Photon-weighted barycentric correction and its importance for precise radial velocities

René Tronsgaard*, Lars A. Buchhave, Jason T. Wright, Jason D. Eastman, Ryan T. Blackman

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Abstract

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 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 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.
Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society
Volume489
Issue number2
Pages (from-to)2395–2402
ISSN0035-8711
DOIs
Publication statusPublished - 2019

Keywords

  • Instrumentation: spectrographs
  • Techniques: radial velocities

Cite this

@article{46bc9abf465743ff9136ccb75efb9425,
title = "Photon-weighted 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 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 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 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.",
keywords = "Instrumentation: spectrographs, Techniques: radial velocities",
author = "Ren{\'e} Tronsgaard and Buchhave, {Lars A.} and Wright, {Jason T.} and Eastman, {Jason D.} and Blackman, {Ryan T.}",
year = "2019",
doi = "10.1093/mnras/stz2181",
language = "English",
volume = "489",
pages = "2395–2402",
journal = "Royal Astronomical Society. Monthly Notices",
issn = "0035-8711",
publisher = "Oxford University Press",
number = "2",

}

Photon-weighted barycentric correction and its importance for precise radial velocities. / Tronsgaard, René; Buchhave, Lars A.; Wright, Jason T.; Eastman, Jason D.; Blackman, Ryan T.

In: Monthly Notices of the Royal Astronomical Society, Vol. 489, No. 2, 2019, p. 2395–2402.

Research output: Contribution to journalJournal articleResearchpeer-review

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.

PY - 2019

Y1 - 2019

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 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 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 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 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.

KW - Instrumentation: spectrographs

KW - Techniques: radial velocities

U2 - 10.1093/mnras/stz2181

DO - 10.1093/mnras/stz2181

M3 - Journal article

VL - 489

SP - 2395

EP - 2402

JO - Royal Astronomical Society. Monthly Notices

JF - Royal Astronomical Society. Monthly Notices

SN - 0035-8711

IS - 2

ER -