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:

• Stéphane Meloche: Gold / White
• Edwin H. Kaufman, Jr.: White / Deep Blue
• Steve Coe: White / Blue
• An observer at Cloudynights.com (MS Excel document): Yellow / Blue
• Dave Holt: Yellow / Blue

Further information about this double can be found here:
http://www.astro.uiuc.edu/~kaler/sow/deltaboo.html

*Based on published data.