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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!  😎

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3 Responses

  1. Thank you for always adding to our knowledge base.

  2. Hi John!
    As always, well researched and wonderfully narrated. You’ve peaked my curiosity with the “Collinder” tale. I will spend some cloudy night time reading about “Per Collinder”, a swedish born astronomer. His catalogue was published in 1931. I suspect he and his contemporaries did not have access to radial velocity data….might help to explain his grouping results. Thank-you Wikipedia!! 🙂

    Cheers, Chris.

    • Thanks to Saberonyx and Chris for the comments — always appreciated.

      I did a bit more research on the CR clusters and found this paper by Per Collinder, which according to this discussion, was actually a dissertation. (The Collinder disseration is 46 pages long, so it’ll take a bit for it to come up on your screen. This is only the part that deals specifically with the numbered clusters. The rest of the dissertation is on file at the University of Arizona).

      You’ll find an entire list of all the CR clusters in that paper, and on page 26 you can see Collinder’s description of CR 65. And it’s a bit confusing, to say the least.

      First, he refers to three “Draper” stars which he includes in the cluster. It turns out those three numbers are BD (Bonner Durchmusterung) numbers, not Draper numbers. Once I figured that out, I cross-referenced them and got these identities for them:

      BD +16 00775 = 113 Tau
      BD +17 00298 = STT 107
      BD +14 00947 = 35 ORI

      That last one, 35 ORI, is three degrees southeast of the center of CR 65, meaning it’s not a member of the group.

      Collinder then includes a list of six stars with proper motions and radial velocities, some of which are not in the cluster. He references 114 Tau, which is located five degrees north of the center of CR 65, and 118 Tau, which is 8.5 degrees north of CR 65. His 13° 903, which is BD +13 00903 (also HIP 25638) is a 6.35 magnitude star located three degree southeast of CR 65’s center (near 35 Ori, mentioned above).

      He provides a distance of 525 LY for the cluster on page five. He also includes the parallax, which came out to 432 LY when I ran the conversion on it (divide 1 by the parallax of .00755 and multiple the result by 3.26 to convert from parsecs to light years).

      So, more questions than answers once again. But — it’s always an adventure to go back through original sources to see what’s lurking there!

      Cheers,

      John

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