> 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_rmjnZ2d@[EMAIL PROTECTED]
>,
Erik Max Francis <max@[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, 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.
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.
--
Steve Willner Phone 617-495-7123 swillner@[EMAIL PROTECTED]
MA 02138 USA
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