Ngc 2281

[Sue French]

Folks,

At one of our club's star parties this week, someone asked me about the star cluster NGC 2218 in Auriga. His SkySafari has, word for word, the description in the Night Sky Observer's Guide:

"NGC 2281 is bright, large, and loose with three dozen stars. A dozen 10th to 11th magnitude stars are elongated E-W, the fainter stars spreading southward. A diamond-shaped asterism is at center, each of its four stars having a fainter companion. A faint star of about 13th magnitude is visible within the diamond. The northernmost double in the diamond displays a fine contrast of reddish and blue stars. This nice cluster is often neglected by observers."

Note especially that each of the four diamond stars is said to have a companion, but he could only see companions to two of the stars. As far as I can tell, only the eastern and southeastern stars of the diamond have companions. Can I get folks with large scopes take the challenge to see if the other two diamond stars have companions?

Clear skies, Sue

[Clear Skies]

Of the four observations I logged for this cluster the most recent one was on 16 January 2012. During this observation I payed particular attention to the stars in the central diamond shape. I noticed components on the northeastern and southeastern side, along with the "central" mag. 13 star, which I described as follows:

"To the SW of the center is a white mag. 8 star with a mag. 9.5 star to its NE (double star?... AB of Herschel 271), to their SSW are two mag. 9.5 stars in a line from WNW to ESE (double star?... one of these two stars is component C of Herschel 271) with a mag. 13 star to the WNW of the WNW star."

Had I observed components near the northwestern and southwestern stars I would have described them.
My other three observations don't mention components for these stars either.

While a close, faint components would of course be lost in the glare of the brighter star, DSS does not show components either, while companions to the northeastern and southeastern stars are obvious: http://archive.stsci.edu/cgi-bin/dss_search?v=poss2ukstu_red&r=06+48+17.04&d=%2B41+04+40.8&e=J2000&h=5.0&w=5.0&f=gif&c=none&fov=NONE&v3=

WDS does not indicate either of the western stars as double. It does reveal the northeastern stars (AB of Herschel 271) is also designated as double star Aitken 2359, where AB of Herschel 271 is AC of Aitken 2359, with component B of Aitken 2359 at PA243, sep. 1.8".

[Marko]

My two observations don't note the doubles mentioned but MegaStar claims the SW star is a 1.8 arcSec double with about a 3 mag difference 9.1/11.9. I was only noting size, concentration and variance of magnitudes and of course total visible star count at the time.
I did note that the brighter stars in this cluster reminded me of Perseus where the diamond would be the area of Mirfak and it's rotated almost 180 degrees. It was only a thought and a very loose pattern match at that.

[Sue French]

Mark,

MegaStar often places a double star marker on the wrong star in a cluster. I suspect they used truncated coordinates, whatever WDS listed back then, and then picked the cloest star of about that magnitude.
06483+4105A 2359AB 1919 243º 1.8" 8.99, 11.8 064820.84+410502.9
06483+4105A 2359AC 2004 47º 8.2" 8.99, 10.6 064820.84+410502.9
These are the latest data from the online WDS. If you use center the more precise coordinates given at the end of each line, you will see MegaStar's cursor land squarely on top of the diamond's easternmost star.

I assume most folks here aren't huge fans of double stars, but checking with the WDS is always a wise precaution for anyone who writes about them.

Thanks very much for the report of your observations.

Clear skies, Sue


My two observations don't note the doubles mentioned but MegaStar claims the SW star is a 1.8 arcSec double with about a 3 mag difference 9.1/11.9. I was only noting size, concentration and variance of magnitudes and of course total visible star count at the time.

[Sue French]

Victor,

Thank you kindly for the observations. I retrieved images of the diamond in some non-visual wavelengths where the stars aren't so overexposed and saw nothing near the westernmost star nor the star at PA ~35° from it. I saw the 13.4-magnitude star, but it isn't close enough to those stars to look as though it's a component of a double formed with either of them.

Clear skies, Sue