Spectrum of b Aur
The two components of b Aur have the same spectral class and almost the same luminosity
For this reason the lines belonging to both components can be easily observed.
The lines appear periodically doubled because of the Doppler effect. The maximum separation corresponds to
a relative speed of the two components of 107.5+111.5 Km/sec that gives 3,27 ┼ for Mg II 4481 ┼ line.
The spectrum in the picture 1 shows the situation almost at the maximum of separation of the lines.
With a program that can do peak fitting it is possible to find the line separation with a precision that can be
better than 1/5 th of pixel, thus 0,15 ┼ that at this working wavelenght correspond to 9 Km/sec.
Working in the red can improve the results of a factor 2.
Picture 1: A small part of the spectrum of b Aur centered on the Hg line,
recorded with 0,7 ┼ resolution and 5 minutes exposure. The black stripe shows the original image on the CCD. |