Apparent Birghtness And Absolute Brightness

1. Nov 25, 2014

Plutonium88

Question: Considering the effect of an earth sized plaent transiting a star, and blocking its light. How big will the change in ABSOLUTE birghtness be for different stellar classs O and A, if we subtract off this blocked light.

telescopes can detect very small changes in brightness, corresponding to DetlaFlux = 10^-18 w/m^2. What is the max distance at which we could detect the planet transiting the star.

Data And Formulas:
M = m - 5log(d/10pc) where M is absolute Magnitude
L = 4PiR^2*F
m - m_x,0 = -2.5log(f/f_x,0) (where m is apparent magnitude)

For Spectral Class O: M = 3MassSun, R = 12RadiusSun , Temp = 42000K , AbsMag(M) = -6.7 , L = 36000LumSun Number Within 30 pc = 3

For Spectral Class A: M = 3 MassSun , R= 3RadiusSun , Temp = 10000K , AbsMag(M) = 0.7 , L = 40LumSun
#Within 30 Pc = 360

My Attempt:

So initially it's asking me to find, the change in Absolute magnitude. So i will find a second absolute magnitude M, which includes the blocked portion of the light. Then i will do the AbsMag - AbsmagnitudeFound..

I was thinking that i could express the flux as a differene of the Luminosity of the star, over the Area of the star, and subtract the Luminosity of the star divided by the Area of the planet.. IE:

Change In Flux = L/4PiR*^2 - L/4PiRe^2

With this i could then use the formula for apparent birghtness, m - m_x,0 = -2.5log(changeinflux/f_x,0).

THen with the apparent brightness,i could find the second absolute magnitude

M2 = m - 5log(3) (considering the distance as 30pc)

Which would then allow me to solve for the change in absolute magnitde..

However i am not sure what i should use for F_x,0 and m_x,0 in the apparent brightness equation, or if this strategy is even valid at all.

For the second part of the question, i am assuming i will use m - m_x,0 = -2.5log(deltaflux/f_x,0) and then use the formula
M = m - log(d/10pc), and for each spectral class solve for the distance. Once again i'm not sure what to use for Fo. Could i just use the flux of the sun, and apparent brightness of the sun for this?

2. Nov 30, 2014