WASP-50 b: A hot Jupiter transiting a moderately active solar-type star

We report the discovery by the WASP transit survey of a giant planet in a close orbit (0.0295 +/- 0.0009 AU) around a moderately bright (V = 11.6, K = 10) G9 dwarf (0.89 +/- 0.08 M(circle dot), 0.84 +/- 0.03 R(circle dot)) in the Southern constellation Eridanus. Thanks to high-precision follow-up photometry and spectroscopy obtained by the telescopes TRAPPIST and Euler, the mass and size of this planet, WASP-50 b, are well constrained to 1.47 +/- 0.09 M(Jup) and 1.15 +/- 0.05 R(Jup), respectively. The transit ephemeris is 2 455 558.6120 (+/- 0.0002) + N x 1.955096 (+/- 0.000005) HJD(UTC). The size of the planet is consistent with basic models of irradiated giant planets. The chromospheric activity (log R'(HK) = -4.67) and rotational period (P(rot) = 16.3 +/- 0.5 days) of the host star suggest an age of 0.8 +/- 0.4 Gy that is discrepant with a stellar-evolution estimate based on the measured stellar parameters (p(*) = 1.48 +/- 0.10 rho(circle dot), T(eff) = 5400 +/- 100 K, [Fe/H] = -0.12 +/- 0.08) which favors an age of 7 +/- 3.5 Gy. This discrepancy could be explained by the tidal and magnetic influence of the planet on the star, in good agreement with the observations that stars hosting hot Jupiters tend to show faster rotation and magnetic activity. We measure a stellar inclination of 84(-31)(+6) deg, disfavoring a high stellar obliquity. Thanks to its large irradiation and the relatively small size of its host star, WASP-50 b is a good target for occultation spectrophotometry, making it able to constrain the relationship between hot Jupiters' atmospheric thermal profiles and the chromospheric activity of their host stars.

[1]  L. Hebb,et al.  Improved parameters for the transiting hot Jupiters WASP-4b and WASP-5b , 2008, 0812.1998.

[2]  R. G. West,et al.  Efficient identification of exoplanetary transit candidates from SuperWASP light curves , 2007, 0707.0417.

[3]  Shih-Hsin Chang,et al.  TIDAL AND MAGNETIC INTERACTIONS BETWEEN A HOT JUPITER AND ITS HOST STAR IN THE MAGNETOSPHERIC CAVITY OF A PROTOPLANETARY DISK , 2009, 0911.4532.

[4]  S. Baliunas,et al.  No Planet for Hd 166435 , 2022 .

[5]  A. Claret,et al.  A new non-linear limb-darkening law for LTE stellar atmosphere models III - Sloan filters: Calculations for –5.0 ≤ log [M/H] ≤ +1, 2000 K ≤ T$\mathsf{_{eff}}$ ≤ 50 000 K at several surface gravities , 2004 .

[6]  William H. Press,et al.  Book-Review - Numerical Recipes in Pascal - the Art of Scientific Computing , 1989 .

[7]  A. Cox,et al.  Allen's astrophysical quantities , 2000 .

[8]  Sara Seager,et al.  Exoplanet Atmospheres: Physical Processes , 2010 .

[9]  Sofia Randich,et al.  Time scales of Li evolution: A Homogeneous analysis of open clusters from ZAMS to late-MS , 2005 .

[10]  J. Wright,et al.  Radial velocity jitter in stars from the california and carnegie planet search at keck observatory , 2005 .

[11]  Nikole K. Lewis,et al.  WARM SPITZER PHOTOMETRY OF THE TRANSITING EXOPLANETS CoRoT-1 AND CoRoT-2 AT SECONDARY ECLIPSE , 2010, 1011.1019.

[12]  P. Stetson.  DAOPHOT: A COMPUTER PROGRAM FOR CROWDED-FIELD STELLAR PHOTOMETRY , 1987 .

[13]  R. Scuflaire,et al.  CLÉS, Code Liégeois d’Évolution Stellaire , 2007, 0712.3471.

[14]  C. Moutou,et al.  Transiting exoplanets from the CoRoT space mission XIII. CoRoT-13b: a dense hot Jupiter in transit around a star with solar metallicity and super-solar lithium content , 2010, 1007.5481.

[15]  S. Barnes.  Accepted for publication in The Astrophysical Journal Ages for illustrative field stars using gyrochronology: viability, limitations and errors , 2022 .

[16]  A. Collier Cameron,et al.  A fast hybrid algorithm for exoplanetary transit searches , 2006, astro-ph/0609418.

[17]  Eike W. Guenther,et al.  HD15082b, a short-period planet orbiting an A-star , 2011 .

[18]  C. Moutou,et al.  Transiting exoplanets from the CoRoT space mission. XII. CoRoT-12b: a short-period low-density planet transiting a solar analog star , 2010, 1007.2497.

[19]  Frederic Pont,et al.  Empirical evidence for tidal evolution in transiting planetary systems , 2008, 0812.1463.

[20]  V. S. Dhillon,et al.  Estimating the masses of extra-solar planets , 2010, 1006.2069.

[21]  A. Collier Cameron,et al.  The thermal emission of the young and massive planet CoRoT-2b at 4.5 and 8 μm , 2009, 0911.5087.

[22]  John Asher Johnson,et al.  HOT STARS WITH HOT JUPITERS HAVE HIGH OBLIQUITIES , 2010, 1006.4161.

[23]  Drake Deming,et al.  SYSTEM PARAMETERS, TRANSIT TIMES, AND SECONDARY ECLIPSE CONSTRAINTS OF THE EXOPLANET SYSTEMS HAT-P-4, TrES-2, TrES-3, and WASP-3 FROM THE NASA EPOXI MISSION OF OPPORTUNITY , 2010, 1011.2229.

[24]  A. F. Lanza,et al.  Hot Jupiters and the evolution of stellar angular momentum , 2009, Proceedings of the International Astronomical Union.

[25]  A. Gimenez,et al.  Accurate masses and radii of normal stars: modern results and applications , 2009, 0908.2624.

[26]  R. G. West,et al.  WASP-12b: THE HOTTEST TRANSITING EXTRASOLAR PLANET YET DISCOVERED , 2008, 0812.3240.

[27]  Observatoire de Geneve,et al.  VLT transit and occultation photometry for the bloated planet CoRoT-1b , 2009, 0905.4571.

[28]  D. Rubin,et al.  Inference from Iterative Simulation Using Multiple Sequences , 1992 .

[29]  A. Collier Cameron,et al.  An improved method for estimating the masses of stars with transiting planets , 2010, 1004.1991.

[30]  D. F. Gray,et al.  The Observation and Analysis of Stellar Photospheres , 2021 .

[31]  I. Hubeny,et al.  Theoretical Spectra and Light Curves of Close-in Extrasolar Giant Planets and Comparison with Data , 2007, 0709.4080.

[32]  E. Agol,et al.  Analytic Light Curves for Planetary Transit Searches , 2002, astro-ph/0210099.

[33]  Mark S. Marley,et al.  Planetary Radii across Five Orders of Magnitude in Mass and Stellar Insolation: Application to Transits , 2006 .

[34]  Joshua N. Winn,et al.  THE TRANSIT LIGHT-CURVE PROJECT. XIV. CONFIRMATION OF ANOMALOUS RADII FOR THE EXOPLANETS TrES-4b, HAT-P-3b, AND WASP-12b , 2011, 1103.3078.

[35]  Howard Isaacson,et al.  A CORRELATION BETWEEN STELLAR ACTIVITY AND HOT JUPITER EMISSION SPECTRA , 2010, 1004.2702.

[36]  John Southworth,et al.  Homogeneous studies of transiting extrasolar planets – IV. Thirty systems with space-based light curves , 2011, 1107.1235.

[37]  Michel Mayor,et al.  ELODIE: A spectrograph for accurate radial velocity measurements , 1996 .

[38]  David Charbonneau,et al.  The transit light curve project. I. Four consecutive transits of the exoplanet XO-1b , 2006 .

[39]  Joel D. Hartman,et al.  A CORRELATION BETWEEN STELLAR ACTIVITY AND THE SURFACE GRAVITY OF HOT JUPITERS , 2010, 1004.4252.

[40]  S. Seager,et al.  Exoplanet Atmospheres , 2010 .