Estimating the sizes of stars
•
Recall L
µ
R
2
x T
4
–
knowing L, T
®
R
•
•
For Mira, L = 400 L
¤
(L
¤
= 3.8 x 10
33
ergs/sec)
•
T= 2700K = 0.5T
¤
(T
¤
= 5800K)
•
so, R = 20/0.25 = 80 R
¤
(R
¤
=6.9 x 10
10
cm
•
•
For Sirius B,
L = 0.04 L
¤
•
T= 23,200K = 4T
¤
•
so, R = 0.2/16 = 0.01 R
¤
•