Double stars. Sometimes I wonder if that term isn’t a complete misnomer. It’s not that there aren’t plenty of paired stars that are really that (meaning no more than two components present). But it seems like I keep running into complicated stars with lots of stellar company – as in triple stars, quadruple stars, quintuple stars, sextuple stars, septuple stars, and on and on until you reach those with more components than you care to count . . . . . . . . otherwise known as argh!-tuple stars. I ran into quite a collection of most of those categories not too long ago while pursuing a few nocturnal targets under the watchful gaze of gold-tinged Caph.
I started with a simple sextuple star, then graduated to a sumptuous septuple, and from there I stumbled into one of those argh!-tuple stars that even had a tricky triple hovering nearby. Some nights you literally need a scorecard to keep track of all the stars on, or in this case, in, the field.
When last we left Cassiopeia, we were hanging on the edge of our chairs in admiration of the restrained orange primarial light escaping from OΣ 511. But as we lingered there, we weren’t far from an entirely new world – just a short degree, in fact.
If you’re not still sitting on OΣ 511 after our previous adventure, the easiest way to get to our first target is to start at Caph and then move two degrees north and slightly west to 5.80 magnitude HIP 418. That star is the first of four stars that form a gently curving line leading to our first target. Follow it northward to 5.55 magnitude HIP 124, 6.60 magnitude OΣ 512, and 6.70 magnitude OΣ 511 (those last two stars were discussed in the post prior to this one). Then continue another degree in the same direction and you’ve reached Σ 3037.
Σ 3037 HIP: 117227 SAO: 20832
RA: 23h 46.1m Dec: +60° 28’
. Magnitudes Separation Position Angle WDS
AB: 7.35, 9.20 2.60” 212° 2004
AC: 7.35, 9.96 29.10” 189° 2007
AD: 7.35, 10.86 52.60” 233° 2007
AE: 7.35, 9.70 109.90” 63° 2007
AF: 7.35, 11.13 123.50” 147° 2007
BC: 9.20, 9.96 27.10” 186° 2003
Distance: 1200 Light Years
Spectral Classifications: “A” is K0, “C” is M3, “E” is A0
All the components of this six-starred system were present and accounted for on first glimpse in the 9.25 inch SCT, and it didn’t take long to figure out which was which. The 11.13 magnitude “F” companion might be a bit elusive in a four inch refractor, although at just over two arcminutes away from the primary, it should at least be visible with averted vision. And with almost two magnitudes of difference between the primary and secondary, “B” would be a good test for a four inch refractor.
The AB pair was discovered by F.G.W. von Struve in 1828, and he added the “C” component in 1832. That star has a spectral classification of M3, meaning it should have a noticeable orange tint, but because of its weak tenth magnitude glow it eluded my vision. The other three components, “D”, “E”, and “F”, were added in 1898 by someone whose name has also eluded me so far. As the excerpt from Lewis’s book at the right shows, there has been little change in separation and position angle of the AB and AC pairs since their discovery. A quick look at the WDS shows very little proper motion in any of these stars, so you might call them solidly stable citizens of the galaxy.
Now on to our eccentric septuple star, ENG 88.
To get there from where we are we need to aim for 4.88 magnitude Tau (τ) Cassiopeiae, which can be found directly south at a distance of two degrees (click here to open the chart above in a separate window). After arriving at Tau (τ) we’ll turn southwest and hop three-fourths of a degree to reach ENG 88, which is situated just past the midpoint between Tau (τ) and 7.26 magnitude HIP 116843.
Take a moment and look closely at the position angles above for the AB through AG pairs – there’s a visual image encoded in those numbers. (You can click on the table of data below to get a clearer view of it).
Seeing all of the components in a six inch refractor is no real challenge (excepting of course the mysterious un-magnituded secondary of the Aa,Ab pair with its .10” separation), although I had to look very carefully to pick out the subdued flicker of 12.24 magnitude “G”. Matching the letter designations to the various stars was little problem, but as I did that I became curious about the three letter code assigned to this mini-open cluster.
ENG, as it turns out, is a prefix that has belonged to two different people. Originally it was assigned to Baron Vasily Pavlovich von Engelhardt. The ENG designation was later re-assigned to R. Engelmann, who prior to that had been assigned EN. With that change, the Baron’s prefix was changed to ENH. However, according to the WDS discover code file, all but three of the double stars in its catalog which carry the ENG prefix were actually discovered by the Baron von Engelhardt (the exceptions are ENG 21, 39, and 68). So in order to avoid confusing the issue further, it was decided best if the prefixes assigned prior to the change were left as is. All of which proves you also need a scorecard for the discoverer names if you want to know who was first on first.
All of that aside, if you go back to the last entry in the data above for ENG 88, you’ll see a note on proper motion, plus another designation for the primary, LHS 4004 (the “L” refers to a sub-division of the Luyten Proper Motion Catalog which is cleverly named the Luyten Half Second Catalog). A quick look at the Simbad chart shows very vividly how quickly the primary (actually the Aa, Bb pair) is moving relative to the other stars in the group:
As you can see, the primary is zipping along through the galaxy rather briskly in comparison to the lettered companions surrounding it. What those proper motion numbers tells us is the primary is moving eastward in right ascension at the rate of .390 of an arcsecond per year and .481 arcseconds per year north in declination – which means it’s very detectable from year to year, especially in comparison to the other stars in the group, whose proper motions are also shown in the data above (far column at the right labeled “companion”). So if you want proof the heavens really do change, come back in a few years and you’ll see an obvious difference.
Meanwhile, it’s time to move on to our argh!-tuple star (here’s our last chart again). A close look at the chart will show 7.0 magnitude HIP 116650 is located almost exactly halfway between Tau (τ) and the fifth magnitude glow of OΣ 496/SHJ 355 (it goes by both names). It’s a one degree hop almost due west to HIP 116650 and another one degree leap into the west to OΣ 496.
The ΟΣ 496 Collection is a virtual stellar shrine to the double star greats of the late 18th and the entire 19th century. From top to bottom we have Otto Struve (STT), Sirs James South and John Herschel (SHJ), John Herschel by himself (HJ), S.W. Burnham (Bu), and finally, the Reverend W.R. Dawes (DA). And all alone over in the east corner of the sketch below is F.G.W. von Struve (Σ), represented by Σ 3022. Sir William Herschel also makes his presence known as the first to measure the AB pair of Σ 3022.
I included the dates of first measures in the data above to illustrate how the addition of the many components took place. John Herschel and James South started the whole thing off with their 1800 measures of what are now the AC pair (they were AB in the beginning), then John Herschel added the “H” and “G” members in 1828. He also added the “E”, “F”, and “G” components at the same time, as can be seen in the excerpt at the left from his 1830-31 catalog. His measures of the AE and AF pairs were later refined by Baron Dembowski in 1869, and AG was improved on in 1914, possibly by S. W. Burnham.
Reverend Dawes and Otto Struve both discovered “D” independently in 1841, and ten years later Herr Otto added the 9.30 magnitude member now identified as “B”. That star, which is presently well out of the reach of most of us with its .80” separation from the primary and its 4.43 magnitudes of difference, was measured at 1.42” and 1.51” by Otto Struve in 1851. If you look at the excerpt at the right from W. J. Hussey’s compilation of Pulkowa observations, you can see the distances between the primary and secondary have slowly decreased over the years, reaching the tight 0.80” separation listed in the WDS as of 2002.
There’s no orbit shown in the WDS for the AB pair, so it’s an open question as to whether some kind of physical relation exists between the two stars. Nor are there any proper motion figures listed in the WDS for “B”, so there’s no basis to make any conjecture as to what might be taking place between the two stars. “A” could be pulling “B” toward it, or there may be a burgeoning bundle of light years separating them and we just happen to be seeing what looks like a close approach that isn’t.
But let’s not forget F.G.W. von Struve’s triple star down in the east corner of the sketch:
Σ 3022 No HIP number assigned SAO: 35491
RA: 23h 30.9m Dec: 58° 25’
Identifier Magnitudes Separation Position Angle WDS
STF 3022 AB: 8.34, 9.94 20.50” 227° 2012
STF 3022 AC: 8.34, 9.30 118.70” 191° 2012
Bu 1151 CD: 9.30, 9.30 .40” 291° 2008
Spectral Classification: “A” is Am
Notes: AB is H IV 65
This is another star with a remarkable list of names attached to it, although you can’t tell that from the data listed above. Sir William Herschel first came across the AB pair on August 25th, 1782, and provided measures of both the separation and position angle. (The source for the excerpt below is the sixth title down on this page).
Apparently a mistake was made in regard to the position angle when his observing notes were transferred to the printed copy. The 41° 12’ south following shown above translates to 131° 12’ in our current usage, which is way off from the actual PA. More than likely “south following” was supposed to be “south preceding,” which would result in a much closer position angle of 228° 48’. At any rate, F.G.W. von Struve came along in 1828 and provided the correct measure of the position angle, so his name is now attached to the star.
The Reverend Dawes added the “C” component in 1841, and then S.W. Burnham pried the “D” component loose from “C” in 1889, which can be seen in the inset at the right (source), which also includes measurements between “A” and “C”. He was using the 36 inch refractor at the Lick Observatory (see below), by the way, so he had a slight advantage over the refractor inventory I have within reach of the tips of my focus fingers. Not that it matters – with his double-star tuned vision, he probably would have at least detected an elongation in his six inch Clark refractor.
Before I forget to give credit where credit is due, many thanks to Peter Morris of the UK for pointing my attention in the direction of OΣ 496/SHJ 355 and Σ 3022/Bu 1151.
Time for something different on our next nocturnal excursion – there’s a surprise hovering in Perseus just waiting for a someone with a six inch refractor to pay it a leisurely visit, and I just happen to know someone who has both the time and the refractor.
Clear Skies until then! 😎