Detection of solar-like oscillations in the bright red giant stars γ Piscium and θ1 Tauri from a 190-day high-precision spectroscopic multi-site campaign

Author(s): P. G. Beck, E. Kambe, M. Hillen, E. Corsaro, H. Van Winckel, E. Moravveji, J. De Ridder, S. Bloemen, S. Saesen, P. Mathias, P. Degroote, T. Kallinger, T. Verhoelst, H. Ando, F. Carrier, B. Acke, R. Oreiro, A. Miglio, P. Eggenberger, B. Sato, K. Zwintz, P. I. Pápics, P. Marcos-Arenal, S. A. Sans Fuentes, V. S. Schmid, C. Waelkens, R. Østensen, J. M. Matthews, M. Yoshida, H. Izumiura, H. Koyano, S. Nagayama, Y. Shimizu, N. Okada, K. Okita, A. Sakamoto, T. Yamamuro, C. Aerts
Abstract: Context: Red giants are evolved stars that exhibit solar-like oscillations. Although a multitude of stars have been observed with space telescopes, only a handful of red giant stars were targets of spectroscopic asteroseismic observing projects. Aims: We search for solar-like oscillations in the two bright red giant stars γ Psc and θ¹ Tau from a time series of ground-based spectroscopy and determine the frequency of the excess of oscillation power νmax and the mean large frequency separation Δν for both stars. Seismic constraints on the stellar mass and radius will provide robust input for stellar modelling. Methods: The radial velocities of γ Psc and θ¹ Tau were monitored for 120 and 190 days, respectively. Nearly 9000 spectra were obtained. To reach accurate radial velocities, we used simultaneous thorium-argon and iodine-cell calibration of our optical spectra. In addition to the spectroscopy, we acquired interferometric observations of γ Psc for an independent estimate of the radius. We also analysed 22 days of observations of θ¹ Tau with the MOST satellite. Results: The frequency analysis of the radial velocity data of γ Psc revealed an excess of oscillation power around 32 μHz and a large frequency separation of 4.1 ± 0.1 μHz. θ¹ Tau exhibits oscillation power around 90 μHz, with a large frequency separation of 6.9 ± 0.2 μHz. Scaling relations indicate that γ Psc is a star of about 1 M_⊙ and 10 R_⊙. The object θ¹ Tau appears to be a massive star of about 2.7 M_⊙ and 10 R_⊙. The radial velocities of both stars were found to be modulated on timescales much longer than the oscillation periods. Conclusions: The estimated radii from seismology are in agreement with interferometric observations and also with estimates based on photometric data. While the mass of θ¹ Tau is in agreement with results from dynamical parallaxes, we find a lower mass for γ Psc than is found in the literature. The long periodic variability agrees with the expected timescales of rotational modulation.Based on observations made with the HERMES spectrograph mounted on the 1.2 m Mercator Telescope at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofsica de Canarias; the CORALIE spectrograph mounted on the 1.2 m Swiss telescope at La Silla Observatory, the HIDES spectrograph, mounted on the 1.9 m telescope at Okayama Astrophysical Observatory, NAOJ, the MOST space telescope, and and observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 086.D-0101.
Organisation(s): Department of Astrophysics
External organisation(s): Katholieke Universiteit Leuven, National Astronomical Observatory of Japan, Radboud University, Université de Genève, Université Toulouse-I-Capitole, Royal Belgian Institute for Space Aeronomy, Instituto de Astrofísica de Andalucía (CSIC), University of Birmingham, Tokyo Institute of Technology (TIT), University of British Columbia (UBC), Hiroshima University, OptCraft
Journal: Astronomy & Astrophysics
Volume: 573
No. of pages: 15
ISSN: 0004-6361
DOI: https://doi.org/10.1051/0004-6361/201323019
Publication date: 01-2015
Peer reviewed: Yes
Austrian Fields of Science 2012: 103003 Astronomy, 103004 Astrophysics
Keywords
ASJC Scopus subject areas: Astronomy and Astrophysics, Space and Planetary Science
Portal url: https://ucrisportal.univie.ac.at/en/publications/detection-of-solarlike-oscillations-in-the-bright-red-giant-stars--piscium-and-1-tauri-from-a-190day-highprecision-spectroscopic-multisite-campaign(b20cd679-cea0-4bde-a68a-2d62a001f6de).html

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