# Estimating the reddening of a star? [closed]

I'm stuck on a question concerning how to estimate the reddening of a star. The question is:

"A star near the Galactic plane has observed apparent magnitudes in the blue and visual bands of $B = 15.48$, $V = 14.58$.

Comparison of a spectrum of the star to a library of local star spectra indicates that it has absolute magnitudes $M_B = 3.20$, and $M_V = 2.70$.

Given that the reddening ratio for interstellar dust is $A_V /E_{B − V} = 3.0$, estimate (i) the reddening of the star, (ii) the V-band extinction in magnitudes, and (iii) the distance to the star in parsecs."

I can see how to do both parts (ii) and (iii) but I am stuck on the first part. I assume in estimating the reddening I would need to calculate the colour excess

$E_{B-V}=(B-V)-(B-V)_{intrinsic}=A_B-A_V$,

with $A_{B(V)}=B(V)-B(V)_{intrinsic}$.

So I would need the intrinsic $B$ and $V$ values, which aren't given in the question or rubric and I don't know how to obtain these. Any help is greatly appreciated.

## closed as off-topic by John Rennie, Rob Jeffries, Kyle Kanos, ZeroTheHero, Emilio PisantyMay 4 '18 at 21:42

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• The intrinsic B and V values are given in the question. – Rob Jeffries May 4 '18 at 10:01
• @RobJeffries are the intrinsic values just the absolute magnitudes? – Brad May 4 '18 at 10:04
• The absolute magnitudes are the magnitudes the stars would have if they were 10pc away and take no account of extinction. – Rob Jeffries May 4 '18 at 11:05