September 25, 2006

Kappa Bootis (Struve 1821)

Observation Notes:
This was a subtle and uneven pair. The PA appeared to be 225° with a separation that was obout 1/36 of the 12 arc minute FOV--which works out to about 20 arc seconds. Actual values are 236° and 13.4 arc seconds.

The primary appeared pale yellow with a dull blue secondary. I became a bit frustrated when I was preparing the report for this observation because the primary of this pair is A7V with a F1V secondary. So if anything, I should have seen a light blue primary with a pale yellow primary or a version of that where one of the components was white. Instead I actually had the colors swapped. I decided to do some hunting to see what other observers saw. I found that quite a few that actually mentioned color noted the same swap that I did. Here are the links to those sites:

Jeff Burton's Astronomy Blog (White/Blue)
Bootes Object List - Steve Coe (White/Light Blue)
Astronomy Daily Forum - Trane Francks (White/Blue)
Multiple Star List - Bill Anderson, et. al. (White/Blue)
Constellation Observer Guide - Mark S. Baines (Gold/Blue)
Canberra Astronomical Society - Ross Gould (Pale Yellowish-Green/Bluish Purple)
AL Double Star Observating Log - M. Bracewell (Yellow/Bluish)

Search for "Kappa" at those links until you encounter Kappa BOO. These observers (as long as they are listing the primary first) are seeing a bluish secondary every time, and a white or yellow primary. This appears to be a pretty deceptively colored double. But not everyone was deceived:

Double and Multiple Stars and How to Observe Them by James Mullaney features a sketch by Sissy Haas that sports a white primary with a pale yellow secondary.
See also, Richard Bell's Double Star Log, where he also sees a white primary with a secondary that has a hint of yellow.

One suggestion I came across in James Mullaney's book is to stop down the aperture of the scope to 3 or 4 inches to see if that helps increase the strength of the star colors. I'll be paying a visit to the fabric store to grab one of those embroidery circles to set up an aperture mask and give this a shot.

Posted by Jeremy at September 25, 2006 8:10 PM .