July 15, 2007
Alpha Scorpii (Antares / GNT 1)
Click image for larger version.
Observation Notes:
The goal of splitting the double star, Antares, has been tempting me for a while. I never have the sort of seeing conditions that would make it a nice clean observation. So I gave it a try on this less-than-perfect evening, and was successful in spotting the secondary star. Antares' primary star flickered like a coppery flame in the jumping air currents, so I had to be patient and wait for the ripples of diffracted light to show me the way. The secondary began to coalesce as a consistent lump in the fluttering kidney beans of orange light near the position of the primary star's second diffraction ring. It's color was hard to pick up, but gradually, I perceived what looked like a yellow-green tint. I had not checked data on the secondary's current position angle to help keep me honest, and it looked to be at a PA of about 280 degrees. Checking Brian Workman's double star calculator a couple days later gave a PA of 277° for 2007.5. The separation comes out to 2.18 arcseconds, which is about right for my 'second diffraction ring' sighting--that works out to 2.5 arcseconds in my scope.
I wanted to convey what the diffraction pattern looked like, and how the secondary appeared in the midst of it. The digital sketch I prepared was a bit of a learning experience for me, but I think it does a halfway decent job of rendering what I saw. This can be seen in the detail portion of the sketch. Just imagine all of that jumping around and moving from moment to moment. Clicking the sketch will provide a larger image that is easier to see. You'll notice that I was fortunate enough to have the spider vanes in a position that didn't interfere with the secondary star. It really was a beautiful and challenging sight. Give it a try sometime and see if you can identify the secondary in that bubbling mass of starlight.
I'd love to see what they look like under near-perfect seeing.
| Subject | Alpha Scorpii (Antares / GNT 1) |
| Classification | Double Star |
| Position (J2000) | Scorpius [RA: 16:29:24.4 / Dec: -26:25:55]* |
| Position Angle* | 277° (2007.5) |
| Separation* | 2.18" (2007.5) |
| Magnitudes* | 0.96 / 5.4 |
| Spectral Types* | M1.5 IB E / B2.5V |
| Date/Time | MAY 11, 2007 - 11:35 PM MST (MAY 12, 2007 - 06:35 UT) |
| Observing Loc. | Anderson Mesa, AZ |
| Instrument | Orion SVP 6LT Reflector (150 mm dia./1200 mm F/L) |
| Eyepieces/Mag. | 10 mm + 2X Barlow (240X) |
| Conditions | Mostly clear, calm |
| Seeing | 5-6/10 Pickering |
| Transparency | NELM Mag ~6.0 |
| References | The Washington Visual Double Star Catalog, 1996.0 (Worley+, 1996); 12th General Catalogue of MK Spectral Classification (Buscombe+ 1995); Brian Workman's Double Star Calculator |
Posted by Jeremy at July 15, 2007 4:12 AM .
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