sukisa
Oct26-10, 10:20 AM
1. The problem statement, all variables and given/known data
The central wavelength and the flux calibration are given in Table 2 (f5500= Cv * 10^-0.4V)
Calculate the flux measured at Earth f5500, the blackbody surface fluxes B5500, and the radius (in m and solar radii)
For Sirus A and B
Table 1:
brightness Sirius A: Va= -1.46
brightness Sirius B: Vb= 8.44
TeffA= 9900K
TeffB=25,200K
Table 2: Data for the Johnson V filter
central wavelength lambda=5500 Angstrom
filter Constant Cv= 3.58*10^-2 W m^-2 m^-1
3. The attempt at a solution
I noted when attempting the problem that the apparent magnitude is the same as Va and Vb respectively.
I used the equation in the question to figure out the flux f5500 = (3.58*10^-2)(10^-0.4*-1.46)
I get an answer of 0.137 Wm^-2 for the flux.
I can tell this is wrong because I then need to find the radius and hence luminosity and I get figures several orders of magnitudes off from the actual values.
Do I need the surface flux B5500 to figure out the radius also? And is the surface flux B5500 the blackbody plank function?
If I get the flux I should be able to determine the luminosity (and thus radius) using L=4piR^2F then using L=4piR^2(boltsman)Teff^4 for the radius of sirius.
I know the distance to sirius as I figured out from a previous problem. My answer is 2.639pc which is constant with the measured values. Any help would be greatly appreciated.
The central wavelength and the flux calibration are given in Table 2 (f5500= Cv * 10^-0.4V)
Calculate the flux measured at Earth f5500, the blackbody surface fluxes B5500, and the radius (in m and solar radii)
For Sirus A and B
Table 1:
brightness Sirius A: Va= -1.46
brightness Sirius B: Vb= 8.44
TeffA= 9900K
TeffB=25,200K
Table 2: Data for the Johnson V filter
central wavelength lambda=5500 Angstrom
filter Constant Cv= 3.58*10^-2 W m^-2 m^-1
3. The attempt at a solution
I noted when attempting the problem that the apparent magnitude is the same as Va and Vb respectively.
I used the equation in the question to figure out the flux f5500 = (3.58*10^-2)(10^-0.4*-1.46)
I get an answer of 0.137 Wm^-2 for the flux.
I can tell this is wrong because I then need to find the radius and hence luminosity and I get figures several orders of magnitudes off from the actual values.
Do I need the surface flux B5500 to figure out the radius also? And is the surface flux B5500 the blackbody plank function?
If I get the flux I should be able to determine the luminosity (and thus radius) using L=4piR^2F then using L=4piR^2(boltsman)Teff^4 for the radius of sirius.
I know the distance to sirius as I figured out from a previous problem. My answer is 2.639pc which is constant with the measured values. Any help would be greatly appreciated.