A multi-method approach to radial-velocity measurement for single-object spectra

Abstract

\n Context. The derivation of radial velocities from large numbers of\n spectra that typically result from survey work, requires automation. However, except for\n the classical cases of slowly rotating late-type spectra, existing methods of measuring\n Doppler shifts require fine-tuning to avoid a loss of accuracy due to the idiosyncrasies\n of individual spectra. The radial velocity spectrometer (RVS) on the Gaia mission, which\n will start operating very soon, prompted a new attempt at creating a measurement pipeline\n to handle a wide variety of spectral types.\n Aims. The present paper describes the theoretical background on which\n this software is based. However, apart from the assumption that only synthetic templates\n are used, we do not rely on any of the characteristics of this instrument, so our results\n should be relevant for most telescope-detector combinations.\n Methods. We propose an approach based on the simultaneous use of several\n alternative measurement methods, each having its own merits and drawbacks, and conveying\n the spectral information in a different way, leading to different values for the\n measurement. A comparison or a combination of the various results either leads to a “best\n estimate” or indicates to the user that the observed spectrum is problematic and should be\n analysed manually. \n Results. We selected three methods and analysed the relationships and\n differences between them from a unified point of view; with each method an appropriate\n estimator for the individual random error is chosen. We also develop a procedure for\n tackling the problem of template mismatch in a systematic way. Furthermore, we propose\n several tests for studying and comparing the performance of the various methods as a\n function of the atmospheric parameters of the observed objects. Finally, we describe a\n procedure for obtaining a knowledge-based combination of the various Doppler-shift\n measurements.\n

Keywords

Affiliated Institutions

• Centre National de la Recherche Scientifique FR
• Centre de Recherche en Astronomie Astrophysique et Géophysique DZ
• Délégation Paris 7 FR
• Université Paris Cité FR
• University of Antwerp BE
• University of Liège BE
• Royal Observatory of Belgium BE
• Galaxies, Etoiles, Physique et Instrumentation FR

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