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Transcript of Exoplanet-Doppler effect
What is an Exoplanet?
An exoplanet is a planet outside the Solar System.
How can we find them??
We can observe the dimming of light!!
What about planets that don't transit the star??
In that case we can use the doppler effects!!
Different ways of finding Exoplanets
What is the Doppler effect?
Doppler Effect :
The Doppler effect is the change in frequency of a wave when the source and the receiver have relative movement between each other.
What is Kepler’s 3rd Law??
Kepler’s 3rd Law :
The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.
Too little mass -> insufficient wiggle to be measured -> Can't be used
Limitation of using the doppler effect
How do we find the exoplanet with the doppler effect?
How do we acquire the mass of the exoplanet
Find wavelengths of the first and second Sodium spectrum line in each day(𝜆1, 𝜆2).
Calculate the wavelength shift using ordinary wavelength(Δ𝜆1, Δ𝜆2).
Using the doppler method, find the radial velocity of the star.
Using model, , fitting the data, find a period.
Using the mass of the star estimated by its Spectral type, we can find a orbit radius of the planet(Kepler’s 3rd law).
According to the formula of gravity and centripetal force, we can acquire the velocity of the exoplanet.
Finally, calculate the mass of the exoplanet using the conservation of linear momentum.
As a planet orbits a star, both objects orbit around the center of mass. The movement of the star can be detected by looking at its spectral lines.
Result and Conclusion
Minimum Mass of the exoplanet
The Orbit of Exoplanet could be tilted from our point of view causing the decrease from the true velocity of star by cos i (angle of tilt)
This is an inhabitable planet
Real FWHM : 0.04nm -> 0.01nm is caused by rotation
-> rotation velocity of the star 5km/s
Thermal doppler broadening Rotation