A systematic bias in template-based radial velocity extraction algorithms

Article Article scientifique Article A systematic bias in template-based radial velocity extraction algorithms eng 2025-08-12 2025-08 author Silva A. M. http://orcid.org/0000-0003-4920-738X author Santos N. C. http://orcid.org/0000-0003-4422-2919 author Faria Joao http://orcid.org/0000-0002-6728-244X 416418 Département d'astronomie (ASTRO) author Martins J. H. C. http://orcid.org/0000-0002-1532-9082 author Cristo E. A. S. http://orcid.org/0000-0001-5992-7589 author Sousa S. G. http://orcid.org/0000-0001-9047-2965 author Viana P. T. P. http://orcid.org/0000-0003-1572-8531 author Artigau É. http://orcid.org/0000-0003-3506-5667 author Al Moulla K. http://orcid.org/0000-0002-3212-5778 author Castro-González A. http://orcid.org/0000-0001-7439-3618 author Folha D. F. M. http://orcid.org/0000-0003-0150-0288 author Figueira Pedro Ricardo http://orcid.org/0000-0001-8504-283X 637397 Département d'astronomie (ASTRO) author Schmidt Tobias http://orcid.org/0000-0002-4833-7273 954324 author Pepe Francesco Alfonso http://orcid.org/0000-0002-9815-773X 124203 Département d'astronomie (ASTRO) author Dumusque Xavier http://orcid.org/0000-0002-9332-2011 583253 Département d'astronomie (ASTRO) author Demangeon O. D. S. http://orcid.org/0000-0001-7918-0355 author Campante T. L. http://orcid.org/0000-0002-4588-5389 author Delfosse X. http://orcid.org/0000-0001-5099-7978 author Wehbe B. http://orcid.org/0000-0003-0979-513X author Lillo-Box J. author Da Costa Lopes Da Silva Ana Rita http://orcid.org/0000-0003-2245-9579 418591 author Rodrigues J. http://orcid.org/0000-0001-5164-3602 author González Hernández J. I. http://orcid.org/0000-0002-0264-7356 author Azevedo Silva T. author Cristiani S. http://orcid.org/0000-0002-2115-5234 author Tabernero H. M. http://orcid.org/0000-0002-8087-4298 author Palle E. http://orcid.org/0000-0003-0987-1593 author Lavie Baptiste http://orcid.org/0000-0001-8884-9276 861546 Département d'astronomie (ASTRO) author Suárez Mascareño A. author Di Marcantonio P. http://orcid.org/0000-0003-3168-2289 author Cabral A. author Martins C. J. A. P. http://orcid.org/0000-0002-4886-9261 author Nunes N. J. author Sozzetti A. A93 10.1051/0004-6361/202554955 0004-6361 https://www.aanda.org/10.1051/0004-6361/202554955 Context . The radial velocity (RV) method plays a key role in modern-day astrophysics. One of the most common techniques for extracting precise RVs from state-of-the-art spectrographs is template-matching (TM) algorithms. They have been shown to perform better than a cross-correlation function (CCF) approach in cases of cooler stars (e.g. M dwarfs) and multiple implementations have appeared over the past years. More recently, line-by-line (LBL) approaches offer an alternative avenue to extract RVs by analyzing individual spectral lines. Aims . In this paper, we identify and explore a previously unidentified, multi-meter-per-second, systematic correlation between time and RVs inferred through TM and LBL methods. We evaluate the influence of the data-driven stellar template in the RV bias and hypothesise on the possible sources of this effect. Methods . We used the s-BART pipeline to extract RVs from three different datasets gathered over four nights of ESPRESSO and HARPS observations. We demonstrate that the effect can be recovered on a larger sample of 19 targets, totalling 4124 ESPRESSO observations over 38 nights. We also showcase the presence of the bias in RVs extracted with the SERVAL and ARVE pipelines. Lastly, we explore the construction of the stellar template over the five years of ESPRESSO observations of HD 10700, totalling more than 2000 observations. Results . We find that a systematic quasi-linear bias affects the RV extraction with slopes that vary from —0.3 ms −1 h −1 to —52 m s −1 h −1 in our sample. This trend is not observed in CCF RVs and only appears when all observations of a given star are collected within a short time period (timescales of hours). We show that this systematic contamination exists in the RV time series of two different template-matching pipelines and one line-by-line pipeline, and it is agnostic to the spectrograph. We also find that this effect is linked to the construction of the stellar template, as we were able to mitigate it through a careful selection of the observations used to construct it. Our results suggest that a contamination of micro-telluric features, coupled with other sources of correlated noise, could be the driving factor of this effect. We also show that this effect does not impact the usual usage of template-matching for the detection and characterisation of exoplanets. However, the short-timescale science cases, such as asteroseismology as well as transit and atmospheric characterisation, can be severely affected. Dewey 520 26 Département d'astronomie 12 false 862 Direction de recherche "Planètes extrasolaires" Astronomy & astrophysics 700 c50903f3-ee8c-49de-ac8a-8c36b4b7aaea Article (Published version) Public Article_scientifique_from_crossref.pdf 5959909 application/pdf CC BY-4.0 e18daa84d824576e247fc310a135594a21bd08fba9d7eb8a829cf584df19fd3f openAccess Faculté des sciences / Département d'astronomie

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A systematic bias in template-based radial velocity extraction algorithms	Astronomy & astrophysics			2025	21	54

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Schmidt, Tobias