Radial velocities of ER Vul

Accordingly, the two stars rotate very fast, leading to a blending of many spectral features at all phases. Therefore, measuring the radial velocity curve without systematic errors is not trivial.

Here, we use a two-dimensional cross-correlation method applied to 137 high quality spectra, collected over 3 years, in order to obtain the radial velocity curve and determine the orbital and some physical parameters of the system from it. Primarily, we improve the binary period to 0.69809458d+/-0.00000014d, and find that the two amplitudes are slightly smaller than those measured by others, while the mass ratio is still similar.