The Solar Twin Planet Search

I. Fundamental parameters of the stellar sample^⋆

¹ McDonald Observatory and Department of Astronomy, University of Texas at Austin, 2515 Speedway, Stop C1402, Austin, Texas 78712-1206, USA
e-mail: ivan@astro.as.utexas.edu
² Departamento de Astronomia do IAG/USP, Rua do Matão, 1226 Cidade Universitária São Paulo-SP, Brasil
³ Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Ave, Chicago, IL 60637, USA
⁴ Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, The Australian National University, Canberra, Australia
⁵ Institut für Astrophysik, University of Göttingen, Wilhelmsplatz 1, 37073 Göttingen, Germany
⁶ Steward Observatory, Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Rm. N204, Tucson, AZ 85721-0065, USA
⁷ Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015-1305, USA
⁸ The Observatories of the Carnegie Institution For Science, Pasadena, California, CA91101, USA
⁹ Instituto de Fisica, Universidade Federal do Rio Grande do Sul, 91501-970 Porto Alegre, RS, Brazil
¹⁰ Ebenböckstraße 4, 81241 München, Germany

Received: 21 May 2014
Accepted: 12 August 2014

Abstract

Context. We are carrying out a search for planets around a sample of solar twin stars using the HARPS spectrograph. The goal of this project is to exploit the advantage offered by solar twins to obtain chemical abundances of unmatched precision. This survey will enable new studies of the stellar composition – planet connection.

Aims. We determine the fundamental parameters of the 88 solar twin stars that have been chosen as targets for our experiment.

Methods. We used the MIKE spectrograph on the Magellan Clay Telescope to acquire high resolution, high signal-to-noise ratio spectra of our sample stars. We measured the equivalent widths of iron lines and used strict differential excitation/ionization balance analysis to determine atmospheric parameters of unprecedented internal precision: σ(T_eff) = 7 K, σ(log g) = 0.019, σ( [Fe/H] ) = 0.006 dex, σ(v_t) = 0.016 km s^-1. Reliable relative ages and highly precise masses were then estimated using theoretical isochrones.

Results. The spectroscopic parameters we derived are in good agreement with those measured using other independent techniques. There is even better agreement if the sample is restricted to those stars with the most internally precise determinations of stellar parameters in every technique involved. The root-mean-square scatter of the differences seen is fully compatible with the observational errors, demonstrating, as assumed thus far, that systematic uncertainties in the stellar parameters are negligible in the study of solar twins. We find a tight activity-age relation for our sample stars, which validates the internal precision of our dating method. Furthermore, we find that the solar cycle is perfectly consistent both with this trend and its star-to-star scatter.

Conclusions. We present the largest sample of solar twins analyzed homogeneously using high quality spectra. The fundamental parameters derived from this work will be employed in subsequent work that aims to explore the connections between planet formation and stellar chemical composition.