Exposre time, S/N and mean V band magnitude

American Association of Variable Star Observers (AAVSO)
Thu, 05/08/2014 - 09:43

Dear all,

How can one decide the exposure time for recording a spectrum of a variable star of W-UMa type given the magntiude and the period of the star (keeping in mind that a good S/N > 100 is required and a high - resolution spectroscopy is required to be perform)? What are the calculations and formula involved in it?