- #1
Morpheus
Here are a few more questions that I really need help on, thanks!
3. A Cepheid variable star is observed in the nearby galaxy M31. Its period of variation
is measured to be 40 days. Using the period - luminosity relation given in the table
below, what is the luminosity of the Cepheid in solar luminosities?
Period Luminosity
(days) (solar luminosities)
2.5 645
4.0 1120
6.3 2000
10.0 3550
15.8 6310
25.1 11500
40.0 20900
63.1 38000
4. For the Cepheid in M31, what is its luminosity in ergs/sec? (Recall that the solar
luminosity is 3.85 x 1033 ergs/sec.)
5. The Cepheid in M31 has its apparent brightness measured at 1.06 x 10-12 ergs/sec/cm2.
The inverse square law of light may be written as
b = L ÷ 4 pi r^2
Where b is the apparent brightness, L is the luminosity and r is the distance.
How far away is the Cepheid in centimeters? Convert your answer to parsecs by
knowing that one parsec contains 3.09 x 1018 centimeters.
3. A Cepheid variable star is observed in the nearby galaxy M31. Its period of variation
is measured to be 40 days. Using the period - luminosity relation given in the table
below, what is the luminosity of the Cepheid in solar luminosities?
Period Luminosity
(days) (solar luminosities)
2.5 645
4.0 1120
6.3 2000
10.0 3550
15.8 6310
25.1 11500
40.0 20900
63.1 38000
4. For the Cepheid in M31, what is its luminosity in ergs/sec? (Recall that the solar
luminosity is 3.85 x 1033 ergs/sec.)
5. The Cepheid in M31 has its apparent brightness measured at 1.06 x 10-12 ergs/sec/cm2.
The inverse square law of light may be written as
b = L ÷ 4 pi r^2
Where b is the apparent brightness, L is the luminosity and r is the distance.
How far away is the Cepheid in centimeters? Convert your answer to parsecs by
knowing that one parsec contains 3.09 x 1018 centimeters.