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Caught in the Coma Cluster, Part 2: SHJ 143, HJ 517, Σ 1639, and Σ I 21

We’re back once again in northwestern Coma Bernices to finish looking at the double and multiple stars in the Coma Cluster. The last time out we covered the north half of the cluster (if you missed part one, you can get there by clicking on this link), so this time we’ll wander among the stars in the southern half.

If you need to get oriented, here’s an overview of where we’re headed:

You’ll find Coma Bernices wedged between the eastern edge of Leo and western edge of Boötes.   The Coma Cluster sits just south of Gamma (γ) Comae Bernices. (Stellarium screen image with labels added, click for a larger view).

You’ll find Coma Bernices wedged between the eastern edge of Leo and western edge of Boötes. The Coma Cluster sits just south of Gamma (γ) Comae Bernices. (Stellarium screen image with labels added, click for a larger view).

Once you locate the cluster, which is easily seen under dark skies as a ghostly scattering of star dust, point your telescope at Gamma (γ) Com and then pan a couple of degrees south:

The Coma Cluster also goes by two other designations, Collinder 256 (Cr 256) and Melotte 111 (Mel 111).   We’re headed for the south half of the cluster, but we’ll start by centering 14 and 16 Com in our finder. (Stellarium screen image with labels added, click to enlarge the chart).

The Coma Cluster also goes by two other designations, Collinder 256 (Cr 256) and Melotte 111 (Mel 111). We’re headed for the south half of the cluster, but we’ll start by centering 14 and 16 Com in our finder. (Stellarium screen image with labels added, click to enlarge the chart).

Once you’ve got 14 and 16 Com positioned in the center of your finder field, look one degree southwest of 16 Com to the white glow of 5.17 magnitude 13 Com. From there move half of a degree southwest (a bit more west than south this time) to 4.81 magnitude 12 Com, also known as SHJ 143.

SHJ 143 (12 Com)      HIP: 59468   SAO: 82273
RA: 12h 22.5m   Dec: +25° 51’
Identifier          Magnitudes       Separation       Position Angle      WDS
SHJ 143   AB:  4.86, 11.80           36.70”                   57°              2012
H V 121    AC:  4.86,  8.90           59.00”                 168°              2012
ARN 6      AD:  4.86, 10.10         213.10”                 132°              2012
SMR 57    DE: 10.10,14.30           12.80”                 167°              2013
Distance: 775 Light Years
Spectral Classifications:  “A” is F6, “B” is F8, “C” is F5, “E” is K5

 I found the primary to be a beautiful gold, which fits somewhat closely with its F6 spectral classification (yellow-white leaning toward yellow), “B” was very hard to see in the primarial glare, and “C” and “D” stood out clearly. 14.30 magnitude “E” was visually out of reach for my six inch lens. (East & west reversed to match the refractor view, click on the sketch for a better image).

I found the primary to be a beautiful gold, which fits somewhat closely with its F6 spectral classification (yellow-white leaning toward yellow), “B” was very hard to see in the primarial glare, and “C” and “D” stood out clearly. 14.30 magnitude “E” was visually out of reach for my six inch lens. (East & west reversed to match the refractor view, click on the sketch for a better image).

To give credit where credit is due, we need to start with Sir William Herschel who was here first on January 1st, 1783, with an observation (scroll down to the sixth title) of what is now the AC pair:

Wm. Herschle on 12 Com

One of the odd things I noticed about his observation was although he provided a very precise measurement of separation, 58.55”, his position angle was only an estimate, although a pretty good one since his “77° s. following” works out to our present day 167°. However, as we’re about to see, it turns out his estimated position angle was the more accurate of the two numbers.

When Sirs John Herschel and James South looked at the same pair on the evening of May 21st, 1821, they came up with a similar position angle, 168.47°, but a considerably different separation, 65.950”, as you can see in this page from their 1824 catalog (scroll down to last title):

Herschel-South on HJ 143

We have to leap ahead to 1904 to discover the Herschel/South separation is the more accurate number, as this excerpt from S.W. Burnham’s 1906 catalog shows:

Burnham on 12 Com

Burnham was the first to detect what is now “B”, which he measured at 54.1° and 35.00”. You may have also noticed the William Herschel catalog number he lists for the AC pair is incorrect, which is one of the rare errors in Burnham’s many publications.

The WDS doesn’t list the AC pair with the H V 121 identifier, instead using SHJ 143, presumably because the Herschel-South measure was more accurate than Sir William’s. On the other hand, Burnham’s prefix of “Bu” hasn’t been assigned to the AB pair, which should be the case if the same logic was applied.

Click to enlarge.

Click to enlarge.

But since splitting hairs can be as intriguing as splitting stars, I stumbled across what appears to be another error, or at least a puzzling problem.   Brian Mason at the USNO (home of the Washington Double Star Catalog, or WDS) was kind enough to send me the text file for SHJ 121, which includes forty-eight measurements of the AC pair from 1783 through 2012 (see insert at right).

All of them, with the exception of William Herschel’s 1783 measure (58.91″) and the most recent 2012 measure (58.97″), show the AC pair with a separation varying between 63.6” (2009.14) and 66.8” (2011.323). The vast majority of the forty-eight observations are in the 65 arc second plus range – in fact, when the 1783 and the most recent 2012 measures are excluded, the remaining forty-six average out to 65.34”. For some reason, three of the last five measures listed in the WDS are particularly erratic: 63.6” (2009.14), 66.8” (2011.323), and 58.97” (2012.414). So in that context, maybe Sir William Herschel’s separation error should be forgiven. The position angle, on the other hand, has been consistently in the 167 degree range all that time.

At any rate, it would appear there’s been very little change in the AC pair, which isn’t surprising since its proper motion is minimal. In fact, one odd thing I noticed about the multiple stars we’re going to look at on this tour is the proper motion of all of them is relatively small, which is quite a contrast to what we saw for the three stars covered in the northern half of the Coma Cluster in part one.

Now if you go back to your finder while SHJ 143 is centered and look southwest once again (here’s our last chart), you’ll see the weak glimmer of 8.06 magnitude HIP 60233 just twenty arc minutes away. Center it your finder and you’ll find the even weaker ninth magnitude light of HJ 517 five arc minutes to the northwest – and you’ll have to sit very still to see the faint 12.50 magnitude secondary.

HJ 517          HIP: 60206   SAO: 82256
RA: 12h 20.8m   Dec: +25° 46’
Magnitudes: 9.09, 12.50
Separation:  20”
Position Angle: 239° (WDS 2001)
Distance: 242 Light Years
Spectral Classification: “A” is F8
Note: Optical pair

Hmmm – look closely or you’ll miss this one! Note that HIP 60233/SAO 82261 makes a handy reference point for locating HJ 517. (East & west reversed again, click on the sketch to see the secondary more easily).

Hmmm – look closely or you’ll miss this one! Note that HIP 60233/SAO 82261 makes a handy reference point for locating HJ 517. (East & west reversed again, click on the sketch to see the secondary more easily).

Like a lot of Sir John Herschel’s discoveries (1827 for this one), this is a faint pair with a very hard to see secondary. I needed averted vision to catch my first glimpse of it, but after that initial glimpse, it flickered in and out of view with direct vision. As you can see, the field is rather sparse and colorless. Apart from the eighth magnitude glow of HIP 60233, there’s nothing here to write home about.

Now let’s go back and center SHJ 143/12 Com in the finder and locate Σ 1639. If you look at our last chart closely, you’ll see 12 Com and 13 Com form a triangle with 6.47 magnitude Σ 1639. It shines thirty arc minutes southeast of 12 Com/SHJ 143 and thirty-one arc minutes south of 13 Com.

Σ 1639         HIP: 60525   SAO: 82293
RA: 12h 24.4m   Dec: + 25° 35’
Magnitudes   AB: 6.74, 7.83      AC: 6.74, 11.50
Separations   AB: 1.82”             AC: 91.60”
Position Angles  AB: 323.2° (WDS 2014)   AC: 160° (WDS 2009)
Distance: 319 Light Years
Spectral Classifications: “A” is A7, “B” is F4
Note: “A” and “B” are a binary pair

The real test here is splitting the AB pair, both of which appeared white to me. Although dim at a magnitude of 11.50, “C” is far enough away to stand out clearly. (East & west reversed once more, click on the sketch to improve the view).

The real test here is splitting the AB pair, both of which appeared white to me. Although dim at a magnitude of 11.50, “C” is far enough away to stand out clearly. (East & west reversed once more, click on the sketch to improve the view).

With poor seeing once again ruling the heavens, it took a determined effort to mentally hold the AB pair still for long enough to detect a hint of duplicity. After several minutes of serious 127x staring, an elongation eventually became evident. I coaxed both stars into view at 203x with a 7.5mm Celestron Plössl, but their energetic up/down/sideways dance made it impossible to see any black space between them.

Click on the image to enlarge it.

Click on the image to enlarge it.

The primary and secondary are a true binary pair with an orbital period which has never been quite pinned down. In his 1906 catalog, S. W. Burnham estimated it to be in excess of four hundred years and mentions Thomas Lewis estimated it at 180 years. The WDS data (which can be seen here) shows two numbers for the orbital period: 575.44 years is the number shown with the orbital chart, and 678 years is shown if you scroll further down the page to the note below the second chart.

There is one thing about the orbital data which is definite: the separation of the pair will gradually increase for about another twenty or thirty years, although not by much – 1.925” is the separation shown for the last year listed (2030) in the table to the left of that chart. In the past, the primary and secondary have been as close as .20” (1889 in Burnham’s data at the right), and in fact was probably less than that in 1892 when Burnham shows he was unable to separate them with the 36 inch refractor at Lick Observatory.

Back to the finder now as we head for out last star (here’s our chart again).  Sitting in the middle of the east leg of the triangle formed by 12 Com/13Com/Σ 1639 is 6.71 magnitude HIP 60490.   A line drawn from 12 Com/SHJ 143 directly through HIP 60490 will lead you to 6.67 magnitude HIP 60797 (69 arc minutes east of 12 Com/SHJ 143), and another seventeen arc minute hop in the same direction will land you on our last target, 5.32 magnitude 17 Com, aka Σ I 21, aka STFA 21.

Σ I 21  (17 Com)  (AB is also S 638)        HIP:60904   SAO: 82330
RA: 12h 28.9m   Dec: +25° 55’
Identifier         Magnitudes        Separation       Position Angle       WDS
STFA 21   AB: 5.23,  6.64           144.90”                250°               2012
Bu 1080   AD: 5.23, 13.70           324.20”                269°               2001
SLE 898   AE: 5.23, 12.10           447.50”                270°               2001
SLE 898   AF: 5.23, 12.70           125.90”                146°               2001
Bu 1080   BC: 6.64, 13.70               1.50”                175°               2009
Bu 1080   BD: 6.64, 13.70            193.00”                284°               2001
Distance: 270 Light Years
Spectral Classification:  “A” is A0

All of the components can be seen in my sketch except for “C”, which was well beyond my reach because of the 7.06 magnitudes of difference between it and “B”. Both “A” and “B” were white, as was HIP 60797. (East & west reversed, click on the sketch for a much better view).

All of the components can be seen in my sketch except for “C”, which was well beyond my reach because of the 7.06 magnitudes of difference between it and “B”. Both “A” and “B” were white, as was HIP 60797. (East & west reversed, click on the sketch for a much better view).

When I first looked at this system I had a tough time prying 12.7 magnitude “F” out of the glare, so I returned three nights later for another look. Surprisingly I saw it immediately at 84x with an 18mm Radian, although it flickered in and out of sight after the first sighting. When I moved up to 118x with a 14mm Radian, it pretty much disappeared into the primarial glare because of an over-abundance of moisture in the air.

One of the things I noticed quickly as I located the components of Σ I 21 was that “D” appeared brighter than the 13.70 magnitude listed for it in the WDS. The UCAC4 catalog shows “D” (UCAC4-580-047409) at a magnitude of 11.50, which matches closely with what I saw. I also thought “E” was a bit brighter than the 12.10 magnitude shown in the WDS, but the UCAC4 catalog has it (UCAC4-580-047416) at a magnitude of 12.08.

The first date of observation for the AB pair in the WDS is listed as 1836, but Burnham’s 1900 catalog of double stars (A General Catalogue of 1290 Double Stars Discovered from 1871 to 1899) refers to it as S 638, which quickly lured me to Sir James South’s 1826 catalog. And sure enough, he made two observations of the AB pair in March of 1825, coming up with a final PA and separation of 251° 13’ and 144.436”.

South on SFTA 21 (S 638)

I was also curious about what Burnham had used to cut through the seven magnitudes of difference between 6.64 magnitude “B” and 13.70 magnitude “C”, and not surprisingly it was that great optical equalizer, the 36 inch Lick refractor (click on the arrow at the right side of the photo — there are four different views of the refractor!).

Burnham on STFA 21

There appears to be some significant motion in one of those two stars since the two similar measures of BC shown in the excerpt above (the first by Burnham, the second by R.G. Aitken) differ in separation, and especially in position angle, from the 2009 data in the WDS.

That’s it for the Coma Cluster, which you’ll have to catch quickly since it’s now sinking into the western sky. Next time out we’ll wander east to Hercules and take advantage of some rare good seeing to pry apart two doubles that have eluded me for the past year.

Clear Skies until then! 😎

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Caught in the Coma Cluster, Part 1: Σ 1633, Σ 1643, and Σ 1651

Many is the night I’ve cast a curious glance at that faint cluster of jewel-like stars that follow Leo through the heavens, thinking I should point a telescope into it and see what kind of double star life lurks within. With the aid of an eleven inch SCT I combed through the cluster several years ago in search of the many galaxies that lurk at dim magnitudes beyond the reach of my six inch refractor, but the large SCT was meant for deep sky exploration, not double stars, so I zipped right past them – if I noticed them at all – as I peered millions of light years into the past.

But times change – as well as telescopes – and I eventually abandoned the eleven inch SCT when I discovered the double star world that springs to life in small and medium sized refractors. Other than peering into the past in terms of light years, I’ve never looked back to regret selling the SCT since on most nights it was way too much aperture for the typical seeing conditions at my location. But I always intended to return to the Coma Cluster and satisfy my double star curiosity, and that’s exactly what I’m going to do now.

The Coma Cluster is the faint collection of shimmering stars located immediately south of Gamma (γ) Comae Bernices. If you have trouble picking it out because of overly bright skies, point a pair of binoculars about two-thirds of the way between Denebola (Beta/β Leonis) and Cor Coroli (Alpha/α Canum Venaticorum) and it will spring into life. (Stellarium screen image with labels added, click on the chart to enlarge it).

The Coma Cluster is the faint collection of shimmering stars located immediately south of Gamma (γ) Comae Bernices. If you have trouble picking it out because of overly bright skies, point a pair of binoculars about half way between Denebola (Beta/β Leonis) and Cor Coroli (Alpha/α Canum Venaticorum) and prepare to be dazzled by the light. (Stellarium screen image with labels added, click on the chart to enlarge it).

The Coma Cluster goes by two designations, Collinder 256 and Melotte 111, and is generally considered to be about four to five degrees in diameter. It was described by Garrett P. Servis as “gossamers spangled with dewdrops”, a description I’m not about to try to improve on.  (Thanks to the late Walter Scott Houston for that reference — scroll down to the bottom of this page for his account of the Coma Cluster, along with a pretty good photograph).  Latest estimates of the cluster distance put it at about 280 to 288 light years from us.

Gamma (γ) Comae Bernices is located at the top center of this chart, which will help you to get oriented.  All of the stars we’re going to look at are sprawled out south of Gamma γ). (Stellarium screen image with labels added, click on the chart for a larger view).

Gamma (γ) Comae Bernices is located at the top center of this chart, which will help you to get oriented.  The diameter of the circle is about 3.5 degrees, so the entire cluster will fit into the typical five degree field of an 8×50 finder.  All of the stars we’re going to look at are sprawled out south of Gamma (γ).  (Stellarium screen image with labels added, click on the chart for a larger view).

Surprisingly, the seven multiple stars I looked at in the Coma Cluster are conveniently separated into two groups. We’ll cover the north half of the cluster in this post – which means Σ 1633, Σ 1643, and Σ 1651 – and tackle the southern half in the next post.

The best place to start is at Gamma (γ) Comae Bernices, which is located in the northwest corner of the constellation, as shown in the first chart above.   Once you locate it, center it in your finder and one degree south of it you’ll see 4.92 magnitude 14 Com, with 4.98 magnitude 16 Com half a degree to its south.  We’re going to start with Σ 1633, which lies almost a degree and a half west of 14 Com.  8.47 magnitude HIP 60364, which is about two-thirds of the distance to Σ 1633, can be used as a convenient stepping stone.

Σ 1633 (H N 31)  (SHJ 141)  55 Com
HIP: 60197   SAO: 82254
RA: 12h 20.7m   Dec: +27° 03’
Magnitudes: 7.04, 7.13
Separation:  8.9”
Position Angle: 245°  (WDS 2013)
Distance: 301 Light Years
Spectral Classifications: F3, F3

A classic case of a pair of headlights coming right at you, so duck! Both stars appeared perfectly white to me. (East & west reversed to match the refractor view, click on the sketch for a much better image).

A classic case of a pair of headlights coming right at you, so duck! Both stars appeared perfectly white to me. (East & west reversed to match the refractor view, click on the sketch for a much better image).

As you can tell by the first line of the data above, this pair of stars has had a lot visitors. Sir William Herschel was here first, on April 6th, 1785 (p. 170 of this link), F.G.W. Struve in 1820 and 1831 (p. 329 of Lewis book), but it was the observations by Sirs John Herschel and James South in 1821 and 1823 which are the most interesting (source — scroll to bottom of page).

Click to enlarge.

Click to enlarge.

Their observations (shown at the right) show a frustrating effort to wrestle consistent measures from the pair of stars on three separate nights. And if you look at their position angles for each of the three dates shown, you can see they had a difficult time deciding which of the two stars were brightest.

On March 14th, 1821, the average of their five position angles is presented as one number with both sp (south preceding) and nf (north following) added to it.  The 23° 46’ sp, which refers to what is now “A”, translates to our present day 246° 14’; and 23° 46’ nf, for what is now “B”, is exactly 180° less (66° 14’).  You can see they settled on the dimmer of the two stars for their April 10th, 1823, position angle (23° 12’ nf is 66° 48’), but nine days later they measured their position angles from what is actually the brighter of the two stars, 24° 13’ sp (245° 47’). I didn’t have any problem determining which of the two stars was brightest, but I had the benefit of using a six inch refractor, whereas Herschel and South were using a 3.8 inch refractor.

They also had problems measuring the separations of the two stars, with averages of 9.646”, 10.007”, and 8.843”. You can read their comments on the influence of the seeing conditions at the bottom of the page, which apparently were pretty darn good on the second night of their observations. At least once this year I would love to see the night of “steadiness and exact definition of the stars” they describe.

Surprisingly, their measure which is closest to that of the current WDS figures didn’t come on the night of the best seeing.  And there’s really no reason to suspect much change in the separation because these two stars are locked in a tight physical relationship defined by proper motion. In fact, both “A” and “B” have the same motion, +009 -120 (.009”/year east and .120”/year south), which is shown clearly in this Simbad chart:

Labels added for clarity, click on the chart to enlarge it.

Labels added for clarity, click on the chart to enlarge it.

Savor the comparatively wide separation of these two stars for a moment . . . . . . . . . . . because the next two selections get progressively tougher.

Let’s move the scope back to 14 and 16 Comae Bernices now.  A careful look in an 8×50 finder will reveal Σ 1643 sitting midway between 14 and 16 Com, or if that doesn’t work for you, place those two stars in your eyepiece so they’re at opposites sides of the field of view. (Here’s our last chart again).

And then look closely – very closely.

Σ 1643  (C is LEP 54)     HIP: 60759   SAO: 82315
RA: 12h 27.2m   Dec: 27° 01’
Magnitudes   AB: 9.03, 9.45     AC: 9.03, 14.78
Separations   AB: 2.7”              AC: 221.70”
Position Angles   AB: 4.1° (WDS 2014)     AC: 261 (WDS 2001)
Distance: 90 Light Years
Spectral Classifications:  “A” is K2, “B” is K4, “C” is M 4.5
Notes: “C” is a variable, V* CX Com

If you look carefully at the east-center of the field of view, you should see two faint and very close stars, provided you have enough magnification. I could barely separate them at 84x in an 18mm Radian, so I increased the magnification to 118x with a 14mm Radian. Even then, they were still tough to separate visually. The 14.78 magnitude “C” component is hiding west of the AB pair, but it was well beyond the reach of my six inch refractor. (East & west reversed again, click on the sketch to improve the view).

If you look carefully at the east-center of the field of view, you should see two faint and very close stars, provided you have enough magnification. I could barely separate them at 84x in an 18mm Radian, so I increased the magnification to 118x with a 14mm Radian. Even then, they were still tough to separate visually. The 14.78 magnitude “C” component is hiding southwest of the AB pair, but it was well beyond the reach of my six inch refractor. (East & west reversed again, click on the sketch to improve the view).

And for those who prefer a less cluttered view, here’s an unlabeled version of the same sketch:

Click on the sketch to enlarge it.

Click on the sketch to enlarge it.

One of the things you’ll probably notice in the sketch – and which you definitely notice at the eyepiece — is the Σ 1643 pair is easy to overlook because of the dominating fifth magnitude white brilliance of 14 Com (mag 4.92, spectral class F0) and 16 Com (mag 4.98, spectral class A4).  And sitting two and half arc minutes west of 16 Com is an innocent looking white star, LDS 1308 (magnitudes of 8.8 and 18.3, 51.1”, 214°, WDS 2004), which hides a secondary well out of our visual reach.

The AB pair of Σ 1643 is performing a very slow dance around each other, which is estimated by WDS orbital charts at either 549 years or 1628 years (those charts can be seen here if you scroll down to the middle of the view). Each of the charts show the two stars are actually about as far apart as they can be — don’t rush, though, you’ve got a few hundred years before they get noticeably closer.

And both stars also have significantly high rates of proper motion, which is shown in this Simbad chart:

Labels added for clarification, click on the chart for a larger view.

Labels added for clarification, click on the chart for a larger view.

Simbad combines the AB pair into one arrow on that chart, since the two are orbitally attached. It shows the proper motion of the pair at +094 -249 (.094”/year east, .249”/year south), but the WDS lists slightly different numbers for each of the components (A at +096 -229, B at +085 -240). You can also see that 14.78 magnitude “C” is moving parallel to the AB pair at +089 -250 (Simbad and WDS numbers).

Now let’s slide one degree east to 8.65 magnitude Σ 1651, which is shadowed to its north by the slightly brighter HIP 61118 (7.5 magnitude).  Here’s that last chart again.

Σ 1651  (88 Com)      No HIP Number   SAO: 82357
RA: 12h 31.7m   Dec: 27° 01’
Magnitudes: 8.56, 10.20 (from Simbad)
Separation:  7”
Position Angle: 214° (WDS 2012)
Distance: 148 Light Years
Spectral Classification: “A” is G1, “B” is K1

Now you REALLY have to look closely this time. Even though this pair is wider, the 1.56 magnitudes of difference makes a HUGE difference. The primary was white, and the secondary was barely visible without averted vision. (East & west reversed again, click on the sketch to get a much better glimpse of the faint secondary).

Now you REALLY have to look closely this time. Even though this pair is wider than our previous pair, the 1.56 magnitudes of difference makes a HUGE difference when compared with the equal magnitudes of that one. The primary was white, and the secondary was barely visible without averted vision. (East & west reversed again, click on the sketch to get a much better glimpse of the faint secondary).

Shown in the sketch just three and half arc minutes northwest of the Σ 1651 pair is the same 7.5 magnitude HIP 61118 we saw in the finder earlier.  I’m surprised one of the late eighteenth/early nineteenth double star observers didn’t include it in one of their observations, if for no other reason than to use it as a reference point for the proper motion of Σ 1651. Simbad places HIP 61118 at 465 light years from earth, so it’s obviously not related to the Σ 1651 pair, which are located 148 light years from us. I didn’t see any color in that star, but with a spectral class of K3 there should have been some reddish/orange visible in it.

The two stars of Σ 1651 aren’t orbitally attached, but they do appear to be related physically by proper motion.  And again, a Simbad chart illustrates that very clearly:

Labels added for clarity, click on the chart for a larger view.

Labels added for clarity, click on the chart for a larger view.

Click to enlarge.

Click to enlarge.

The proper motions illustrated on the chart above are +027 +008 [.027”/year east, and .008”/year north] for “A”, and +026 +006 for “B”. Shown at the right is an excerpt from Lewis’ book on Struve’s double stars, which shows quite a bit of consistency when the position angle of 1858 is excluded. S.W. Burnham (p. 608 of this book) measured the pair at 217.4° and 6.83” in 1905, resulting in an impression of very little change, if any, over the seventy-five year period of the data.

I also found WDS data showing the PA in 1982 was measured at 215°, in 1991 at 214°, and in 2004 again at 214°. Separation for that same period was measured at 7” (1982), 6.9” (1991), and 6.9” (2004). Based on the proper motion numbers, you might expect a very slight change in relative positions of the stars, which may well be what the slight change in PA and separation show. On the other hand, the changes are so slight, especially the separation, they could simply be statistical fluctuations.

And that’s it for the north part of the Coma Cluster.   Coming up next is a tour of four stars lurking in the southern half.

Until then, Clear Skies! 😎

Untangling the Knots in Bernice’s Hair: 32 Com, Σ 1685, and Σ 1686

Wedged between Boötes and Leo, Coma Bernices is one of those dim and non-descript constellations that gets completely lost in a light-polluted sky. But even when the background of the celestial vault is dark, the only notable characteristic of this collection of stars is a faint and fuzzy open cluster appearance emanating from its northwest corner.  Consequently, navigation via star hopping can be a treacherous experience if you make a wrong turn. Fortunately for this tour, I found three distinctive multiple stars that not only are within four degrees of each other, but are also located almost directly in line with one another.  All you have to do to get started is throw a rope around Alpha (α) Comae Bernices and then fling it out to the west a few degrees.

First, though, you have to find Alpha (α) Com, which requires a sharp eye and a reasonably dark sky.

I got there by starting at Porrima (Gamma/γ Virginis) in northern Virgo and working my way up to Delta (δ) and then to Epsilon (ε). The line formed by Delta (δ) and Epsilon (ε) Virginis points almost directly at Alpha (α) Com, which lies a short seven degrees away. Another way is to follow the line that runs through Arcturus (Alpha/α Boötis) and Eta (η) Boötis. Extending it for ten and half degrees it leads you directly to Alpha (α) Comae Bernices. (Stellarium screen image with labels added, click on the chart to enlarge it).

I got there by starting at Porrima (Gamma/γ Virginis) in northern Virgo and working my way up to Delta (δ) and then to Epsilon (ε). The line formed by Delta (δ) and Epsilon (ε) Virginis points almost directly at Alpha (α) Com, which lies a short seven degrees away. Another way is to follow the line that runs through Arcturus (Alpha/α Boötis) and Eta (η) Boötis. Extending it for ten and half degrees it leads you directly to Alpha (α) Comae Bernices. (Stellarium screen image with labels added, click on the chart to enlarge it).

Once you’ve groped your way in the dark to Alpha (α) Com, turn your attention to the west and follow me to our first stop, 32 Com:

From 4.32 magnitude Alpha (α) Com make a short two and a half degree hop due west and slightly south to 4.79 magnitude 36 Com. Another one and a half degrees further west, with a slightly more inclined lean to the south will get you to the orange and white starlight of 32 and 33 Com.   You’ll find them sitting midway between 36 Com and 5.12 magnitude 27 Com. (Stellarium screen image with labels added, click for a larger version).

From 4.32 magnitude Alpha (α) Com make a short two and a half degree hop due west and slightly south to 4.79 magnitude 36 Com. Another one and a half degrees further west, with a slightly more inclined lean to the south will get you to the orange and white starlight of 32 and 33 Com. You’ll find them sitting midway between 36 Com and 5.12 magnitude 27 Com. (Stellarium screen image with labels added, click for a larger version).

32 Com  (STFA 23)        HIP: 62807   SAO: 100309
RA: 12h 52.2m  Dec: +17° 04
Magnitudes    AB: 6.50, 6.99   AC: 6.50, 8.95
Separations   AB: 195.90”       AC: 905.10”
Position Angles  AB: 51° (WDS 2011)   AC: 262° (WDS 2001)
Distance: 1833 Light Years
Spectral Classifications: “A” is M0, “B” is F8
Note: “B” is 33 Com

This is a pleasantly tinted wide triple star that would work well in a 60mm refractor, so my 9.25 inch SCT view was way more aperture than you need for it.  Even at that aperture, though, there weren’t a lot of stars to be seen in the field of view.

The orange/gold primary is at the center of the sketch, the slightly weaker secondary is parked above and to its right (northeast), and the considerably weaker and more distant “C” component lies at the west edge of the field of view. Lying almost directly in line with the AB pairing to the southwest is a pair of faint stars (the first is 13th magnitude, the second 12th) which add a little extra visual appeal to the scene.   (East and west reversed to match the SCT view, click on the sketch for a much better version).

The orange/gold primary is at the center of the sketch, the slightly weaker secondary is parked above and to its right (northeast), and the considerably weaker and more distant “C” component lies at the west edge of the field of view. Lying almost directly in line with the AB pairing to the southwest is a pair of faint stars (the first is 13th magnitude, the second 12th) which add a little extra visual appeal to the scene. (East and west reversed to match the SCT view, click on the sketch for a much better version).

You’ll notice the “C” component is waaaaay out there.  The 905.10” of separation for it in the WDS translates to a distant 15.085 arc minutes, which meant I needed a wide field of view to catch it in the same eyepiece view with the AB pair.  My seldom-used 40mm Celestron Plössl was barely enough to snare the 8.95 magnitude star.

The wide separation of the three stars of 32 Com raises a question as to what kind of physical relation exists among them. Considering the rather distant 1833 light years of the primary, you can pretty much rule out any kind of orbital relationship between the three stars because visually they’re too far apart. On the other hand, it’s always possible another kind of physical relationship exists. The best way to get a feel for that is to look at their proper motions, and fortunately the data for all three components is listed in the WDS:

Proper motion of A: +002 -005  (.002” east per year, .005” south/year)
Proper motion of B: +038 -036  (.038” east per year, .036” south/year)
Proper motion of C:  -035 -006  (.025” west per year, .006” south/year)

Pictorially, those movements look like this on a Simbad plot:

Click on the image to enlarge it.

If you look closely at the red mark which is 32 Com, you can see an indication of southeasterly movement, which is the “B” component.  (Click on the image to enlarge it.  NOTE: east is on the left in this view).

So what the WDS data and the Simbad plot tell us is there’s no relation whatever between the three stars. As to what led F.G.W. Struve to measure the AB pair in 1836, I have no idea since I’ve unsuccessfully turned the internet upside down numerous times trying to locate his 1837 catalog, Stellarum duplicium et multiplicium mensurae micrometricae per magnum Fraunhoferi tubum annis a 1824 ad 1837 in specula Dorpatensi institutae.  What I did find (in the WDS) was his initial data on the AB pair, 194.7” and 49 degrees, showing very little change in the almost 180 years since that observation was made. As for AC, its first measurement was made in 1875, 898.1” and 262 degrees, which again shows very little change.

We’ll move south now and take a look at Σ 1686, which lies two degrees south of 32 Com. You can use 6.25 magnitude HIP 62825 as a stepping stone since it conveniently lies halfway between 32 Com and Σ 1686.   (Here’s our last chart again).

Σ 1686  (SHJ 155)     HIP: 62852   SAO: 100315
RA: 12h 53.0m   Dec: +15° 02
Magnitudes: 8.58, 8.72
Separation:  5.7”
Position Angle: 186° (WDS 2013)
Distance: 482 Light Years
Spectral Classification: F5, F8

Two lovely white dots of light! (East & west reversed, click on the sketch for a better look).

Two lovely white dots of light! (East & west reversed, click for a better view).

As you can see, there’s a peculiar absence of background stars in this view. That’s because Coma Bernices lies well outside the plane of the Milky Way, which means we’re looking deep into inter-galactic space. In fact, it’s that particular trait that makes Come Bernices such a happy hunting ground for galaxies.

Even though this pair of stars carries F.G.W. Struve’s designation, their first measurement was made by Sirs James South and John Herschel on June 6th, 1823.

 Click on the image to enlarge it.

Click on the image to enlarge it.

Click to enlarge.

Click to enlarge.

The separation they measured is too wide, which James South calls attention to in the remark he added at the bottom of the observation.   Their position angle, which refers to both south preceding (sp) and north following (nf), is vague because they weren’t sure which of the two stars was the brightest. The correct PA is 79° 53’ sp (190° 07’), which is also noticeably off by a few degrees when compared with the data in the excerpt from Thomas Lewis’s Measures of the Double Stars Contained in the Mensurae Micrometricae of F.G.W. Struve (shown at the right).  That data shows virtually no change at all in the position angles and separations of the two stars between 1829 and 1897, and in fact, most of the numbers aren’t all that different from the 2013 WDS figures.

Let’s go back to 32 Com now and then hop north two degrees to Σ 1685, which you’ll find wedged between 7.05 magnitude HIP 62930 and 7.22 magnitude HIP 62724. (Here’s our previous chart again).

Σ 1685  (SHJ 153)  (AB is H IV 58, and also HJL 173)     
HIP: 62783   SAO: 100307
RA: 12h 51.9m   Dec: 19° 10’
Identifier         Magnitudes      Separation      Position Angle       WDS
STF 1685   AB: 7.31, 7.78          15.90”                201°              2012
SHJ 153     AC: 7.31, 8.22        243.10”                328°              2012
SHJ 153     BC: 7.78, 8.22        252.50”                331°              2012
Distance:  “A” is 720 LY, “B” is 481 LY, “C” is 282 LY
Spectral Classification:  “A” is A3m, “B” is F8, “C” is G7

If by some chance you’re approaching Σ 1685 without having been centered on 32 Com, there’s another way to get here, which is best described by the admirable Admiral William H. Smyth:

A neat double star, between Bernice’s Hair, and Virgo’s left wing:  it lies due west of Arcturus, or on its parallel, at the distance of 22°, where a line dropped south from Cor Caroli will intercept it.  A 7 ½, and B 8, both white; other stars in the field, but small and distant.  This object is 58 H IV; and is also formed by Nos. 201 and 202, Hora XII., of the Palermo Catalogue.”  (From The Bedford Catalog, p. 284)

In fact, even William Herschel provided pretty good directions (source):

Wm Herschel on STF 1685The stars he refers to as 42nd and 15th Comae Bernices are Alpha (α) and Gamma (γ) Com, which are included on our first chart.  His comment about being parallel to those stars refers to the alignment of the AB pair of Σ 1685, which is parallel to a line drawn from Alpha (α) to Gamma (γ) Com.

Regardless of how you get there, this is what you’ll see when you arrive:

The AB pair is at the center of this view, and “C” is suspended about fifteen times further away to the northwest (above and to the left). The unrelated 7.22 magnitude HIP 62724, surrounded by eleventh and thirteenth magnitude stars, adds a little visual spice to the scene over in the far west corner of the view. The only color to be seen here was white. (East & west reversed, click on the sketch for a much better view).

The AB pair is at the center of this view, and “C” is suspended about fifteen times further away to the northwest (above and to the left). The unrelated 7.22 magnitude HIP 62724, surrounded by eleventh and thirteenth magnitude stars, provides an interesting contrast to the primary/secondary pairing. The only color to be seen here was white. (East & west reversed, click on the sketch for a much better view).

Again, even though F.G.W. Struve’s name is associated with this multiple star, both Sir William Herschel and the Hershel/South duo arrived on the scene a few years ahead of him. Admiral Smyth was kind enough to compile a list of the dates and data from all of those observations, which I’ve summarized below. The Admiral accurately noted there was little difference between the various measures: “A comparison of my own with the following measures, afford presumptive proof of fixity.”

Wm. Herschel             Pos. 202° 03’      Dist. 15”.86        Ep. 1782.30
H. and S.                            202° 11’              16”.96              1823.41
Σ..                                      200° 48’              15”.82              1829.87
Wm. Smyth                        201°.40’              15”.90              1831.39
Wm. Smyth                        201°.90”              16”.20              1838.28

Actually, that “fixity” is a bit deceiving, but before we get to that, we’ll take a look at John Herschel and James South’s observation, which includes the “C” component not included by William Herschel (source):

Click on the image to enlarge it.

Click on the image to enlarge it.

They only made one measure of the AC pair, which is the “3rd star” referred to below their measures of the AB pair. Their 59° 23’ np works out to 329° 23’, and their 4’ 9”.666 equals 249.666 when converted into arc seconds, both of which are remarkably close to the 2012 WDS data of 328° and 243.10”. They also include a reference to a fourth star, which they locate at 4° 0’ sp (266.0°) and 10’ 31.644”. That star is HIP 62724, which is shown at the left edge of the field in my sketch above.

That takes us back to Admiral Smyth’s remark about “fixity”, which later astronomical observations would probably term “relative fixity.” As it turns out, there’s quite a bit of motion within this grouping of stars, which looks like this on Simbad’s plot of the motion:

Click to enlarge the chart.

Click to enlarge the chart.

Another way of peering into what’s taking place here is to look at the actual proper motion numbers for the stars labeled in the plot (all the data is from Simbad, which varies slightly from the WDS data):

Σ 1685 A:                 -079 +006  (.079” per year west, .006” per year north)
Σ 1685 B:                 -092 +007  (.092” per year west, .007” per year north)
Σ 1685 C:                +017 +012  (.017” per year east, . 012” per year north)
HIP 62724                -145 +019  (.145” per year west, .019” per year north)
TYC 1452-724-1        -068 +045  (.068” per year west, .045” per year north)
TYC 1452-588-1        -066  -023  (.066” per year west, .023” per year south)

And now let’s return to my sketch of Σ 1685 and add labels:

Click for a larger image!

Click for a larger image!

Now if you compare my sketch side-by side with the Simbad chart (click here to open it an adjacent window), you’ll quickly realize something’s not quite right. That’s because east and west are reversed in my sketch, while the Simbad plot is a correct (erect) image view.  So you can either view this as an opportunity to stretch you mental agility by horizontally flipping either image in your mind, or if that proves to be too confusing, here’s a mirror-image version of the Simbad plot, which matches the labeled sketch above:

Click to enlarge the chart.

Click to enlarge the chart.

You can see that not only are the “A” and “B” components of Σ 1685 marching slowly west (virtually in tandem), but HIP 62724 is also moving in the same direction, although as the both the length of the arrow on the chart and the proper motion numbers above show, its speed is greater. On the other hand, the two stars with the TYC designations, 11.1 magnitude TYC 1452-074-1 and 10.9 magnitude TYC 1452-588-1, seem to be intent on marching to the beat of their own drummers.

There’s also an interesting range of distances among these stars:

Σ 1685 A:     720 Light Years
Σ 1685 B:     481 Light Years
Σ 1685 C:     282 Light Years
HIP 62724:   221 Light Years.

If those distances are correct (all of those are based on the parallaxes found in Simbad), not even the “A” and “B” components of Σ 1685 are related. The “C” component is already at such a visual distance from the AB pair that any type of gravitational influence is unlikely.

So that little scenic trip off the beaten path provides an interesting look into an aspect of double stars that is in no way apparent to the telescopically-aided eye. Sometimes it’s interesting to probe just a bit further in order to get a three dimensional image of what would otherwise be invisible.

Next stop – maybe in Coma Bernices, maybe not.  This has been such an uncooperative year from both a clear sky and a seeing standpoint that good nights have been as rare as a long focus refractor at a Dobsonian convention.

 Meanwhile, Clear and Stable Skies —— somewhere!   😎

(Actually, I did make it back to Coma Bernices — here’s the first part of a two part post).

24 Comae Berenices – easy split with any scope, but bigger sure helps colors

I “discovered” – well, stumbled upon – 24 Comae Berenice while trolling for galaxies with a 12-inch Dob. That immediately prejudiced my opinion of it – it was beautiful! A spring rival for Albireo. How had I never  seen it before? And why did I  find it so hard to find again?

24 Comae Berenices – Σ1657 – H IV 27 – HIP 61415 – SAO 100159
RA: 12h 35.1m Dec: +18°23′
Mag: 5.11, 6.33  Sep: 20.1″ PA: 270°  (WDS 2012)
Distance:  2631 Light Years
Spectral type: K0, A9

Well, for starters I didn’t know what I was looking at in that first view and I guess I am focused on this region as the happy hunting ground for galaxies so I never seriously thought about doubles here. Should have, though, because there are several. We’ll stick with 24 – aka Σ1657, though. This little gem is between the Virgo Cluster of galaxies and the Coma Berenice cluster of stars, so it’s a prime candidate for stumbling upon – especially if you like just prowling about for galaxies in  this region.  Haas lists it as a “showcase” and  “the Night Sky Observer’s Guide” calls it a “springtime version of Albireo.”  It’s still reasonably accessible in early summer. In fact,  as 24 Comae Berenices heads for the western horizon you can check out the real Albireo in the east. A couple hours after sunset  on the Summer solstice  they are both roughly 40 degrees above their respective horizons when viewed from  mid-northern latitudes.

That said, I thought it would be a piece of cake to find 24 again, but when I looked on different nights  with a 60mm Unitron, a 100mm Skywatcher ED, and  a classic RV-6 Dynascope I found myself spending much more time searching than I expected. Problem is, there are a lot of stars in the 5-7 magnitude range in this region and I ended up developing both a bottom up strategy, and a top down strategy for a star hop and I still can’t tell you which works best. Let me show you what I mean.

Two suggested star hops to 24 Comae Berenices prepared from Starry Nights Pro screen shot. Click image for larger view.

As to colors, I had the primary as yellow going to orange – I settled on “tangerine-in-bright-sunlight”  for the primary and the secondary as “summer-sky-blue” – especially if your summer skies tend towards the murky as mine do right now. But these colors screamed at me when using the light grasp of the 12-inch and they were fine in the 6-inch reflector. But they lost some of their zip in the 4-inch refractor and I was a bit disappointed with the view in the  60mm. All of which makes sense since are eyes need a lot of light to see color and when you look at the numbers, Albireo has a full two magnitudes on this pair.

Speaking of numbers, though, the spectral types of K0, A3 do confirm my color descriptions, making the colors similar to, but a bit more subdued than Albireo – that is the Albireo blue is more intense.. Use those numbers then look at this chart.

The “apparent” column is what we tend to see.

Now using the same chart, look at the colors for the Albireo pair – Spectral type: K3, B0

The 20-second split should be easy in just about any scope – in fact, I think this would make a real nice binocular double, though I haven’t tried that yet.

The colors I saw on the night I made this sketch weren't quite as obvious as when Greg looked at it, but it's a colorful pair nonetheless.   (East & west are reversed here to match the refractor view, click on the sketch for a larger version).

The colors I saw on the night I made this sketch weren’t quite as obvious as when Greg looked at it, but it’s a colorful pair nonetheless. (East & west are reversed here to match the refractor view, click on the sketch for a larger version).