Gaia Data Release 3

Stellar chromospheric activity and mass accretion from Ca II IRT observed by the Radial Velocity Spectrometer

¹ INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
² Dipartimento di Fisica e Astronomia “Ettore Majorana”, Università di Catania, Via S. Sofia 64, 95123 Catania, Italy
³ Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
⁴ INAF – Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy
⁵ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Bd de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
⁶ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Naples, Italy
⁷ Observational Astrophysics, Division of Astronomy and Space Physics, Department of Physics and Astronomy, Uppsala University, Box 516 751 20 Uppsala, Sweden
⁸ ATG Europe for European Space Agency (ESA), Camino Bajo del Castillo, s/n, Urbanizacion Villafranca del Castillo, Villanueva de la Cañada, 28692 Madrid, Spain
⁹ CIGUS CITIC – Department of Computer Science and Information Technologies, University of A Coruña, Campus de Elviña s/n, A Coruña, 15071, Spain
¹⁰ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹¹ National Observatory of Athens, I. Metaxa and Vas. Pavlou, Palaia Penteli, 15236 Athens, Greece
¹² Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, Allée Geoffroy Saint-Hilaire, 33615 Pessac, France
¹³ Telespazio for CNES Centre Spatial de Toulouse, 18 Avenue Edouard Belin, 31401 Toulouse Cedex 9, France
¹⁴ Dpto. de Matemática Aplicada y Ciencias de la Computación, Univ. de Cantabria, ETS Ingenieros de Caminos, Canales y Puertos, Avda. de los Castros s/n, 39005 Santander, Spain
¹⁵ GEPI, Observatoire de Paris, Université PSL, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
¹⁶ CNES Centre Spatial de Toulouse, 18 Avenue Edouard Belin, 31401 Toulouse Cedex 9, France
¹⁷ Centre for Astrophysics Research, University of Hertfordshire, College Lane, AL10 9AB Hatfield, UK
¹⁸ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, TO, Italy
¹⁹ Institut d’Astrophysique et de Géophysique, Université de Liège, 19c, Allée du 6 Août, 4000 Liège, Belgium
²⁰ Apave Sudeurope SAS for CNES Centre Spatial de Toulouse, 18 Avenue Edouard Belin, 31401 Toulouse Cedex 9, France
²¹ Theoretical Astrophysics, Division of Astronomy and Space Physics, Department of Physics and Astronomy, Uppsala University, Box 516 751 20 Uppsala, Sweden
²² European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino Bajo del Castillo, s/n, Urbanizacion Villafranca del Castillo, Villanueva de la Cañada, 28692 Madrid, Spain
²³ Data Science and Big Data Lab., Pablo de Olavide University, 41013 Seville, Spain
²⁴ Department of Astrophysics, Astronomy and Mechanics, National and Kapodistrian University of Athens, Panepistimiopolis, Zografos, 15783 Athens, Greece
²⁵ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 Place Jules Janssen, 92190 Meudon, France
²⁶ Université Rennes, CNRS, IPR (Institut de Physique de Rennes) – UMR 6251, 35000 Rennes, France
²⁷ Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
²⁸ DXC Technology, Retortvej 8, 2500 Valby, Denmark
²⁹ Aurora Technology for European Space Agency (ESA), Camino Bajo del Castillo, s/n, Urbanizacion Villafranca del Castillo, Villanueva de la Cañada, 28692 Madrid, Spain
³⁰ CIGUS CITIC, Department of Nautical Sciences and Marine Engineering, University of A Coruña, Paseo de Ronda 51, 15071 A Coruña, Spain
³¹ IPAC, Mail Code 100-22, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA, 91125, USA
³² IRAP, Université de Toulouse, CNRS, UPS, CNES, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
³³ Thales Services for CNES Centre Spatial de Toulouse, 18 Avenue Edouard Belin, 31401 Toulouse Cedex 9, France
³⁴ Dpto. de Inteligencia Artificial, UNED, c/ Juan del Rosal 16, 28040 Madrid, Spain
³⁵ Institute of Global Health, University of Geneva, Geneva, Switzerland
³⁶ Applied Physics Department, Universidade de Vigo, 36310 Vigo, Spain
³⁷ Sorbonne Université, CNRS, UMR7095, Institut d’Astrophysique de Paris, 98bis Bd. Arago, 75014 Paris, France

Received: 31 May 2022
Accepted: 23 August 2022

Abstract

Context. The Gaia Radial Velocity Spectrometer (RVS) provides the unique opportunity of a spectroscopic analysis of millions of stars at medium resolution (λ/Δλ ∼ 11 500) in the near-infrared (845−872 nm). This wavelength range includes the Ca II infrared triplet (IRT) at 850.03, 854.44, and 866.45 nm, which is a good indicator of magnetic activity in the chromosphere of late–type stars.

Aims. Here we present the method devised for inferring the Gaia stellar activity index from the analysis of the Ca II IRT in the RVS spectrum, together with its scientific validation.

Methods. The Gaia stellar activity index is derived from the Ca II IRT excess equivalent width with respect to a reference spectrum, taking the projected rotational velocity (vsini) into account. We performed scientific validation of the Gaia stellar activity index by deriving a R^′_IRT index, which is largely independent of the photospheric parameters, and considering the correlation with the R^′_HK index for a sample of stars. A sample of well-studied pre-main-sequence (PMS) stars is considered to identify the regime in which the Gaia stellar activity index may be affected by mass accretion. The position of these stars in the colour–magnitude diagram and the correlation with the amplitude of the photometric rotational modulation is also scrutinised.

Results.Gaia DR3 contains a stellar activity index derived from the Ca II IRT for some 2 × 10⁶ stars in the Galaxy. This represents a ‘gold mine’ for studies on stellar magnetic activity and mass accretion in the solar vicinity. Three regimes of the chromospheric stellar activity are identified, confirming suggestions made by previous authors based on much smaller R^′_HK datasets. The highest stellar activity regime is associated with PMS stars and RS CVn systems, in which activity is enhanced by tidal interaction. Some evidence of a bimodal distribution in main sequence (MS) stars with T_eff ≳ 5000 K is also found, which defines the two other regimes, without a clear gap in between. Stars with 3500 K ≲ T_eff ≲ 5000 K are found to be either very active PMS stars or active MS stars with a unimodal distribution in chromospheric activity. A dramatic change in the activity distribution is found for T_eff ≲ 3500 K, with a dominance of low activity stars close to the transition between partially- and fully convective stars and a rise in activity down into the fully convective regime.