Celestia Forums

I was wondering whether anybody knew of a star catalogue that contained stars' spectral classes, not just their measured colours?
I'd like to use it with the Hertzsprung-Russell (sp?) diagram to make rough estimates of absolute magnitudes, and therefore their distances.

I realise that a decent-sized catalog may not exist. It sounds like Canada's first space telescope may be set to remedy this:

http://www.astronomy.com/Content/Dynami ... 5nhpai.asp

If a catalogue already exists, I'm thinking it probably doesn't cover stars that aren't already in the Hipparcos catalogue - but I'd still like to know.

Also, I'm wondering whether there's a straightforward method for deducing possible spectral classes from red/blue apparent magnitudes (I guess it'd have to ignore absorption from the interstellar medium), with a view to having a similar attempt on the massive USNO 2.0 catalogue...

Cheers,
Paul

Paul,

Do you mean catalogs that include the MK spectral type code, or something more?

FWIW, there are lots of them for clusters (see webda).

One list of star catalogs can be found at
HEASARC


Unfortunately, you need to use the color classifications, too, so you can account for the interstellar extinction due to dust affecting the apparent "visual" magnitude. (blue is attenuated more due to scattering than red is and the way it differs gives a measure of the dust). Local variation in attenuation seems to be one of the reasons why there are so many different estimates for the distance to M16. Its HR diagram is a mess, too. *grump*

I suspect a very large lookup table with local interpolation is going to be necessary.

Paul wrote:I was wondering whether anybody knew of a star catalogue that contained stars' spectral classes, not just their measured colours?
I'd like to use it with the Hertzsprung-Russell (sp?) diagram to make rough estimates of absolute magnitudes, and therefore their distances.

See

http://cdsweb.u-strasbg.fr/cats/III.htx

for catalogues concentrating on spectra. However, you should be able to get plots of the HR diagram with B-V colour or temperature along the horizontal axis, rather than spectral type. Often called a color-magnitude diagram, they're valuable because they're plotted using directly observed quantities.

I realise that a decent-sized catalog may not exist. It sounds like Canada's first space telescope may be set to remedy this:

http://www.astronomy.com/Content/Dynami ... 5nhpai.asp

MOST does not appear to have a spectrograph.

Also, I'm wondering whether there's a straightforward method for deducing possible spectral classes from red/blue apparent magnitudes (I guess it'd have to ignore absorption from the interstellar medium), with a view to having a similar attempt on the massive USNO 2.0 catalogue...

The precise spectral classification depends on the spectral lines present in the star. You would be able to get a rough idea of the spectral type from the star's colour index. Try

http://xml.gsfc.nasa.gov/archive/catalo ... index.html

for a list of MK standards. If you plot B-V against spectral type for these stars, that will give you a range of colours for each classification in the absence of reddening (hopefully the resulting curve won't be multi-valued). You might see if interstellar reddening will be a problem for a particular star by using a sky map of galactic dust (I don't have a handy reference, but try searching on http://adsabs.harvard.edu) Such maps are derived from measurements in the infra-red.