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On the Hercules-Draco Border – South of Eltanin: HDS 2572, Σ 2277, OΣ 343, and Σ 2293

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:

Cast your eye north of Hercules to Gamma Draconis, aka Eltanin, a second magnitude K5 (orange) beauty worth lingering over. It also happens to be a multiple star with six faint components buried in its glare, ranging in magnitude from 11.2 to 13.4, cataloged as Bu 633. One of S.W. Burnham’s devilish delights, we’ll save it for another night. (Stellarium screen image with labels added, click on the chart to enlarge it).

Cast your eye north of Hercules to Gamma Draconis, aka Eltanin, a second magnitude K5 (orange) beauty worth lingering over. It also happens to be a multiple star with six faint components buried in its glare, ranging in magnitude from 11.2 to 13.4, cataloged as Bu 633. One of S.W. Burnham’s devilish delights, we’ll save it for another night. (Stellarium screen image with labels added, click on the chart to enlarge it).

To get to our first star, HDS 2572, we’ll retrace the route we took last time out to reach OΣ 344. Move east and somewhat south for a distance of 1° 45’ to reach 6.3 magnitude HIP 88732. Another half degree leap directly southeast will take us across the Draco-Hercules border to 7.3 magnitude HIP 88975. Now switch to the southwest and hop a short degree (actually 48’) to 6.5 magnitude OΣ 344. Pause for breath and then leap a full degree east to our goal, 9.65 magnitude HDS 2572.   If you have trouble seeing it in your finder, you should be able to pick out the 8.77 magnitude light of SAO 47315 (this one doesn’t have an HIP number). (Stellarium screen image with labels added, click on the chart for a larger view).

To get to our first star, HDS 2572, we’ll retrace the route we took last time out to reach OΣ 344. Move east and somewhat south for a distance of 1° 45’ to reach 6.3 magnitude HIP 88732. Another half degree hop directly southeast will take us across the Draco-Hercules border to 7.3 magnitude HIP 88975. Now switch to the southwest and hop a short degree (actually 48’) to 6.5 magnitude OΣ 344. Pause for breath and then leap a full degree east to our goal, 9.65 magnitude HDS 2572. If you have trouble seeing it in your finder, you should be able to pick out the 8.77 magnitude light of SAO 47315 (this one doesn’t have an HIP number), or you could just land halfway between OΣ 344 and 6.39 magnitude HIP 89943. (Stellarium screen image with labels added, click on the chart for a larger view).

HDS 2572           HIP: 89299   SAO: 47320
RA: 18h 13.3m   Dec: +49° 44’
Magnitudes: 9.65, 10.49
Separation:  14.5”
Position Angle: 70° (WDS 2006)
Distance: 596 Light Years
Spectral Classifications: “A” is K0, “B” is G0

Delicate and dim describes this pair (trio?) rather well. I detected a very pale orange fragment of light trying to escape from the primary. (East & west reversed to match the SCT image, click on the sketch to get a much better look).

Delicate and dim describes this pair (trio?) rather well. I detected a very pale orange fragment of light trying to escape from the primary. (East & west reversed to match the SCT image, click on the sketch to get a much better look).

Note the star peeking out between the primary and secondary! Click to enlarge.

Note the star peeking out between the primary and secondary! Click to enlarge.

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:

 “A” and “B” seem intent on going their own way.  Click to enlarge.

“A” and “B” seem intent on going their own way. Click to enlarge.

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])

The primary is a very definite white, but between the secondary’s relative faintness compared with the primary and its proximity to it, I didn’t see any trace of the orange which is normally present in a K class star. (East & west reversed to match the SCT view, click on the sketch to enlarge it).

The primary is a very definite white, but between the secondary’s relative faintness compared with the primary and its proximity to it, I didn’t see any trace of the orange which is normally present in a K class star. (East & west reversed to match the SCT view, click on the sketch to enlarge it).

SCStI photo, click to enlarge.

STScI photo, click to enlarge.

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.

Click to enlarge.

Click to enlarge.

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).

Click to enlarge.

Click to enlarge.

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
Separation:  13.4”
Position Angle: 83° (WDS 2008)
Distance: 257.5 Light Years (Simbad)
Spectral Classification: “A” is G0

Just your basic primary-secondary pair. The primary appeared white to me, even though its G0 spectral class argues it should have some yellow present.   (East & west reversed once more, click on the sketch to improve the view).

Just your basic primary-secondary pair. The primary appeared white to me, even though its G0 spectral class argues it should have some yellow present. (East & west reversed once more, click on the sketch to improve the view).

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:

Burnham on STF 2293 in 1906

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 rejRejected???  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.

Struve on STF 2293

Click to enlarge.

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.

Burnham-Doolittle-Espin on STF 2293So 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:

Click to enlarge.

Click to enlarge.

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
Separation:  3.3”
Position Angle: 79° (WDS 2002)
Distance: 414 Light Years (Simbad)
Spectral Classification: A2

The primary was white and the secondary was barely a spark of light. I needed 175x (14mm Radian) to see it clearly on 6/23, but two nights earlier when I made the sketch it had been easy to see at 136x (18mm Radian).   (East & west reversed again, click on the sketch to get a much better look at the secondary).

The primary was white and the secondary was barely a spark of light. I needed 175x (14mm Radian) to see it clearly on 6/23, but two nights earlier when I made the sketch it had been easy to see at 136x (18mm Radian). (East & west reversed again, click on the sketch to get a much better look at the secondary).

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.

Hussey on STT 343

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! 😎

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2 Responses

  1. John I would like to commend you on your sketch of HDS 2572 . A very nice piece of work .
    mike hyrczyk

    • Vielen Dank, Mike! It’s one of those delicate gems that’s a real pleasure to come across. It’s worthy of triple status, even though at least two of the stars are unrelated.

      John

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