Re: [Phys-l] stellar distance measurement

[Mark Sylvester <mark.sylvester@spin.it>]

Thanks, Gary.
Since we need the absolute magnitude to plot the HR position, the first 
method is presumably just a guesstimate... we put it somewhere up in the 
supergiant zone. This is what I thought but then databases give 2 or 3 
significant figures for the distance, so I now understand that the 
proper motion and binary orbit measurements are important techniques.

Mark

Gary Karshner wrote:
> Mark,
>          There are a number of ways to estimate the distance to a star like 
> Antares. The crudest is from its position on the HR diagram one can 
> estimate it absolute magnitude, from its proper motion and a model of the 
> galaxy again a distance cam be measured. Also it is an optical  binary so 
> we can use its companion as well. If we had a good orbit again it would be 
> possible to use its orbital elements to compare its angular separation with 
> the measured angular separation. There are a number of other possible 
> techniques as well. Usually astronomers   use a number of these to bracket 
> its distance. It is a nice example of "bootstrapping,"  where we take what 
> we know about stars whose parallax we can measure and use this to 
> extrapolate further out.
>          I hope this helps.
> Gary
>
> At 03:31 PM 5/20/2009 +0200, you wrote:
>   
> > How is the distance to a star like Antares measured? It's too far for
> > trigonometrical parallax and not being a main sequence star is not a
> > candidate for spectroscopic parallax... so how is it done?
> >
> > Mark
> >
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