Chromospheric activities and kinematics for solar type dwarfs and subgiants: analysis of the activity distribution and the AVR

Jenkins, J. S.; Murgas, F.; Rojo, P.; Jones, H. R. A.; Day-Jones, A. C.; Jones, M. I.; Clarke, J. R. A.; Ruiz, M. T.; Pinfield, D. J.
Referencia bibliográfica

Astronomy and Astrophysics, Volume 531, id.A8

Fecha de publicación:
7
2011
Número de autores
9
Número de autores del IAC
1
Número de citas
105
Número de citas referidas
97
Descripción
Aims: In this work we present chromospheric activity indices, kinematics, radial-velocities, and rotational velocities for more than 850 FGK-type dwarfs and subgiant stars in the southern hemisphere and test how best to calibrate and measure S-indices from echelle spectra. Methods: We measured our parameters using the high-resolution and high-S/N FEROS echelle spectra acquired for this purpose. Results: We confirm the bimodal distribution of chromospheric activities for such stars and highlight the role that the more active K-dwarfs play in biasing the number of active stars. We show that the age-activity relationship does appear to continue to ages older than the Sun if we simply compare main sequence stars and subgiant stars with an offset of around 2.5 Gyr between the peaks of both distributions. Also we show evidence of an increased spin-down timescale for cool K dwarfs compared with earlier F and G type stars. We highlight that activities drawn from low-resolution spectra (R < 2500) significantly increase the rms scatter when calibrating onto common systems of measurements like the Mt. Wilson system. Also we show that older and widely used catalogues of activities in the south appear to be offset compared to more recent works at the 0.1 dex level in log R'HK through calibrator drift. In addition, we show how kinematics can be used to preselect inactive stars for future planet search projects. We see the well known trend between projected rotational velocity and activity, however we also find a correlation between kinematic space velocity and chromospheric activity. It appears that after the Vaughan-Preston gap there is a quick step function in the kinematic space motion towards a significantly broader spread in velocities. We speculate on reasons for this correlation and provide some model scenarios to describe the bimodal activity distribution through magnetic saturation, residual low level gas accretion, or accretion by the star of planets or planetesimals. Finally, we provide a new empirical measurement for the disk-heating law, using the latest age-activity relationships to reconstruct the age-velocity distribution for local disk stars. We find a value of 0.337 ± 0.045 for the exponent of this power law (i.e. σtot ∝ t0.337), in excellent agreement with those found using isochrone fitting methods and with theoretical disk-heating models. Based on observations made with the ESO telescopes at the La Silla Paranal observatory under programme ID's 076.C-0578(B), 077.C-0192(A), 082.C-0446(A) and 082.C-0446(B).Full Table 4 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A8