How do I find the distance of a star with mv= 10 and the spectral class of O on the HR Diagram?

The star has an apparent magnitude of 10 and a spectral class of O on the HR Diagram. How far away is the star in light years? I know I need to fnd the absolute magnitude, and how do you do this? Thanks!How do I find the distance of a star with mv= 10 and the spectral class of O on the HR Diagram?As can be seen here: http://en.wikipedia.org/wiki/File:H-R_di鈥?/a> an O type class has an absolute magnitude of -7, independent of its type. (Note: actually it doesn't show on the graph but class O is on the left of class B).



Absolute magnitude M and apparent magnitude m are related by

M=m - 5 (log_10 D -1), where D is the distance in parsec.



This leads to D = 10^(1 + (m-M)/5) = 10^(1 + (10+7)/5)= 25,000 parsec = 82,000 light years.How do I find the distance of a star with mv= 10 and the spectral class of O on the HR Diagram?To get a truly precise answer, besides the apparent magnitude you need to know EITHER the absolute magnitude OR the distance. Without either what conclusion can one make?



Your assignment also didn't say whether the star is a Main Sequence star, a supergiant, or a white dwarf, any of which can have an O-type spectral class. Assuming it is a Main Sequence star, this would give a typical luminosity of 1000x the Sun's brightness or an absolute magnitude of about -3



My math on this isn't very good but the formula for figuring it out is here:

http://en.wikipedia.org/wiki/Distance_mo鈥?/a>

mbusa