- #1

d97

## Homework Statement

The Cepheid variable star l Carinae pulsates with a period of about 36 days. During each pulsation, the star becomes about twice as bright and its radius grows by about 25%.

(a) In its smaller state, the star has a surface temperature of about 5100 K. Treating the star as a blackbody, use Wein’s displacement law to compute the wavelength at which l Carinae is brightest. [2 marks]

(b) If l Carinae swells by 25% and becomes twice as bright, what is its surface temperature in its swollen state? At what wavelength is it brightest in this state? [4 marks]

## Homework Equations

λ=2.898*10^-3/T

T=(L/16πσa^2)^0.25

## The Attempt at a Solution

For (a) I think I have got the correct solution from the first equation which was 5.68*10^-7 m. My main problem is (b) because I'm unsure on how to work out luminosity with the variables I have been given. Do you work out 'a' in the equation by saying that P^2=a^3?, I'm unsure.

Any help would be much appreciated thank you [/B]