## Saturday, June 27, 2015

### High Precision Photometry of Transiting Exoplanets as I currently know it : Part III

Background &
Doppler Shift  cont.

The results from a star's spectrum are used to plot the data shown on radial velocity curves.  The following gif illustrates how the moving position of the absorption lines in a spectrum can directly relate to the velocity at which the star is moving/wobbling away or toward us observers.

 Animation exhibiting the real phenomenon known as Doppler Shift.  As the star moves/wobbles away or toward the observer, the absorption lines that are indicative of the star's outer atmospheric composition shift from left to right or right to left on the spectrum.
The displacement between the absorption lines' original positions and their new position insinuate the velocity at which the star moves away or toward the observer.  However, this technique alone keeps observer's oblivious to the velocity of the star when it is moving in a direction that moving along the observer's line of sight.  This means that stellar systems that we view from pole-on or top-view will not provide any velocity information when using this doppler shift technique.

 An exemplary orbiting stellar-planet system that would not exhibit doppler shift for the observing reader because as you look at your monitor, your line of sight is perpendicular to the plane of the screen, i.e. the directions at which the star and planet move.

The concept of doppler shift can be further elaborated by the equation
$\frac{\Delta\lambda}{\lambda{_0}}=\frac{v_{star}}{c}$

where $$\Delta\lambda$$ is the change in wavelengths of the moved absorption lines, $$\lambda{_0}$$ is the initial wavelength, $$v_{star}$$ is the velocity of the star moving radially and c is the speed of light.  Evidently, there is a direct relationship between the radial velocity of the star and the change of wavelengths exhibited by the star's absorption lines in the spectrum.  Thus, the radial velocity curves are made.

to be continued...