Measuring Radial Velocities of Low Mass Eclipsing Binaries

Abstract

Due to the complex nature of the spectra of low-mass M type stars, it is difficult to determine their metallicities and temperatures directly. By studying eclipsing binary pairs comprising one F, G, or K type star with an M type star, we are able to use what we know about the primary star to learn more about the secondary star. Measuring the orbital reflex motion of the primary star, together with the eclipse light curve of the M star as it transits the primary star, allows us to determine the mass, radius, temperature, and metallicity of the M star.

We studied 23 low mass eclipsing binaries (EBLMs) previously discovered by SuperWASP photometry. We obtained spectra using the Cerro Tololo Inter-American Observatory (CTIO) SMARTS 1.5-meter echelle spectrograph between June 2009 and January 2011. Each EBLM target was typically observed ~8 times over this time period. The spectra were processed using standard astronomical software, and a cross-correlation method was used to measure the radial velocity of the target star at each observed epoch.

Radial velocities were successfully determined for 21 of the 23 EBLM target objects. Orbital periods, radial velocity amplitudes, and eccentricities for these EBLMs could be determined from these radial velocities together with the preexisting light curves. Using these values and by assuming a mass for the primary star, we will be able to calculate the masses of the secondary M type star in each EBLM system.