Bibcode
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
Revista
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