TY - JOUR
T1 - Photon-weighted barycentric correction and its importance for precise radial velocities
AU - Tronsgaard, René
AU - Buchhave, Lars A.
AU - Wright, Jason T.
AU - Eastman, Jason D.
AU - Blackman, Ryan T.
N1 - Funding Information:
We would like to thank the referee, Artie Hatzes, for carefully reading the manuscript and supporting its conclusions. We also thank the members of the EXPRES and HARPS-N GTO teams for useful input and fruitful discussions. Our simulations involved an extensive amount of coordinate transformations made possible with the excellent ASTROPY.COORDINATES module3 (Astropy Collaboration et al. 2013; Price-Whelan et al. 2018). All figures were prepared with MATPLOTLIB4 (Hunter 2007). The Center for Exoplanets and Habitable Worlds is supported by the Pennsylvania State University, the Eberly College of Science, and the Pennsylvania Space Grant Consortium.
Publisher Copyright:
© 2019 The Author(s).
PY - 2019/10/21
Y1 - 2019/10/21
N2 - When applying the barycentric correction to a precise radial velocity measurement, it is common practice to calculate its value only at the photon-weighted mid-point 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 second-order 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 ms-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 photon-weights for the barycentric correction. In existing data, if the flux curve is no longer available, we argue that second-order errors in the barycentric correction can be mitigated by adding a correction term assuming constant flux.
AB - When applying the barycentric correction to a precise radial velocity measurement, it is common practice to calculate its value only at the photon-weighted mid-point 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 second-order 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 ms-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 photon-weights for the barycentric correction. In existing data, if the flux curve is no longer available, we argue that second-order errors in the barycentric correction can be mitigated by adding a correction term assuming constant flux.
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U2 - 10.1093/mnras/stz2181
DO - 10.1093/mnras/stz2181
M3 - Article
AN - SCOPUS:85075182313
SN - 0035-8711
VL - 489
SP - 2395
EP - 2402
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 2
ER -