On Mon, Aug 18, 2014 at 09:55:22PM +0100, Timothy Collinson wrote:
> Ah.  My mistake, must have been looking at the wrong thing - thought it was
> a dwarf and almost something to ignore...  glad I asked.

I almost skipped over it too, but then noticed the "IV" instead of
"V".  The "M1" means that it's at the hot end of M stars, almost K
class.  I'm not actually sure that M-class subgiants can exist, but
willing to accept it as an oddity of random generation.

> > For similar temperature to Earth, the primary star would be slightly
> > smaller in the sky, though a little more "dazzling" than our Sun from
> > Earth.  Without knowing the orbit of the companion star,
>
> (that's what I assume I can pretty much just decide)

Yes, that can be chosen.  If I recall, such a subgiant is likely to be
similar or slightly more massive than an F main sequence dwarf, so
that the stars will be orbiting about a common point somewhere in the
middle of the two.  Planetary orbits in such systems are only stable
substantially closer or more distant than the separation of the stars.
If the planet is in stable orbit at 2 AU or so about the F7V (a
plausible habitable orbit), then the stars should orbit each other
either closer than about 0.4 AU, or at least 10 AU apart.