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Traveling through Southern Aquila: 15 and 5 Aquilae, OΣΣ 176 and Σ 2447

I was poking around a star atlas the other day looking for somewhere interesting to go and my eye was drawn to the southern tip of Aquila and the northern edge of Scutum, an obscure constellation probably best known for the Wild Duck Cluster (M11).  I counted over a dozen reasonably bright (fifth to ninth magnitude) multiple stars in this small area.  So we’ll start with the southern tip of Aquila and save the north end of Scutum for a later time.  But — be warned!  It may get warm here since this trip will keep us very close to the celestial equator.

All four of the stars for this tour can be seen on this chart, along with the sparkling beauty of the Milky Way just north of our galaxy’s center in Sagittarius. (Stellarium screen image with labels added, click for a larger view).

15 Aquilae  (Sh 286)  (H V 33)      HIP: 93717    SAO: 142996
RA: 19h 05.0m   Dec: -04° 02′
Magnitudes: 5.5, 7.0
Separation:  38.2″
Position Angle: 210°  (WDS 2011)
Distance: 325 Light Years
Spectral Classification: K0

The tip of Aquila’s tail is marked by two stars, Lambda (λ) and 12 Aquilae.  Just north of Lambda are two faint naked eye stars, 15 and 14, the first of which is really a pleasing double in a 60mm scope.  At just over thirty-nine arc seconds apart, 15 Aquilae is an easy split at 50x in my 60mm scope.  The primary appeared yellow to me with a slight tinge of red, and the secondary was white with maybe a bit of gray present.  Haas describes them as “amber-yellow and bluish-turquoise.”

Hmmm — we’re not even close on this one!   So I took another look, this time in a 105mm refractor, and at 83x they were still yellow with a slight tinge of red and white with a bit of gray.   Must be something in the air.  😉

5 Aquilae  (Σ 2379)  (H III 33)      HIP: 92117    SAO: 142606
RA: 18h 46.5m   Dec: -00° 58′
Magnitudes  AB: 5.9, 7.0    AC: 5.9, 10.9
Separation   AB: 12.6″        AC: 25.0″
Position Angle  AB: 121°  (WDS 2011)   AC: 148°  (WDS 2005)
Dist: 258 Light Years
Spectral Classification: A2

If you continue on this trip to the northwest and stop just short of the eastern edge of the Serpens Cauda border, you’ll come to an interesting multiple star, 5 Aquilae.  The AB pair is another pleasant sight in a 60mm scope at 50x, with their 12.6 arc second separation making for a nice contrast to the wider 15 Aquilae.  The 105mm scope at 83x put more distance between them, but I think I prefer the tighter appearance in the 60mm scope.  Both appeared white to my eyes — but after that last experience judging color, I think I’ll keep it to myself for a while.

But the real challenge here is to dig out the AC pair.  The first night I tried with the 105mm, my session was cut short by an invasion of creeping clouds.  Before they took over, I had time to try it at 83x and wasn’t able to see “C” at all.  I did just barely catch a glimpse of it at 150x, but the clouds swallowed it before I could get a good look at it.  I tried again the following night with a 102mm refractor and was able to catch it with averted vision at 63x and could see it clearly with direct vision at 98x.  I didn’t get a chance that night to try it with a 60mm scope, but with averted vision it should be possible on a good night at around 100x or so.  Fortunately, it’s a bit faint for color, so I can’t go wrong on this one!

OΣΣ 176   (STTA 176)       HIP: 92794      SAO: 124028
RA: 18h 54.5m   Dec: +01° 54′
Magnitudes   AB: 7.45, 7.51   AC: 7.45, 10.8    BD: 7.51, 11.0
Separation    AB: 94.3″            AC: 155.3″          BD: 151.2″
Position Angle   AB: 113°  (WDS 2011)    AC: 4° (WDS 2002)   BD: 358°  (WDS 2002)
Distance: 289 Light Years
Spectral Classification: F5  for  A

Turning back to the northeast and again approaching the Serpens Cauda border, you’ll come to a wide pair of stars known as OΣΣ 176, or by it’s Washington Double Star Catalog designation, STTA 176.  These are easy in a 60mm at 50x, but I spent most of my time looking at them with a 102mm refractor because of the interesting pattern they form with another pair of stars to their north.  Haas describes both of the OΣΣ 176 stars as “greenish-white,” but I’ll just leave it at white.  Hey, at least we’re getting closer.  🙂

OΣΣ 176 — north is up, west is to the left. (STScI photo)

There is also a tight pair of much fainter stars just to the west which are not cataloged as a double star, and a more interesting pair to their right, which has some interest for us.  On the attached photo, I added the magnitudes of these four stars in order to provide an idea of the brightness range.  (Note: decimal points are omitted – 119 is actually 11.9)   As it turns out, the star labeled “106” is the 10.8 magnitude “C” component listed in the data line above, and the one to the right and just below it labeled “107” is the 11.0 magnitude “D” component.  The magnitudes used on the chart are from MegaStar, and obviously they don’t match the WDS magnitudes exactly — but that isn’t unusual for magnitudes on star charts.  The main thing is the separations and position angles do match well.

Σ 2447   (H IV 127)     HIP:  93836    SAO: 143029
RA: 19h 06.6m   Dec: -01° 21′
Magnitudes: 6.8, 9.6
Separation:  14.4″
Position Angle: 341°  (WDS 2006)
Distance: 440 Light Years
Spectral Classification: B5

Reversing direction and heading back to the southeast, about two-thirds of the way back to Lambda we reach Σ 2447, also known as STF 2447.  At 14.4 arc seconds, you would expect this to be a fairly easy split, but I found I needed to use the 102mm to get a good look at it.  Two things make this one a bit difficult (though not at all impossible): the three magnitudes of difference in brightness, and the fact that the faint component is just a pinpoint of light compared to the larger primary.  My notes describe the bright white glare of the primary contrasted with the faint pinpoint of the companion at 63x as a “subtle sight, but nice.”  Not quite as poetic as some of Haas’s descriptions, but it strikes me as about right.  And I don’t care what anyone else says, the primary really is WHITE.

And just as I was about to move on to something else, a meteor streaked through the field of view and left a very brief glowing streak of light!  I can’t remember having been fortunate enough to have seen anything of the sort in an eyepiece before, but it certainly is better than watching a satellite silently tumble past.

(WDS data updated 4/14/2013)


One Response

  1. John,
    I recently did a sketch of Struve 2379 discussed in this post. I sent it to you and a couple others in the D.S.I.P. Yahoo Group.
    Let me know how you like it. I got a light blue primary, a yellow/white “B” and a slightly orange “C” companion. My “C” companion in the sketch may be a little brighter that it really is…
    More fun.
    Steve McGee

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