•Question 12: If interstellar dust makes an RR Lyrae star
look 1 magnitude fainter than
it should, by how much will we overestimate its distance?
•
•We know how
to get distances based on the distance modulus equation:
•d(pc) = 10 (m-M+5)/5
•So the
apparent magnitude “m” increases by 1 compared to the no dust case.
Our distance overestimate can be expressed:
•d(dust)/d(no dust) = 10(md-M+5)/5/10(mn-M+5)/5 = 10 (md-mn)/5
•This is just 100.2 which
is 1.6 (answer a).
•Another way
you might do it and might seem easier is just to pick some numbers for M and m and do it with m
changing by 1. The distance ratio will be the same for any
choices.
•
•