Observable double??

[Paul73]

I was having a mooch around Cepheus when I happened upon Alfirk (Beta Ceph).

It looked most odd. Half Yellow and half blue (ok 80:20 yellow/blue). Sky Safari lists this as a double, but one that should be easily splitable. I went up to x250 which was pretty mushy and couldn't split it.

Was I looking to split the unsplitable? Was the Blue / Yellow effect just an optical illusion?

Paul

[NGC 1502]

Hi Paul. Just checked my Cambridge Double Star Atlas, it lists Alfirk Beta Cepheus as - Struve 2806, mags 3.2 and 8.6 with a separation of 13 arc secs.

That's a large magnitude difference, but a wide separation, so should be seen as a double star with your 10" Dob.

Could be poor seeing or cooldown not complete or collimation a tad off ? Cepheus is almost overhead on Autumn evenings so a good time to try.

Maybe better luck next time.

Regards, Ed.

[acey]

Sounds like chromatic aberration.

[ronin]

Seems it is a triplet where one of the secondaries is well seperated while the other is in close.

When a search is done I think it is described as a blue main sequence, odd then that about 30% of the images show a big red star.

Unfortunately it is the classic Beta Cepheid type variable and just about everything seems to concern that aspect, it rarely gets mentioned as a double/triple.

Nothing I have gives any real information, thought I had a pdf of a big list of doubles with seperations and other information. Seems not however, which is odd as I can picture the list in my mind so not sure where that is, or has gone.

Seems the distant companion is (should) be an easy split at 100x, assuming the sky is dark enough I suppose. From what I can read the close companion is probably too close to be distinguished from Alfirk itself.

[Moonshane]

My notes are as follows;

Wide pair with bright primary and speck of a secondary, a little like polaris.

Bright white primary secondary dim and possible greyish ? This was with my 12" f4 masked to 120mm at 150x on 31/5/14.

[Paul73]

Thanks guys.

From separation, magnitude etc I was expecting something like Polaris so was a bit surprised not to get the split. By the sound of it, the colour was a compilation of mediocre optics and wishful thinking.

I'll try stopping the scope down a bit and try again.

Paul