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Still in Sagitta: S 737 and Theta (θ)

Alright, if you just jumped to this sojourn through Sagitta from here, the light screen is up and were moving on!  If you didn’t jump to here from there, you missed a nice trip.

S 737           HIP: ????    SAO: 88274
RA: 20h 09.9m   Dec: +21° 00′
Magnitudes: 7.9, 9.3
Separation:  100.3″
Position Angle: 128°  (WDS 2009)
Distance: ?????
Spectral Classification: K0

S 737 is at top center, Theta (θ) at center – north is up, west is to the left. Click on the image for a larger view. (STScI photo)

Just northeast of Eta (η), which marks the sharp point of the Sagittan arrow, lies a multiple star system which has a cluster-like appearance.   The “S” in   S 737 refers to the person who discovered this one, James South, and his discovery is part of an obscure open cluster, NGC 6873, which was first cataloged by William Herschel.  A revised edition of the NGC catalog described the cluster as “non-existent,” but more than likely Herschel was referring to the small collection of stars immediately surrounding S 737, which can be seen in the attached photo of this area.  The two brighter and more northerly of the three stars in a diagonal line are the “A” and “B” components of S 737.  All three of these are easily seen in a 60mm refractor at low power (40x).

Theta  (θ)  (Σ 2637)  (H III 24 — AB only)        HIP: 99352    SAO: 88276
RA: 20h 09.9m   Dec: +20° 55′
Magnitudes  AB: 6.6, 8.9     AC: 6.6, 7.5      AD: 6.6, 11.0
Separation   AB: 11.6″         AC: 89.9:           AD: 170.6″
Position Angles   AB:331° (WDS 2011)   AC: 222° (WDS 2009)   AD: 227° (WDS 2000)
Distance: 147 Light Years
Spectral Classification: F3 (AB), K2 (AC)
Status: AC is an optical pair

Theta (θ) is an eye-catching triple star system.  I had no problem separating all three stars in the 60mm at 40x (“B” is lost in the glare of “A” in the photo above), but I preferred the view at 53x.  Since I had it set up, I took a peek in my 152mm scope at 87x and was pleased to see lots of black sky between the primary and secondary, while the the bright third component gleamed just south of them.  “A” and “C” appeared to me as white with a bit of yellow, and “B” was a pale white.  In the 152mm refractor, there was a hint of background nebulosity in the area of S 737, which was probably the fainter stars seen in the photo.

This is an area well worth coming back to when the sky is darker.  There are many fainter doubles within the boundaries of Sagitta that would be worth tracking down in a five or six inch refractor, as well as M71, which seems to be a cross between a globular and an open cluster.  And of course M27, a surprisingly nice object in a 60mm scope, lies just to the north in Vulpecula — which is on my list of areas to be explored soon for double and multiples stars.

These observations were made in the early morning hours of July 24th, 2010, with a bright moon peering at me over my light screen from behind some tall hemlock trees.


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