A test field for Gaia

Radial velocity catalogue of stars in the South Ecliptic Pole^{⋆,⋆⋆,⋆⋆⋆,⋆⋆⋆⋆}

¹ Royal Observatory of Belgium, 3 avenue circulaire, 1180 Brussels, Belgium
e-mail: yves.fremat@observatory.be
² Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
³ SYRTE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, LNE, 61 avenue de l’Observatoire, 75014 Paris, France
⁴ INAF–Osservatorio Astronomico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
⁵ ASI Science Data Center, via del Politecnico snc, 00133 Rome, Italy
⁶ LAB UMR 5804, Univ. Bordeaux – CNRS, 33270 Floirac, France
⁷ Institute of Astronomy, University of Cambridge, Madingley Road CB3 0 HA Cambridge, UK
⁸ Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
⁹ Centre de Recherche en astronomie, astrophysique et géophysique, route de l’Observatoire, BP 63 Bouzareah, 16340 Algiers, Algeria
¹⁰ Space sciences, Technologies, and Astrophysics Research (STAR) Institute, Université de Liège, 19c, Allée du 6 Août, 4000 Liège, Belgium
¹¹ Department of Physics and Astronomy, Uppsala University, PO Box 516, 75120 Uppsala, Sweden
¹² GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, place Jules Janssen, 92195 Meudon Cedex, France
¹³ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
¹⁴ INAF–Osservatorio Astronomico di Padova, Vic. dell’Osservatorio 5, 35122 Padova, Italy
¹⁵ Observatoire de Genève, Université de Genève, 1290 Versoix, Switzerland
¹⁶ LUPM UMR 5299 CNRS/UM2, Université Montpellier II, CC 72, 34095 Montpellier Cedex 05, France
¹⁷ ESO – European Organisation for Astronomical Research in the Southern Hemisphere, Alonso de Cordova 3107, Vitacura, Santiago de Chile, Chile
¹⁸ UCA, Laboratoire Lagrange, UMR 7293, OCA, CS 34229, 06304 Nice Cedex 4, France
¹⁹ Universiteit Antwerpen, Onderzoeksgroep Toegepaste Wiskunde, Middelheimlaan 1, 2020 Antwerpen, Belgium
²⁰ Max Planck Institut für Sonnensystemforschung, Justus-von- Liebig-Weg 3, 37077 Göttingen, Germany
²¹ Max-Planck Institut für Astronomie (MPIA), 69117 Heidelberg, Germany
²² KU Leuven, Afdeling Sterrenkunde, Celestijnenlaan 200d – bus 2401, 3001 Leuven, Belgium
²³ Sorbonne Universités, UPMC Université Paris 6 et CNRS UMR 7095, Institut d’Astrophysique de Paris, 75014 Paris, France

Received: 18 August 2016
Accepted: 22 September 2016

Abstract

Context. Gaia is a space mission that is currently measuring the five astrometric parameters, as well as spectrophotometry of at least 1 billion stars to G = 20.7 mag with unprecedented precision. The sixth parameter in phase space (i.e., radial velocity) is also measured thanks to medium-resolution spectroscopy that is being obtained for the 150 million brightest stars. During the commissioning phase, two fields, one around each ecliptic pole, have been repeatedly observed to assess and to improve the overall satellite performances, as well as the associated reduction and analysis software. A ground-based photometric and spectroscopic survey was therefore initiated in 2007, and is still running to gather as much information as possible about the stars in these fields. This work is of particular interest to the validation of the radial velocity spectrometer outputs.

Aims. The paper presents the radial velocity measurements performed for the Southern targets in the 12−17 R magnitude range on high- to mid-resolution spectra obtained with the GIRAFFE and UVES spectrographs.

Methods. Comparison of the South Ecliptic Pole (SEP) GIRAFFE data to spectroscopic templates observed with the HERMES (Mercator in La Palma, Spain) spectrograph enabled a first coarse characterisation of the 747 SEP targets. Radial velocities were then obtained by comparing the results of three different methods.

Results. In this paper, we present an initial overview of the targets to be found in the 1 sq. deg SEP region that was observed repeatedly by Gaia ever since its commissioning. In our representative sample, we identified one galaxy, six LMC S-stars, nine candidate chromospherically active stars, and confirmed the status of 18 LMC Carbon stars. A careful study of the 3471 epoch radial velocity measurements led us to identify 145 RV constant stars with radial velocities varying by less than 1 km s^-1. Seventy-eight stars show significant RV scatter, while nine stars show a composite spectrum. As expected, the distribution of the RVs exhibits two main peaks that correspond to Galactic and LMC stars. By combining [Fe/H]  and log g  estimates, and RV determinations, we identified 203 members of the LMC, while 51 more stars are candidate members.

Conclusions. This is the first systematic spectroscopic characterisation of faint stars located in the SEP field. During the coming years, we plan to continue our survey and gather additional high- and mid-resolution data to better constrain our knowledge on key reference targets for Gaia.