With all due deference to the Queen’s royal status, I think it’s fair to say Cassiopeia is one of the most well-endowed constellations visible from the northern hemisphere. Other than a definite deficiency in galaxies, she’s amply abundant in open clusters and nebulae, not to mention double and multiple stars. You’ll find enough of that last group within the Queen’s stellar realm to keep you busy for several light years.
In fact, there’s a particularly compact concentration of double and multiple stars around Beta (β) Cassiopeiae, also known as Caph. I spent a couple of months in the fall of 2012 exploring within a one degree radius of Caph, resulting in a three part exposition of fifteen double and multiple stars (the first part begins here). Even with that, though, I didn’t come close to mining the celestial caverns for all the stellar gold still lurking in the royal veins.
If you peruse one of the commonly used star atlases (chart two in The Cambridge Double Star Atlas, or chart seventy-two in Sky and Telescope’s Pocket Sky Atlas), you’ll find about ten stars designated with the double star legend (black dot with a line through it) within five degrees north, east and west of Caph. And if you delve deeper into the details, you’ll find all sorts of less luminous double and multiple stars peering back at you.
So we’re going to return to Caph, using it for a jumping off point, and plot our way northwest in search of more stellar gold.
Stellarium screen image with labels added. Click on the chart for a larger view.
Fix your eye on 2.43 magnitude Caph, aka Beta (β) Cassiopeiae, which will be our starting point. Notice that north is at the left in this chart and west is at the top. That’s because Polaris is directly to Caph’s left, while west is the direction Cassiopeia is moving. In other words, from the position shown here, the entire constellation will rotate up and over Polaris. For more on astronomical directions, see this very illuminating and informative post by Greg.
Stellarium screen image with labels added.
We’ll start with the colorful OΣΣ 254, which is located a short one and half degrees northwest of Caph (click here to open a full size version of the chart above in a second window). Notice it’s in a dark desert of dim stars, so you may find it easier to align yourself on the four star line-up formed by 5.80 magnitude HIP 418, 5.55 magnitude HIP 124, 6.60 magnitude OΣ 512, and 6.70 magnitude OΣ 511. From HIP 124 a short hop of one degree due south will bring you to OΣΣ 254. Look for a weak orange glow. Once you’re there, you’ll also notice it’s halfway between 6.15 magnitude HIP 43 and 5.55 magnitude HIP 124.
OΣΣ 254 (STTA 254) HIP: 99 SAO: 21002
RA: 00h 01.3m Dec: +60° 21’
. Magnitudes Separation Position Angle WDS
AB: 7.40, 8.33 57.70” 89° 2007
AC: 7.40, 9.56 155.00” 324° 2007
AD: 7.40, 10.35 181.50” 118° 2007
BD: 8.33, 10.35 133.30” 130° 2007
Distance: 2900 Light Years
Spectral Classifications: “A” is NIab,C9; “B” is “A”, and “C” is G5
Notes: “A” is also a variable, WZ Cas, with a magnitude range of 6.8 to 7.7 over 186 days
I’m not sure who was first to point me in the direction of OΣΣ 254 (it was either Steve McGee, Steve Smith, or Chris Thuemen, all residents of the Double Star Imaging Project site), but regardless of whose description it was, I heard two words that caught my curiosity: carbon star.
So what in the name of the Queen is a carbon star? Basically it’s a star well along in its senior years that has evolved to the point where it has more carbon than oxygen in its atmosphere. As those two elements unite to form an evil brew of carbon monoxide, the oxygen is depleted, forcing carbon to search for other elements in the atmosphere with which to combine. That gives rise to a sooty appearance, resulting in the dark and deep red color we usually see, which in turn makes them a feast for our eyes on a pitch black night. More information can be found here, including an explanation of the spectral classes unique to carbon stars. This one is classed as NIab, C9, which is explained in that link.
So what color did I see when I first cast eyes upon this star?
“Very orange” is the way my notes describe the primary, and “distinctly blue” was my comment on the secondary. In a five inch refractor the blue was still distinct, but the primary veered in the direction of red with the orange still making its presence known. At any rate, the primary-secondary combination results in an almost Albireo-like pair. (East & west are reversed here to match the refractor view, click on the sketch for a much better version).
There are two more pairs of double stars in the star-spangled field surrounding OΣΣ 254, both of them located to its northwest. MRI 4 (magnitudes of 12.0 and 12.3, separation of 21.4” at 360°) lies about four arcminutes beyond the primary, and STI 1248 (10.37, 10.78, 12.4”, 48°) lies another four arcminutes beyond in the same northwesterly direction. There are a lot of other suspicious looking stellar pairs in that sketch, but none of them have been elevated to double star status. Also adding some dazzle to this colorful scene is 8.46 magnitude SAO 20989, its M2 orange glow hovering at the west edge of the field.
Now we’ll continue north a short distance to our next stellar target, OΣ 512, a strange combination of starlight if ever there was one. Probably the easiest thing to do is go back to HIP 124. From there, a quick half degree hop to the west with a slight southerly lean will take you to our target. (Here’s our last chart).
OΣ 512 (STT 512) HIP: 118090 SAO: 20954
RA: 23h 57.3m Dec: +61° 02’
Identifier Magnitudes Separation Position Angle WDS
STT 512 AB: 6.85, 9.72 2.70” 305° 1991
STT 512 AC: 6.85, 9.79 367.90” 84° 2003
ARG 99 CD: 9.79, 10.05 4.60” 318° 2011
ARG 99 CE: 9.79, 13.00 19.90” 86° 2011
Distance: 935 Light Years
Spectral Classifications: “A” is M2.5, “C” is F4
Notes: CD is also known as D 28 and TDS 1229.
The sketch is much more illuminating than staring at the numbers, so let’s start there first:
Now don’t be fooled by what your eyes tell you. This isn’t a sketch of two unrelated stars at opposite ends of the eyepiece. The two labels you see at either end of the field of view belong to the same group of stars. You may as well allow your eyes to linger on the orange warmth of OΣ 512’s primary while thinking about that. The weak puff of light that is “B” is parked at about the one o’clock position, and just over six arcminutes to the east is that lonely pair designated ARG 99, which does double duty as the CD pair of OΣ 512. If you look closely, you’ll catch the weak 13th magnitude light of the “E” component almost twenty arcminutes to the south of the CD pair. (East & west reversed once again, click on the sketch to enlarge it for a much better view).
This is a strange collection of stars with a strange history. Otto Struve staked his claim to discovery of the AB pair in 1843, which is why it carries his initials (the Greek letters OΣ are OS in our usage). In 1865 or so, someone – either Baron Dembowski (the source of the “D” in D 28) or Friedrich Argelander (the source of the ARG in ARG 99) discovered the CD pair. And then someone – no idea who – extended the influence of “A” over six arcminutes east to “C”. The puzzling thing is the two sources I use for historical background on Otto Struve’s observations, Hussey and Burnham, ignore ARG 99 completely, even though their catalogs were published several decades later (1901 and 1906, respectively).
What mystifies me is why the connection between the “A” and “C” components was made. A quick look at the proper motion of those stars (-008 and -005 for “A”, +026, -004 for “C”) in the Washington Double Star Catalog (WDS) shows no similarity in motion. This Simbad chart provides a visual display of what those proper motion numbers mean:
Click on the chart for a larger view.
(If you look closely, you’ll notice the movement in declination for “C” doesn’t match the -004 figure published in the WDS. The negative sign in front of the number indicates southerly motion, but the motion shown on the Simbad chart is north (which means it should have a plus sign in front of it). So either the WDS or Simbad has an error in that declination number. If you look even more carefully, you’ll also notice the rate of motion in declination shown on the chart is greater than .004″ per year. Nevertheless, the chart does illustrate the opposing directional movements of the stars, which is the main point of including it here).
One of these days I would like to find a discussion, written by the person or persons directly involved, of what it is exactly that prompts the decision to link a pair of stars that have no apparent relation to one another.
But let’s leave OΣ 512 behind and move another quick half degree southwest to get a peek at its sequential sibling, OΣ 511. (Here’s that chart again).
OΣ 511 (STT 511) HIP: 117775 SAO: 20915
RA: 23h 53.1m Dec: +60° 42’
. Magnitudes Separation Position Angle WDS
AB: 6.89, 10.58 9.80” 34° 2007
AC: 6.89, 14.10 35.80” 40° 2007
AD: 6.89, 10.34 68.30” 131° 2007
Distance: 1100 Light Years
Spectral Classification: “A” is K5
OΣ 511 and its gold-tinted primary sit at the center of this field, with its components labeled in the inset at the right. Three arcminutes west and slightly south is Bu 1153. (East & west reversed once again, click on the sketch to improve the view considerably).
“A”, “B”, and “D” were easily seen in the 9.25 inch SCT, but the real surprise was 14th magnitude “C”. As close as it is to the glare of the primary, I really didn’t expect to see it, but averted vision ogled it out of the glare.
Click on the image for a larger view.
The AB pair was discovered in 1848 by Otto Struve, and 10.34 magnitude “D” was added in 1903, probably by S.W. Burnham, who was definitely responsible for adding the very faint 14.10 magnitude “C” component in 1911. He noted it as a “14 m star near A” as can be seen in the excerpt at the right from his 1913 Proper Motion Catalogue. Note that the star he refers to there as “C” is now “D”, having been re-designated after the addition of the 14th magnitude star to the system.
And if you look at the last entry on that page, you’ll notice he also linked OΣ 511-A to his 1889 discovery, Bu 1153:
Bu 1153 No HIP or SAO number assigned
RA: 23h 52.7m Dec: +60° 42’
. Magnitudes Separation Position Angle WDS
AB: 9.70, 9.90 0.50” 319° 2003
AB, C: 9.70, 10.10 14.00” 336° 2007
AB, D: 9.70, 6.89 176.90” 66° 2007
Distance: ?????
Spectral Classification: none listed
Notes: “D” is the AB pair of OΣ 511
Click for a larger view.
He made that connection at the same time he discovered Bu 1153, which he noted at the bottom of his observation, shown at the right. His 1889 measurements for the AB,D pair, 66° and 176.51”, are virtually identical with the 2007 WDS numbers, indicating little motion during the intervening 118 years. If you glance back at the data above for OΣ 511, though, you’ll see the connection to Bu 1153 is absent – not sure whether that’s an error or by design. (Link to book at right).
However, in contrast to our previous star, OΣ 512, which is connected to another system (ARG 99) for no apparent reason I can detect, there is a definite connection between the AB pair of OΣ 511 and the AB pair of Bu 1153. That connection is their proper motion, which is listed in the WDS as +005 -002 for OΣ 511 and +007 -004 for Bu 1153. So this one at least is understandable.
I had no problem picking the AB,C pair out of the field of view (“B” was way too close for conditions), a real surprise based on the magnitudes of 11.4 and 12.25 assigned to the AB,C pair in the WDS. That doesn’t makes sense when it also lists magnitudes of 9.7 and 9.9 for “A” and “B” separately. Simbad shows magnitudes of 9.7 and 10.1 for AB,C, which matches much better with what I saw, so I’ve used those values in the data line above.
Don’t wander away quite yet. There’s another trio of rather intricate and bewildering multiple stars just a few photonic leaps away, which are coming up next.
Meanwhile, keep your skies clear! 😎
Filed under: 4. Choose a Constellation:, Cassiopeia |
John Nanson
Greg Stone
Star-Splitters 
Hi John!
Some very curious stellar relationships uncovered here. A beautiful sketch of OZZ 254. You must have spent a couple of hours plotting all those stars and without a tracking mount?? How the heck are you getting your Greek letters into your text…I need a “Word” tutorial. I continue to have my concerns as to how all these doubles were catalogued. I’m still of the opinion that most of the pre-1900’s was simply finding, then measuring and then finally publishing the catalogues. Given the instruments of the day, it is incredible what they achieved. I don’t believe any of the double star pioneers made multiple measurements, primarily because the changes of PA and separation, in their individual lifetimes for the most part, could not be measured. I contend that they were setting up the data base in the hope that others would follow in their footsteps and that future observers would be able to confirm the true binary nature or the fact that listed doubles were only visual pairs. Just getting the PA’s and separations with the primitive tools, poor lighting and mostly mounts without clock drives, puts their accomplishments at close to the miraculous. I submit the brevity of the USNO’s orbital catalogue as my argument. I just wish there was some historical anecdote that would shed some light on this dilemma…I suspect that it will remain so for some time to come.
Another fine read, Keep up the great work, John!
Cheers, Chris.
Thanks again for the comments, Chris — sent you an email on coaxing the Greek letters out of Word.
It took until the early 1800’s, but William Herschel actually was able to detect motion in a few of the stars he discovered. Among those were Castor, Gamma Leonis, Izar, Zeta Herculis, Delta Serpentis, and Porrima. I pulled all those out of an 1803 paper written by Sir William with this descriptive title:
“Account of the Changes That Have Happened, during the Last Twenty-Five Years, in the Relative Situation of Double Stars; With an Investigation of the Cause to Which They Are Owing”.
Clicking on the title will take you to the table of contents of the 1803 volume of the Royal Society of London’s Philosophical Transactions — scroll down to the bottom of the page, and the paper is the next to the last one listed.
That paper aside, though, you’re entirely correct. William Herschel and the 19th century observers had no idea whether there was any gravitational influence at work between pairs of stars at the time they cataloged them. That took time to develop, and of course many of those stars were later found to be physically unrelated. To some extent, at least as near as I can tell, that’s still the situation today.
John