Subclassifications in spectral classes?

Question

In the spectral classification of stars, there are the major classes--OBAFGKM in the old HKK system--which are subdivided into subclasses, O5, G2, G1, K2, M4. What I seek is the relationship used to compute these subclasses. What formula lets an astronomer say a star is G2 verses G3 or G5?

I realize the old HKK system doesn't include Wolf-Rayet stars, Carbon Stars, the proposed new L-class stars, etc, and that my question ignores the White Dwarves and a number of other issues. The issue is the assignation of the digit that represents the subclassification of the alphabetic major spectral class. I've also ignored the issue of giants, supergiants, dwarves, etc. Thanks for the input, though.

Answer 1

One source that breaks down these classifications by temperature, or maybe it was only color photometry (I don't recall) is Kenneth Lang's Astrophysical formula:

http://www.amazon.com/Astrophysical-Formulae-Radiation-Processes-Astrophysics/dp/3540296921/sr=1-1/qid=1163374728/ref=sr_1_1/102-7735916-8685767?ie=UTF8&s=books

Volume I has some tables I think you will find helpful. You might need to do a little interpolation...

another place to look would be the iau website http://www.iau.org . The IAU is the kind of group that would define a standard, though this might be too detail oriented for them to mess with.

You will be hard pressed to find an equation, however. You are going to be stuck with a lookup table.

Answer 2

The numbers within the major classes run from hottest to coolest. The specifics of the classification system are somewhat complex, and depend on the relative strengths of various spectral lines.

Answer 3

Basically, it is color temperature. For example, A0 denotes the hottest stars in the A class and A9 denotes the coolest ones. So there isn't a formula, it is just a way of classifying stars by temperature. I suppose they could have not had classes at all and just listed the temperature in degrees if they wanted to.

Answer 4

Hi. You left out carbon stars, Class N. OBAFGKMN. All stars are classified by spectrum. Sorry, I do not know the criteria for G2 to G5. Try this link : http://www.answers.com/main/ntquery?s=spectral%20classes&gwp=16

Answer 5

I extracted this from Wikipedia, study the finished article for readability. interior the present celebrity type device, the Morgan-Keenan device, the spectrum letter is better with the help of a style from 0 to 9 indicating tenths of the variety between 2 celebrity instructions, so as that A5 is 5 tenths between A0 and F0, yet A2 is two tenths of the finished variety from A0 to F0. yet another length this is blanketed interior the Morgan-Keenan device is the luminosity type expressed with the help of the Roman numbers I, II, III, IV and V, expressing the width of particular absorption lines interior the celebrity's spectrum. this is been shown that this option is a familiar degree of the size of the celebrity, and for this reason of the full luminosity output from the celebrity. type I are oftentimes referred to as supergiants, type III only giants and sophistication V the two dwarfs or greater suitable important series stars. for occasion our solar has the spectral form G2V, that are interpreted as "a 'yellow' 2 tenths in the direction of 'orange' important series celebrity".