (Stellarium screen image with additional labels, click to enlarge).

The six double stars we’re going to look at are identified here in tantalizing turquoise. (Stellarium screen image with additional labels, click to enlarge).

The image above is a close approximation of what you would see in an 8×50 finder. In order to find your way around and have a sense of scale, it helps to know the distances between the various points, as well as the direction from star to star.   Those morsels of information were invaluable later when I navigated from one star to the next while looking through an eyepiece.  Below is the same image as above, but with the distances and directions added:

This is an erect image chart, which will match the orientation you see in an RACI (right angle,correct image) 8x50 finder. (Stellarium screen image, labels added, click to enlarge).

This is an erect image chart, which will match the orientation you see in an RACI (right angle,correct image) 8×50 finder. (Stellarium screen image, labels added, click to enlarge).

For use at the eyepiece of a refractor or SCT, here’s a mirror-reversed image of the same scene:

Stellarium screen image, labels added, click to enlarge:

Stellarium screen image, labels added, click to enlarge:

We’ll start with Σ 730, which is located at the center of the eastern edge of CR 65.

Σ 730       HIP: 25950    SAO: 94630
(AB is also H III 93, H N 124, and Sh 58; Aa, Ab is OCC 999)
RA: 05h 32.2m   Dec: +17° 03’
Magnitudes  Aa, Ab: 7.30, 7.30   AB: 6.06, 6.44
Separations  Aa, Ab: 0.10”          AB: 9.60”
Position Angles  Aa, Ab: ?????   AB: 141° (WDS 2013)
Distance: 2991 Light Years (Simbad)
Spectral Classifications: “A” and “B are both B7

There was no doubt about the color of the AB pair – pure white.   Not included among the components of Σ 730 is the eleventh magnitude star located about 1.5’ southeast of AB at about 155 degrees. (East & west are reversed here to match the refractor view, clicking on the sketch will enlarge it).

There was no doubt about the color of the AB pair – pure white. Not included among the components of Σ 730 is the eleventh magnitude star located about 1.5’ southeast of AB at about 155 degrees. (East & west are reversed here to match the refractor view, clicking on the sketch will enlarge it).

This is a pair of stars that received attention from all the well-known double stars observers of the late 18th and early 19th centuries: William Herschel, John Herschel, James South, and F.G.W. Struve.  It began with William Herschel seemingly confusing this pair of stars with 117 Tauri (source, scroll down to sixth title):

Wm Herschel on STF 730 as H 3 93

His position angle (which translates to 142° 27’) and separation for the two stars are reasonably close . However, his identification of this pair as 117 Tauri is an error which was discovered in 1821 by John Herschel and James South when they went in search of 117 Tauri and found it was a single star. Their discussion below is very clear and easy to follow (source, scroll down to last title):

Click to enlarge.

Click to enlarge.

If you read the quotes from Herschel’s observing notes carefully, which are just past the mid-point of the page, it’s clear that William Herschel was using 117 Tauri as a reference point to reach the star now identified as Σ 730.  Herschel frequently included a Flamsteed-numbered star as a reference point in the first line of his observations, but in this case he left out the distance between 117 Tauri and the double star he observed in the published version, which led to John Herschel’s and James South’s search for it.  Fortunately, they had access to William Herschel’s notes.

Prior to the John Herschel-James South observation, William Herschel apparently observed this pair of stars a second time in 1800 and cataloged it again as H N 124 (source):

Herschel on STF 730 as HN 124

That observation is rather difficult to follow.   Apart from the coordinates, which match reasonably closely with those of Σ 730, his magnitudes of 9.9 don’t match at all, and I haven’t yet figured out what the Orion reference in the second line refers to.  I’m not all that convinced the pair of stars he described in 1800 is the same pair he saw in 1782. Nevertheless, H N 124 is treated as a duplicate of H III 93 by S.W. Burnham in his 1906 catalog, and the WDS refers to H N 124 in its notes on Σ 730.

Next, we’ll traverse the middle of CR 65 in search of S 478, which is on the west side of this cluster at a distance of 1° 52’. You can see by the 280° position angle I included on the last chart (here’s the erect image, and the mirror image) that we’re going to move almost due west with a very slight inclination toward the north.  Using 5.77 magnitude 117 Tauri as a stepping stone should get you to S 478 with little problem.

S 478      HIP: 25278    SAO: 94526
(AB is also H V 110; AC is WNO 52)
RA: 05h 24.4m   Dec: +17° 23’
Magnitudes   AB: 5.06, 8.79    AC: 5.06, 7.88
Separations  AB: 106.70”        AC: 705.20”
Position Angles   AB: 271°  (WDS 2011)   AC: 252° (WDS 2010)
Distance: “A” is 46.9 Light Years, “C” is 45.9 LY  (Simbad)
Spectral Classifications:  “A” is F8, “B” is K0, “C” is K4

The S 478 trio is a captivating visual delight. The white primary dominates the view, but the very slight hints of reddish-orange in the ninth magnitude “B” component and the wide eighth magnitude “C” component adds a touch of magic to the scene, and the 7.6 magnitude white light of SAO 94531 adds an extra touch of luster. (East & west reversed once more, click on the sketch to improve the view).

The S 478 trio is a captivating visual delight. The white primary dominates the view, but the very slight hints of reddish-orange in the ninth magnitude “B” component and the wide eighth magnitude “C” component adds a touch of magic to the scene, and the 7.6 magnitude white light of SAO 94531 adds an extra touch of luster. (East & west reversed once more, click on the sketch to improve the view).

The AB pair was measured by Sir William Herschel during his observation of November 13th, 1782 (source, scroll down to sixth title):

Wm Herschel on S 478

His Flamsteed number, 111 Tauri, is correct in this case, but the separation he recorded is off considerably, which was noticed by James South when he observed the AB pair on January 17th and February 2nd, 1825 (source):

South on S 478

On the last line of his observation, South refers to the minor change in position angle of the primary and secondary as being too small to account for the large difference in his and Herschel’s separation measures. Those position angles translate to 273° 48’ for Herschel and 271° 17’ for South, and they’re the first hint of significant motion taking place in one of the two stars.

As it turns out, the primary has a rather high rate of proper motion, which is partly attributable to its relatively close distance of 46.9 light years from us.  The “C” component, cataloged in 1897 as WNO 52, has a very similar rate of proper motion, and is located at a comparable distance, 45.9 light years.  The Aladin photo below shows the rates of proper motion of all three of the S 478 components:

Note that this in an erect image view, so east and west are opposite of what is shown in the sketch above of S 478. Click for a larger view.

Note that this in an erect image view, so east and west are opposite of what is shown in the sketch above of S 478. Click for a larger view.

Click to enlarge.

Click to enlarge.

The similar motions of “A” and “C” are obvious, which in combination with their almost identical distances from us, has led to the conclusion the probability of their being physically related is close to 100%. The AB pair, on the other hand, is an optical pair, which is evident from the different rates of motion and direction of “A” and “B”.

The “C” component was added to S 478 in 1897 by the Washington Naval Observatory, which is the source of the WNO identifier assigned to AC. Also, there’s an eleventh magnitude star (TYC 1300-355-1) located 32” from “C” at a PA of 136°, for which there is no proper motion data, so it may or may not be moving in tandem with S 478 “A” and “C”.

You may have also noticed on the image above that S 478 “A” is labeled “BY Dra”, which is a reference to a class of variable star. The AAVSO (American Association of Variable Star Observers) designation for S 478 “A” (or 111 Tauri) is V1119 Tau.  Their data on the star shows a magnitude range of 4.98 to 5.02, so don’t hold your breath in anticipation of a wild swing in brightness.   The WDS data (shown above at right) also includes a note that S 478 “A” is a spectroscopic binary, which may account for its slight change in magnitude level.

So as you can see, hidden behind the visual appeal of the three stars of S 478, there are several layers of intriguing detail.

To get to our third stellar destination, Σ 697, we’ll move south and very slightly west a distance of 42.5’ to 6.1 magnitude 110 Tauri, and then continue due south another 39’ to our goal.  (Here’s the erect image again, and the mirror image).

Σ 697       HIP: 25207    SAO: 94512
RA: 05h 23.5m    Dec: +16° 02’

Identifier Magnitudes Separation PA WDS
STF 697 AB: 7.27,   8.10      26.00″ 287°  2014
WAL 38 AC: 7.27, 10.83      97.90″ 284°  2012
SMR 3 AD: 7.27, 10.07    249.30″ 285°  2012
SMR 27 AE: 7.27, 12.00    163.00″ 290°  2012

Distance: 874 Light Years (Simbad)
Spectral Classifications: “A” is B8, “B” is A, “D” is B9

When I first looked at the data on Σ 697, I was immediately intrigued by the similar position angles of all five of the components. And even though I was prepared for what I saw, I was still impressed by the sheer unlikely beauty of the configuration.  Even 7.50 magnitude SAO 94498 and 8.53 magnitude HIP 25287 managed to line up with the components of Σ 697:

“A” and “B” caught my eye first, but it didn’t take more than a few seconds before “C” and “D” popped into view. I never did catch sight of twelfth magnitude “E”, which puzzled me since it should have been within reach of my five inch refractor. Both “A” and “B” are white, as are SAO 94498 and HIP 25287. (East & west reversed to match the refractor view, click on the sketch to get a better look at “C” and “D”).

“A” and “B” caught my eye first, but it didn’t take more than a few seconds before “C” and “D” popped into view. I never did catch sight of twelfth magnitude “E”, which puzzled me since it should have been within reach of my five inch refractor. Both “A” and “B” are white, as are SAO 94498 and HIP 25287. (East & west reversed to match the refractor view, click on the sketch to get a better look at “C” and “D”).

I had a suspicion the 10.07 magnitude shown in the WDS for “E” was too bright, so I pulled up an Aladin photo in order to first make sure the star existed. What I found was a reddish-orange star, which partially explained why it was difficult to see. I never was able to come up with a spectral classification for that star, but I did find magnitudes for it in both the UCAC4 and the Nomad-1 catalogs. UCAC4 shows a visual magnitude of 13.885 for “E”, and Nomad-1 lists it at a visual of 13.710, which explains why I couldn’t detect any sign of it in my five inch refractor. That component is a candidate for a magnitude change, so I’ll be in contact with Bill Hartkopf at the WDS.  (NOTE: The magnitude of “E” has been changed to 13.89 as of 2/13/2015 and the UCAC4 proper motion data has also been added).

This is an erect image, so east and west are opposite of my sketch above. Click to enlarge.

Click on the image and the data will be easier to read!

Click to enlarge.

Click to enlarge.

The AB pair, which seems to have eluded William Herschel, was discovered in 1828 by F.G.W. Struve, as shown at the left (source).  As the excerpt shows, there’s been little change in the position angle and separation since 1828, which matches well with Simbad’s proper motion data on the two stars: -001 -008 (.001”/yr west, .008”/yr south) for the primary, and -003 -004 (.003”/yr west, .004”/yr south) for the secondary.  In fact, there’s little movement among all four of the stars for which proper motion numbers exist, but what little motion there is suggests none of them are related physically to one another:

This is an erect image, so east and west are opposite of my sketch above. Click to enlarge.

This is an erect image, so east and west are opposite of my sketch above as well as the photo above. Click to enlarge.

We’ll cover the last three multiple stars of CR 65 in the next post, along with a bonus that wasn’t on my list.  Hopefully we’ll have some good seeing — we’re going to need it for this group!

Clear Skies!  :cool:

A Cassiopeian Quartet: OΣΣ 248, OΣΣ 251, OΣ 498, and ARY 33

As you can see from the title, Otto Wilhelm von Struve, aka OΣ, left his calling card at several locations in this part of the galaxy. In fact, a brief glance at a star atlas, such as the apparently out of print Cambridge Double Star Atlas, shows his footsteps all through Cassiopeia, especially the northeastern part of the constellation.

Depending on which source his observation comes from, you’ll find his stars identified with either an OΣ (or STT) or OΣΣ (or STTA) prefix. The OΣ designation represents the Greek letters assigned to the stars in Sir Otto’s first catalog, and are equivalent to the Arabic “OS”, while the STT designation is the WDS prefix now in more common use. Struve published an appendix of additional stars later in life, which are identified by the addition of the extra letter in the OΣΣ and STTA prefixes.

Both of his Pulkowa catalogs are non-existent on the internet, at least based on my repeated searches for them. Fortunately, the group of stars in his first catalog, including the original observational data, are all listed in W. J. Hussey’s 1901 Lick Observatory publication, Micrometrical Observations of the Double Stars Discovered at Pulkowa Made with the Thirty-Six Inch and Twelve Inch Refractors of the Lick Observatory, Together with the Mean Results of the Previous Observations of these Stars. I’ve searched high and low and everywhere in between for Struve’s appendix, but have yet to come up with a source. If anyone reading this is aware of an internet source for that appendix, I would be extremely grateful if he or she would contact me by adding a comment to this post.

As for ARY 33, there’s a tale there, but you’ll have to wait for a few paragraphs before we can get to it.

We’re going to start this four-starred tour at a familiar place, Beta Cassiopeiae, also known as Caph.

Stellarium screen image with labels added, click on the chart to enlarge it.

Stellarium screen image with labels added, click on the chart to enlarge it. The object at the right edge of the chart is M 31, the Andromeda galaxy.

Caph is located at the western tip of the Cassiopeian framework, which is shown above as it appears at about 8:30 PM in mid-October. Polaris is located to the left of Cassiopeia in this chart, which means north is to the left.   West is at the top because Cassiopeia is rotating up and over Polaris. If that’s confusing, remember that astronomical west is always the direction of stellar motion through the sky. If that’s still confusing, here’s the same scene at the end of January at about 7:30 PM:

Stellarium screen image again with additional labeling, click to enlarge.

Stellarium screen image again with additional labeling, click to enlarge.

North still points to Polaris, which is now to the right of Cassiopeia.   West is now down, because as Cassiopeia continues to rotate around Polaris it will pass beneath it.   If I’ve confused you beyond all understanding, take a look at this excellent piece on astronomical direction written by Greg several years ago.

We’re going to explore an area near the western edge of Andromeda, and we’ll begin at Caph by projecting a line southwest that runs between fourth magnitude Sigma (σ) Cassiopeiae and 5.15 magnitude Rho (ρ) Cas.  Extending that line further to the southwest will lead us to 5.35 magnitude 18 Andromedae.  For scale, the distance from Caph to Sigma (σ) Cas is 3.4 degrees, and the Sigma (σ) Cas to 18 Andromedae distance is six degrees.

To get to our first star, we’ll zoom into the area with the chart below.   This is how the scene appears at the end of January at about 7:30 PM. (If you decide to take this tour in the fall, here’s a chart showing the scene at about 8:30 PM in October).

Stellarium screen image with labels added, click on the chart for an easier to use version.

Stellarium screen image with labels added, click on the chart for an easier to use version.

Using 18 Andromedae as a star base, we’ll prepare to move out to our first star, OΣ 498. You’ll notice three stars of about seventh magnitude arrayed in a line along the west edge of 18 And.   Start by moving to the middle of those three stars, 6.87 magnitude HIP 116440. Move north one degree to 6.90 magnitude HIP 116418, and then move 38’ west with a slight tilt to the north to reach OΣ 498.

OΣ 498       HIP: 116082   SAO: 35501
RA: 23h 31.3m   Dec: +52° 25′

Identifier Magnitudes Separation  PA WDS
STT 498 AB: 7.62, 10.40     17.30″ 244°  2011
STT 498 AC: 7.62, ????      9.10″ 289°  1913

Distance: 249 Light Years (Simbad)
Spectral Classification: “A” if F6
Note: Only one recorded observation of AC.

The field is rather sparse here, which may be because a 60% waxing moon was behind me. The primary was white. Also shown in the field is TDS 4085 with magnitudes of 11.47 and 11.56, separated by 0.7” at 271°. There’s only been one observation of that pair, which comes from the 1991 Tycho data. (East & west reversed to match the refractor view, click on the sketch to improve the view).

The field is rather sparse here, which may be because a 60% waxing moon was behind me. The primary was white. Also shown in the field is TDS 4085 with magnitudes of 11.47 and 11.56, separated by 0.7” at 271°. There’s only been one observation of that pair, which comes from the 1991 Tycho data. (East & west reversed to match the refractor view, click on the sketch to improve the view).

Click to enlarge.

Click to enlarge.

Missing from the sketch is the mysterious “C” component, which is listed without a magnitude in both the WDS and Simbad. I also checked the UCAC4 and Nomad-1 catalogs in Vizier and came away empty-handed, although Nomad-1 includes a 13th magnitude star at a distance of 1.7” from the “B” component.   I superimposed the distance and position angle for “C” on the Aladin photo at the right to identify where it should be according to the 1913 data, but I also noticed there hasn’t been an observation of that star since.

According the information in the WDS notes file (which can be seen here in Stelledoppie), at one time the “C” component was identified as Aa, Ab. That seems to have led to some confusion since Simbad shows CCDM designations of “C” and “D” for the components, and excludes “B”.

The AB pair appear to be physical linked by proper motion, which is clear from this 7.5 arc minute Simbad plot:

The proper motion shown here is +101 -030 for the primary (.101”/year east, .030”/year south) and +095 -037 for the secondary.   (Click on the chart to enlarge it).

The proper motion shown here is +101 -030 for the primary (.101”/year east, .030”/year south) and +095 -037 for the secondary. (Click on the chart to enlarge it).

Click to enlarge.

Click to enlarge.

Since the two stars appear to be moving in tandem at a similar rate, you would expect there to be little change in position angle and separation over the years. That appears to be the case, as can be seen in the excerpt at the left from Hussey’s book (referred to above).

Now let’s go back to our starting point, 18 Andromedae, before moving on to our next star, OΣΣ 248 (here’s our January chart again, and here’s the October version). It’s easy to navigate to since it’s located just slightly more than a degree (1° 7’) due east of 18 Andromedae. You’ll find it at the middle of an arc it forms with 7.72 magnitude HIP 117145 and 7.98 magnitude HIP 117231.

OΣΣ 248       HIP: 117224   SAO: 35742
RA: 23h 46.1m   Dec: +50° 40′

Identifier Magnitudes Separation  PA WDS
HDS 3377 Aa Ab:  7.11, 11.10      0.40″ 198° 1991
STTA 248      AB:  7.45,  9.82     50.90″ 144°  2012
STTA 248      AC:  7.45, 12.20     24.80″ 332°  2002

Distance: 760 Light Years (Simbad)
Spectral Classification: “A” is K0

Considering the primary’s spectral class of K0, I was surprised to see a white star with only a trace of orange. The secondary was obvious, but colorless, and “C” was visible only with averted vision. 7.98 magnitude HIP 117231 marks the north edge of the field, which again is surprisingly sparse, most of which is probably attributable to the sky glow caused by the 60% full waxing moon at my back. (East & west reversed, click on the sketch to get a better look at “C”).

Considering the primary’s spectral class of K0, I was surprised to see a white star with only a trace of orange. The secondary was obvious, but colorless, and “C” was visible only with averted vision. 7.98 magnitude HIP 117231 marks the north edge of the field, which again is surprisingly sparse, most of which is probably attributable to the sky glow caused by the 60% full waxing moon at my back. (East & west reversed, click on the sketch to get a better look at “C”).

Based on the proper motions of the primary and secondary, they don’t appear to be related as this Simbad plot shows:

This is the same size plot as the previous one, which allows you to compare the rate of motion of the two stars.   Note this is an erect image plot (as are the others shown for this tour), so east and west are opposite of what is shown in the sketch above.   The proper motion of the primary is +041 +010 (.041”/year east, .010”/year north) and for the secondary -001 -002 (.001”/year west, .002”/year south).  Both numbers come from Simbad (no data was shown for “C”).   HIP 117231 is beyond the north edge of this chart.

This is the same size plot as the previous one, which allows you to compare the rate of motion of the two stars. Note this is an erect image plot (as are the others shown for this tour), so east and west are opposite of what is shown in the sketch above. The proper motion of the primary is +041 +010 (.041”/year east, .010”/year north) and for the secondary -001 -002 (.001”/year west, .002”/year south). Both numbers come from Simbad (no data was shown for “C”). HIP 117231 is beyond the north edge of this chart.

Since Otto Struve’s appendix catalog isn’t available, a good source to turn to for information on OΣΣ 248 is the second part of S.W. Burnham’s 1906 General Catalogue of Double Stars Within 121° of the North Pole.

Burnham on STTA 248

There are two measures each of the AB and AC pairs, which are about what would be expected given the proper motion of the primary.  In other words, if you back up the position of the primary to either the 1883 or 1905 measures, you would see an increase in separation between “A” and “B”. You can visualize that by using a neat little tool available in Aladin, which allows you to move the Epoch, the measures (or positions) for a given year, forward and backward.   In the case of OΣΣ 248, this is what you see when you compare Epoch 2000 with Epoch 1700:

Click to enlarge!

Click to enlarge!

In this case, I backed up the position of the primary to the year 1700, resulting in the change in separation and position angle shown below each of the images. Also included at the bottom of the two images is the slider tool I used, which shows the two epochs, J2000 and J1700.

To get to our next star, which is another selection from Otto Struve’s appendix catalog, move from OΣΣ 251 to 7.98 magnitude HIP 117231 (which is included at the north edge of the sketch above), continue northeasterly to 7.49 magnitude HIP 117290, and then nudge your direction of travel a bit more to the east in order to reach 6.47 magnitude HIP 117551.  Now move due east with a slight southern tilt to reach OΣΣ 251.   The direct line distance from OΣΣ 248 to OΣΣ 251 is 1° 27’. (Here’s the January chart again, and the October chart).

OΣΣ 251       HIP: 117808   SAO: 35869
RA: 23h 53.6m   Dec: +51° 31′

Identifier Magnitudes Separation  PA WDS
STTA 251   AB:  6.89,  9.14     47.70″ 208°  2012
STTA 251   AC:  6.89, 11.70     46.60″ 134°  2006
STTA 251   BD:  6.89, 13.10     14.20″ 165°  2006

Distance: 580 Light Years (Simbad)
Spectral Classifications: “A” is K0, “B” is K5

This is an interesting quadruple combination, and it took some persistent application of averted vision to pry thirteenth magnitude “D” out of the combined glare of “A” and “B”.   The primary had a slight yellow-gold tint, instead of the orange flavor promised by its K0 spectral classification. Much of the field is very faint, which again is partly attributable to the moon’s 60% full sky glow. (East & west reversed once more, click on the sketch to get a better look at “D”).

This is an interesting quadruple combination, and it took some persistent application of averted vision to pry thirteenth magnitude “D” out of the combined glare of “A” and “B”. The primary had a slight yellow-gold tint, instead of the orange flavor promised by its K0 spectral classification. Much of the field is very faint, which again is partly attributable to the moon’s 60% full sky glow. (East & west reversed once more, click on the sketch to get a better look at “D”).

Again, when you look at Simbad’s proper motion plot of these two stars, you can see the primary and secondary are unrelated:

“A” is moving at the rate of +053 +004 (.053”/year east, .004”/year north) and “B” is creeping along at -015 -008 (.015”/year west, .008”/year south).   Simbad didn’t list proper motion data for the other two components. Click to enlarge!

“A” is moving at the rate of +053 +004 (.053”/year east, .004”/year north) and “B” is creeping along at -015 -008 (.015”/year west, .008”/year south). Simbad didn’t list proper motion data for the other two components. Click to enlarge!

Now on to our last star, ARY 33. It’s easy to spot from our current location since it’s a bit more than a degree (1° 20’) southeast of OΣΣ 251.   As was the case with OΣΣ 248, ARY 33 is also located at the center of an arc of stars, this one formed by 6.72 magnitude HIP 118162 and 7.19 magnitude HIP 118289.   (Here’s the January chart, and here’s the October chart).

ARY 33         HIP: 118264   SAO: 35954
RA: 23h 59.2m   Dec: 50° 32’
Magnitudes: 7.32, 8.12
Separation:  99.7”
Position Angle: 139° (WDS 2012)
Distance: “A” is 809 Light Years, “B” is 956 Light Years (from Simbad)
Spectral Classifications: “A” is G5, “B” is K2

This is the widest pair of this tour, and in fact if you look carefully, both components can be seen in an 8x50 finder. Both the primary and secondary are white, which again isn’t quite what you would expect from a G5 star (yellowish) and a K2 star (orangish). I’ll blame the moon again! (East & west reversed once again, click on the sketch for a more endearing view).

This is the widest pair of this tour, and in fact if you look carefully, both components can be seen in an 8×50 finder. Both the primary and secondary are white, which again isn’t quite what you would expect from a G5 star (yellowish) and a K2 star (orangish). I’ll blame the moon again! (East & west reversed once again, click on the sketch for a more endearing view).

There are several faint, but obvious, stars surrounding this pair, two of which form an interesting parallelogram with “A” and “B”. Surprisingly, the 11.2 magnitude star just southwest of “A” has never been included in the system. On the other hand, the ARY pair wasn’t even cataloged until 2002, a fact which I stumbled across accidentally.

Click to enlarge.

WDS Notes file info, click to enlarge.

As I usually do when looking up data on a double or multiple star, I entered ARY 33 into the Stelladoppie database of the WDS catalog . . . . . . . and found a surprise when I saw the WDS notes file referred to R.W. Argyle as the discoverer of the pair. Bob Argyle is known to many people as the editor of Observing and Measuring Visual Double Stars and is also Director of the Webb Society Double Star Section. The surprise resulted from the WDS’s date of first observation for the ARY 33 pair, 1903 . . . . . . . which is a bit before Bob’s time.

I turned up Bob Argyle’s observation on page five of The Webb Society Double Star Circular No. 11, which is shown below:

Click to enlarge

Click to enlarge

You can see his data at the end of the list, which is labeled “Anon”.   He included a note of identification for the two stars at the end of his list of observations, which I added below the list. That information matches the BD designations in the WDS, which confirms his anonymous pair is the same as the pair identified as ARY 33 in the WDS. So how, where, and why does the 1903 date of first observation enter the picture?

Click to enlarge.

Click to enlarge.

I had a hunch, but I requested the WDS text file from Bill Hartkopf at the USNO/WDS.   In addition to containing all known published measures of a given double star, there’s also other interesting information coded into the file.   As I suspected, the 1903 date is a photographic measure derived from Carte du Ciel plates (source), which was an international photographic attempt to catalog all stars brighter than eleventh magnitude. I found other measures which had also been made from photographic plates prior to Bob Argyle’s 2002 measurements, which are actually the first made with a micrometer. What caught my eye is how consistent all the measures are. The 1903 position angle (139.0°) and separation (101.386”) change very little up to Bob’s measurements (139.5°, 98.75”).

A look at the proper motions of the two stars shows why there’s been little change.   I overlaid Simbad’s proper motion data on an Aladin photo of the ARY 33 pair, which provides a visual image of their motion:

Click to make the data at the bottom of the image more legible.

Click to make the data at the bottom of the image more legible.

The proper motion shown there for “A” is +004 -012 (.004”/year east, .012”/year south); for “B” it’s -005 -002 (.005”/year west, .002”/year south). That data is shown in a slightly different and more precise format at the bottom of the photo: +004.17 -012.29 for “A”, -004.59 -001.77 for “B”. At any rate, as you can see, although these two stars are moving away from each other, the rate of motion is very slow.

Adding further to the case for this pair not being physically related are their distances. Simbad’s parallax data places “A” at 809 light years from us and “B” at 956 LY. Even granting the imprecision of parallax at those distances, when combined with the proper motion data, we can conclude with a high degree of certainty the ARY 33 pair are not gravitationally linked in any way.

Which is more than you knew when you sat down to read this.   ;)

Thanks once again to Bill Hartkopf at the USNO/WDS for the informational support!

Next time out, we’ll turn to Taurus for a pair of star hopping adventures.   Until then, clear and stable skies! :cool:

Phi (φ) Cassiopeiae, Multiple Stars in NGC 457, and ET

It was a dark, damp, and murky Halloween-like night (minus the moon), but fortunately there was a window of relatively murk-free sky surrounding Cassiopeia, so I turned my four inch refractor in the Queen’s direction. On my list for the night was Phi (φ) Cassiopeia, a fifth magnitude multiple star embedded in NGC 457 and located two degrees south of Delta (δ) Cassiopeiae.

Phi (φ) Cas is shown here in radiant red. (Stellarium screen image with labels added, click to enlarge).

Phi (φ) Cas is shown here in radiant red. (Stellarium screen image with labels added, click to enlarge).

It only took one try to locate Phi (φ), and as I adjusted the focus for my first look at this five-part star, I had an uncanny feeling I had company – apart from my usual companion, Astro Dog Klaus. After I located all the members of Phi’s entourage, I started searching for the other multiple stars surrounding Phi (φ), but I couldn’t quite shake that eerie feeling – something was watching me.

Suddenly a charge of electricity rippled across the hair on the back of my neck and my focus fingers froze. I saw it: a two-eyed critter with arms and legs was staring back at me from inside my eyepiece.  I jerked my head back and leaped off my chair at the speed of light with a shout that shook every star in the murky sky. Astro Dog Klaus barely opened one eye in mock surprise, snorted in disgust at his weak-nerved master, and went back to sleep.

After recovering what was left of the dignity I had lost in front of my dog, curiosity got the best of me. Creeping cautiously back to the eyepiece, I approached its dark and forbidding rim with trembling trepidation, braced myself for the shock, hesitated for a moment, leaned over, and there it was again:  E.T. himself.

He even winked.

Argh!

** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** **

OK – it wasn’t quite like that.   But there’s more to the story.

Phi (φ) Cassiopeiae sits in the middle of an open cluster of stars known as NGC 457, which also has a nickname: The ET Cluster.

East & west reversed to match refractor view, click to a better view.

East & west reversed to match refractor view, click for a better view.

Now I have to admit, I sure couldn’t see how that name had become attached to the cluster when I first looked at it. But if we rotate the sketch above about sixty degrees and turn up the contrast, it gets a bit easier:

Click to enlarge!

Click to enlarge!

Still don’t see it?   How about a crude visual aid, then:

Any better? (You probably better enlarge it). Can’t really tell if he/she/it has a helmet on or not.

Any better? (You probably better enlarge it). Can’t really tell if he/she/it is wearing a helmet or not.

Honestly, it wasn’t obvious at all to me until I saw this rendition of the critter.

NGC 457 also has another nickname, the Owl Cluster . . . . . . . apart from the eyes, I don’t get it.

On to serious stuff now.

Phi (φ) Cassiopeiae (H III 23)   HIP: 6242   SAO: 22191
Note: “A” is Phi-1, “C” is Phi-2
RA: 01h 20.1m   Dec: +58° 14’

    Magnitudes   Separation Position Angle WDS
AB: 5.07, 12.30       48.80″         209°  2010
AC: 5.07,   7.04     134.00″         231°  2012
AD: 5.07, 10.26     178.70″         288°  2010
AE: 5.07, 10.38     170.80″         239°  2010
CE: 7.04, 10.38      42.00″         265°  2010

Distance:  Rather uncertain – we’ll come back to it shortly
Spectral Classifications: “A” is F0; “C” is B6; “D” is B3; “E” is B5   (Simbad)


You can’t keep track of the players without a score card – or a chart – so this version identifies the various components of Phi (φ) Cassiopeiae. East & west are reversed here to match the refractor view, click to enlarge.

You can’t keep track of the players without a score card – or a chart – so this version identifies the various components of Phi (φ) Cassiopeiae. East & west are reversed here to match the refractor view, click to enlarge.

You can see a slight yellow-gold tinge in the primary, some of which may have been caused by the moisture in the air the night I made the sketch, although it does correspond reasonably well to the star’s F0 spectral classification (yellow-white). None of the additional four components were difficult to see, although I had to call on averted vision to catch my first glimpse of 12.30 magnitude “B” which was right at the limit of the four inch lens that night.

“A” and “C” make an interesting pair, and you have to wonder why they haven’t been cataloged as two separate double/multiple stars since each is surrounded by another companion or companions. But the two stars do show a similarity in proper motion, which suggests a tentative physical link.

Looking at the Simbad data, we find these two stars are moving very little in relation to our position in the galaxy.   In fact, you have to resort to five decimal places to begin to pick up the subtleties of their motion. The proper motion of “A” is -000.59 -001.59 (.00059”/year west and .00159”/year south), and for “C” we have -000.46 -000.79 (.00046”/year west and .00079”/year south). The only other companion for which I could find proper motion data is “E”, which is listed in Simbad at -006.50 -001.80 (.00650”/year west and .00180”/year south). So from those numbers it’s possible to conclude the three stars originated from the same cloud of gas, as Kaler points out.

None of which is surprising if Phi (φ) Cas is part of the NGC 457 cluster.   A look at a 7.5 arcminute resolution Simbad plot of the proper motion data for the cluster of stars surrounding Phi (φ) Cas shows the same subtlety of motion:

Click for a larger view.

Click for a larger view.

So all we need to know now is whether Phi (φ) Cas and its retinue are at the same distance as the other stars in NGC 457 . . . . . . . . but the judge and jury have called a recess until an improvement in distance technology (as in GAIA) resolves the conflicting data. By way of explanation for what follows, parallax-based distances (which means virtually all current star distances) are notoriously unreliable beyond about 450 light years, including those based on the 2007 Hipparcos revisions.  Hopefully that will change as data from GAIA begins to come in.

At any rate, going with what have at the moment, Jim Kaler refers to a distance of 7900 light years for NGC 457, while other sources place it as far away as 10,000 LY.  Kaler’s distance for Phi Cas “A” is 2300 light years, but he also mentions the error of that measurement is “perilously high”, and states there’s a significant chance of a distance of 4500 light years, as well as a possibility the star is at the same distance as the cluster.  Simbad’s parallax for Phi Cas “A” is little help, since it results in a distance of 12074 light years.  And it’s parallax for Phi Cas “C” results in a distance of 5344 light years.  So we may have to get some input from ET.

Meanwhile . . . . . . . Sir William Herschel discovered the pair in a less complicated era, namely on August 8th, 1780 (source — scroll down to the twelfth title):

Herschel on Phi Cas

But apparently the era was more complicated than I thought . . . . . . because it’s difficult to conclude from Herschel’s description that he was looking at Phi (φ) Cas.  The Flamsteed number (FL. 34) is correct, but after that the words resemble my normal observing conditions – murky.  “One of two telescopic stars” would seem to indicate Herschel was referring to “A” and “C”, but on the other hand his “Extremely unequal” description points to twelfth magnitude “B”. Couple that with his estimated distance of “12” or more” and we’re stuck in the murk again, because that separation doesn’t come anywhere close to resembling the current WDS distance between “A” and “B” of 48.80”, much less between “A” and “C” (134”).

Hoping for words of wisdom and some penetrating insight from my usual oracular source, I turned to S.W. Burnham’s 1906 catalog and found this:

Burnham on Phi Cas

His measures of AB and AC are very close to the current WDS data, which comes as no surprise since there’s very little proper motion taking place.  But on the first line he includes this statement: “Triple Cl. III and IV”.  That reads distinctly as if it was written by Sir William Herschel, but those words aren’t included in Herschel’s observation above.  Fortunately, Bill Hartkopf at the USNO/WDS came to the rescue when I sent him a request for the WDS text file on Phi (φ) Cas.  Among other things, the WDS text files include bibliographic references to the published source of the various observations listed in the file.

What I found there was a reference to an 1865-66 volume of Memoirs of the Royal Astronomical Society containing an article by Sir John Herschel entitled “A Synopsis of all Sir William Herschel’s Micrometrical Measurements and Estimated Positions and Distances of the Double Stars Described by him, together with a Catalogue of those Stars in order of Right Ascension, for the epoch 1880.0, so far as they are capable of identification.”   A rather long and very descriptive title for a publication I just happen to have been trying to find for quite some time.

On page 54, I found the entry for Phi (φ) Cas, aka H III 23:

This is a pasted together version of the title headings and the entry for H III 23 – the resolution for the entire page was too poor for reproduction.   Click to enlarge!

This is a pasted together version of the title headings and the entry for H III 23 – the resolution for the entire page was too poor for reproduction. Click to enlarge!

So that resolved the issue of the source for Burnham’s “Triple Cl. III and IV” quotation, but it didn’t clear up the murk.  In fact, with the addition of Herschel’s position angle for AC (271.85°) that wasn’t included in the 1782 catalog, it seems even more likely Herschel was looking at another star or simply made a mistake . . . . . . . which is supported by his estimated separation of 12” to 15” for AB, rather short of the current 48.80” and Burnham’s 48.61”.

Then there’s the matter of Herschel’s references to Classes III and IV. In Herschel’s language, Class III refers to separations of 5” to 15”, which would include his estimated separation of AB, and Class IV refers to separations of 15” to 30”, which doesn’t include any of the distances among the five stars of Phi (φ) Cas. And I’m also left wondering about his description of the star he described as being “Triple.” The 10.38 magnitude “E” component is obviously more obvious than the much fainter 12.30 magnitude “B” component, so “E” would have been a more likely inclusion than “B”.  But the separation between “C” and “E” is too wide at 42” to fit into Herschel’s Class III category, so that excludes any possibility that Wm. Herschel could have been referring to “E” when he made his measurements.

I suspect an error, maybe caused by poor weather or from being in a hurry, but the reality is there may be only one way to clear up this five-part stellar conundrum . . . . . . . ask E.T, again.

** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** **

As for the other stars surrounding Phi (φ) Cas/aka H III 23 . . . . . . .

I was dubious about approaching NGC 457 with a four inch refractor – especially a $59 Celestron that was irresistibly on sale – because the entourage of stars surrounding Phi (φ) Cas are on the dim side.  But when I looked more closely at the faint secondaries, I realized they would probably be out of reach for my six inch refractor also.  So I stuck with my low cost experimental refractor, which actually turned out to be a very pleasant surprise.

Here’s the sketch again, this time with the additional stars in the field labeled:

Focus your attention on the inset at the left and click to enlarge!

None of this group of stars was particularly spectacular in the four inch refractor, although the grouping of ES 408 and STI 1560 struck me as being well worth a visit with a six inch or larger scope, so a year later I went back and took another look.  The seeing wasn’t the best, as usual, so I stuck with the 109x view shown in the inset at the left of the sketch above.  I did manage to pick out one additional pair, STI 1564, that wasn’t visible in the four inch scope.

As you can see, the small area within the inset is a complicated and congested area – almost every star in it is part of a double or multiple star system. In fact, if you care to count them all, you’ll come up with six different designations (there’s actually one more which isn’t shown because it wasn’t visible, BKO 1057) – not bad for an area that measures about 3.5’x 3.5’!  And it’s actually more complicated than that because there are components that were beyond my visual grasp.

You might call this a stellar traffic jam.   Make sure to click on the image so the labeling on the image and the data at the bottom are legible.   (Aladin image with WDS data overlay).

You might call this a stellar traffic jam. Make sure to click on the image so the labeling on the image and the data at the bottom are legible.  East and west are reversed here to match the view in a refractor.  (Aladin image with WDS data overlay).

Rather than include a long list of data here for all seven of the stars shown, I added it to the bottom of the image. The proper motion data is included as well, which for the most part indicates very little movement, in turn suggesting some of them may have a common origin.   Most are moving in the same general direction, west and south, although there are some exceptions.  The primaries of ES 408 and STI 1565 are moving in a northwesterly direction, while the secondary of ES 1808 stands out with a considerably higher rate of southwesterly motion.

[Quick course on proper motion numbers: the PM numbers listed below the image show the PM in right ascension (RA) and declination (DE) for the primary (pmRA1 and pmDE1) and in most cases for the secondary (pmRA2 and pmDE2) of each pair of components listed. Each number represents motion in thousandths of an arc second per year.   Using ES 408 AB as an example, the -10 and 23 shown there should be read as -.010”/year west and +.023”/year north, and the -3 and 3 should be read as -.003”/year west and +.003”/year north. A plus sign in front of the numbers indicates eastward motion in right ascension (RA) or northerly in declination (DE), and a negative sign means westward in RA or southerly in DE].

I discovered some of the proper motion data in Simbad conflicts quite noticeably with the WDS data shown above. For example, Simbad shows the primary of ES 1808 at +012 -015 (different direction and rate) and the primary of STI 1560 at -003 +003 (different direction). Still, there’s not much movement here, which again is characteristic of NGC 457.

There are also no distances shown for any of the seven primary stars or their components, so there’s really no way to know which stars are or aren’t part of NGC 457 . . . . . . .  except, of course, to ask E.T.

Thanks again to Bill Hartkopf for the assistance, and also thanks to Peter Morris, who I believe first mentioned Phi (φ) Cas to me. Thanks also are due to that on-sale $59 Celestron f/10 achromatic refractor, which is living proof you don’t have to invest a fortune in a telescope in order to delve deeply into double stars.

Next trip, we’ll return to Cassiopeiae for an Otto Struve odyssey.  Until then, clear skies! :cool:

 

Pouring Starlight from an Aquarian Water Jar: Bu 1515, HJ 5529, and Bu 172 (and a Bow to Zeta Aquarii)

Ahhhhh, there’s nothing like a sip of cold water on a hot summer day . . . . . . . . but if you’re waiting for water to flow from the Aquarian water jar, you’re likely to be well past parched by the time Aquarius hoists his massive framework into the heavens. Still, even though the Aquarian may be a little late for thirsty lips, he nevertheless has one other redeeming quality: a penchant for pouring starlight out of that jar tucked under his right arm.

Distance:  92 Light Years (Simbad) Spectral Classifications:  “A” is F3, “B” is F6 PM of “A” is 183 050, of B 191 037 (which includes the third companion).

The Aquarian jar in outline: Eta (η), Zeta (ζ), Pi (π), and Gamma (γ) frame the water jar, while Alpha (α) rests on Aquarius’ right shoulder.  (Stellarium screen image with labels and outline added, click on the image for a larger version).

As an informative aside, the German language has a much more descriptive name for Aquarius: der Wassermann — which, if it isn’t obvious, translates as The Water Man.  At any rate, flowing from The Water Man’s jar are the three main stars of this excursion: Bu 1515 (60 Aqr), HJ 5529 (Kappa/κ Aqr), and Bu 172 (51 Aqr), which are mapped into their respective places on the left side of this chart:

 Stellarium screen image with labels added, click to enlarge.

Stellarium screen image with labels added, click to enlarge.

Mainly an autumn constellation, Aquarius hangs around into the beginning of winter provided you get outside when the December dusk descends. But before we look at a the three main attractions for this tour, it would really be inexcusable to pass up an opportunity to take a short peek at the real star of Aquarius, Zeta (ζ).

Zeta Aqr  (55 Aqr)  (Σ 2909)  (H II 7)      HIP: 110960   SAO: 146107
RA: 22h 28.8m   Dec: -00° 01’

Identifier Magnitudes Separation   PA WDS
EBE-1 Aa, Ab:  4.34, ????     0.65″ 147.8° 2014
STF 2909  AB:  4.34, 4.49     2.247″ 164.9° 2015

Distance:  92 Light Years (Simbad)
Spectral Classifications:  “A” is F3, “B” is F6
Note: Orbital data is here; 2015 separation and PA based on WDS Ephemerides data.

Greg has already covered Zeta (ζ) rather well in a previous post (be sure to continue into the comments section for more discussion), so I’ll keep this brief and to the point: this is one of the genuine gems of the ecliptic.

In a smaller scope, and when Zeta (ζ) is lower in the sky, I’ve caught flashes of lemon and orange from these two stars.   The night I caught it for this sketch, Zeta was parked on the meridian, so I captured it at its highest point in the sky.   This time, the primary and secondary boasted an attractive white-gold hue, which was just slightly more distinctive in the northern member of the pair. (East & west reversed to match the refractor view, click on the sketch for an improved version).

In a smaller scope, and when Zeta (ζ) is lower in the sky, I’ve caught flashes of lemon and orange from these two stars. The night I caught it for this sketch, Zeta was parked on the meridian, so I captured it at its highest point in the sky. This time, the primary and secondary boasted an attractive white-gold hue, which was just slightly more distinct in the northern member of the pair. (East & west reversed to match the refractor view, click on the sketch for an improved version).

We’ll get this excursion started with Bu 1515, also known as 60 Aquarii.  It’s an easy one to find: starting at fourth magnitude Eta (η) Aquarii, drop a degree and a half south and just slightly west (here’s our previous chart once again). For reference, Bu 1515 is parked halfway between Eta Aqr and 6.15 magnitude HIP 111171.

Bu 1515  (60 Aqr)        HIP: 111394   SAO: 146160
RA: 22h 34.0m   Dec: -01° 34’
Magnitudes   AB: 5.98, 11.54     AC: 5.98, 11.89
Separations  AB: 99.80”            AC: 126.60”
Position Angles   AB: 298° (WDS 2000)    AC: 275°  (WDS 2000)
Distance: 347.5 Light Years (Simbad)
Spectral Classification:  “A” is G6

This is a compact little triple star with a white primary.   The “B” and “C” components are faint enough that you have to look closely to catch your first glimpse of them, but once you have them in view, they willingly stay within visual grasp. (East & west reversed, click on the sketch for an improved view).

This is a compact little triple star with a white primary. The “B” and “C” components are faint enough that you have to look closely to catch your first glimpse of them, but once you have them in view, they willingly stay within visual grasp. (East & west reversed, click on the sketch for an improved view).

Anyone familiar with S.W. Burnham’s double star discoveries is aware the title of his 1900 catalog of discoveries, A General Catalogue of 1290 Double Stars Discovered from 1871 to 1899, tops out at Bu 1290 – hardly a surprise, of course . . . . . . . which raises the question of where the numbering for Bu 1515 came from.  Again, it should come as no surprise that Burnham continued to discover double stars after the publication of that catalog, so the numbering continued. (From what I can determine, it ends at Bu 1540). The origin of the Bu 1515 designation, though, is a bit vague.  After my internet roaming failed to turn up an answer, I got in touch with Brian Mason at the USNO/WDS, who not only provided me with an answer, but also a link to the source.

The source is a four page article published in the July 5th, 1918, issue of The Astronomical Journal, in which Burnham is listed as the author. Although the data in the article is his, the four page article was actually put together by Philip Fox, who had been entrusted by Burnham with a list of unpublished double star measures.

The star that became Bu 1515 is listed at the bottom of the page as 60 Aquarii. Click on the page to ease eye strain.

The star that became Bu 1515 is listed at the bottom of the page as 60 Aquarii. Click on the page to ease eye strain.

In 1932, when R.G. Aitken published the successor to Burnham’s 1906 double star catalog, he apparently dropped Burnham’s listing. (The Aitken catalog is referred to today as the ADS – the actual title is New General Catalogue of Double Stars). Nevertheless, the observation remained assigned to Burnham, although with no designation. The Bu 1515 designation first showed up in a 1996 edition of the Washington Double Star Catalog (WDS), which led Brian to conclude it was added by Charles Worley, who first had responsibility for the WDS as we now know it.  As to how that number was arrived it, we may never know.

Before we leave Bu 1515, there’s an unexpected triple star bonus, Bu 77, parked in the south corner of the view.  Here’s the WDS data on this threesome:

Bu 77      No HIP or SAO Numbers
RA: 22h 34.0m   Dec: -01 47’
Magnitudes   AB: 9.31, 9.92    AC: 9.31, 10.80
Separations  AB: 2.60”            AC: 25.30”
Position Angles  AB: 215° (WDS 2010)   AC: 230° (WDS 2010)
Distance:  None found
Spectral Classification:  “A”is F0

I caught the 10.80 magnitude “C” component, but the 9.92 magnitude “B” companion escaped me since I wasn’t aware Bu 77 was in the field until after I had made the sketch above.  S.W. Burnham first captured this triple in 1872 with his six inch f/15 Clark refractor.

Meanwhile, on to another mystery, HJ 5529, aka Kappa (κ) Aquarii.  You’ll find it just short of three degrees south and slightly east of Bu 1515, where it shines distinctly. Here’s our last chart again.

HJ 5529/Kappa Aquarii   (63 Aqr)      HIP: 111710   SAO: 146210
RA: 22h 37.8m   Dec: -04° 14’
Magnitudes as of Sept. 14th, 2014:  5.00,  8.8
Magnitudes as of Dec. 22nd, 2014:  5.18, 12.2
Separation: 87.1”
Position Angle: 256°  (WDS 2010)
Distance: 234 Light Years
Spectral Classification: “A” is K2
Note: High PM for primary: -069 -120 (WDS and Simbad); secondary at +043 +007

The fifth magnitude primary radiates a rather attractive white-orange hue which is more pronounced in photos of it (see the Aladin image below). The secondary, “B”, is the first star immediately to the west (left) of the primary, which is shown more clearly in the inset – and if you look closely, it doesn’t quite live up to the 8.8 magnitude allotted to at the time I made the sketch.   (East & west reversed once more, click on the sketch for a better view of the secondary).

The fifth magnitude primary radiates a rather attractive white-orange hue which is more pronounced in photos of it (see the Aladin image below). The secondary, “B”, is the first star immediately to the west (left) of the primary, which is shown more clearly in the inset – and if you look closely, it doesn’t quite live up to the 8.8 magnitude allotted to at the time I made the sketch. (East & west reversed once more, click on the sketch for a better view of the secondary).

Click to enlarge.

Aladin image, click to enlarge.

When I first bent down to the 12mm eyepiece lodged in the diagonal of my six inch refractor, I anticipated a very obvious secondary parked to the west of the primary, but that wasn’t quite what happened.   Instead, I found myself peering into the depths of the west side glare for a glimpse of secondarial light. It took a few seconds, but once I captured it visually, I had little trouble keeping it in view. The surprising absence of a brighter star initially baffled me until I realized it wasn’t my eyesight, but an oversight – of some sort.

But of what sort was the question.

I did some research in Vizier, in both the UCAC4 and Nomad-1 catalogs, which is shown beneath the image below:

There are three tables of data below the sketch – the WDS is first, UCAC4 is next, and Nomad-1 is last. To avoid confusion, I’ve flipped the image to match the visual orientation of the sketch above. Click to see the data more clearly.

There are three tables of data below the sketch – the WDS is first, UCAC4 is next, and Nomad-1 is last. To avoid confusion, I’ve flipped the image to match the visual orientation of the sketch above. Click to see the data more clearly.

The secondary is decidedly fainter than the WDS magnitude of 8.8. On the other hand, the UCAC4 “f” magnitude of 12.124 struck me as too faint (mainly because of the glow coming from the primary), as did the Nomad-1 “Vmag” of 12.180. However, combining the “J” and “K” magnitudes for the secondary in the UCAC4 data resulted in a visual magnitude of 12.111, so despite my reservations, all indications pointed to the 12.1 to 12.2 range. A comparison with nearby TYC 5236-01401-1, which appears slightly brighter in both my sketch and the Aladin color photo just below it, also seemed to point to the 12.1 to 12.2 magnitude range for the secondary, although I still had concerns as to what extent the primary’s glow might be causing the secondary to appear a bit fainter than it actually was.

I aimed my research through cyberspace to reach Bill Hartkopf at the USNO/WDS, who very quickly answered in less than half an hour.  After making similar magnitude comparisons, and looking at images of HJ 5529/Kappa (κ) Aqr on red and blue plates, he leaned toward the Nomad-1 “Vmag” of 12.18. He also made a small change in the magnitude of the primary, from 5.0 to 5.18.

All of which explains why there are two lines of magnitudes listed in the data above for HJ 5529/Kappa (κ) Aquarii.

But there was yet another surprise lurking in the dark, waiting patiently to reach out and grab me when I least expected it.

.
A Case of Mistaken Identity

The proper motion of HJ 5529 A is rather significant at -069 -120 (.069”/year west, .120”/year south) . . . . . . .

The red arrows show the proper motion of both HJ 5529 A and TYC 5236-01401-1. Click to enlarge the image.

The red arrows show the proper motion of both HJ 5529 A and TYC 5236-01401-1. Click to enlarge the Aladin image: note, this image is also inverted to match my sketch.

. . . . . . . which prompted me to see if S.W. Burnham had commented on it in his 1906 catalog. So there I was again, staring semi-somnolently (this time at a computer screen, not into an eyepiece), when I was jolted from lethargy to a loss of words:

Click to enlarge and clear-ify.

Click to enlarge and clear-ify.

I have never been able to see any trace of the small star in the last thirty years.

?????

But I certainly saw it — not to mention it being clearly visible in the photos . . . . . . .

When in doubt (or somewhat stunned), go to the source:

J. Herschel on HJ 5529

HJ 5529 is the last entry. Click for a clearer version.

An exceedingly minute point strongly suspected.

Which explains the origin of the quote at the beginning of Burnham’s catalog entry.

But as I looked at John Herschel’s observation more closely, I noticed the position angle and distance were decidedly discordant with the current measures . . . . . . . and then I realized there were no magnitudes shown.

I aimed my new discovery through cyberspace with instructions to land in Bill’s in-box, which it did.  He researched a bit further and found this entry in Burnham’s 1913 Proper Motion Catalog:

Burnham on HJ 5529 - 1913

Click to enlarge and clear-ify once more.

“ . . . has never been seen since and certainly does not exist.

Another surprise.

But at least this entry by Burnham included measures of Kappa (κ) Aquarii, which meant Burnham had seen something. In fact, if you compare his measures with the most recent 2010 data in the WDS, you’ll notice a significant difference between the two, which is attributable to the considerable proper motion of the primary.

As to what Herschel was looking at when he assigned a catalog number of 5529, we’ll probably never know.  It’s possible the 12th magnitude secondary would have been very difficult to detect with the twenty inch mirror Herschel used at the time, but his measures seem to indicate he was looking at another star entirely — and the absence of magnitudes makes it even more impossible to figure out what he might have been looking at.

We may also never know where the 8.8 magnitude of the secondary in the WDS originated. Bill sent me the text file for HJ 5529/Kappa Aqr, which shed no light whatever on the origin of that magnitude. But what it did show is S.W. Burnham was the first person to actually make and publish measures of Kappa (κ) Aquarii. (There was an 1896 measure by P. L. Gauchet, 246.4° and 103.11”, which wasn’t published until 1926). So credit for the double star status of Kappa (κ) Aquarii should go to Burnham, and as for HJ 5529 – wherever and whatever it originally was, it wasn’t Kappa (κ) Aquarii.

Now on to the last of our four stars, in which the ever-present S.W. Burnham also had a hand – and it also is a puzzle of sorts. Bu 172, aka 51 Aquarii, is less than a finder field (8×50) away from Kappa (κ) Aquarii.   Here’s our last chart again, which shows it three and half degrees west and slightly south of Kappa (κ).   A closer look reveals it’s roughly halfway between Kappa (κ) and 5.75 magnitude HIP 110023.   You can also use the three stars surrounding 5.98 magnitude HIP 109466 for a reference point, as well as 5.35 magnitude Rho (ρ) and 4.16 magnitude Theta (θ) Aquarii.

Bu 172 (51 Aqr)            HIP: 110578   SAO: 146067
RA: 22h 24.1m   Dec: -04° 50’

Identifier Magnitudes Magnitudes Separation Pos’n WDS
  9/14/2014 12/22/2014 Angle
Bu 172     AB:  6.45,  6.63  6.45,  6.63        0.46″    36° 2014
Bu 172 AB,C:  5.77, 10.10  5.77, 12.20      53.10″   343° 2005
Bu 172 AB,D:  5.77, 10.00  5.77, 11.50     123.30″   191° 2002
Bu 172 AB,E:  5.77,   9.87  5.77,  9.87     130.30″   133° 2002
STU 14 AB,F:  5.88,   8.50  5.77, 11.10     256.80″      3° 2000

Distance: 424 Light Years
Spectral Classification: “A” is B9.5
Notes:  AB,C is H V 95;  AB is binary (orbit is here); AB,C is physical; D and E are optical.

5.77 magnitude AB sits in the center of its retinue of four stellar attendants, casting the spell of its white light over “C” and just barely falling short of “D” and “E”. Lying over four arc minutes to the north, “F” fails to live up to its 8.50 magnitude reputation.   (East & west reversed once more, click on the sketch for a much improved version).

5.77 magnitude AB sits in the center of its retinue of four stellar attendants, casting the spell of its white light over “C” and just barely snaring “D” and “E”.  Lying over four arc minutes to the north, “F” distinctly fails to live up to its 8.50 magnitude reputation. (East & west reversed once more, click on the sketch for a much improved version).

This was too good not to post! Aladin image, click on it for the full effect.

This was too good not to post!  Aladin image, click for the full effect.

Once again I found myself looking at a multiple star with magnitudes that didn’t quite match the published numbers, but this time I was expecting it. Peter Morris had sent me two descriptions of Bu 172 earlier in the year, pointing out “F” was much fainter than the 8.50 magnitude assigned to it, and also calling attention to magnitude discrepancies in the “C” and “D” components. Within a few days of receiving Peter’s second description, I pointed my six inch f/10 refractor at Bu 172 and found his description right on target.

Again I called on Vizier for advice and leaned on the UCAC4 and Nomad-1 catalogs for support:

I also flipped this Aladin image horizontally so it would match my sketch and added the data below the image. Click on the image in order read the data more easily.

I also flipped this Aladin image horizontally so it would match my sketch and added the data below the image. Click on the image in order read the data more easily.

My eyes were first drawn to the UCAC4 and Nomad-1 magnitudes for “F” – UCAC4 has it at 10.516 (“f”) and Nomad-1 at 11.050 (“Vmag”), both of which seemed to be in about the right range.   There was a similar range of difference between the two catalogs for “D” (10.890 and 11.500), with Nomad-1’s 11.500 looking like the better choice. I tried a few tricks in order to get Nomad-1 to recognize “C”, but with no luck, so the only values I had were the UCAC4 “f” magnitude of 12.064 and the combined “J” and “K” infrared values, which worked out to a visual magnitude of 12.386.

I had sent this research off to Bill Hartkopf at the same time I sent my findings on HJ 5529, and after some further research, Bill changed the magnitude values for “C”, “D”, and “F” to the numbers shown above in red for the Bu 172 data above.

Apart from the AB pair, the proper motions of the various components of Bu 172 appear to indicate none of them are related physically, especially in the case of “D” (source):

Click on the image for a larger view. NOTE: this is an erect image view (east at the left).

Click on the image for a larger view. NOTE: this is an erect image view (east at the left).

The WDS notes file for Bu 172 describes AB,C as physical, but from looking at the plot above, that doesn’t appear to be the case, although there may well be more involved than I’m aware of.

Click to enlarge the image.

Click to enlarge the image.

The binary AB pair, which at a separation of 0.46” was beyond my reach, was discovered in 1875 by Burnham with the combination of his eagle-eyes and six inch f/15 Clark refractor. More than likely he detected an elongation rather than a separation (he sent his observation off to Ercole Dembowski for measurement), but even at that, I would love to duplicate his feat – if I could only persuade the seeing to cooperate!   Surprisingly, when Dembowski measured it he came up with the same separation as the WDS Ephemerides shows for 2014, which is a remarkable coincidence. That star has been measured many times, which is evident from Burnham’s list at the right, and the orbital data for it is well established.

The WDS shows the first observation of the AF pair, STU 14, was made in 1893. which may be an indication of a measure made by Burnham, although I can’t find any reference to that star in his catalogs. The three letter identifier refers to K. M. Sturdy, who published in the Webb Society Double Star Circulars in the 1990’s.

That’s it for an interesting and unpredictable look at starlight flowing from der Wasserman’s water jar.  You shouldn’t have to read between the lines too much in order to grasp the message underlying the observations of the last two stars: it’s still quite possible for amateur astronomers to contribute in very significant ways to double star research. Remarkable as it may seem, even in the early 21st century you can still point a telescope into the sky and find yourself looking at a sprinkling of stars that don’t quite match the published data. When that happens, it’s well worth the time to do a bit more research and report what you find.  You really can make a difference.

Many thanks to many people for help on this one: First to Peter Morris of England for pointing me toward Bu 172, and second to Bill Hartkopf and Brian Mason at the USNO/WDS for help and suggestions on Bu 1515, Bu 172, and HJ 5529.   Thanks also to an internationally flavored group of persistent double star hunters and accomplices who also keep a sharp eye out for magnitude discrepancies: Chris Thuemen (Canada), Dr. Wilfried Knapp (Austria), Steve Smith (Colorado), and Steve McGaughey (Hawaii).

Clear Skies!   :cool:

The Alpha-Beta-Gamma of Aquarius: α, β, and γ Aquarii

You might call this a kind of A-B-C of Aquarius, since it’s a look at three of the brightest stars in the constellation . . . . . . . except that in Greek the first three alphabetical letters are α,β, and γ — as in alpha, beta, and gamma. In case you don’t stay up late at night wondering about linguistic details, the Greek language has managed to do just fine without the equivalent of the Arabic “c”.  Instead, it leans on Kappa (κ) for the “k” sound and Sigma (σ) for the “s” sound (along with Xi (ξ) and Chi (χ) for additional variations) – subtly suggesting we could dispense with the Arabic “c” just as easily, although that might throw the English language into a torrent of turmoil. (But Kapricornus and Setus have a certain irresistible allure).

At any rate, while Homer-era Greek grammarians were debating linguistic intricacies over glasses of grape and urns of olives, the “g” of Gamma (γ) managed to slip into the slot behind the “b” of Beta (β) . . . . . . . and the rest is ancient history, so to speak.

And you probably thought linguistics was a dry subject.

But to get to the main point, in order to prepare for a few excursions through Aquarius, I did some quick stellar research and discovered several of the brighter stars which make up the Aquarian framework are also double or triple.  So I decided to begin at the beginning of the alphabet . . . . . . . and here we are.

Or to be more specific, this is where we are:

The constellations immediately surrounding Aquarius suffer from a noticeable lack of first magnitude stars, not surprising considering the absence of the Milky Way. Fortunately, the diamond-shaped asterism partially outlined here by Alpha (α) and Gamma (γ) Aquarii is distinctive enough to stand out from its stellar surroundings.   (Stellarium screen image with labels added, click on the chart for a better view).

The constellations immediately surrounding Aquarius suffer from a noticeable lack of first magnitude stars, not surprising considering their location beyond the galactic boundaries of the Milky Way.  Fortunately, the diamond-shaped asterism partially outlined here by Alpha (α) and Gamma (γ) Aquarii is distinctive enough to stand out from its dim stellar surroundings. (Stellarium screen image with labels added, click on the chart for a better view).

And here’s a closer look, along with some tongue-twisting Arabic names:

 Stellarium screen image with labels added, click to enlarge.

Stellarium screen image with labels added, click to enlarge.

We’ll start at the alphabetical beginning, but first a word of warning to small aperture users.   The companions of the three stars we’re going to look at are all eleventh and twelfth magnitude, and all are handicapped in varying degrees by the third and fourth magnitude glares of the primaries.   A six inch refractor is the minimum required to pry the secondarial and tertiary lights loose from their high-spirited primarial parents.

Alpha (α) Aqr  (34 Aqr) (BUP 232)        HIP: 109074   SAO: 145862
Sadalmelik (lucky stars of the king)
RA: 22h 05.8m   Dec: -00° 19’

Identifier   Magnitudes   Separation    Position Angle    WDS
BUP 232 AB:   2.96, 12.20      110.00″             40°    2008
SKF 1651 AC:   2.96,  2.90      999.90″           239°    2010

Distance:  523 Light Years (Simbad)
Spectral Classification:  “A” is G2
Note: SKF 1651 AC is Beta Aqr, shares common PM with Alpha Aqr

This is one of the easier pairs we’ll look at, thanks to the 12.20 magnitude secondary’s 110” location from the primary.   Even at that, I had to struggle at first to get a glimpse of it, but once I snagged it with averted vision, it was easy to keep in view.   A 40% waxing moon in the sky didn’t do a lot to help the situation.   I detected a slight gold tinge in the otherwise white primary. Apart from 8.40 magnitude SAO 145858 in the northwest corner of the field, the rest of the field was populated very faintly. (East & west reversed to match the refractor view, click on the sketch to get a better view).

This is one of the easier pairs we’ll look at, thanks to the 12.20 magnitude secondary’s 110” distance from the primary. Even at that, I had to struggle at first to get a glimpse of it, but once I snagged it with averted vision, it was easy to keep in view.  A 40% waxing moon in the sky didn’t do a lot to help the situation, but despite the moonlight I was able to detect a slight gold tinge in the otherwise white primary.  Apart from 8.40 magnitude SAO 145858 in the northwest corner of the field, the rest of the field was populated very faintly. (East & west reversed to match the refractor view, click to get a better view).

But what happened to the 2.90 magnitude “C” component referred to in the data above? The first clue there’s something out of the ordinary with regard to SKF 1651 AC is the strange separation listed for it, 999.90”. Fortunately, a look at the WDS notes for SKF 1651 identifies “C” as Beta (β) Aquarii, which as it happens is located slightly over 10 degrees to the southwest.  That enigmatic 999.90” figure is simply a way of indicating a separation too large to fit into the space allotted for it in the WDS.

So why would you include a star located ten degrees from the primary as a component?  The answer has to do with their shared proper motion.  That prompted me to look up the numbers and compare Simbad plots . . . . . . . and this is what I came up with:

Alpha (α) Aquarii is on the left and Beta (β) Aqr is on the right. Also shown in the left panel is Alpha Aqr B and on the right, Beta Aqr C.   Click on the image for a more legible view.

Alpha (α) Aquarii is on the left, Beta (β) Aqr on the right. Also shown in the left panel is Alpha Aqr B and on the right, Beta Aqr C. Click on the image for a more legible view.

As you can see, the primaries of Alpha and Beta Aquarii are undoubtedly moving in the same direction. For the curious, Simbad shows Alpha Aqr with a proper motion of +018.25 -009.39 (.01825”/year east and .00939”/year south) and it lists Beta at +018.77 -008.21. In a case like this, you would expect their distances from where we are to be similar, and they are: 523 light years for Alpha and 537 for Beta – which is reasonably close given the imprecision of parallax based measures at those distances.

One last item to consider for the curious minded is the WDS designation for the AB pairing of Alpha Aqr, BUP 232.   The three letters refer to S.W. Burnham’s 1913 proper motion catalog (Measures of Proper Motion Stars Made with the 40 Inch Refractor of the Yerkes Observatory in the Years 1907 to 1912).  Shown below are his measures and comments on the AB pair from page 71 of that catalog:

Click to enlarge the image.

Click to enlarge the image.

You can see a slight change taking place between his 1879 and 1907 measurements, which agrees with the directional change indicated by the 2008 WDS numbers. His comment about the motion of the large star (the primary) being “nearly in the direction of the faint companion” is basically correct, since “A” is moving east and “B” is moving west. But when you include the northerly and southerly components, the two stars are actually moving away from each other. The proper motion of Alpha Aqr B, by the way, is -006.7 -007.4 (.0067”/year west and .0074”/year south).

And since we’ve been referring to it frequently, not to mention it being the next letter in the Greek alphabet, we’ll head ten degrees to the southwest and look at Beta (β) Aquarii.  Here’s our second chart again in case you need a navigational reminder.

Beta (β) Aqr  (22 Aqr)  (H V 76)     HIP: 106278   SAO: 145457
Sadalsuud (luckiest of the lucky)
RA: 21h 31.6m    Dec: -05° 34’

Identifier Magnitudes Separation  Position Angle   WDS
H 5 76 AB:   2.91, 11.0     37.60″          319°    2013
Bu 75  AC:   2.91, 11.6     61.00″          189°    2013

Distance: 537 Light Years (Simbad)
Spectral Classification:  “A” is G0
Note: Common proper motion with Alpha Aquarii

If you look closely, you can detect a slight yellow trying to escape from the white glow of the primary. That glow made it rather hard to detect both “B” and “C”, with “C” being the toughest of the two dim companions. The 40% full moon was also hovering nearby, adding to the challenge of seeing “C”.

If you look closely, you can detect a slight yellow trying to escape from the white glow of the primary. That glow made it rather hard to detect both “B” and “C”, with “C” being the toughest of the two dim companions. The 40% full moon was also hovering nearby, adding to the challenge of seeing “C”.

There are two other stars in the field that caught my attention, the first located northwest of “B” and the second southeast of “C”. I decided to see what the UCAC4 showed for magnitudes of those two stars, which generated this image:

Click on the image in order to make the data more legible.   Note this is a mirror-reversed image, which matches the orientation of the sketch above.

Click on the image in order to make the data more legible. Note this is a mirror-reversed image, which matches the orientation of the sketch above.

I’ve labeled the star to the northwest of “B” with a “1”, as well as the corresponding data below the image.  That data shows star “1” with an “f” magnitude of 14.772, which is far too dim.  Allowing for a dimming of “B” because of the primary’s glow, star “1” is at least the same magnitude as “B”, if not slightly brighter.   Southeast of “C”, I labeled two stars (“2” and “3”), but I only saw one of those – more than likely it was star “2”.   Again, it was brighter than “C”, and making allowance for the effect of the primary’s glow on “C”, I would lean toward star “2” being at least as bright as the 11.6 listed for “C” in the WDS.  The UCAC4 data also shows “C” as being fainter than what I saw, but considering the glare, the WDS magnitude of 11.6 is a better match.

The AB pair of Beta (β) Aquarii was discovered by William Herschel on July 20th, 1782:

Wm. Herschel on Beta Aqr

A translation of his Latin on the first line places Beta (β) on the Aquarian’s left shoulder, and as you read further he describes both the separation (33.27”) and position angle (55° 48’) as “very inaccurate.”  That last number should include the phrase north preceding, which would make it equivalent to a present day figure of 325° 48’ (source, scroll to the sixth title).

To get a better idea of how accurate Herschel’s estimates were, we can look at Burnham’s entry for Beta Aqr in his 1906 catalog:

 (Click on the image for a larger view).

(Click on the image for a larger view).

The AB pair is the second entry shown above, and you can see the first observation Burnham includes is that of John Herschel (H), which doesn’t tell us much since it apparently includes a very rough estimate of the separation.   Starting in 1893, the data becomes more consistent and matches well with the 2013 WDS data.

Burnham also includes a comment about “C” being discovered with his six inch refractor (f/15), which occurred in 1871.   His 1898 measure of it was probably made with the 40 inch Yerkes refractor, since “C” was far too dim to measure in the six inch Clark. It looks like the AC pair have shifted noticeably relative to each other since 1893.

Let’s hop back to the east side of Alpha (α) Aquarii now and take a look at the star graced with the third letter of the Greek alphabet, Gamma (γ) Aquarii.   Here’s the second chart once again.

Gamma (γ) Aqr  (48 Aqr)  (HJ 3106)     HIP: 110395   SAO: 146044
Sadachbia (lucky star of the tents)
RA: 22h 21.7m   Dec: -01° 23’
Magnitudes: 3.84, 12.2
Separation:   33.3”
Position Angle: 150° (WDS 2008)
Distance:  164 Light Years (Simbad)
Spectral Classification:  “A” is A0
Notes:  Optical pair based on PM: +130 +008, +000 -015

You gotta look close, but there really is a secondary just below the primary at the 150 degree position – not that I saw it on the first look at this star. There’s a slight touch of yellow in the primary, which showed up despite the moon’s insistent 40% glare.   (East & west reversed once more, click on the sketch to see the secondary better).

You gotta look close, but there really is a secondary just below the primary at the 150 degree position – not that I saw it on the first look at this star. There’s a slight touch of yellow in the primary, which showed up despite the moon’s insistent 40% glare. (East & west reversed once more, click on the sketch to see the secondary better).

It took two attempts to pry the 12.2 magnitude secondary loose, the first attempt being defeated by both the moon and Pacific ocean murk.  When I returned for attempt number two, atmospheric clarity had improved enough to allow the secondary to fight its way out of the primarial glare.  The 12mm Radian (127x) provided my first glimpse of the elusive star, and a 6mm AT Plössl (253x) confirmed it wasn’t my imagination working overtime.

The UCAC4 catalog shows the secondary at a magnitude of 12.011, which is basically in agreement with the WDS number.   Considering both the glare from the primary and the secondary’s proximity to it, it’s even possible the secondary may be much as a magnitude brighter.

Click on the image for a larger view.

Click on the image to enlarge it and improve the legibility of the data.

Also shown on the image above is the proper motion of the primary, which both Simbad and the WDS show as +130 +008 (.130”/year east, .008”/year north).   The WDS shows very little motion for the secondary: +000 -015 (the last number is southerly motion).

In fact, if you look at earlier observations of Gamma Aquarii, as in the excerpt below from Burnham’s 1906 catalog, the change in position angle and separation is strikingly obvious.

Click on the image to enlarge it.

Click on the image for a more crisp view.

A comparison of the position angles and separations in Burnham’s observations with the 2008 data from the WDS (150° and 33.3”) shows the primary is almost racing through its sector of the galaxy.

Sir John Herschel is credited with being the first observer to detect Gamma Aquarii’s faint secondary, which according to the first date of first observation in the WDS took place in 1831 (source):

Click to enlarge the image.

Click to improve the clarity of this image also.

The numbers he listed for the separation seem rather unlikely, though, when compared with the numbers published in Burnham’s catalog. And in fact, Herschel’s comment in the right column – “An extraordinary difference of estimates in distance” – points to his being aware there was a problem with the two numbers.

We’re not done yet in Aquarius, so don’t wander off too far.   We’ll continue east in the next tour to look at two more stars in the Aquarian water jar, and then go south for a couple of more.

Clear skies until then! :cool:

A Smorgasbord of Delphinian Delights, Part 3: Σ 2735, OΣΣ 210, and Σ 2730

Now on to part three of our tour of Delphinus – if you missed them, Part One can be found here and Part Two is located here.

We’re headed into the southeast sector of Delphinus this time, and to get there we’re going to have to cut ourselves loose from Epsilon (ε) Delphini, which has been our navigational anchor. There are no beaming lighthouses to guide us this time, so we’ll have to be content with using fainter reference points to get to where we want to go.

First though, we need to get oriented, which is especially important this time because we’ll need to become familiar with a dim parallelogram of stars known as Equuleus, also known as das kleine Pferd (the small horse):

Small and unimposing in comparison to the larger constellations surrounding it, Delphinus is nevertheless distinctive thanks to its diamond-shaped configuration. It would be a real stretch to call Equuleus distinctive, though, since it’s noticeably dimmer. In fact, it’s difficult to notice at all, especially if you’re under light-polluted skies or having to deal with interference from lunar light. (Stellarium screen image with labels added, click on the chart for a larger view).

Small and unimposing in comparison to the larger constellations surrounding it, Delphinus is nevertheless distinctive thanks to its diamond-shaped configuration. It would be a real stretch to call Equuleus distinctive, though, since it’s noticeably dimmer. In fact, it’s difficult to notice at all, especially if you’re under light-polluted skies or having to deal with interference from lunar light. (Stellarium screen image with labels added, click on the chart for a larger view).

BUT — if you’re under dark skies – say fifth or sixth magnitude – with no interfering moonlight, Equuleus is not all that hard to find.  Start by locating Enif, aka Epsilon (ε) Pegasi, which lies at the southwest edge of Pegasus.   Equuleus is located halfway and just south of a line drawn between Enif and Delphinus.  If your skies are too bright to catch Equuleus with bare naked eyes, a pair of binoculars will pry it out of the sky with little effort. By the way, I poked around in Equuleus for several nights back in 2010 and 2011, and the results can be found here and here.

We’ll zoom in now with this chart, which shows the locations of all the stars included in our three Delphinian tours. We’re going to start at the southwest corner of Equuleus and look at Σ 2735, OΣΣ 210, and Σ 2730. (Stellarium screen image, labels added, click for a larger version).

We’ll zoom in now with this chart, which shows the locations of all the stars included in our three Delphinian tours. We’re going to start at the southwest corner of Equuleus and look at Σ 2735, OΣΣ 210, and Σ 2730. (Stellarium screen image, labels added, click for a larger version).

A word of caution: It’s very easy to become disoriented by mistaking either 3 or 4 Equulei (both sixth magnitude) for the southwest corner of Equuleus, so take a close look at the chart above or the star atlas you’re using. The distance from the northeast corner of Equuleus, which is held down by Delta (δ) Equulei, to the southwest corner is seven degrees — just slightly larger than the five degree field of view of most 8×50 finders — so make sure to pan your scope far enough to the southwest to pick up our starting point at 1 Equulei (Epsilon (ε) Equulei), which is also sixth magnitude.

If you need a second reference point for locating 1 Equulei, you can go back to Epsilon (ε) Delphini.   The distance from it to 1 Equulei is nine and a half degrees, or about two finder fields, due southeast.   Traveling distance from 1 Equ to our first star, Σ 2735, is a very short 53’ to the west and slightly north – you can use 6.84 magnitude HIP 103472 as a reference point.

Σ 2735 (H I 61)            HIP: 103301   SAO: 126373
RA: 20h 55.7m   Dec: +04° 32’
Magnitudes: 6.45, 7.54
Separation:  2.00”
Position Angle: 281° (WDS 2011)
Distance: 362 Light Years (Hipparcos), 462 LY (Simbad), 522 LY (Tycho-2)
Spectral Classification: “A” is G6

We’re starting with a somewhat tough little devil – at two arc seconds of separation, with a full magnitude of difference between components, it can be a challenge under uncooperative skies.  But if you can pry this pair apart, you’ll be rewarded with a heart-stopping sight:

The primary is mainly white, with a weak but noticeable gold-yellow tinge. Nestled up tightly against it, the secondary just barely succeeds in appearing as a separate entity. I also noticed it appears surprisingly small considering it’s only a magnitude fainter than the primary, which means it may actually be a bit fainter than the 7.54 magnitude listed for it. When the seeing cooperates enough to allow a sharply focused view of a pair of stars such as this, the resulting view strikes me as one of the most satisfying in all of double-stardom.   (East & west reversed, click on the sketch for a much better view).

The primary is mainly white, with a weak but noticeable gold-yellow tinge. Nestled up tightly against it, the secondary just barely succeeds in appearing as a separate entity. I also noticed it appears surprisingly small considering it’s only a magnitude fainter than the primary, which means it may actually be a bit fainter than the 7.54 magnitude listed for it.  (East & west reversed, click on the sketch for a much better view).

When the atmosphere graciously allows a sharply focused view of a pair of stars such as this, the resulting view strikes me as one of the most satisfying in all of double-stardom.  Sir William Herschel, who stumbled across this pair on October 26th, 1782, also noticed it requires a cooperative sky in order to be separated (source, sixth title from top):

Wm Herschel on STF 2735

Click to enlarge the image.

Click to enlarge the image.

If you consult a star atlas, his directions are actually very precise, including his Latin phrase at the top left of this excerpt, which translates as “preceding Flamsteed 1 Equulei.” His 18° 24’ north preceding is equivalent to our present day 288° 24’, which puts the secondary a bit further north from the primary than the most recent WDS data.   As you can see in the excerpt at the right from Lewis’s book on Struve’s double stars, there has been a slow change in the position angle in the direction of the current WDS PA.  Older WDS catalogs show the PA at 282° in 1991 and 1999 and 281° in 2003, which falls into line with the numbers in Lewis’s book.

The separations shown in his book, though, are anything but consistent, varying from John Herschel’s 1.85” in 1829 and William Smyth’s 1.80” in 1833 to Struve’s 2.13” in the same year as John Herschel’s measure, as well as Secchi’s 2.13” in 1856. On the other hand, WDS numbers are very consistent, with the 1991 and 1999 catalogs showing 2.1” and the 2003 showing 1.9”, followed by 2.00” in 2011.   So do we have an orbital pair or not?

A look at the proper motion numbers for the primary (+064 +014, or .064”/year east and .014”/year north) and the secondary (+045 +012), leave the impression these two stars are almost moving in tandem with each other. The Simbad proper motion plot shows the motion very clearly:

Click for a larger view.

Click for a larger view.

Given a few million years, the primary will eventually outdistance the secondary, but I wouldn’t advise waiting around for it.

One other interesting aspect of this pair of stars is its distance.  If you look at the light year measures on the next to last line of the data at the beginning of this discussion of Σ 2735, you’ll notice I’ve included three different numbers.   If I had to hazard a guess as to which one is correct, I would lean toward the Simbad number (parallax of 7.06 mas) because it’s based on a 2007 revision of the 1997 Hipparchos data, which is the most recent information available.

Next star on our tour: OΣΣ 210, also known as STTA 210.  Here’s a look at our last chart once again, which shows it lies 1° 45’ northwest of our current position at Σ 2735.  If you look closely, you’ll also notice OΣΣ 210 is slightly southeast of 5.6 magnitude 13 Delphini, aka Bu 65.

OΣΣ 210  (STTA 210)       HIP: 102833   SAO: 126267
RA: 20h 50.0m   Dec: +05° 33’
Magnitudes   AB: 6.30, 9.18    BC: 9.18, 14.70
Separations  AB: 78.50”          BC: 12.70”
Position Angles  AB: 127° (WDS 2010)   BC: 220° (WDS 2000)
Distance: 496 Light Years (WDS), 413 LY (Simbad)
Spectral Classification: “A” is K0

The “A” and “B” companions make a pretty pair, with the primary a subtle gold-white and the secondary all white. I had hopes the “C” component would be brighter than the 14.70 magnitude listed for it, but apparently not since I wasn’t able to catch a glimpse of it.   (East & west reversed once again, click on the sketch to get a better view).

The “A” and “B” companions make a pretty pair, with the primary a subtle gold-white and the secondary all white. I had hopes the “C” component would be brighter than the 14.70 magnitude listed for it, but apparently not since I wasn’t able to catch a glimpse of it. (East & west reversed once again, click on the sketch to get a better view).

There are three faints stars surrounding the west and southwest sides of the primary, which came as a surprise since none of them are included as components, even though a significantly fainter 14.7 magnitude star was added in 2000 as “C”.   All three of the stars were elusive in my five inch refractor, but quite obvious when the seeing cooperated for varying fragments of time.  S.W. Burnham apparently noticed the same three stars in 1903, as well as the one now labeled as “C” (source):

Burnham on STTA 210

Curious about the magnitudes of those three stars, I pulled up an Aladin image with the UCAC4 catalog overlaid on it and added the data for each star by clicking on the red circles and squares superimposed on the image:

The letters and numbers for each of the stars correspond with the data at the bottom of the photo. Click on the image for a larger view.

The letters and numbers for each of the stars correspond with the data at the bottom of the photo. Click on the image to improve the legibility of the data.

The magnitudes in the “f” column for stars 1, 2, and 3 are much too faint to be detected in the five inch refractor I was using. Stars 2 and 3 have magnitudes listed in the “J” and “K” columns which are more in line with what I saw visually — in fact “K” is probably closer than “J”. There’s no magnitude listed in those two columns for star 1, but it was very similar in brightness to the other two, so it should be in the neighborhood of 11.5.

The proper motions for those three stars, as well as “A” and “B”, are also included in the data below the image. The only stars which look like they may be related physically through proper motion are “A” and star 1 – all the others are drifting in several different directions.

Simbad’s proper motion plot doesn’t include stars 1, 2, and 3, and since there’s no data for “C”, the plot we end up with illustrates very clearly no physical connection exists between “A” and “B”:

This is an erect image, so east and west are in their normal positions.   The previous images for STTA 201 have all been mirror images (east and west reversed) in order to match the orientation of the sketch.   (Click for a larger view).

Here’s a look at Simbad’s proper motion data (same plot that’s shown in the link above) super-imposed on an Aladin image.  (This is an erect image, so east and west are in their normal positions. The previous images for STTA 210 have all been mirror images (east and west reversed) in order to match the orientation of the sketch).  Click for a larger view.

Click to enlarge.

Click to improve the view slightly.

And that takes us to our last Delphinian delight for this three-part tour.  I’ve included an excerpt from our second chart at the right which zooms in on the Σ 2730 — OΣΣ 210 area.  The distance from OΣΣ 210 to Σ 2730 is 53’, but because Σ 2730 is faint and somewhat difficult to see in an 8×50 finder it helps to use 5.6 magnitude 13 Delphini (Bu 65) and the considerably dimmer 7.75 magnitude HIP 102739 as reference points.

Σ 2730  (S 766)             No HIP Number   SAO: 126289
RA: 20h 51.1m   Dec: +06° 23’
Magnitudes: 8.43, 8.57
Separation:  3.3”
Position Angle: 333° (WDS 2013)
Distance:  68 Light Years (Tycho)
Spectral Classification: “A” is K1

This is an attractively delicate and faint pair, easily separated because their magnitudes are close, but not quite bright enough in the five inch refractor for me to detect the orange hint of light promised by the K1 spectral class of the primary. I just happened to catch them in a vertical configuration, which adds to their visual appeal. (East & west reversed once more, click on the sketch for a larger view).

This is an attractively delicate and faint pair, easily separated because their magnitudes are close, but not quite bright enough in the five inch refractor for me to detect the orange hint of light promised by the K1 spectral class of the primary.  I just happened to catch them in a vertical configuration, which adds to their visual appeal.  (East & west reversed once more, click on the sketch for a larger view).

Even though this pair carries the Greek designation (Σ) for F.G.W. Struve, Sir James South arrived here a few days ahead of the senior Struve, which you can see from the dates in Lewis’s book three paragraphs further down (source for South’s observation below):

Click on the image to enlarge it.

Click on the image to enlarge it.

South’s position angle of 69° 31’ np (north preceding) equates to our present day 339° 31’ and the two separations he measured on August 9th and August 12th of 1825 average out right at 4” – not bad results for the five inch f/16.8 refractor (South described its focal length as seven feet) he used for this observation.  In the introduction to his joint 1824 catalog with John Herschel, he wrote “The ordinary observing power employed with this telescope was 179, but occasionally a low power of 105, and a higher one of 273, were also used.” [see p. 13 of this source (scroll down to the last title)]

If South had viewed this pair of stars at 179x in his f/16.8 five inch refractor, the view I had at 191x in my five inch f/15 instrument would have been very similar to his. A closer look at his notes shows several comments on the stars themselves – “difficult” and “very difficult” – and on the seeing conditions – “the stars are frequently indistinct” and “stars unsteady” – which was exactly my experience under very similar atmospheric conditions.

Click to enlarge.

Click to enlarge.

Looking at the list of observations at the right in Lewis’s book, which span eighty years, you can see a slow change in both position angle and separation. The separations jump around quite a bit, probably due to the difficulty in measuring such a short distance, which is apparent from the separations measured within a few days of each other by South and Struve. In fact, Struve’s separation stands out as rather unlikely when compared to the others.   I found old WDS measures for 1988 (335° and 3.3”) and 1999 (334° and 3.2”) which continue the trend seen in Lewis’s data.

As to whether there’s some type of gravitational attraction between these two stars, a look at the proper motion numbers shows very little movement.   However, both the WDS and the UCAC4 catalog show the same numbers for both stars, +004 -006 (.004”/year east and .006”/year south), which if true, conflicts with the slow changes in position angle and separation that has taken place since 1825.   So who knows – we’ll need another thousand years to tell at this rate, or better technology in order to make more precise measurements.

That’s it for Delphinus for a while, although there’s plenty more to look at in this small constellation.   Next time out we’ll slide over to Aquarius and take a look at some of its naked eye suns which have risen to double star status.   Until then, I hope your skies are more cooperative than they’ve been here for the past month!   :cool:

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