Delta Boötis (Struve 27)

Observation Notes:

The constellation of Boötes is chock full of bright, colorful double stars. Delta Boötis is a wide double that presented me with an interesting color scheme. PA appeared to be about 78 degrees, and separation about 144 arcseconds. Actual values are 78 degrees (Yes!) and 104.9 arcseconds. The primary color was yellow-orange, and the secondary appeared deep blue. This coloration appeared strongest at low power (37.5X). The strange thing is that while the primary’s spectral classification of G8III is appropriate for the yellow-orange color, the secondary is a G0V star, and should appear yellowish rather than blue. Since this is a wide double, I was perplexed that color contrast effects could take place over such a wide distance. I did some searching online, and found that I’m not alone in seeing this spurious color. Here is a sample of what other observers have seen:

Further information about this double can be found here:

Subject Delta Boötis (STF 27)
Classification Double Star
Position (J2000) Boötes [RA: 15:15:30.2 / Dec: +33:18:52]*
Position Angle* 78° (1835)
Separation* 104.9″ (1835)
Magnitudes* A: 3.47 / B: 7.84
Spectral Types* A: G8III / B: G0V
Date/Time APR 29, 2007 – 12:20 AM MST (APR 29, 2007 – 07:20 UT)
Observing Loc. Flagstaff, AZ (Home)
Instrument Orion SVP 6LT Reflector (150 mm dia./1200 mm F/L)
Eyepieces/Mag. 10 mm + 2X Barlow (240X)
Conditions Mostly clear, slightly breezy, nearly full moon
Seeing 5-6/10 Pickering
Transparency NELM Mag ~5.0
References The Washington Visual Double Star Catalog, 1996.0 (Worley+, 1996); 13th General Catalogue of MK Spectral Classification (Buscombe 1998)

*Based on published data.