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|Title:||Detection of solar-like oscillations in the bright red giant stars γ Piscium and θ<SUP>1</SUP> Tauri from a 190-day high-precision spectroscopic multi-site campaign||Authors:||Beck, P. G.
CORSARO, ENRICO MARIA NICOLA
Van Winckel, H.
De Ridder, J.
Pápics, P. I.
Sans Fuentes, S. A.
Schmid, V. S.
Matthews, J. M.
|Issue Date:||2015||Journal:||ASTRONOMY & ASTROPHYSICS||Number:||573||First Page:||A138||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. <BR /> Aims: We search for solar-like oscillations in the two bright red giant stars γ Psc and θ<SUP>1</SUP> Tau from a time series of ground-based spectroscopy and determine the frequency of the excess of oscillation power ν<SUB>max</SUB> and the mean large frequency separation ∆ν for both stars. Seismic constraints on the stellar mass and radius will provide robust input for stellar modelling. <BR /> Methods: The radial velocities of γ Psc and θ<SUP>1</SUP> 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 θ<SUP>1</SUP> Tau with the MOST satellite. <BR /> 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. θ<SUP>1</SUP> 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<SUB>☉</SUB> and 10 R<SUB>☉</SUB>. The object θ<SUP>1</SUP> Tau appears to be a massive star of about 2.7 M<SUB>☉</SUB> and 10 R<SUB>☉</SUB>. The radial velocities of both stars were found to be modulated on timescales much longer than the oscillation periods. <BR /> Conclusions: The estimated radii from seismology are in agreement with interferometric observations and also with estimates based on photometric data. While the mass of θ<SUP>1</SUP> 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. <P />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.||Acknowledgments:||The research leading to these results has received funding from the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007–2013)/ERC grant agreement No. 227224 (PROSPERITY). This research is (partially) funded by the Research Council of the KU Leuven under grant agreement GOA/2013/012. E.K. is supported by Grants-in-Aid for Scientific Research 20540240 from the Japan Society for the Promotion of Science (JSPS). K.Z. receives a Pegasus Marie Curie Fellowship of the Research Foundation Flanders (FWO). M.Y., H.I., and B.S. are supported by Grants-in-Aid for Scientific Research 18340055 from JSPS. J.D.R. and E.C. acknowledge the support of the FWO-Flanders under project O6260 - G.0728.11. T.K. also acknowledges financial support from the Austrian Science Fund (FWF P23608). S.B. is supported by the Foundation for Fundamental Research on Matter (FOM), which is part of the Netherlands Organisation for Scientific Research (NWO). V.S.S. is an aspirant Ph.D. fellow at the Fonds voor Wetenschappelijk Onderzoek (FWO), Vlaanderen. E.M. is a beneficiary of a mobility grant from the Belgian Federal Science Policy Office co-funded by the Marie Curie Actions FP7-PEOPLE-COFUND-2008 n246540 MOBEL GRANT from the European Commission. The ground-based observations are based on spectroscopy made with the Mercator Telescope, operated on the island of La Palma by the Flemish Community, at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. We are grateful to the Geneva Observatory’s technical staff for maintaining the 1.2 m Euler Swiss telescope and the COARALIE spectrograph. We are grateful to all staff members at OAO, National Astronomical Observatory of Japan (NAOJ) for their continuous and various support throughout our project with HIDES. We thank the technical team at Haute-Provence Observatory for their support with the SOPHIE instrument and the 1.93-m OHP telescope. We thank the referee for constructive comments and stimulating discussions.||URI:||http://hdl.handle.net/20.500.12386/23237||URL:||https://www.aanda.org/articles/aa/abs/2015/01/aa23019-13/aa23019-13.html||ISSN:||0004-6361||DOI:||10.1051/0004-6361/201323019||Bibcode ADS:||2015A&A...573A.138B||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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