1. As long as you have 2 of the three variables in the equation, you can use it for any star. You can even use it for supernovae (specifically, Type Ia-which is a standard candle)Hi I'm working on astronomy over the summer, and I have some questions (several, really) about spectroscopic parallax:
1. Can you use this for any star? I understand that you can only really estimate absolute magnitude given spectral classification for main sequence stars, but you could still use the distance modulus for any star, right?
2. This website http://outreach.atnf.csiro.au/education ... allax.html mentions a B-V color index that they somehow use to do spectroscopic parallax for a red giant (Gamma Crucis, in the example). How does knowing the color index show that it's a red giant? (And for the example, what is the significance of Gamma Crucis being a M3.5 III star? I know that the M3.5 is the spectral classification, but what is the III? In the explanation part, they mention luminosity class--is that what this is by any chance?)
3. At the end of this webpage there's a little comment about how spectroscopic parallax "is not accurate for individual stars...[but] can yield statistically useful values" when done for many stars--why do we do spectroscopic parallax, then?
4. The Science Olympiad training handout for astronomy (http://www.soinc.org/sites/default/file ... andout.pdf) mentions that spectroscopic parallax tables might be a nice thing to have--what exactly is a spectroscopic parallax table? I googled it but couldn't find anything that seemed even vaguely useful.
Thanks so much for any help .
2. Finding the color index of a star is an indirect measurement of its temperature (I think there's a way to convert-correct me if I'm wrong on this one, please), so you can correspond a star's color index with its temperature/class. There are some H-R diagrams that use a B-V color index along its horizontal axis instead of temperature or spectral class
3. I'm confused by this remark too. I can only think of two things: a) it won't work for optical binaries or b) (I think this is more probable) that spectroscopic parallax has only real application when used upon a variety of stars (i.e. to calculate distances to larger objects, such as clusters)?
4. I think what they're referring to is a table of spectral data. For each spectral class (like, say, B1, B2, B3...etc) they list the characteristics of stars at each respective class, such as luminosity, radius, surface temp, etc. I think you'll have to do a little digging to put one together