# Color Indices and Absolute and Apparent Bolometric Magnitude

1. Feb 10, 2013

### HeLiXe

1. The problem statement, all variables and given/known data
Given: Spherical blackbody with
surface temperature of 30000K
radius of 6.0 x 10^9 m
located 123pc from earth

2. Relevant equations

Find the absolute and apparent bolometric magnitudes

3. The attempt at a solution

My camera needs batteries so I cannot post my work, but I will explain what my reasoning and attempts. Please bear in mind this is my first astrophysics class and this is all new to me e.g. I am totally clueless!

From the given data I have found the luminosity, distance modulus, radiant flux at the star's surface and the Earth's surface and the peak wavelength. I know what a bolometric magnitude is by definition, but every equation I have seems to need more variables and cannot be solved by a system of equations. I think my key problem is I do not know how to find the star's absolute color magnitudes. My textbook indicates that the star's absolute color magnitudes can be found once the distance from earth is known, but there is no equation given for this. Information that I have been given in the textbook is the UBV filters centered and the effective bandwith.

I will screenprint the equations I have used and post them along with the problems I encounter for each one.

2. Feb 10, 2013

### cepheid

Staff Emeritus
You need to show your work/calculations. Also, so far all your problem statement says is that you need to find the absolute and apparent bolometric magnitudes. If you know the luminosity of the star, then you can calculate the first one easily just from the definition of bolometric magnitude.

3. Feb 10, 2013

### HeLiXe

Thanks cepheid. I just cannot see where it is so easy. I will type out my work and post it.

4. Feb 12, 2013

### I like Serena

Hey HeLiXe!

What's a bolometric magnitude?

5. Feb 12, 2013

### HeLiXe

ILS! <3

The bolometric magnitude is the magnitude for all wavelengths emitted by a given star. I figured out how to do this...the task of retyping all of my work in latex seemed daunting to me so I asked my professor for guidance. I totally overlooked the most essential equation with the comparison of luminosity and I totally saw how easy it was as cepheid indicated :D