Hey guys, i made a thread a couple of weeks ago about how to derive equations for exoplanet data, and so far i´ve managed to derive an equation for the radial velocity as:(adsbygoogle = window.adsbygoogle || []).push({});

[tex]V_{rad}=K[cos(\theta + \omega) + ecos(\theta + \omega)[/tex]

Which i'm guessing would be the function to be plotting against the radial velocity data i get, although i have not been able to derive how [tex]\theta[/tex] is a function of time yet. But that's not what i'm trying to derive at right now. Right now i'm having troubles finding a equation to give me the mass of the planet from the given data i get from the plot. I'm guessing i get [tex]\omega, e, P,a[/tex] and the mass of the sun is already known, where e is eccentricity, P the period and a the semi-major axis.

This is pretty much where i'm stuck, i thought today i'd found a way. Since [tex]K=\frac{2\Piasin(i)}{P(1-e^2)^{1/2}}[/tex] and a can be written as [tex]a=\frac{L^2}{(1-e^2)GMm^2}[/tex], then i saw a formula (must admit that i have not trie deriving this formula yet, i just wanted to see if i could use it to get writ of L since that's a crossproduct and i wanted something with known constants insted of L), [tex]L=\frac{2\Pia^2(1-e^2)^{1/2}mM}{P(m+M)}[/tex], so i was thrilled and figured i could now write a as [tex]a=\frac{4 \pi^2 a^4M)}{GP^2(M+m)}[/tex] and could substitute that into my K equation to get [tex]K=\frac{8 \pi^3 a^4Msin(i)}{P^3G(M+m)^2(1-e^2)^{1/2}}[/tex] From which i could simply isolate m and get a nice equation for my mass, but this doesn't seem to give right results (if i just take data from exoplanets.org and put it in it does not agree with what they get), although checking the units i do seem to end up with Kg's.

Sorry for asking questions about this again and starting a new thread, but this isn't going too smoothly for me :yuck:

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# More exoplanet equation problems :/

**Physics Forums | Science Articles, Homework Help, Discussion**