β Scorpii
June 2011 :
This month, we travel southward to the constellation Scorpius and the showpiece double star beta (?) Scorpii. Also known as Graffias or Akrab (take your pick – I’ll go with Graffias), beta Scorpii is an eye-pleasing pair of magnitude 2.6 and 4.5 stars separated by 13.6 arc-seconds. The magnitudes and separation are quite similar to those of the better-know Mizar; indeed, Graffias rivals Mizar in visual splendor.
Graffias is an ideal target for any backyard astronomer, regardless of his/her experience or size telescope. Its brightness and prominent location (it’s the uppermost of a vertical row of bright stars just west (to the right) of Antares) makes Graffias an easy-to-find target. An ample separation allows Graffias to be split with the smallest of telescopes and a magnification as low as 25X.
What makes beta Scorpii particularly intriguing are its colors. A number of observers describe the pair as blue-white, which is in keeping with their B-type spectra. But look closely. I’ve always seen the companion as decidedly bluish, even turquoise. What’s your opinion?
There appears to be disagreement as to whether Graffias is a true binary pair or an optically aligned duo. The two have shown little movement relative to one another since the earliest measures in 1779, but they share a common proper motion. If Graffias is a binary system, the orbital period must be in excess of one thousand years. This must-see double star lies about 600 light years away.
Your comments on this column are welcome. E-mail me at gchaple@hotmail.com.
