Gamma Velorum (Dunlop 65)

Binocular Observation – February 26, 2007:


Click above image for larger version (20K).

I made this binocular observation from my front doorstep with moonlight strongly lighting up the field. The primary of Gamma Velorum was the brightest star in the murky view near the horizon, and gave off a blue light. The secondary snuggled close to the glare of its buddy and at times seemed to appear orange in contrast. I tried for about 15 minutes to pick out the combined light of the third and fourth components, and couldn’t convince myself I had seen them.

Subject Gamma Velorum (DUN 65)
Classification Multiple Star
Position (J2000) [RA: 08:09:31.9 / Dec: -47:20:11]*
Position Angle* A-B: 220° (1826)
A-C: 151° (1835)
A-D: 141° (1846)
Separation* A-B: 41.3″ (1826)
A-C: 62.3″ (1835)
A-D: 93.5″ (1846)
Magnitudes* A = 2.2; B = 4.5; C = 8.5; D = 9.4
Spectral Types* A = O9+W; B = B3; C = A0; D = A0
Date/Time FEB 26, 2007 – 09:20 AM MST (FEB 27, 2007 – 04:20 UT)
Observing Loc. Flagstaff, AZ – Home
Instrument 10 x 50 Binoculars
Conditions Clear, breezy, waxing gibbous moon
Seeing
Transparency NELM ~ Mag 4
References The Washington Visual Double Star Catalog, 1996.0 (Worley+, 1996), Visual Double Stars in Hipparcos (Dommanget+, 2000) via VizieR, and Burnham’s Celestial Handbook.

Observation Notes:

This is my most southern observation yet. At a declination of -47 degrees, it was about 8 degrees above my southern horizon–add some low hills, and I was only barely able to catch it. As you can imagine, the seeing was horrible, but despite this, Gamma Velorum was a brilliant and worthwhile multiple star to view. Due to the fluttering atmosphere, and strong spreading of the spectrum, estimating color was a bit difficult. Still, I was able to pick out a blue-white color for the primary and bluish coloration to the next two brightest stars.

I estimated the PAs as AB=215°, AC=160°, and AD=150°. Actual values are 220°, 151°, and 141°. I sketched separations as AB=65″, AC=80″, and AD=106″. Those are a bit stretched, with the actual values being 41.3″, 62.3″, and 93.5″. I was surprised not to find a Struve number attached to this one. Rather it was listed as Dunlop 65. I guess I hadn’t considered the southern limit for Struve’s catalog.

According to Burnham, the primary star of this multiple is actually a spectroscopic binary composed of an O9 blue giant and a Wolf-Rayet giant that orbit with a period of 78.5 days.

Date/Time OCT 22, 2006 – 05:00 AM MST (OCT 22, 2006 – 12:00 UT)
Observing Loc. Cinder Hills Overlook, Sunset Crater National Monument, AZ
Instrument Orion SVP 6LT Reflector (150 mm dia./1200 mm F/L)
Eyepieces/Mag. 10 mm + 2X Barlow (240X)
Conditions Clear, calm

Seeing 1-2/10
Transparency NELM Mag 6.8+

*Based on published data.

One Reply to “Gamma Velorum (Dunlop 65)”

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