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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.

Leo in a Minor Key, Part Two: 7 LMi, 11 LMi, and Σ 1374

This excursion in Leo Minor will take us along the western edge of the constellation, close to its border with Lynx. (If you missed it, the first part of this tour is here).  All three of the stars we’re going to look at this time are aligned along a north-south line, so the chances of getting lost and disappearing into the starless black void typical of this area are pretty slim.

First, here’s an overview of where we’re headed (if you find Leo Minor difficult to track down because it’s frustratingly faint, the paragraphs above and below the first chart in part one describe how to locate it and trace its outline):

 Stellarium screen image with labels added, click to enlarge.

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

Here’s a closer look, which includes the three destinations for this tour, all of which are north or south of 10 LMi, and all of which are labeled in tantalizing turquoise:

Stellarium screen image with labels added, click to enlarge.

Stellarium screen image with labels added, click to enlarge.

Since 10 LMi is situated in the middle of our target area, we’ll start there and begin by moving north to Σ 1374, which is located three degrees north and slightly east of 10 LMi.   There’s a triangle of fifth magnitude stars (42 and 43 Lyn, and HIP 47029) just north of Σ 1374, which makes it easy to locate.

Σ 1374  (AC is ABT 7)      HIP: 47527   SAO: 61629
RA: 09h 41.4m   Dec: +38° 57’
Magnitudes   AB: 7.28, 8.65    AC: 7.28, 13.13
Separations  AB: 2.80”            AC: 307.60”
Position Angles   AB: 313° (WDS 2013)   AC: 10° (WDS 2002)
Distance:  167 Light Years (Simbad)
Spectral Classifications:  “A” is G3

This is what you might call a spatially diverse triple star. The secondary is close enough to hide in the primary’s glow produced, aided by the 1.37 magnitudes of difference between the two stars. At 152x the two stars were barely separated, but as the inset at the right shows, the view improved considerably at 253x. Both of those stars appeared white to my eyes, with no trace of the yellow hinted at by the G3 spectral classification of the primary. The “C” component is both very faint and very distant, and requires adequate aperture and a discerning eye to locate it.   (East & west reversed to match the refractor view, click on the sketch to get a better view).

This is what you might call a spatially diverse triple star. The secondary is close enough to hide in the primary’s glow, aided by the 1.37 magnitudes of difference between the two stars. At 152x the two stars were barely separated, but as the inset at the right shows, the view improved considerably at 253x. Both of those stars appeared white to my eyes, with no trace of the yellow hinted at by the G3 spectral classification of the primary. The “C” component is both very faint and very distant, and requires adequate aperture and a discerning eye to locate it. (East & west reversed to match the refractor view, click on the sketch to improve the view of one heck of a lot).

If you look closely (you’ll have to enlarge the sketch), you’ll see three very faint stars at the southwest (left) edge of the field.   By overlaying the WDS catalog on the Aladin image below, I was able to determine those three stars are not cataloged in the WDS.  I used the UCAC4 catalog to identify the three, which shows they’re all in the twelfth and thirteenth magnitude range.

Aladin image with UCAC4 data, click to enlarge.

Aladin image with UCAC4 data, click to enlarge.

The proper motions are also listed in the data at the bottom of the image and show some similarity in motion for the stars numbered “1” and “2”.  Considering how slight that motion is, the chances are the two stars are located quite a distance from us, which makes it difficult to come to any conclusion as to whether the pair is physically related.  Interestingly enough, the pair that are closest together visually, “2” and “3”, are moving away from each other.

But to get back to our main interest, the “A” and “B” components of Σ 1374 are a genuine orbital pair with a period of 1377 years (the orbit and data can be seen here).  The pair are in a phase of their orbit where they’re moving closer together, although at a very slow rate.  The WDS Ephemerides shows them with a separation and position angle of 2.778” and 314.2 degrees in 2030, so there’s no need to feel anxious about catching them before they get too close together to be caught.

As for “C”, why it was added to the Σ 1374 pair is something of a mystery (the ABT initials of ABT 7 refer to Giorgio Abetti).   At the bottom of the image above, I included the UCAC4 data on the three components of Σ 1374, which also include the proper motions of each of the stars.  It’s obvious “C” has no relation whatever to the AB pair of Σ 1374, and given that it’s over five arc minutes away from that pair, it’s hard to say what prompted Abetti’s inclusion of it in 1921 — possibly its position angle and separation were measured as a reference point for the proper motion of the AB pair.

Sometimes when you dig deep, the stellar puzzles seem to multiply at an astronomical rate.

Let’s go back south to 10 LMi now and take a look at a more difficult pair, 11 LMi, also known as HU 1128.   It’s easy to find since it’s parked just 39’ south and slightly east of 10 LMi (here’s our chart again).

11 LMi  (HU 1128)     HIP: 47080   SAO: 61586
RA: 09h 35.7m   Dec: +35° 49’
Magnitudes: 4.8, 12.5
Separation:  6.41”
Position Angle: 49.9° (WDS 2015 Ephemerides)
Distance: 37 Light Years (Simbad)
Spectral Classifications:  “A” is G8, “B” is M5

With just under eight magnitudes of difference between the primary and secondary, this is a very tough pair. I barely caught a glimpse of it at 152x in the glare of the yellow-white primary, and did a bit better at 253x.   (East & west reversed once again, click on the sketch to get a better view of the secondary).

With just under eight magnitudes of difference between the primary and secondary, this is a very tough pair. I barely caught a glimpse of it at 152x in the glare of the yellow-white primary, and did a bit better at 253x. (East & west reversed once again, click on the sketch to get a better view of the secondary).

Located 4.8′ north and slightly east of 11 LMi is ALI 357, with magnitudes of 12.5 and 12.6, separated by 7.60” at a PA of 96° (WDS 2002).  I didn’t notice them, probably because they were more closely spaced than the fainter pair of stars seen about 1.6’ southwest (left in the sketch) of the primary of 11 LMi.  That’s another pair which is not cataloged in the WDS, and as the data at the bottom of the image below shows, the two stars don’t appear to be linked by proper motion. The UCAC4 catalog data shows the northernmost of the pair with a magnitude of 13.5 and the southernmost at a magnitude of 12.98 — the separation is about 19″.

Click on the image to make the data more legible.

Click on the image to make the data more legible.

Click to enlarge.

Click to enlarge.

11 LMi, aka HU 1128, is also an orbital pair (here’s the orbit and data), with a relatively short period of 201 years.   The last date of observation in the WDS is 2006, but because the position of the two stars is changing significantly, I used the 2015 WDS Ephemerides for the data above, which is included in the chart at the right.  Notice it shows the stars will continue to widen over the next fifteen years.

The 11 LMi pair have a rather high rate of proper motion, which isn’t surprising considering they’re a short 37 light years from us:

Click to enlarge.

Click for a much better view.

Rounded off to three decimal figures, the column labeled PMRA shows motion of .729”/year west in right ascension and .260”/year south in declination, which means this pair are strolling across the sky at a rate of almost one arc second per year. There are two more stars in the photo above with significant proper motion (the data there is from Simbad also), neither of which are associated with 11 LMi.

The HU in HU 1128 refers to William Joseph Hussey, a prolific observer who spent much of his career at Lick Observatory in northern California.  When he first caught sight of this pair of stars in 1904, they were at a different point in their orbital waltz (source):

Click to enlarge.

Click to enlarge.

Let’s drop south and slightly west now for a distance of about two and half degrees to 7 LMi (here’s our chart once more).  You can use 5.39 magnitude 8 LMi as a reference point, which sits almost midway between the two stars and about 20’ west of the line which connects them.

7 LMI  (H V 69)  (HJ 1166)  (STTA 100)     HIP: 46652   SAO: 61529
RA: 09h 30.7m   Dec: +33° 39’
Magnitudes   AB: 5.97, 9.66    AC: 5.97, 11.58
Separations  AB: 61.30”          AC: 95.90”
Position Angles   AB:  125° (WDS 2011)   AC: 217° (WDS 2001)
Distance:  502 Light Years (Simbad)
Spectral Classifications:   “A” is G8, “B” is K0

We haven’t heard from the admirable Admiral William Smyth for a while, so let’s see what he has to say about 7 Leonis Minoris:

A wide double star, immediately under the animal’s right fore-paw. A 6, bluish white; B 11, livid. This object was registered 69 H V, in 1782, with a distance of 58.30”, but no angle of position; and it is No. 1116 of H.’s twenty-foot Sweeps. The companion is one of those minute and dusky objects which are best seen by averting the eye to the verge of the field; but there are many of much smaller magnitude, which shine quite sharply, and emit a strong blue ray. It may be found by carrying a line from Regulus close to the eastward of ε Leonis, and passing it exactly as far again into the north-north-west region.”   (The Bedford Catalogue, p. 217)

I’m not quite sure what the good Admiral meant with his description of “B” as livid, but I saw a hint of orange in it, and I saw yellow-orange in the primary instead of the Admiral’s bluish white.  “C”, which was added in 1912, was colorless, but no problem to see. The field of view is rather sparse, which has been typical of the stars we’ve looked at in this area.   (East & west reversed once more, click on the sketch to improve the view).

I’m not quite sure what the good Admiral meant with his description of “B” as livid, but I saw a hint of orange in it, and I saw yellow-orange in the primary instead of the Admiral’s bluish white. “C”, which was added in 1912, was colorless, but no problem to see. The field of view is rather sparse, which has been typical of the stars we’ve looked at in this area. (East & west reversed once more, click on the sketch to improve the view).

7 Leonis Minoris has had a lot of visitors, as is evident from the first line of data above.  William Herschel (H V 69), John Herschel (HJ 1166), and Otto Struve (STTA 100) — and of course, Admiral Smyth — all stopped here for a visit.  The father-son observations of the two Herschel’s are shown below (source for Wm. Herschel [six titles down), source for John Herschel):

Sir William’s work is at the top, Sir John’s is at the bottom. Click to enlarge.

Sir William’s work is at the top, Sir John’s is at the bottom. Click to enlarge.

As Admiral Smyth mentioned, William Herschel didn’t include a position angle in his notes, and in case you’re wondering, his Latin translates roughly as “in the extreme of the front foot.”  John Herschel’s 45° sf (south following) translates to 135°, which misses the 2001 WDS number by ten degrees, but since Sir John’s number was an estimate, we can call it in the ball park.  Their separations are considerably less than the 2001 WDS figure of 61.30”, and as was the case with Admiral Smyth’s magnitude estimates, their numbers are different from the 5.97 and 9.66 values shown in the WDS.

S.W. Burnham included another three measures in his 1906 catalog (the first is William Herschel’s original observation), which show gradual changes in both the position angle and separation:

Burnham on 7 LMi

Those numbers suggest the proper motions of the primary and secondary should show the two stars are gradually moving away from each other, and in fact that’s exactly what we see:

“A” is moving west at a rate of .023”/year and south at .048”/year, while “B” is moving west at .002”/year and south at a rate of .029”/year. Simbad doesn’t’ show any data on “C”, but the UCAC 4 catalog shows it moving due west at the rate of .051”/year with a very slight southern tendency of .0004”/year – in other words, it’s moving away from the other two stars as well. Notice the Simbad and UCAC4 proper motion for “A” and “B” are slightly different. (Click to enlarge the image).

Simbad’s data is shown in the top panel, UCAC4 is shown in the bottom one.  Click to make the date more legible!

“A” is moving west at a rate of .023”/year and south at .048”/year, while “B” is moving west at .002”/year and south at a rate of .029”/year. Simbad doesn’t show any data on “C”, but the UCAC 4 catalog shows it moving due west at the rate of .051”/year with a very slight southern tendency of .0004”/year – so it’s moving away from the other two stars as well.  Notice the Simbad and UCAC4 proper motions for “A” and “B” are slightly different.

And that should cover Leo Minor for a good while. Our next tour will take us down into the larger Leo for a look at some rather difficult stars, so order up some good seeing and break out the five and six inch scopes.

Clear Skies until then! :cool:

Leo in a Minor Key, Part One: 42 LMi, Σ 1432, and OΣΣ 104

It’s not distinctive, but it’s there if you look closely – Leo Minor, that is.

During the many hours I’ve spent in the larger Leo, perusing double stars and galaxies, I’ve always been aware of the smaller Leo to the north. Most atlases portray Leo Minor in a skewed diamond-shaped configuration, but the few times I’ve glanced up that way in a semi-serious search for it, I’ve never found anything but a wide scattering of faint and un-spectacular stars. Sooner or later I knew I would have to grab my Sky &Telescope Pocket Atlas, hold it up to the sky, and pin little Leo into place.

Sooner came later than I had planned, but at least it arrived.

Leo Minor is sandwiched between several somewhat dim, but discernible, reference points in a fairly faint part of the sky: Allula Australis, Allula Borealis, Tania Australis, Tania Borealis (all in Ursa Major), and Alpha (α) Lynicis, the brightest star in another faint constellation known for being spectacularly faint.

 Stellarium screen image with labels added, click to enlarge.

Stellarium screen image with labels added, click to enlarge.

The easiest way to pin down Leo Minor is to begin by locating one of the Great Bear’s (Ursa Major’s) three distinctive feet. We’ll start at third magnitude Delta (δ) Leonis, also known as Zosma, which marks the rear of Leo the Lion’s back. Fourth magnitude Allula Australis, located at the south tip of the Great Bear’s rear leg, is eleven degrees due north of Zosma, where it sits linked to its slightly fainter neighbor, Allula Borealis, one and half degrees further north. From Allula Borealis, a five degree leap due west with a very slight tilt to the north will get you to 3.83 magnitude 46 Leonis Minoris.  From there, it’s a matter of branching out both northwest and southwest about five and half degrees to reach 4.21 magnitude Beta (β) LMi and 4.74 magnitude 30 LMi.  And from there, continue west and slightly north to pick out 4.49 magnitude 21 LMi and 4.56 10 LMi.

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

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

We’re going to start with fifth magnitude 42 Leonis Minoris, also known as S 612, which is four degrees south and slightly west of 46 LMi.   On the chart, you can see it’s the southernmost of a line of three stars formed with 4.74 magnitude 30 LMi and 4.72 magnitude 37 LMi.

42 LMi (S 612)        HIP: 52638   SAO: 62236
RA: 10h 45.9m   Dec: +30° 41’

Identifier Magnitudes Separation  PA WDS
S 612 AB:  5.34, 7.78    196.50″ 174° 2012
ARN 3 AC:  5.34, 8.31    424.60″  94° 2012

Distances   A: 382 Light Years     B: 661 LY     C: 373 LY  (Simbad)
Spectral Classifications   “A” is A1, “B” is K2, “C” is F0

A wide triple star that comes darn close to forming a perfect right angle triangle. “A” and “C” appeared white, and a careful look at “B” turned up a slight hint of orange, which dims it just enough to make it look about the same magnitude as “C”.   (East & west reversed to match the refractor view, click on the sketch for a better version).

A wide triple star that comes darn close to forming a perfect right angle triangle. “A” and “C” appeared white, and a careful look at “B” turned up a slight hint of orange, which dims it just enough to make it look about the same magnitude as “C”. (East & west reversed to match the refractor view, click on the sketch for a better version).

The AB pair was discovered by Sir James South on a frosty March night in 1825, which he describes rather well in this page from his 1826 catalog:

Frost prevention in the days before dew heaters and electrical power!

Frost prevention in the days before dew heaters!  Click to enlarge.

Sir South’s final position angle of 82° 36’ sf (south following) works out to a present day PA of 172° 36’ and when converted to arc seconds, his separation is 200.304”.

A look at S.W. Burnham’s 1906 double star catalog turns up two more observations of 42 LMi  . . . . . . .

Burnhan on 42 LMi

. . . . . . . and when the three measures are listed together, they show a gradual decrease in separation as well as a gradual change in PA toward the south, both of which are confirmed by the 2012 WDS measures which continue that trend:

South-Leiden-Burnham chart

A look at an Aladin photo of 42 LMi with Simbad’s proper motion data super-imposed on it clarifies why those changes are taking place:

The motion here is south and west in this erect image version of 42 LMi (east and west are reversed in the mirror-image refractor sketch above). Decoded, the proper motion data for “A” means motion in arc seconds of .026”/year west and .037”/year south. The negative signs indicate westward motion in right ascension and southerly in declination.

The motion here is south and west in this erect image version of 42 LMi (east and west are reversed in the mirror-image refractor sketch above). Decoded, the proper motion data for “A” means motion in arc seconds of .026”/year west and .037”/year south. The negative signs indicate westward motion in right ascension and southerly in declination.

The southerly motion of “A” towards “B” is obvious here, and given enough time, the two stars will probably appear to intersect. However, as the distances of “A” (382 LY) and “B” (661 LY) listed in the data lines above for 42 LMi indicate, there are 279 light years between the two star, so a stellar scale impact isn’t looming in the very distant future.

The “C” component (ARN 3), at 373 LY, is much closer to “A”, and is moving pretty close to parallel with it. But there’s enough difference in direction and rate of motion to cast doubt on a physical connection between the two stars, as well as the nine light years of distance between them.  ARN 3 refers to Dave Arnold, who added the “C” component sometime around 2000 or 2001, as near as I can tell.   At that time, he published his results in the Double Star Observer, which was succeeded in 2005 by the Journal for Double Star Observers, better known as the JDSO. I’ve had no luck with numerous internet searches for back issues of the Double Star Observer, so if anyone is aware of their existence, please leave a comment and I’ll follow up on it.

Next on our list is Σ 1432, a faint double located in a lonely part of the sky southwest of 42 LMi.  To get there, we’ll need to negotiate  a distance of almost four degrees (3° 45’) west and slightly south through relatively featureless terrain until we reach 6.61 magnitude HIP 51325 (here’s our last chart again).  Σ 1432 is a faint dot of eighth magnitude light wedged between HIP 51325 on the east and 6.36 magnitude HIP 50904 on the west.

Σ 1432     HIP: 51158   SAO: 81347
RA: 10h 27.0m   Dec: +29° 41’
Magnitudes: 7.84, 10.28
Separation:  28.5”
Position Angle: 121° (WDS 2012)
Distances   A: 327 Light Years   B: 399 LY (Simbad)
Spectral Classification:  “A” is F2

The field of view surrounding Σ 1432 is about as bleak and featureless as the terrain we navigated to get here. Apart from the ash white glow of the primary, the only other notable object is TDS 7264, a faint pair with magnitudes of 11.1 and 11.39 separated by 0.7” at a position angle of 134° as of 1991 – and well below the threshold of my detection.   (East & west reversed once more, click on the sketch to enlarge it).

The field of view surrounding Σ 1432 is about as bleak and featureless as the terrain we navigated to get here. Apart from the ash white glow of the primary, the only other notable object is TDS 7264, a faint pair with magnitudes of 11.1 and 11.39 separated by 0.7” at a position angle of 134° as of 1991 – and well below the threshold of my detection. (East & west reversed once more, click on the sketch to enlarge it).

This is one of F.G.W. Struve’s more challenging pairs, with a 2.44 magnitude difference between the primary and secondary. It’s not particularly difficult, but you have to look closely to catch the much fainter secondary’s diminutive dot of light.

There’s been a slight narrowing of the separation and a minor change in direction in the position angle since Struve’s first measures, which can be seen in the following fifty years of observations taken from Thomas Lewis’s book on Struve’s double star catalog:

Lewis on STF 1432

That narrowing of separation and the slight PA change can be seen taking place in this Aladin photo, which shows the direction and rate of motion of both stars:

The motion shown here in this erect image is west and south, and the explanation of the numbers included in the Aladin-Simbad photo above of 42 LMi applies here as well.   Click for an improved version!

The motion shown here in this erect image is west and south, and the explanation of the numbers included in the Aladin-Simbad photo above of 42 LMi applies here as well. Click for an improved version!

We can get a three-dimensional feel for what’s actually taking place here if we mentally super-impose the distances of “A” (327 light years) and “B” (399 light years) on the photo.  Since it’s obvious in the photo that “A” is the brighter of the pair, it’s not difficult to perceive it as being in the foreground of the image.  If you can pull it off, you’ll have an inkling of what a difference of 72 light years looks like!

Now we’ll move on to a pair that is wider, more colorful, and almost evenly matched in magnitude, OΣΣ 104From Σ 1432, we’re going to move four degrees due north to 4.74 magnitude 30 LMi (our second chart once more).  Once you have that star centered in your finder, you’ll see the twin glow of OΣΣ 104 a short 31’ to the northwest.

OΣΣ 104     HIP: 50951   SAO: 62021
RA: 10h 24.4m   Dec: +34° 11’
Magnitudes: 7.21, 7.27
Separation:  209.4”
Position Angle: 287°  (WDS 2012)
Distances    A: 1028 Light Years   B: 953 LY  (Simbad)
Spectral Classifications:  “A” is M4, “B” is K0

The appearance of a pair of weakly tinted yellow-orange stars in the center of my eyepiece was a welcome change after the persistent white of our two previous objects. These two stars point almost due west on first glance, and the scene is improved by the intriguing parallelogram of three twelfth magnitude stars and one tenth magnitude star on the south side of the OΣΣ 104 pair.   (East & west reversed once more, click to enlarge).

The appearance of a pair of weakly tinted yellow-orange stars in the center of my eyepiece was a welcome change after the persistent white of our two previous objects. These two stars point almost due west on first glance, and the scene is improved by the intriguing parallelogram of three twelfth magnitude stars and one tenth magnitude star on the south side of the OΣΣ 104 pair. (East & west reversed once more, click to enlarge).

There’s a distance of 75 light years between the two stars of OΣΣ 104 according to Simbad’s data, so they’re purely a line of sight pair. They’re also moving away from each other as seen below:

“A” is moving east at .006”/yr (east is indicated by the plus sign) and south at the rate of .021”/year, while “B” is moving west at .005”/yr and south .014”/year.   Click to make the data more legible.

“A” is moving east at .006”/yr (east is indicated by the plus sign) and south at the rate of .021”/year, while “B” is moving west at .005”/yr and south .014”/year.  Notice the NOMAD-1 PM is slightly different.  Click to make the data more legible.

The UCAC4 and NOMAD-1 data is included at the bottom of the photo above because I found a magnitude conflict with the AAVSO data.  I stumbled on that discrepancy after discovering the primary of OΣΣ 104 is a variable star (Simbad labels it a semi-regular pulsating star). The AAVSO identifies the primary as UU LMi, with a magnitude range of 6.89 to 7.03. Since that magnitude range conflicts with the 7.21 magnitude assigned to the primary in the WDS, I checked the UCAC4 and NOMAD-1 catalogs and found visual magnitudes of 7.202 (UCAC4) and 7.048 (NOMAD-1) for the primary. So it’s possible the WDS magnitude for “A” is off slightly (although the similar UCAC4 Vmag value was probably generated by the AAVSO’s APASS data), but certainly not enough to be detectable visually unless you happen to have photometric cells in your eyes.

We’re not done with Leo Minor quite yet.  On our next trip, we’ll wander to the west edge of little Leo for a look at three more stars.

In the meantime, Clear Skies!   :cool:

Double and Triple Stardom in Taurus: 37 and 39 Tau, Σ 479, and Σ 494

Floating in the sky northwest of the V-shaped asterism in Taurus which is home to the Hyades is a pair of stars that would probably be better known if fate hadn’t decreed they should occupy a stellar address within a few degrees of the Pleiades. Over-shadowed by the brilliant blue-white light and glowing nebulosity of the most dazzling naked eye open cluster in the heavens, 37 and 39 Tauri are ignored night after night by double star sleuthers.

But . . . . . . . not tonight!

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

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

There are a couple of different paths to 37 and 39 Tauri, both starting from well-known objects.  First, you can start at first magnitude Aldebaran and scoot across the northeast edge of the Hyades to 3.5 magnitude Epsilon (ε) Tauri (also known as Ain), a distance of about three degrees. From there, adjust your direction of travel very slightly to the south and leap another three degrees to fifth magnitude Omega (ω) Tauri, which sits just south of a trio of stars known as 56, 51, and 53 Tauri.  Continue along the same line of travel another three and a half degrees and you’ll find yourself looking at 37 and 39 Tauri.

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.

A shorter approach is to start from the Pleiades and move southeast a distance of 2.75 degrees to 5.6 magnitude 32 Tauri, and then correct your direction slightly to the north and hop another two degrees to reach 37 and 39 Tauri. That route is shorter, although you may find yourself mesmerized by the Pleiadic glow and forget what you came for.

Depending on how much aperture you’re wresting with, you’ll find yourself looking at either a double-double or a triple-triple:

37 Tau glows orangely on the left side of this mirror-image view, and 39 Tau gleams whitely on the right, but if you look carefully you can see a weak shade of orange in its secondary.   The distance separating the two primaries is about 10’. The secondaries of both stars are obvious even in a 60mm refractor. However, to pry the 12.6 magnitude “C” components out of interstellar space you’ll need five to six inches of aperture. (East & west reversed to match the refractor image, click on the sketch for a better view).

37 Tau glows orangely on the left side of this mirror-image view, and 39 Tau gleams whitely on the right, but if you look carefully you can see a weak shade of orange in its secondary. The distance separating the two primaries is about 10’. The secondaries of both stars are obvious even in a 60mm refractor. However, to pry the 12.6 magnitude “C” components out of interstellar space you’ll need five to six inches of aperture. (East & west reversed to match the refractor image, click on the sketch for a better view).

Also shown to the south of 37 Tauri is SCA 30, with magnitudes of 9.54 and 12.92, separated by 42.6” at 345° (WDS 2000), which I was unaware of at the time I made the sketch. With some careful attention and averted vision, it should be possible to separate that pair with a six inch refractor.

37 Tau (OΣΣ 558)        HIP: 19038   SAO: 76430
RA: 04h 04.7m   Dec: +22° 05’

Identifier Magnitudes Separation  PA WDS
STT 558 AB: 4.46, 10.01    134.30″ 193°  2003
STG 4 AC: 4.46, 12.62    235.80″ 215°  2000

Distance: 187 Light Years (Simbad)
Spectral Classifications: “A” is K0, “B” is G0

37 Tauri captured my attention first because of its attractive orange tint. The tenth magnitude secondary shines south of it, and a careful perusal south and west of the secondary turned up the much weaker “C” companion, which is designated as STG 4. That three letter designation refers to Georg Hermann Struve, one of the lesser known members of the famous Struve family – more information on him can be found here.

39 Tau (OΣΣ 559)         HIP: 19076   SAO: 76438
RA: 04h 05.3m   Dec: +22° 01’

Identifier  Magnitudes Separation  PA WDS
CHR 158 Aa, Ab:  None listed       0.40″ 252°  2003
STT 559 AB:  5.97,   8.09    176.80″ 359°  2003
STT 559 AC:  5.97, 12.60    148.80″   16°  2000
STT 559 BC:  8.09, 11.50      58.30″ 124°  2000

Distance: 55 Light Years (Simbad);  also Simbad shows “B” at 797 LY
Spectral Classifications: “A” is G5, “B is K0

When you first look at the data on 37 and 39 Tauri, they seem to resemble each other because their three main components are all widely separated. But 39 Tauri includes an additional component, an elusive star of undetermined magnitude, CHR 158 (the CHR stands for Center for High Angular Resolution Astronomy). According to the WDS notes file, there were numerous attempt to resolve that companion between 1985 and 1998 that resulted in an “uncertain” resolution at a distance of 0.22”, followed by a successful attempt at resolution in 2003 at a distance of .41”.

Click to enlarge.

Click to enlarge.

Both 37 and 39 Tauri have significantly high rates of proper motion, which are shown below in this Aladin photo with Simbad’s proper motion rates added as an overlay:

This is an erect image, so east and west are opposite of what’s shown in the sketch above.  Click to enlarge the image.  (All motions are east (“+”) and south (“-“); for example in the case of 39 Tau A, +172 -031 means motion of .172”/yr east and .031”/yr south).

This is an erect image, so east and west are opposite of what’s shown in the sketch above. Click to enlarge the image. (All motions are east (“+”) and south (“-“); for example in the case of 39 Tau A, +172 -131 means motion of .172”/yr east and .131”/yr south).

At first glance, it appears there may be some relation between the primaries of 37 and 39 Tauri, but a look at their distances shows they’re much too far apart. Simbad has 37 Tau “A” at a distance of 187 light years and shows 39 Tau “A” quite a bit closer at 55 light years.  None of the other components shown appear to have any relation to their primarial parents, and in fact, Simbad includes a distance for 39 Tau “B” of 797 light years, placing it much further away than its primary.

Our next star on this tour, Σ 479, is located about one and half degrees (1° 25’) northwest of 39 Tauri.   (Here’s our last chart again). You can use 7.8 magnitude HIP 18833 as a stepping stone, which is a 40’ hop northwest of 37 Tau. Another short jump of 50’ more north than west will land you on Σ 479.  HIP 18833 is also a double star, by the way, sporting an identification of LDS 5477 (magnitudes of 7.88 and 12.93, separated by 58.8” at a PA of 356° as of 2000).

Σ 479  (H N 93)  (S 442)        HIP: 18748   SAO: 76388
RA: 04h 00.9m   Dec: +23° 12’
Magnitudes   AB: 6.92, 7.76     AC: 6.92, 9.45
Separations  AB: 7.20”            AC: 57.40”
Position Angles  AB: 127° (WDS 2013)    AC: 242° (WDS 2012)
Distance: 1072 Light Years (Simbad)
Spectral Classifications: “A” is B9, “B” is A3, “C” is A5

This Struvian selection is a compact triple star with a yellow-white primary and a similarly colored secondary in which the hues are a bit less pronounced. Eleventh magnitude TYC 1813-981-1 sits a bit more than 2.5’ northwest of the AB pair of Σ 479.   (East and west reversed once more, click on the sketch for a larger view).

This Struvian selection is a compact triple star with a yellow-white primary and a similarly colored secondary in which the hues are a bit less pronounced. Eleventh magnitude TYC 1813-981-1 sits a bit more than 2.5’ northwest of the AB pair of Σ 479. (East and west reversed once more, click on the sketch for a larger view).

William Herschel was the first person to come across what later became Σ 479.  He found it on January 4th, 1793, and cataloged it as a double star, but seems to have made several errors in describing its location (source):

Wm Herschel on STF 479

His “north preceding 36 (A.) Tauri 1 1/2°” is an error, since Σ 479 is located just over a degree southwest of 36 Tauri, not north (our chart again) – but it does precede 36 Tau. The distance separating the two stars is 1° 12’, so he’s sort of in the ballpark with his  measure of 1 1/2°.

Click to enlarge.

Click to enlarge.

Herschel also refers to Σ 479 and 36 Tauri as being “parallel to 54 (ν) and Pleiades.”   54 Tauri is Gamma (γ) Tauri, which is located at the point of the “V” at the southwest tip of Taurus (here’s our first chart, which has a wider view). Nu (ν) Tauri (also designated 38 Tauri) on the other hand, is located ten and half degrees southwest of Gamma (γ) Tauri and eighteen and a half degrees almost due south of the Pleiades. But if you look closely at the chart just mentioned, you’ll see Σ 494 and 36 Tauri are parallel with a line drawn from 54 Tauri (γ Tauri) to the Pleiades. So it appears Sir William confused Σ 494 and Σ 479.   Must have been a bad night at the scope, and we’ve all had that happen.

In his book on F.G.W. Struve’s double stars, Thomas Lewis includes measures of both the AB pair and the BC pair (shown at right).   James South seems to have been the first person to measure the AB pair in 1823, which would normally mean the star should carry his catalog number, S 442. Struve didn’t get to it until 1831, followed by Admiral William H. Smyth in 1835.

For the most part, all of the measures listed by Lewis for both the AB and BC pairs are remarkably consistent, with the exception of an 1861 measure of AB by Mädler.   A look at the Aladin image below provides a visual clue as to why:

Click to make the data more legible -- see the previous Aladin image of 37 and 39 Tau for an explanation of how to read the proper motion data.  (Erect image once again).

Click to make the data more legible — see the previous Aladin image of 37 and 39 Tau for an explanation of how to read the proper motion data. (Erect image once again).

It’s obvious all three components of Σ 479 are moving in the same direction, as well as at pretty close to the same speed, although “B” is lagging behind a bit. Unfortunately the only star we have a distance for is the primary, “A”, which Simbad shows at 1072 light years.   Simbad lists radial velocities of +13.80 km/sec for the primary and +10 km/sec for secondary, but doesn’t list a number for “C”.   So even though the stars appear to be physically related, there’s not enough data yet to be sure.

Our last star, Σ 494, is waiting patiently for us about two degrees (1° 50’) due east of our present location (here’s our second chart again). 8.3 magnitude HIP 19078 lies midway between the two, so it’s an ideal place to pause. That stars has a spectral classification of K0, so it’s worth taking a close look to see if you can detect any hint of orange in it. Simbad, by the way, shows a distance for it of 1468.5 light years.

 Σ 494  (H N 17)  (S 444)        HIP: 19363   SAO: 76476
RA: 04h 08.9m   Dec: +23° 06’
Magnitudes:  7.53, 7.65
Separation:   5.3”
Position Angle: 188° (WDS 2013)
Distance: 343 Light Years (Simbad)
Spectral Classifications:  Both stars are A8

Nothing like an old fashioned pair of closely spaced stars similar in magnitude! Both stars were unmistakably white. Barely seen in the southwest corner of the view is Cou 152, with matched magnitudes of 10.70 for both the primary and secondary, spaced a claustrophic 0.30” apart at a PA of 40° (WDS 2008). Cou 152 also includes a 16th magnitude third component at a distance of 3.40” and a PA of 204° (WDS 1970) – all well out of my reach, unfortunately. The inset at the right shows another double stars, GRV 206, which we’ll come back to shortly. (East and west reversed once more, click on the sketch to improve the view).

Nothing like an old fashioned pair of closely spaced stars similar in magnitude! Both stars were unmistakably white. Barely seen in the southwest corner of the view is Cou 152, with matched magnitudes of 10.70 for both the primary and secondary, spaced a claustrophic 0.30” apart at a PA of 40° (WDS 2008). Cou 152 also includes a 16th magnitude third component at a distance of 3.40” and a PA of 204° (WDS 1970) – all well out of my reach, unfortunately. The inset at the right shows another double star, GRV 206, which we’ll come back to shortly. (East and west reversed once more, click on the sketch to improve the view).

William Herschel was first on the scene of this pair of stars also, discovering it on November 16th, 1784 (source):

Herschel on STF 494

Click to enlarge.

Click to enlarge.

Once again, Sir William’s directions are confusing.   He seems to be saying 65 Tauri is preceding Σ 494 at a distance of 16’35” as well as being located north of 65 Tau at a distance of 0° 45’.   I checked those measures against Sky Tools 3 and found the 0° 45’ measure is very close, but the other measure should be in the vicinity of 3.75°. (You can see 65 Tauri at the left middle edge of this chart). At any rate, his right ascension and polar distance (P.D.) numbers are correct.

Thomas Lewis’s entry (shown at right) on Σ 494 includes a long list of measurements, starting with that of James South in 1825, and including measures by Struve in 1828 and 1832, John Herschel (h) in 1829, and the Reverend W.R. Dawes in 1842 and 1860.

Starting with Mädler’s measures in 1844, the separation and position angle begin to be remarkably consistent (source).

And again, when we look at the proper motion numbers for the primary and secondary of Σ 494, that makes sense:

Erect image once again, click to see all the data more clearly.

Erect image once again, click to see all the data more clearly.  PMRA stands for proper motion right ascension and PMDEC is proper motion in declination.

Whoops – we got more than we bargained for here! Not only did we turn up a restless collection of stars, but we also uncovered another double I was unaware of at the time I did the sketch. GRV 206 (WDS ID 04086+2301) is a pair of stars with magnitudes of 12.56 and 13.39, separated by 41.2” at a PA of 44° (WDS 2013). I went back and looked at my sketch and found I captured the primary, but not the secondary, although it may have been there with some judicious use of averted vision.

The object with the 2MASS label is a star with a visual magnitude of 16.3 (determined by combining the J (14.033) and K (13.204) values).   There’s no distance shown in Simbad for that star, but chances are that with the rate of proper motion it displays, it’s relatively close to us.

If you look closely at the overlay, you’ll see three circles super-imposed on the STF 494 pair. One of those circles belongs to HD 26128, which is an identification assigned to both stars. There are proper motion numbers for that designation, as well as for the identifications assigned to both “A” and “B”, which is confusing, to say the least. Simbad shows the data for HD 26128 is from 2007 (the shorter of three arrows), the data for “A” is from 2012 (the longest of the arrows), and the data for “B” is from 2000.   At any rate, it appears STF 494 “A” and “B” may be physically related, although the only distance we have is for “A”, so more definitive information would be helpful.

That’s it for Taurus this year.   Next time we’ll head east and see what there is to see in Leo Minor, a constellation known for being small, faint, and populated with about as many galaxies as double stars.

Clear Skies! :cool:

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.

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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:

 

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