On 29 veebr, 01:40, will...@[EMAIL PROTECTED]
(Steve Willner) wrote:
> > Gene Hatch wrote:
> > > planet with a highly eccentric orbit would be easier to detect
(using
> > > stellar doppler ****ft) than one with a circular orbit of similar
period.
>
> In article <WeKdnSsas5qdsl7anZ2dnUVZ_rmjn...@[EMAIL PROTECTED]
>,
> Erik Max Francis <m...@[EMAIL PROTECTED]
> writes:
>
> > ...there are several interacting effects
> > here. An eccentric orbit would result in greater speeds at periapsis,
> > but they'd be briefer. So they spikes would be more prominent, but
> > they'd be easier to miss without more sampling.
>
> The idea is right, of course, but it isn't at all clear to me how the
> net selection effects would go. I'd expect them to depend on planet
> mass. For a massive planet, circular orbits might be easier to
> detect. The velocity would be plenty big enough, no matter when you
> look,
Except that you do not see the velocity - it is fundamentally
impossible to distinguish from overall peculiar motion of the star
itself.
You can only see the acceleration.
whereas you might well miss planets in an eccentric orbit at
> apoapsis. For low-mass planets, you wouldn't ever see them in a
> circular orbit, but you might get lucky and catch them at periapsis
> in an eccentric orbit. But I'm not sure about this, because the
> velocities also depend on inclination.
And direction of the orbit.
Pretty obviously, a planet seen at a right angle to the plane of its
orbit is invisible.
>
> You could probably quantify this if you started with an initial guess
> of what planets exist in what orbits. Then model the selection
> effects, and see whether the resulting distribution is consistent
> with what is observed.
>
> > On the other hand, the selection effect is significant, since our
> > methods of detection so far only allow us to detect large bodies,
close
> > in. These objects will tend to have orbits that have been
circularized
> > through tidal forces by their primary, so we're not seeing the true
picture.
>
> Right. Kepler, when it flies, should provide much better data. At
> least the selection effects will be very different.
>
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