# Stellar Classification

1. Feb 4, 2014

### ckirmser

Is there a specific limit that defines the boundaries of each classification category?

For example, a main sequence G class star is between X and Y temperatures and has an absolute magnitude between A and B Solar units.

Or, an O hypergiant is between X and Y temperatures and has an absolute magnitude between A and B Solar units.

Along those lines. Essentially, something mathematical that can be used to plug in the characteristics of a star and will produce the classification.

So, if I have a star that has a temperature of 5699K and a Mabs of 0.9M, it pops out with a G2IV (the "2" is just a guess from eyeballing an HR chart).

Or, are the classifications not that explicit?

2. Feb 5, 2014

### joseamck

In terms of temperature and luminosity that's what the HR diagrams shows, the star's classifications.

3. Feb 7, 2014

### ckirmser

Well, yes, but the various charts I've found are not in total agreement on the boundaries.

I've found several tables listing numeric limits for, say, a 'K'-class star, but there is a substantial variance in the listed or pictured properties.

For example, one table I have says a 'K'-class star has a temperature range of 3.5 kK to 5 kK, whereas another has just 5.3 kK, not even an average, but totally outside the bounds listed in the other table.

It looks like stellar classification is a very subjective matter and I'm trying to determine if I am wrong and that there is a set definition that determines a star's spectral type, its luminosity class and its Yerkes class.

If it is truly all subjective, then I can go with that, but I would expect that there are set, objective boundaries.