Seismic constraints on rotation of Sun-like star and mass of exoplanet Laurent Gizona,b, Jérome Ballotc,d, Eric Michele, Thorsten Stahna,b, Gérard Vauclairc,d, Hans Bruntte, Pierre-Olivier Quirionf, Othman Benomarg,h, Sylvie Vauclairc,d, Thierry Appourchauxh, Michel Auvergnee, Annie Bagline, Caroline Barbane, Fréderic Baudinh, Michaël Bazoti, Tiago Campantei,j,k, Claude Catalae, William Chaplink, Orlagh Creeveyl,m,n, Sébastien Deheuvelsc,d, Noël Dolezc,d, Yvonne Elsworthk, Rafael Garcíao, Patrick Gaulmep, Stéphane Mathiso, Savita Mathurq, Benoît Mossere, Clara Régulol,m, Ian Roxburghr, David Salabertn, Réza Samadie, Kumiko Satoo, Graham Vernerk,r, Shravan Hanasogea,s, and Katepalli R. Sreenivasant,1 aMax-Planck-Institut für Sonnensystemforschung, 37191 Katlenburg-Lindau, Germany; bInstitut für Astrophysik, Georg-August-Universität Göttingen, 37077 Göttingen, Germany; cInstitut de Recherche en Astrophysique et Planétologie, Centre National de la Recherche Scientifique, 31400 Toulouse, France; dUniversité de Toulouse, Université Paul Sabatier/Observatoire Midi-Pyrénées, 31400 Toulouse, France; eLaboratoire d’Études Spatiales et d’Instrumentation en Astrophysique, Observatoire de Paris, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8109, Université Pierre et Marie Curie, Université Denis Diderot, 92195 Meudon, France; fAgence Spatiale Canadienne, Saint-Hubert, Québec, Canada J3Y 8Y9; gSydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, NSW 2006, Australia; hInstitut d’Astrophysique Spatiale, Université Paris Sud–Centre National de la Recherche Scientifique (Unité Mixte de Recherche 8617), 91405 Orsay Cedex, France; iCentro de Astrofísica da Universidade do Porto, 4150-762 Porto, Portugal; jDanish AsteroSeismology Centre, Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark; kSchool of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom; lDepartamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain; mInstituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain; nLaboratoire Lagrange, Unité Mixte de Recherche 7293, Université de Nice Sophia-Antipolis, Centre National de la Recherche Scientifique, Observatoire de la Côte d’Azur, 06300 Nice, France; oLaboratoire Astrophysique, Instrumentation, et Modélisation, Institut de Recherche sur les Lois Fondamentales de l’Univers/Service d’Astrophysique–Commissariat à l’Energie Atomique/ Direction des Sciences de la Matière–Centre National de la Recherche Scientifique–Université Paris Diderot, 91191 Gif-sur-Yvette Cedex, France; pDepartment of Astronomy, New Mexico State University, Las Cruces, NM 88003-8001; qHigh Altitude Observatory, National Center for Atmospheric Research, Boulder, CO 80307; rAstronomy Unit, School of Physics and Astronomy, Queen Mary University of London, London E1 4NS, United Kingdom; sDepartment of Geosciences, Princeton University, Princeton, NJ 08544; and tPhysics Department and Courant Institute of Mathematical Sciences, New York University, New York, NY 10012 Contributed by Katepalli R. Sreenivasan, February 27, 2013 (sent for review September 26, 2012) ASTRONOMY Rotation is thought to drive cyclic magnetic activity in the Sun and of the space telescope “convection, rotation, and planetary Sun-like stars. Stellar dynamos, however, are poorly understood transits” (CoRoT) (15). This relatively bright star (visual mag- owing to the scarcity of observations of rotation and magnetic nitude, 6.3) was selected as a primary target because it hosts fields in stars. Here, inferences are drawn on the internal rotation a planetary companion, which was detected through the wob- of a distant Sun-like star by studying its global modes of oscillation. bling of the star via the radial velocity method (16–18). With an We report asteroseismic constraints imposed on the rotation rate and effective temperature (4) of 6;100 ± 60 K and an absolute lu- the inclination of the spin axis of the Sun-like star HD 52265, a principal minosity (4) of 2:09 ± 0:24 LSun, HD 52265 is a main-sequence target observed by the CoRoT satellite that is known to host a G0V star. Combining these two values, the stellar radius is de- planetary companion. These seismic inferences are remarkably consis- duced to be 1:30 ± 0:08 R . Isochrone fits (19, 20) give a stellar tent with an independent spectroscopic observation (rotational line Sun mass near 1.2 M with a typical error of 0.05 M and a stellar broadening) and with the observed rotation period of star spots. Sun Sun age between 2.1 and 2.7 Gy. The planetary companion, HD Furthermore, asteroseismology constrains the mass of exoplanet HD 52265b, orbits the star with a period of 119 d, a semimajor axis 52265b. Under the standard assumption that the stellar spin axis and M i = the axis of the planetary orbit coincide, the minimum spectro- of 0.5 astronomical unit (AU), and a minimum mass p sin p : ± : M M scopic mass of the planet can be converted into a true mass of 1 09 0 11 Jupiter, where p is the true mass of the planet and + : : 0 52M ip is the inclination of the orbital axis to the line of sight (18). 1 85−0:42 Jupiter, which implies that it is a planet, not a brown dwarf. HD 52265 is overmetallic with respect to the Sun ð½M=H = extrasolar planets | stellar oscillations | stellar rotation 0:19 ± 0:05Þ, a property that has been associated with the for- mation of hot Jupiters (21). See Table 1 for a summary of pace photometry has made possible high-precision seismol- basic properties. Sogy of Sun-like stars (1–5). Precise measurements of the The power spectrum of the HD 52265 CoRoT data exhibits frequencies of the global modes of acoustic oscillations place a series of peaks near 2 mHz caused by global acoustic oscil- tight constraints on the internal structure of these stars (6). For lations (Fig. 1). As in the Sun and other stars with outer con- example, improved stellar parameters are used to refine the vection zones, these oscillations are continuously excited by near- physics of stellar interiors and find many applications in astro- surface convection (2). The star oscillates in high-overtone modes whose horizontal spatial patterns are given by spherical physics. Accurate determinations of the radii, masses, and ages m harmonics Yl , where l is the harmonic degree and m the azi- of planet-host stars are essential for the characterization of −l ≤ m ≤ l exoplanets detected in transits (7–9). muthal order with . The comb-like structure of the In this paper, we present an unambiguous measurement of power spectrum is due to a repeating sequence of pulsations ðl = Þ ðl = Þ ðl = Þ mean internal rotation (rotation averaged over the entire stellar observable in quadrupole 2 , radial 0 , and dipole 1 l = l = interior) and inclination angle of a Sun-like star by means of modes. The 2and 0 modes are remarkably well resolved in fi asteroseismology. Internal rotation is a fundamental physical frequency space and enable unambiguous identi cation of modes. property of stars: it affects stellar evolution through increased mixing of chemicals and mass loss, and is responsible for mag- Author contributions: L.G. and T.S. designed research; L.G., J.B., E.M., T.S., G. Vauclair, netic activity (10). Our study extends earlier studies of the seis- H.B., P.-O.Q., O.B., S.V., T.A., M.A., A.B., C.B., F.B., M.B., T.C., C.C., W.C., O.C., S.D., N.D., Y.E., mic signature of rotation in α Centauri A (11, 12) and in red R.G., P.G., S. Mathis, S. Mathur, B.M., C.R., I.R., D.S., R.S., K.S., and G. Verner performed giant stars (13, 14). research; and L.G., J.B., E.M., T.S., S.H., and K.R.S. wrote the paper. The star HD 52265 was observed continuously for 117 d be- The authors declare no conflict of interest. tween November 2008 and March 2009 in the asteroseismic field 1To whom correspondence should be addressed. E-mail: [email protected]. www.pnas.org/cgi/doi/10.1073/pnas.1303291110 PNAS Early Edition | 1of5 Downloaded by guest on September 24, 2021 Table 1. Parameters of star HD 52265 A B Parameter Value Method Distance 28.95 ± 0.34 pc Astrometry (43) Luminosity 2.09 ± 0.24 LSun Astrometry (4) Effective temperature 6,100 ± 60 K Spectroscopy (4) Metallicity, [M/H] 0.19 ± 0.05 Spectroscopy (4) Main-sequence lifetime ∼ 6 × 109 y Mass–luminosity relation 16 26 1pc = 3:086 × 10 m; LSun = 3:8 × 10 W. To first order (22), the spectrum of the mode frequencies is specified by two characteristic frequencies (Fig. 1, Inset): the “large-frequency separation,” Δν,andthe“small-frequency sepa- ration,” δν. The large-frequency separation between consecutive Fig. 2. Échelle spectrum and comparison with the Sun. (A) Échelle spectrum l = 0 modes is the inverse of the sound travel time across a stellar of HD 52265 using a folding frequency of 98.5 μHz. The power spectrum is diameter. The small-frequency separation between adjacent l = 2 cut into frequency segments, which are stacked in the vertical direction. l = Integers along the right axis indicate the number of frequency segments, and 0 modes is sensitive to the radial gradient of sound speed starting from zero frequency, i.e., the radial order of the l = 0 modes. The in the nuclear-burning core, and thus to helium content and the nearly vertical ridges of power (labeled according to spherical harmonic age of the star (23). degree l) indicate that the folding frequency is close to the large separation Fig. 2A shows the power spectrum in échelle format (24) of Δν.(B) For comparison and mode identification, we show the échelle spec- HD 52265 using a folding frequency of 98.5 μHz. Modes have trum of the Sun using 117 d of SoHO/VIRGO photometry (25) (green chan- measurable power over 10 consecutive oscillation overtones nel) and a folding frequency of 135.3 μHz.