"David Findlay" wrote in message
. au...
Are star spectra relatively unique? Could you use them to positively
identify a star if you knew what area of the galaxy you were in? Thanks,

David

Probably not obviously unique, except in very rare cases. There are two
problems:

1. Most stars can be classified in the MK system, but there are an estimated
100-200 billion(US) stars in the galaxy, and only about 300 or so unique
boxes in the MK system;

2. The spectrum of a star can look different depending on the angle at which
it is viewed, because of stellar rotation. Looking at a the same star
equator-on and pole-on gives very different-looking spectra.

The rare cases a

Chemically peculiar stars, such as magnetic Ap stars and mercury-manganese
stars. These are relatively rare and when looked at with very high
resolution there are subtle differences between individual stars. In
particular, you might be able to identify individual magnetic stars from
their rotation periods, which would be unique. However, this would take a
lot more than just one observation, it would require study over many months
or years. HgMn stars have unusual isotopic compositions of Hg and Pt, and
might be identifiable from this. The Ap stars also have unusual and
sometimes highly individual compositions. Przybylsky's Star would be
readily identifiable by any spectroscopist. However, special cases do not
make good rules...

High luminosity stars. There are very few really luminous stars (MK
luminosity class Ia0), and if you knew both their spectra and their x-y-z
coordinates initially you could probably locate a few known objects if you
knew your location.

This isn't an exhaustive list of all possible unique stars, just some
examples.

--
Mike Dworetsky
(remove "pants" to send email)