Estimating the p-mode frequencies of the solar twin 18 Scorpii^⋆,⋆⋆

¹ Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
e-mail: bazot@astro.up.pt
² School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
³ Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse UPS-OMP/CNRS, 14 Av. Édouard Belin, 31400 Toulouse, France
⁴ Sydney Institute for Astronomy, School of Physics, University of Sydney NSW 2006, Australia
⁵ Observatoire de Genève, 51 chemin des Maillettes, 1290 Sauverny, Switzerland
⁶ VUC Aarhus, Ingerslevs Boulevard 3, 8100 Aarhus C., Denmark
⁷ Depart. de Física Teórica e Experimental, Univers. Federal do Rio Grande do Norte, 59072-970 Natal, R.N., Brazil
⁸ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
⁹ Departamento de Física e Astronomia, Faculdade de Ciencias, Universidade do Porto, Porto, Portugal

Received: 28 August 2011
Accepted: 20 May 2012

Abstract

Solar twins have been a focus of attention for more than a decade, because their structure is extremely close to that of the Sun. Today, thanks to high-precision spectrometers, it is possible to use asteroseismology to probe their interiors. Our goal is to use time series obtained from the HARPS spectrometer to extract the oscillation frequencies of 18 Sco, the brightest solar twin. We used the tools of spectral analysis to estimate these quantities. We estimate 52 frequencies using an MCMC algorithm. After examination of their probability densities and comparison with results from direct MAP optimization, we obtain a minimal set of 21 reliable modes. The identification of each pulsation mode is straightforwardly accomplished by comparing to the well-established solar pulsation modes. We also derived some basic seismic indicators using these values. These results offer a good basis to start a detailed seismic analysis of 18 Sco using stellar models.