HADES RV Programme with HARPS-N at TNG

X. The non-saturated regime of the stellar activity–rotation relationship for M dwarfs^★

¹ INAF – Osservatorio Astronomico di Palermo, Piazza Parlamento 1, 90134 Palermo, Italy
e-mail: esther.gonzalez@inaf.it
² INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
³ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
⁴ INAF – Osservatorio Astronomico di Padua, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁵ INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34143 Trieste, Italy
⁶ Fundación Galileo Galilei-INAF, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja, Tenerife, Spain
⁷ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
⁸ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
⁹ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
¹⁰ Institut de Ciències de l’Espai (IEEC-CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Bellaterra, Spain
¹¹ Dipartimento di Fisica e Astronomia G. Galilei, Università di Padova, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
¹² Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
¹³ INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
¹⁴ Observatoire Astronomique de l’Université de Genève, 1290 Versoix, Switzerland

Received: 5 October 2018
Accepted: 10 February 2019

Abstract

Aims. We extend the relationship between X-ray luminosity (L_x) and rotation period (P_rot) found for main-sequence FGK stars, and test whether it also holds for early M dwarfs, especially in the non-saturated regime (L_x ∝ P_rot⁻²) which corresponds to slow rotators.

Methods. We use the luminosity coronal activity indicator (L_x) of a sample of 78 early M dwarfs with masses in the range from 0.3 to 0.75 M_⊙ from the HArps-N red Dwarf Exoplanet Survey (HADES) radial velocity (RV) programme collected from ROSAT and XMM-Newton. The determination of the rotation periods (P_rot) was done by analysing time series of high-resolution spectroscopy of the Ca II H & K and Hα activity indicators. Our sample principally covers the slow rotation regime with rotation periods from 15 to 60 days.

Results. Our work extends to the low mass regime the observed trend for more massive stars showing a continuous shift of the L_x∕L_bol versus P_rot power law towards longer rotation period values, and includes a more accurate way to determine the value of the rotation period at which the saturation occurs (P_sat) for M dwarf stars.

Conclusions. We conclude that the relations between coronal activity and stellar rotation for FGK stars also hold for early M dwarfs in the non-saturated regime, indicating that the rotation period is sufficient to determine the ratio L_x∕L_bol.