After my last session in Hercules with a rather difficult double, OΣ 344, I found myself rather taken with the surrounding scenery and decided to stay a while. First, there was the allure offered by the chance to see what OΣ 344’s numerical predecessor, OΣ 343, offered, and north of it were two enticing Struve (Σ) delicacies waiting to be cornered in an eyepiece. First, though, I decided to strike out east of OΣ 344 in search of a dim double with a strange prefix, HDS 2572.
But first, we better get oriented:
HDS 2572 HIP: 89299 SAO: 47320
RA: 18h 13.3m Dec: +49° 44’
Magnitudes: 9.65, 10.49
Position Angle: 70° (WDS 2006)
Distance: 596 Light Years
Spectral Classifications: “A” is K0, “B” is G0
Dim though it may be, this is a very striking configuration of stars in a 9.25” SCT. But there are a couple of things about HDS 2572 that jumped out at me right away.
First, the primary and secondary are very similar in brightness. Simbad shows the primary with a visual magnitude of 10.0, which fits better with the relative magnitudes of the two stars. A glance at the inverted image at the right also leads me to believe there’s less than a full magnitude of difference between the pair (source).
Second, there’s that third star (GSC 03533-0606) parked east of the secondary, which is what makes the configuration so attractive. It’s listed with a photographic magnitude of 13.51, although visually it’s somewhere between 12.5 and 13.0. Using the measuring capability of Sky Tools 3, I found it’s separated by 19” from the secondary at a position angle of 84 degrees. It could as easily be included as a third member of HDS 2572 as not, but the cold harsh stellar reality of the matter is the primary and secondary aren’t related anyway, as this Simbad chart shows:
And one last item: if you’ve been wondering what the exotic and rare HDS prefix stands for . . . . . well, it’s not that exotic and the name is really not that rare. HDS stands for Hipparcos Double Star – and even though this one is number 2572, I’ve never run into the prefix before this.
On to other stellar pastures now. Let’s hop back to OΣ 344 now and head south for F.G.W. Struve territory (here’s our last chart again for reference). We’re in luck this time since we have a pointer to direct us. A glance 27’ south and slightly west of OΣ 344 will turn up the 7.39 magnitude orangish light of HIP 88602. Follow the line formed by OΣ 344-HIP 88602 a full degree further southwest and you’ll find sixth magnitude Σ 2277 waiting for you, parked at the north end of a line of four stars of similar magnitude.
Σ 2277 HIP: 88415 SAO: 47173
RA: 18h 03.1m Dec: +48° 28’
Magnitudes AB: 6.28, 8.93 AC: 6.25, 10.19 BC: 8.93, 10.19
Separations AB: 26.40” AC: 99.70” BC: 123.60”
Position Angles AB: 130° (WDS 2011) AC: 299° (WDS 2010) BC: 299° (WDS 2003)
Distance: 526 Light Years (WDS)
Spectral Classifications: “A” is A1, “B” is K
Note: High Proper Motion for C, -006 +231 (.006” west/year, .231” north/year)
(PM for A is +021 +012 [east and north] and for B is -015 -010 [west and south])
Again I noticed the relative magnitudes weren’t matching the data – “C” looked brighter to me than “B”, even though “B” was listed as being 1.26 magnitudes brighter. Checking the visual magnitudes in Simbad, I found the difference was about the same, even though the visual magnitudes themselves were slightly different: 8.83 for “B” and 10.08 for “C”. The glare from the primary, which is 2.65 magnitudes brighter than “B”, accounts for part of that impression, and I suspect “B”’s orange spectral class (orange is less visually intense than white) also has some effect. As the STScI photo above clearly shows, “B” is brighter than “C”, but not by much.
Another interesting aspect of these three stars is the high proper motion of “C”, which was added to the system in 1895. S. W. Burnham (see excerpt at right [source]) credits Glasenapp with some 1897 measures, but the WDS data show 1895 as the date of first measurement. Thomas Lewis (p. 525) also shows Glasenapp making measurements of AB in 1895. Notice that although there has been little change in separation of the AB pair, the position angle has changed quite a bit since the three measures shown by Burnham, apparently a result of the primary and secondary moving in opposite directions from each other.
The Simbad chart below illustrates that very clearly, as well as showing “C” is fleeing the sight rapidly. At any rate, it’s clear from their proper motions, none of the three stars are physically bound to each other. (The proper motion numbers in the data above are from Simbad).
On to Σ 2293 now. With Σ 2277 centered in your finder (here’s the last chart again), look a long degree east (actual distance is 1° 7’) and you should see an eighth magnitude bundle of photons beaming from Σ 2293. For reference, 6.65 magnitude HIP 89143 can be seen 18′ east and slightly south of Σ 2293.
Σ 2293 HIP: 88999 SAO: 47273
RA: 18h 09.9m Dec: +48° 24’
Magnitudes: 8.08, 10.34
Position Angle: 83° (WDS 2008)
Distance: 257.5 Light Years (Simbad)
Spectral Classification: “A” is G0
There are two faint pairs in the field — one on the southeast side of the sketch, the other north and slightly east of the primary – neither of which are identified as doubles from what I can determine. The star labeled TDT 713 was just a bit beyond my reach with magnitudes of 10.85 and 10.90 and a separation of 0.5”, although on a night of steady seeing it ought to be possible to see the pair in a 9.25 inch SCT. (The TDT prefix stands for Tyco Double Star).
There was a surprise lurking for me when I checked Burnham’s 1906 catalog to see what data and notes he had on this pair:
First, it looks like Hussey (Hu) reversed the position angle – the measurement shown is from “B” to “A” (add 180 to the 83 degrees shown in the data above for 2008 to get 263°). And of course, the other was that “rej”! Rejected??? I immediately went to Lewis’s compilation (p. 530) of the senior Struve’s observations and found he skipped over it entirely. I knew there was more here than met they eye at the eyepiece, so I sent off a request to Brian Mason at the USNO (WDS), hoping the data in the text file for Σ 2293 would shed some light here.
But Struve’s initial observation wasn’t included there, so I looked it up in his 1827 Catalogus novus stellarum duplicium, only to find it wasn’t much help. As you can see below, there is no separation or position angle shown, which is actually the case for all of the stars listed in that 1827 catalog.
However, Struve used a classification system of Roman numerals similar to William Herschel to indicate separation, which can be seen in the column labeled “Description”. Unfortunately, I’m not quite sure why he shows two Roman numerals in the listing for Σ 2293. At any rate, neither is much help: the “III” refers to separations of 2” to 4”, and the “IV” refers to separations of 4” to 8” (see page X of Lewis’s book for that information), neither of which applies in the case of Σ 2293 . . . . . . . which I presume is the reason his listing for Σ 2293 was rejected.
Getting back to the text file Brian Mason sent me for Σ 2293, I found the first measure listed was dated 1901, but was unable to track that one down. I had more luck with the second one shown, since it was the W.J. Hussey measure shown above in the excerpt from Burnham’s 1906 catalog. As I scanned further down the list, I discovered Burnham had located Σ 2293 in 1907 (source) and measured it, followed by Eric Doolittle (source) in 1908 and T.E. Espin (source) in 1911.
So as of 1911 it would appear Σ 2293 had been solidly rescued by those three observers. But then it disappears from the record again — for a period of fifty-five years, from 1925 to 1980, there are no measures listed. I’m sure there’s a story there, but I have no idea what it is — maybe a hint of sly stellar sleight of hand?
Whatever the case, it’s fortunate this pair was rescued from wherever it went since it’s actually a physically related pair, unlike our previous star, Σ 2277. You can tell that by looking at the proper motion numbers in Simbad, which for “A” are -028 +062 (.028” west/year, .062” north/year) and for “B” are -027 +060. Graphed they look like this:
Last on our list is OΣ 343, which lies south of and midway between Σ 2293 and Σ 2277 (last chart again). If you’re pacing off distances in the sky, it’s 52’ from Σ 2293 to OΣ 343, and 27’ from Σ 2277.
OΣ 343 HIP: 88555 SAO: 47200
RA: 18h 04.9m Dec: +48° 08’
Magnitudes: 7.63, 10.51
Position Angle: 79° (WDS 2002)
Distance: 414 Light Years (Simbad)
Spectral Classification: A2
I think it would be fair to classify this tight pair as training for its much more difficult numerical successor, OΣ 344, which we covered last time out. We’re dealing with 2.88 magnitudes of difference here between the primary and secondary and 3.3” of separation, compared to 3.84 magnitudes of difference and a full arc second less of separation on OΣ 344. For a visual observer, there’s an abyss of difference between those two scenarios, but even at that, OΣ 343 can be a difficult character when the seeing fails to cooperate.
The good news is these two stars are gradually moving further apart. Otto Struve measured the separation at 2.55” in 1846 when he discovered the pair, and as the excerpt from W. J. Hussey’s compilation shows below, the measures in the following years show a steady widening.
And that’s it for this part of Hercules south of Eltanin. Next time we’ll see what Herculean gems are lurking beneath the star that marks the southwest corner of Draco’s head, Rastaban, aka Beta (β) Draconis.
Clear Skies! 😎