/sci/ - Science & Math

It's not a single body-problem, it's two bodies.
Therefore you combine the formula you mentioned for both bodies and obtain kepler's 3rd law. Also you know the star's mass from it's position in the Hertzsprung-Rusell-diagram. With the period measured you now can calculate the distance.

With the distance to the star and the star to earth both known you can interpret the size of the doppler shifts the star performs as the planets mass.

>>6164906
Holy balls wat. Can you break that down a little more for me? I'm only a first year astronomy student.

>>6164908

That is all covered in first year astronomy.

The transit method only tells us the orbital period and the relative size of star and planet. From the period alone you cannot work out the mass of the planet.

>>6164914
Apparently not in my first quarter when I'm only taking intro to astronomy.

>>6164922
You can tell the mass of the planet by how much it makes its star move, since we can estimate the mass of the star.

>>6164908
ok, let's try:

classical mechanics: using newton 1 you can derive kepler 3.
if unclear, lookup on wiki.
there you see that you have a reduced mass depending on period and elliptic grand axis.
and the reduced mass again contains star and planet mass that is tugging on the star.

the star mass can be deduced from stellar models (= magnetohydrodynamics + radiative transfer + fusion core models) that predict us it's position in the observable Hertzsprung-Russell-Diagram depending on it's mass.
So we 'only' look where it is in the HR-Diagram and know it's mass.

Okay, one problem solved.
Now we take a look at one specific line in the spectrum of the star. It will be doppler-shifted, and this shift will change with time as a result of the planet tugging on it.
So we get a curve for the doppler shift (lookup on wiki), out of which we read the orbital Period and now with Kepler3 the distance.

with all that and the star's distance to earth known (most of them are close enough for the parallaxe method), we can now calculate the force on the star itself exerted by the planet from the amplitude of the doppler curve.

okay sorry man if that's a bit inaccurate or too much, but I'm very tired and too lazy to look up stuff now.

>>6164914
out of interest (eurofag here):
what is a "first year astronomy student"?
did you just begin with your physics bachelor, or your astronomy masters?

>>6164938
No man that's golden, that makes a ton more sense, thanks for the answer.

So once we find the orbital period from the doppler spectroscopy, and we know with kepler3 the distance, and we know our distance to the star, we use the doppler curve amplitude to calculate the force.


That's tons of help. Feels good to understand what the hell I'm reading.

>>6164943
I'm an undergraduate student at an American (as you guessed) university called Dartmouth. I'm not actually an astronomy or physics major, I just meant that I'm taking introductory level (first-year level) classes to astronomy, just to give background to my knowledge level. It was a pretty misleading way to put it on my part.

God damn nigga, science n shit

I don't like kepler 62. its a second gen star, so the planets probably don't have fun amounts of higher elements.