Exercise

Now that you have apparent magnitudes for the stars in both the B and V filters, we can calculate the temperature of the stars. We haven’t accounted for extinction, or reddening, which for M67 is 

E(B-V)=0.04, 

but we could do that knowing that E(B-V)= (B-V)_observed - (B-V)_intrinsic.

Calculate the temperature of the star using the equation below, which uses the magnitudes B and V . The “K” in this equation is a unit of Kelvin, which is a measure of temperature, much like Celsius or Fahrenheit. This equation works well for stars with color indices between 0 and 1.5. Otherwise, here is the real equation.

Alternatively, you can use , which plots the temperature as a function of color index (B-V) and labels the spectral types, to find the relationship between B-V and the Temperature. However, that plot is an idealized relationship that doesn’t account for variations in filters or reddening.

Use the HR diagram below to find the spectral class of each star using the temperature.