Ikkakujyu wrote:

I've been pondering the use of a planet around Sirius as a device in
science fiction for a little while, and I wanted to make sure I have
my facts straight.

The idea is to have a terrestrial planet orbiting Sirius in a fairly
circular orbit at a distance of about two astronomical units. This
would give it a temperature range not unlike Earth's, and the
possibility of liquid water. Support of life is not expected and not
required, though its water would be a valuable fuel for fusion
reactors.

The existence of Sirius B complicates things a little, at least for
me. Since it was much larger in the past, it might have interfered in
this planet's development, or would have pulled it into orbit around
it. This being the case, our planet would be in a relatively far orbit
after its collapse, and liquid water would be impossible.

I think it complicates things a lot! Beside the problem of arriving
at a stable orbit, a critical period would have been when Sirius B
went through its red-giant stage, swelling up to many times the size
of the 'primary' and making the inner regions of the system much too
hot for water to exist on the surface of a planet. But of course
things have cooled down since then (except for the white dwarf
itself, which is still extremely hot), and lost surface water could
have been replenished from the planet's interior.

Assuming that the planet orbits Sirius A, the passing of Sirius B
every fifty years would cause especially hot summers. Not a problem,
just a peculiarity.

I don't think Sirius B would have a very noticeable effect on your
planet's climate any more; at something like 2% the luminosity of the
sun and an opposition distance of some five or six AU the additional
radiation wouldn't be very significant -- except that there'd be
quite a bit in the form of hard UV and even X-rays. OTOH the dwarf's
gravity -- although it's much diminished from its 'glory days' it
still has a mass comparable to our sun's -- would continue to perturb
the planet, especially strongly at each 'encounter'. Some sort of
resonance would likely have to develop between the two orbital
periods to be even 'metastable'. In general the closer the planet is
to Sirius A the safer it's likely to be, it seems.

Anything I'm forgetting, or do I have anything wrong?

Well, some would consider planets and binary star systems so
incompatible as to make the whole notion implausible. For example see

http://www.sciencenet.org.uk/database/Physics/9812/p01204d.html.

--Odysseus