Work

Magnetic Activity–related Radial Velocity Variations in Cool Stars: First Results from the Lick Extrasolar Planet Survey

Year: 1998

Type: article

Abstract: The discovery of the radial velocity ( v r ) signatures of planets around several solar-like stars highlights the importance of exploring the sources of v r variations intrinsic to the stars themselves. We study the stars in the Lick planetary survey for v r variations related to stellar activity: the rotation of starspots and convective inhomogeneities and their temporal evolution. We study the relationships between the weighted v r dispersion, σ' v (which has first been corrected for the orbital contribution from known planets and the mean internal error), and spectral type, rotation, and activity (as measured by Ca II H and K). We find that the largest σ' v values occur among both the coolest (dMe) and the warmest (active F) stars. Values of σ' v increase with H and K emission and scale proportional to v sin i in G and K stars and proportional to ( v sin i ) 1.3 in F stars. For a G star with v sin i ≈ 8-10 km s −1 (age ~0.3 Gyr), for example, 20 m s −1 ≲ σ' v ≲ 45 m s −1 , roughly consistent with the predicted σ' v levels due to magnetic activity (Saar & Donahue). All the stars with proposed planetary companions show σ' v values typical for their spectral type, activity, and/or rotation. However, before the planetary v r perturbations are removed, these stars show significantly enhanced σ' v values. We develop a simple model that can predict the σ' v expected for a given star (within ≈ 40%) as a function of v sin i , spectral type, photometric variability, and macroturbulent velocity. The implications for extrasolar planet searches are discussed.

Source: The Astrophysical Journal

DOI: 10.1086/311325

Authors: Steven H. Saar, R. Paul Butler, Geoffrey W. Marcy

Institutions: Center for Astrophysics Harvard & Smithsonian, Australian Astronomical Observatory, San Francisco State University, University of California, Berkeley

Language: English

Topic: Stellar, planetary, and galactic studies

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: bronze

Funders: National Science Foundation, National Aeronautics and Space Administration

Awards: Detecting Extra-Solar Planets: Crossing the Jupiter Threshold, The Strength, Distribution and Generation of Magnetic Flux on Cool Stars