Chromospheric Activities and Kinematics for Solar Type Dwarfs and Subgiants: Analysis of the Activity Distribution and the AVR

TL;DR

This study analyzes chromospheric activity, kinematics, and rotation in over 850 FGK stars, revealing bimodal activity distribution, age-activity relations, and correlations with kinematic properties, with implications for stellar evolution and planet searches.

Contribution

It provides new calibrations for S-indices, confirms the bimodal activity distribution, and links kinematic behavior with stellar activity and age, enhancing understanding of stellar magnetic evolution.

Findings

Bimodal distribution of chromospheric activity confirmed.

Age-activity relationship persists beyond solar age with a 2.5 Gyr offset.

Kinematic velocity correlates with chromospheric activity.

Abstract

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. 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 Gyrs between the peaks of both distributions. Also we show evidence for an increased spin-down timescale for cool K dwarfs compared with earlier F and G type stars. 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 larger 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. sigma_tot proportional to t^0.337), in excellent agreement with those found using isochrone fitting methods and with theoretical disk heating models. [Abridged]