When Is A Double Not A Double?

[cloudsweeper]

...well, not one you can split with a telescope anyway.

These include astrometric, spectroscopic, and eclipsing doubles.

Out early this evening, I was keen to see something new that the bright Moon would allow me, and aimed for Eltanin, Grumium, and Rastaban in Draco.  I hadn't planned anything, so was working blind, so to speak.  Stellarium indicated that these three are doubles, which is what attracted me.

Stellarium is of course a brilliant aid, and it was correct in this assertion.  But no joy with splitting the three.  Later investigation showed why:

Eltanin might have a companion, some 1000 AU away.  

Grumium probably has a faint optical companion.

Rastaban has a small, cool dwarf companion at about 450 AU, with a period of some 4000 years.

So no actual observation, but still an interesting exercise, and a reminder to do more preparation before venturing out!

Doug.

[domstar]

How true. Stellarium for doubles often leads me to disappointment perhaps because it doesn't give the magnitude of the companion.