STF 2944: A double in Aquarius that looks triple
8/25/2014 2:18 PM
Unlike the previous double star, HD 213067, our next double star is a bit harder to locate, but it's worth seeking out. For one, it's not just a double star at the eyepiece, it's a triple star. HD 215812 / HIP 112559 is a 7.2 magnitude star located northeast of Sigma Aquarii. But it may be easier to find by locating Lambda Aquarii, a star that can be found pretty easily by extending the "Nashira -> Deneb Algiedi" line in Capricornus out ~20 degrees (learn how to measure distance in the sky here).
At Lambda, an average finderscope of 6x26 or larger can show where to go, because at 3.7 magnitude, Lamdba is easily seen now. Moving northward in the direction of Zeta Pegasi, a 7 degrees field of view will also show 5-th magnitude Kappa Aquarii. Our target, STF 2944, is located in a triangle shape with these two stars.
Note the three 6-th magnitude stars just off to the east (left on the chart - there are actually four total, the eastern-most one is just slightly off this chart). It's really about splitting the difference between these stars, and Kappa Aquarii. Note that this graphic is correct-image oriented, and many finderscopes will reverse the field of view both up/down, and left/right.
STF 2944 is interesting; it is a G5V class star, very similar to our G2V Sun, but the "2" indicates a slightly lower temperature than our star. At 102 light years away, the photons from this star left just over a century ago from the time they reach your eyes. And what appears as a single star in a finderscope reveals itself to be three stars at a higher magnification at the eyepiece.
There is an 8.5 magnitude companion star about 60 arc seconds away - easily split in even very low power eyepieces. But the double of STF 2944 is revealed when the two are split to the 2 arc seconds apart that they are. That's a tight split; small telescopes of 60mm or 70mm will likely not achieve full split. While theoretically possible with a superb 4.5" telescopes under steady skies, a 6" or larger scope is ideal.
Can you see these? It's a nice little double to try for, and can be a good test of your optics too.
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