Photonweighted barycentric correction and its importance for precise radial velocities
Abstract
When applying the barycentric correction to a precise radial velocity measurement, it is common practice to calculate its value only at the photonweighted midpoint time of the observation instead of integrating over the entire exposure. However, since the barycentric correction does not change linearly with time, this leads to systematic errors in the derived radial velocities. The typical magnitude of this secondorder effect is of order 10 cm s^{1}, but it depends on several parameters, e.g. the latitude of the observatory, the position of the target on the sky, and the exposure time. We show that there are realistic observing scenarios, where the errors can amount to more than 1 m s^{1}. We therefore recommend that instruments operating in this regime always record and store the exposure meter flux curve (or a similar measure) to be used as photonweights for the barycentric correction. In existing data, if the flux curve is no longer available, we argue that secondorder errors in the barycentric correction can be mitigated by adding a correction term assuming constant flux.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 October 2019
 DOI:
 10.1093/mnras/stz2181
 arXiv:
 arXiv:1908.00991
 Bibcode:
 2019MNRAS.489.2395T
 Keywords:

 instrumentation: spectrographs;
 techniques: radial velocities;
 Astrophysics  Earth and Planetary Astrophysics;
 Astrophysics  Instrumentation and Methods for Astrophysics
 EPrint:
 9 pages, 7 figures, accepted to MNRAS