Star Identification

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

"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)

In article ,
David Findlay writes:
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,

At ordinary classification resolution, certainly not, as Mike has
explained. At very high spectral resolution and very high signal to
noise, perhaps. I doubt enough such spectra have ever been collected
to know, but it wouldn't surprise me if apparently similar stars
would turn out to have subtle differences if you look hard.

As Mike also said, though, the difference between "pole on" and
"equator on" for a given star might well be larger than the
differences between stars.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
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