On 29 Mar 2007 10:25:26 -0700, "George Dishman"
wrote:

On 28 Mar, 01:50, HW@....(Henri Wilson) wrote:
...
Whether or not cepheids are really huff-puff stars doesn't matter. We say their
brightness variations are due to c+v effects caused by their surfaces moving in
and out. A brightess curve produced that way is likely to be similar to that
for a star in elliptical orbit.

What ?????

For years you have been saying that Cepheids were plain
constant-luminosity stars and the variation was due to
c+v effects because they are in binary systems that have
not been recognised as such.

No I changed that opinion some time ago George. I accepted that the presence of
harmonics in the brightness curves was pretty hard to explain on purely 'orbit'
grounds.
So it is quite likely that two factors are contributing to the brightness
curves of these stars. Their orbit motion and the huff-puffing of their
surfaces.



If you are now switching to say they are single stars, why
on Earth would your software be modelling binary systems
and restricting the solutions to Keplerian orbits when the
motion of the surface is due to internal pressure?

I think it is my turn to say you are getting very confused
Henry.

George

It is a fact that most 'cepheids' appear to have a companion...which means they
are in some kind of orbit.
I reckon the movement of their surfaces would feature similar radial velocities
to those of an orbit. It is distinctly possible that the huffing is linked to
the orbit period. It is also possible that the stars are in tidal lock and
distorted into some kind of dumbell shape, leading to a brightness variation as
they orbit....but that wouldn't account for the short periods of many of them.


"When a true genius appears in the world, you may know
him by this sign, that the dunces are all in confederacy against him."
--Jonathan Swift.