In article ,
Keith F. Lynch wrote:
Trouble is, there *are* no stars with known oscillations on this
sort of time scale (except the Sun). These observations are almost
impossible to do from the ground.

Were the observations of the Sun done from the ground?

Some but not all. The Sun is a very different class of problem, because
(in particular) we can resolve its disk, and that makes other methods of
vibration detection available. And yes, there are space observations as
well as ground ones; SOHO in particular specializes in various kinds of
optical solar observations which can't be done from the ground.

Granted that the atmosphere makes stars twinkle, but that can be
factored out by comparing simultaneous data from multiple telescopes
distant from each other.

In principle, yes. In practice, it would take formidable resources to put
together a network that can do this well enough. To pull oscillations out
of normal surface noise, you need fairly continuous observations over a
period of weeks, meaning a worldwide network. (Regular interruptions in
the data -- e.g., a day/night cycle -- are absolutely deadly, injecting
large amounts of noise into the analysis results.) And really getting
the atmospheric scintillation completely out of the data is hard.

I believe people have tried, but nobody has succeeded, doing things that
way. The ground-based stellar detections have all used Doppler data
rather than brightness.

Procyon was, I gather, about the closest thing to a "known
oscillations" star available...

Were the oscillations observed from the ground at the same time as
they weren't observed from MOST? If not, perhaps Procyon has simply
temporarily stopped oscillating.

I don't *think* any of the ground observations were done at the same time.
But a temporary halt in oscillation is another one of those things that
would require revisions to the theories. The Sun doesn't do that.

MOST definitely has observed several other bright stars by now.

It can only observe one at a time? If so, will it be rendered
obsolete by the upcoming Kepler mission?

MOST is definitely a small "pathfinder" mission, with a number of
limitations. It's what could be done quickly on a very small budget, and
a larger and more capable (but much more expensive) satellite would
certainly make it obsolete. I'm not putting bets on which one it will be
until one actually makes it into space, but I'm sure it will happen within
a few years; there are two or three such projects in the works, and I
expect at least one will make it to completion without being canceled.

MOST's telescope has quite a narrow field of view, and it can only observe
a small patch of sky at any one time. Moreover, it can do *continuous*
observing only within a zone about 54deg wide, centered about 8deg above
the ecliptic, moving across the sky at about 1deg/day -- for continuous
observing, you have to be looking pretty much at right angles to the orbit
plane, so the Earth doesn't get in the way -- so you don't get to pick the
small patch arbitrarily.

And for high-precision brightness work, you want to spread the light out
over a number of pixels to avoid saturation and other problems; the
telescope has a small array of "lenslets" that do that, but that
effectively narrows the field of view still more, and adds spacing
constraints on any attempt to do multiple targets. The lenslets cover
only part of the field of view, so you can use the bare CCD for less
constrained observations, but the data won't be as good.

So in practice, you pretty much only get one primary target at a time
(there *has* already been some lower-precision observing of secondary
targets, interesting stars that happened to be in the field of view).

Spend a bunch more money on fancier optics, fancier detectors, and putting
the thing in a high orbit or a Lagrange point so the Earth doesn't get in
the way all the time, and you will definitely get a more flexible and
capable mission. Eventually. :-)
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |