Bibcode
Maldonado, J.; Scandariato, G.; Stelzer, B.; Biazzo, K.; Lanza, A. F.; Maggio, A.; Micela, G.; González-Álvarez, E.; Affer, L.; Claudi, R. U.; Cosentino, R.; Damasso, M.; Desidera, S.; González Hernández, J. I.; Gratton, R.; Leto, G.; Messina, S.; Molinari, E.; Pagano, I.; Perger, M.; Piotto, G.; Rebolo, R.; Ribas, I.; Sozzetti, A.; Suárez Mascareño, A.; Zanmar Sanchez, R.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 598, id.A27, 19 pp.
Fecha de publicación:
1
2017
Revista
Número de citas
36
Número de citas referidas
33
Descripción
Context. Understanding stellar activity in M dwarfs is crucial for the
physics of stellar atmospheres and for ongoing radial velocity exoplanet
programmes. Despite the increasing interest in M dwarfs, our knowledge
of the chromospheres of these stars is far from being complete.
Aims: We test whether the relations between activity, rotation, and
stellar parameters and flux-flux relationships previously investigated
for main-sequence FGK stars and for pre-main-sequence M stars also hold
for early-M dwarfs on the main-sequence. Although several attempts have
been made so far, here we analyse a large sample of stars undergoing
relatively low activity. Methods: We analyse in a homogeneous and
coherent way a well-defined sample of 71 late-K/early-M dwarfs that are
currently being observed in the framework of the HArps-N red Dwarf
Exoplanet Survey (HADES). Rotational velocities are derived using the
cross-correlation technique, while emission flux excesses in the Ca ii H
& K and Balmer lines from Hα up to Hɛ are obtained by
using the spectral subtraction technique. The relationships between the
emission excesses and the stellar parameters (projected rotational
velocity, effective temperature, kinematics, and age) are studied.
Relations between pairs of fluxes of different chromospheric lines
(flux-flux relationships) are also studied and compared with the
literature results for other samples of stars. Results: We find
that the strength of the chromospheric emission in the Ca ii H & K
and Balmer lines is roughly constant for stars in the M0-M3 spectral
range. Although our sample is likely to be biased towards inactive
stars, our data suggest that a moderate but significant correlation
between activity and rotation might be present, as well as a hint of
kinematically selected young stars showing higher levels of emission in
the calcium line and in most of the Balmer lines. We find our sample of
M dwarfs to be complementary in terms of chromospheric and X-ray fluxes
with those of the literature, extending the analysis of the flux-flux
relationships to the very low flux domain. Conclusions: Our
results agree with previous works suggesting that the
activity-rotation-age relationship known to hold for solar-type stars
also applies to early-M dwarfs. We also confirm previous findings that
the field stars which deviate from the bulk of the empirical flux-flux
relationships show evidence of youth.
Based on observations made with the Italian Telescopio Nazionale Galileo
(TNG), operated on the island of La Palma by the Fundación
Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the
Spanish Observatorio del Roque de los Muchachos of the Instituto de
Astrofísica de Canarias.