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Seismic constraints on rotation of Sun-like star and mass of exoplanet.

Author/s: Gizon, L.; Ballot, J.; Michel, E.; Stahn, T.; Vauclair, G.; Bruntt, H.; Quirion, P.-O.; Benomar, O.; Vauclair, S.; Appourchaux, T.; Auvergne, M.; Baglin, A.; Barban, C.; Baudin, F.; Bazot, M.; Campante, T.; Catala, C.; Chaplin, W.; Creevey, O.; Deheuvels, S.; Dolez, N.; Elsworth, Y.; Garcia, R.; Gaulme, P.; Mathis, S.; Mathur, S.; Mosser, B.; Regulo, C.; Roxburgh, I.; Salabert, D.; Samadi, R.; Sato, K.; Verner, G.; Hanasoge, S.; Sreenivasan, K. R.

Reference: Proceedings of the National Academy of Sciences, vol. 110, issue 33, pp. 13267-13271

Constraints on stellar rotation and planet mass. The dark-red and light-red regions are the 1-σ and 2- σ seismic constraints on stellar rotation in the plane (Ω <em>/</em> Ω<sub>Sun</sub>) - (sin <em>i</em>), where Ω is the bulk angular velocity, Ω<sub>Sun</sub> <em>/</em> 2 π= 0.424 μHz is the solar Carrington angular velocity, and <em>i</em> is the inclination of the stellar rotation axis to the line of sight. The black diamond with error bars gives the best-fit seismic values, Ω <em>/</em> Ω<sub>Sun</sub> = 2<em>.</em>31<sup>+0<em>.</em>45</sup><em><sub>-</sub></em><sub>0<em>.</em>69</sub> and sin <em>i</em> = 0<em>.</em>59<sup>+0<em>.</em>19</sup><em><sub>-</sub></em><sub>0<em>.</em>14</sub>. For comparison, the two horizontal green lines mark the angular velocity of stellar activity (starspots) deduced from two prominent peaks in the low-frequency part of the power spectrum. The filled green ellipse represents the 1- σ bound of the equatorial rotation and inclination angle obtained from starspot modeling of the photometric time series. The spectroscopic constraints are given by the dashed (observations) and the solid (1- σ errors) blue curves, as expressed through the sky-projected angular velocity Ωsin <em>i</em> = (<em>v</em> sin <em>i</em>)<em>/R</em>, where <em>v</em> sin <em>i</em> = 3<em>.</em>6<sup>+0<em>.</em>3</sup><em><sub>-</sub></em><sub>1<em>.</em>0</sub> km/s is the observed spectroscopic rotational broadening and <em>R</em> = 1<em>.</em>34 <em>R</em><sub>Sun</sub> is the seismic stellar radius. The minimum mass of the planet from radial velocity measurements is <em>M</em>p sin <em>i</em><sub>p</sub> = (1<em>.</em>09 ±0<em>.</em>11) <em>M</em><sub>Jupiter</sub>, where <em>i</em><sub>p</sub> is the inclination of the normal of the planetary orbit to the line of sight. Assuming <em>i</em><sub>p</sub> = <em>i</em>, the seismic constraint on sin <em>i</em> can be converted into a constraint (top axis and gray region 'HD 52265b') on the true mass of the planet, <em>Mp</em>, which is well below the brown dwarf limit of 13<em>M</em><sub>Jupiter</sub>.
Constraints on stellar rotation and planet mass. The dark-red and light-red regions are the 1-σ and 2- σ seismic constraints on stellar rotation in the plane (Ω / ΩSun) - (sin i), where Ω is the bulk angular velocity, ΩSun / 2 π= 0.424 μHz is the solar Carrington angular velocity, and i is the inclination of the stellar rotation axis to the line of sight. The black diamond with error bars gives the best-fit seismic values, Ω / ΩSun = 2.31+0.45-0.69 and sin i = 0.59+0.19-0.14. For comparison, the two horizontal green lines mark the angular velocity of stellar activity (starspots) deduced from two prominent peaks in the low-frequency part of the power spectrum. The filled green ellipse represents the 1- σ bound of the equatorial rotation and inclination angle obtained from starspot modeling of the photometric time series. The spectroscopic constraints are given by the dashed (observations) and the solid (1- σ errors) blue curves, as expressed through the sky-projected angular velocity Ωsin i = (v sin i)/R, where v sin i = 3.6+0.3-1.0 km/s is the observed spectroscopic rotational broadening and R = 1.34 RSun is the seismic stellar radius. The minimum mass of the planet from radial velocity measurements is Mp sin ip = (1.09 ±0.11) MJupiter, where ip is the inclination of the normal of the planetary orbit to the line of sight. Assuming ip = i, the seismic constraint on sin i can be converted into a constraint (top axis and gray region 'HD 52265b') on the true mass of the planet, Mp, which is well below the brown dwarf limit of 13MJupiter.

Rotation is thought to drive cyclic magnetic activity in the Sun and Sun-like stars. Stellar dynamos, however, are poorly understood owing to the scarcity of observations of rotation and magnetic fields in stars. Here, inferences are drawn on the internal rotation of a distant Sun-like star by studying its global modes of oscillation. We report asteroseismic constraints imposed on the rotation rate and the inclination of the spin axis of the Sun-like star HD52265, a CoRoT prime target known to host a planetary companion. These seismic inferences are remarkably consistent with an independent spectroscopic observation (rotational line broadening) and with the observed rotation period of starspots. Further, asteroseismology constrains the mass of exoplanet HD52265b. Under the standard assumption that the stellar spin axis and the axis of the planetary orbit coincide, the minimum spectroscopic mass of the planet can be converted into a true mass of 1.85 +0.52- 0.42MJupiter which implies that it is a planet, not a brown dwarf.

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