• DOI:10.1086/304392
• Corpus ID: 17628232

Activity-Related Radial Velocity Variation in Cool Stars

@article{Saar1997ActivityRelatedRV,
  title={Activity-Related Radial Velocity Variation in Cool Stars},
  author={Steven H. Saar and Robert A. Donahue},
  journal={The Astrophysical Journal},
  year={1997},
  volume={485},
  pages={319-327}
}

• S. Saar, R. Donahue
• Published 10 August 1997
• Physics, Geology
• The Astrophysical Journal

Planets have been detected orbiting several solar-type stars with the use of high-precision radial velocity (vr) measurements. While changes in vr can be measured with an accuracy of a few meters per second, there has been relatively little study of how other astrophysical processes, such as magnetic activity, may affect the observed velocities. In this paper, we use published data and simple models to explore the contributions to vr from two activity-related sources, starspots and convective inhomogeneities, as these features rotate across the disk and evolve in time. Radial velocity perturbations due to both of these sources increase with rotation and the level of surface activity. Our models indicate that for solar-age G stars, the amplitude of perturbations due to spots is AS 5 m s-1, increasing to AS ~ 30-50 m s-1 for Hyades-age G stars. If fS is the starspot area coverage, we find that A -->Sf -->0.9S v sin i. The effects of convective inhomogeneities (as observed in line bisector variations) appear to depend on both rotation and spectral type. Young (active) F and G dwarfs can have convective vr perturbations with amplitudes AC 50 m s-1, while vr amplitudes are reduced for stars with lower v sin i and cooler Teff. We show that vr data from the literature display similar trends with v sin i and Teff. AS and AC will be strongest at or near timescales related to magnetic activity variations: rotation, active region growth and decay, and activity cycles. Thus, knowledge of these timescales and typical AS and AC values are important in searching for extrasolar planets, especially those around younger, more active stars or those with small vr reflex amplitudes (i.e., 20 m s-1). We discuss implications of our results for current planet detections and planet search strategies.