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).
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).
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).
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:
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
Position Angle: 186° (WDS 2013)
Distance: 482 Light Years
Spectral Classification: F5, F8
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 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):
The 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, 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.
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.
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!
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.
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! :cool:
(Actually, I did make it back to Coma Bernices — here’s the first part of a two part post).
Filed under: 4. Choose a Constellation:, Coma Bernices | 2 Comments »