Re: Galaxies without dark matter halos?

greywolf42 <[EMAIL PROTECTED]> wrote:

: The angular velocity is calculated -- not observed.

What's observed astrometrically is the projected angular velocity.
That's adequate for the purpose of determining the 3-D orbit, except
for a reflection ambiguity about the plane of the sky.  Needless to
say, that ambiguity is resolved if Doppler data are included.

: One cannot determine inclination of a stellar orbit just from astrometry --
: even in the rare cases where you can watch and measure the describing of a
: full ellipse by the orbiting body.  The projection of an ellipse is still an
: ellipse.  You can get an upper bound to the central mass -- but not a
: measurement of the central mass.

You're confusing two very different problems: determining the mass of
the system and determining the orbit.  They are not the same.

-- 
John F. Chandler             [EMAIL PROTECTED]