Object: xi Bootes

Magnitude A / B / C
Separation A-BC/ AC
Position angle A-BC / AC
Spectral class A / B / C
Colour A / B / C
: Bootes
: 14:51:23 / +19.06
: 4.8 / 7.0
: 6.3"
: 315°
: G8V / K5V
: yellow / orange
Detail sketch:
Date / Time
Observing Location
Seeing / Transparency
Magnification / Field of View '
: 09/05/08 / 23:50
: Landgraaf
: 3 / 2
: Orion Optics UK 300 mm
: 17 mm Nagler type 4
: 94 / 52
Xi Bootis

Observing Report

On the evening of May 9th 2008 Leo and I got together to observe a series of double stars in Bootes, inspired by an article in June's Sky and telescope (Binaries in your Bootes). In the period between the beginning of May and the end of July it doesn't get really dark at night, but for observing double stars it was OK. We started at 23.00 hours local time (UT + 2hrs). In three hours time we observed and sketched about six doubles in Bootes and two asterisms, one in Bootes (Picot 1), the other in Ursa Major (Ferrero 6).

The highlight for me that night was Xi Bootes. This colorful double lies about 8 degrees east of Arcturus. The yellow primary star shines at magnitude 4.8 and it's magnitude 7.6 orange companion lies at a position angle of 315°. The separation is 6.3". Through the 17mm Nagler the double looks fairly close.

When looking at Xi Bootes through the 17mm Nagler, the double seems to be part of an asterism that looks like the constellation Cygnus, only much smaller. Xi Bootes is placed at the position of Deneb, the tail of the swan. We decided to call the asterism "Little Cygnus". On the sketch the asterism is oriented West-East. At the tail you find Xi Bootes. The three white stars oriented north-south represent the wings of the little swan. A white star to the east (accompanied by a dimmer companion) is at the position of the head of the swan. The yellow star to the eastern edge of the field of view is just a bright field star.


The magnitude 4.8 primary A component is a G8V main sequence dwarf star, with a temperature of 5400K. The magnitude 7.0 B components is a K5V dwarf star with a temperature of 3400K, which we find a little more down the HR-diagram, more to the lower right corner. Here you see how the colour (and magnitude!) of main sequence stars change if you compare a G star to a K star, which are located at the same distance (22 light-years).

Hartung saw this double as yellow and deep orange. Smyth reported orange and purple while Webb saw them as yellow and purplish red. The strangest report is from Sissy Haas. See saw them as a bright white star touching a vivid little grey star.