THE GJ1214 SUPER-EARTH SYSTEM: STELLAR VARIABILITY, NEW TRANSITS, AND A SEARCH FOR ADDITIONAL PLANETS

The super-Earth GJ1214b transits a nearby M dwarf that exhibits a 1% intrinsic variability in the near-infrared. Here, we analyze new observations to refine the physical properties of both the star and planet. We present three years of out-of-transit photometric monitoring of the stellar host GJ1214 from the MEarth Observatory and find the rotation period to be long, most likely an integer multiple of 53 days, suggesting low levels of magnetic activity and an old age for the system. We show that such variability will not pose significant problems to ongoing studies of the planet's atmosphere with transmission spectroscopy. We analyze two high-precision transit light curves from ESO's Very Large Telescope (VLT) along with seven others from the MEarth and Fred Lawrence Whipple Observatory 1.2 m telescopes, finding physical parameters for the planet that are consistent with previous work. The VLT light curves show tentative evidence for spot occultations during transit. Using two years of MEarth light curves, we place limits on additional transiting planets around GJ1214 with periods out to the habitable zone of the system. We also improve upon the previous photographic V-band estimate for the star, finding V = 14.71 ± 0.03.

[1]  Portugal,et al.  Accurate Spitzer infrared radius measurement for the hot Neptune GJ 436b , 2007, 0707.2261.

[2]  N. Lomb.  Least-squares frequency analysis of unequally spaced data , 1976 .

[3]  S. Zucker,et al.  Reassessing the radial-velocity evidence for planets around CoRoT-7 , 2010, 1008.3859.

[4]  J. Scargle.  Studies in astronomical time series analysis. II - Statistical aspects of spectral analysis of unevenly spaced data , 1982 .

[5]  Jacob L. Bean,et al.  A ground-based transmission spectrum of the super-Earth exoplanet GJ 1214b , 2010, Nature.

[6]  J. Almenara,et al.  A cool starspot or a second transiting planet in the TrES-1 system? , 2008, 0812.1799.

[7]  John Asher Johnson,et al.  Giant Planet Occurrence in the Stellar Mass-Metallicity Plane , 2010, 1005.3084.

[8]  G. Kov'acs,et al.  A box-fitting algorithm in the search for periodic transits , 2002, astro-ph/0206099.

[9]  B. Jackson,et al.  RECENT TRANSITS OF THE SUPER-EARTH EXOPLANET GJ 1214b , 2010, 1008.1748.

[10]  E. Falco,et al.  ON THE ANGULAR MOMENTUM EVOLUTION OF FULLY CONVECTIVE STARS: ROTATION PERIODS FOR FIELD M-DWARFS FROM THE MEarth TRANSIT SURVEY , 2010, 1011.4909.

[11]  G. Laughlin,et al.  Discovery and Characterization of Transiting Super Earths Using an All-Sky Transit Survey and Follow-up by the James Webb Space Telescope , 2009, 0903.4880.

[12]  D. Sasselov,et al.  MOST Space-based Photometry of the Transiting Exoplanet System HD 189733: Precise Timing Measurements for Transits across an Active Star , 2008, 0802.2722.

[13]  A. P. Hatzes,et al.  Transit mapping of a starspot on CoRoT-2. Probing a stellar surface with planetary transits , 2009, 0906.4140.

[14]  M. Shara,et al.  A Catalog of Northern Stars with Annual Proper Motions Larger than 0.15 Seconds of Arc (lspm Catalog -north) , 2004 .

[15]  G. Marcy,et al.  ROTATION AND MAGNETIC ACTIVITY IN A SAMPLE OF M-DWARFS , 2010 .

[16]  J. Valenti,et al.  The Planet-Metallicity Correlation , 2005 .

[17]  Joshua N. Winn,et al.  THE ROTATION PERIOD OF THE PLANET-HOSTING STAR HD 189733 , 2007, 0709.2142.

[18]  M. Skrutskie,et al.  The Two Micron All Sky Survey (2MASS) , 2006 .

[19]  K. F. Huber,et al.  How stellar activity affects the size estimates of extrasolar planets , 2009, 0906.3604.

[20]  B. Scott Gaudi,et al.  Achieving Better Than 1 Minute Accuracy in the Heliocentric and Barycentric Julian Dates , 2010, 1005.4415.

[21]  Frederic Pont,et al.  The effect of red noise on planetary transit detection , 2006, astro-ph/0608597.

[22]  Gino Tosti,et al.  Fermi Gamma-ray Space Telescope Observations of the Gamma-ray Outburst from 3C454.3 in November 2010 , 2011 .

[23]  K. Huber,et al.  Planetary eclipse mapping of CoRoT-2a - Evolution, differential rotation, and spot migration , 2010, 1002.4113.

[24]  S. Seager,et al.  Ocean Planet or Thick Atmosphere: On the Mass-Radius Relationship for Solid Exoplanets with Massive Atmospheres , 2007, 0710.4941.

[25]  G. Hebrard,et al.  Transit spectrophotometry of the exoplanet HD189733b. I. Searching for water but finding haze with HST NICMOS , 2009, 0907.4991.

[26]  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 .

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

[28]  E. Guinan,et al.  ABSOLUTE PROPERTIES OF THE LOW-MASS ECLIPSING BINARY CM DRACONIS , 2008, 0810.1541.

[29]  Xavier Bonfils,et al.  A super-Earth transiting a nearby low-mass star , 2009, Nature.

[30]  J. Bochanski,et al.  CONSTRAINING THE AGE–ACTIVITY RELATION FOR COOL STARS: THE SLOAN DIGITAL SKY SURVEY DATA RELEASE 5 LOW-MASS STAR SPECTROSCOPIC SAMPLE , 2007, 0712.1590.

[31]  David Charbonneau,et al.  MULTIWAVELENGTH CONSTRAINTS ON THE DAY–NIGHT CIRCULATION PATTERNS OF HD 189733b , 2008, 0802.1705.

[32]  B. Scott Gaudi,et al.  Fraction of Stars With Planets in the Open Cluster NGC 1245 , 2004 .

[33]  D. Charbonneau,et al.  THE CLIMATE OF HD 189733b FROM FOURTEEN TRANSITS AND ECLIPSES MEASURED BY SPITZER , 2010, 1007.4378.

[34]  J. Jenkins,et al.  Some Tests to Establish Confidence in Planets Discovered by Transit Photometry , 2002 .

[35]  D. Sasselov,et al.  THE ATMOSPHERIC SIGNATURES OF SUPER-EARTHS: HOW TO DISTINGUISH BETWEEN HYDROGEN-RICH AND HYDROGEN-POOR ATMOSPHERES , 2008, 0808.1902.

[36]  S. Aigrain,et al.  Practical planet prospecting , 2004 .

[37]  Photometry of Proxima Centauri and Barnard's Star Using Hubble Space Telescope Fine Guidance Sensor 3: A Search for Periodic Variations* , 1998, astro-ph/9806276.

[38]  G. Rupprecht,et al.  Correction of Field Rotator-Induced Flat-Field Systematics—A Case Study Using Archived VLT-FORS Data , 2010, 1001.1099.

[39]  C. Moutou,et al.  Detection of atmospheric haze on an extrasolar planet: the 0.55–1.05 μm transmission spectrum of HD 189733b with the Hubble Space Telescope , 2007, 0712.1374.

[40]  D. Ehrenreich,et al.  Transit spectrophotometry of the exoplanet HD 189733b - II. New Spitzer observations at 3.6 μm , 2010, 1008.2481.

[41]  S. Leggett.  Infrared Colors of Low-Mass Stars , 1992 .

[42]  A. Reiners.  The narrowest M-dwarf line profiles and the rotation-activity connection at very slow rotation , 2007, astro-ph/0702634.

[43]  A. West,et al.  A FIRST LOOK AT ROTATION IN INACTIVE LATE-TYPE M DWARFS , 2008, 0812.1220.

[44]  A. Collier Cameron,et al.  Photospheric activity, rotation, and radial velocity variations of the planet-hosting star CoRoT-7 , 2010, 1005.3602.

[45]  et al,et al.  The CoRoT space mission : early results Special feature Transiting exoplanets from the CoRoT space mission VIII . CoRoT-7 b : the first super-Earth with measured radius , 2009 .

[46]  James P. Lloyd,et al.  METAL-RICH M-DWARF PLANET HOSTS: METALLICITIES WITH K-BAND SPECTRA , 2010, 1007.4593.

[47]  E. Bergeron,et al.  NICMOS OBSERVATIONS OF THE TRANSITING HOT JUPITER XO-1b , 2010, 1006.1953.

[48]  M. Holman,et al.  A SEARCH FOR ADDITIONAL PLANETS IN THE NASA EPOXI OBSERVATIONS OF THE EXOPLANET SYSTEM GJ 436 , 2009, 0909.2875.

[49]  Suzanne Aigrain,et al.  The Monitor project: data processing and light curve production , 2006 .

[50]  C. Moutou,et al.  Noise properties of the CoRoT ? data A planet-finding perspective , 2009, 0903.1829.

[51]  C. Moutou,et al.  Hubble Space Telescope time-series photometry of the planetary transit of HD 189733: no moon, no rings, starspots , 2007, 0707.1940.

[52]  S. Seager,et al.  Mass-Radius Relationships for Solid Exoplanets , 2007, 0707.2895.

[53]  William H. Press,et al.  Numerical recipes in C. The art of scientific computing , 1987 .

[54]  D. Ehrenreich,et al.  SEARCH FOR CARBON MONOXIDE IN THE ATMOSPHERE OF THE TRANSITING EXOPLANET HD 189733b , 2009, 0903.3405.

[55]  Jennifer C. Yee,et al.  Analytic Approximations for Transit Light-Curve Observables, Uncertainties, and Covariances , 2008, 0805.0238.

[56]  D. Queloz,et al.  Spectroscopic parameters for 451 stars in the HARPS GTO planet search program - Stellar [Fe/H] and the frequency of exo-Neptunes , 2008, 0805.4826.

[57]  John Southworth,et al.  Homogeneous studies of transiting extrasolar planets – I. Light-curve analyses , 2008, 0802.3764.

[58]  J. Fortney,et al.  OBSERVATIONAL EVIDENCE FOR A METAL-RICH ATMOSPHERE ON THE SUPER-EARTH GJ1214b , 2011, 1103.2370.

[59]  S. Seager,et al.  A Unique Solution of Planet and Star Parameters from an Extrasolar Planet Transit Light Curve , 2002, astro-ph/0206228.

[60]  Arlo U. Landolt,et al.  UBVRI Photometric Standard Stars in the Magnitude Range 11 , 1992 .

[61]  J. Fortney,et al.  THE NATURE OF THE ATMOSPHERE OF THE TRANSITING SUPER-EARTH GJ 1214b , 2010, 1001.0976.

[62]  R. W. Noyes,et al.  A PHOTOMETRIC VARIABILITY SURVEY OF FIELD K AND M DWARF STARS WITH HATNet , 2009, 0907.2924.

[63]  Marc Ollivier,et al.  The SARS algorithm: detrending CoRoT light curves with Sysrem using simultaneous external parameters , 2010, 1003.0427.

[64]  R. Gilliland,et al.  Detection of an Extrasolar Planet Atmosphere , 2001, astro-ph/0111544.

[65]  J. D. Dorren,et al.  A New Formulation of the Starspot Model, and the Consequences of Starspot Structure , 1987 .

[66]  R. Dvorak,et al.  An Investigation into the Radial Velocity Variations of CoRoT-7 , 2010, 1006.5476.

[67]  Antonino Francesco Lanza,et al.  Photospheric activity and rotation of the planet-hosting star CoRoT-4a , 2009, 0901.4618.

[68]  David Charbonneau,et al.  A map of the day–night contrast of the extrasolar planet HD 189733b , 2007, Nature.

[69]  Accurate radius and mass of the transiting exoplanet OGLE-TR-132b , 2004, astro-ph/0407635.

[70]  S. Seager,et al.  A FRAMEWORK FOR QUANTIFYING THE DEGENERACIES OF EXOPLANET INTERIOR COMPOSITIONS , 2009, 0912.3288.

[71]  L. Close,et al.  A TENTATIVE DETECTION OF A STARSPOT DURING CONSECUTIVE TRANSITS OF AN EXTRASOLAR PLANET FROM THE GROUND: NO EVIDENCE OF A DOUBLE TRANSITING PLANET SYSTEM AROUND TrES-1 , 2009, 0906.4320.

[72]  C. Moutou,et al.  Spectropolarimetric observations of the transiting planetary system of the K dwarf HD 189733 , 2007, 0707.2016.

[73]  R. W. Noyes,et al.  A trend filtering algorithm for wide-field variability surveys , 2004 .

[74]  C. Blake,et al.  GJ 3236: A NEW BRIGHT, VERY LOW MASS ECLIPSING BINARY SYSTEM DISCOVERED BY THE MEarth OBSERVATORY , 2009, 0906.4365.

[75]  R. Redmer,et al.  THERMAL EVOLUTION AND STRUCTURE MODELS OF THE TRANSITING SUPER-EARTH GJ 1214b , 2010, 1010.0277.

[76]  David R. Soderblom,et al.  Calculating Galactic Space Velocities and Their Uncertainties, with an Application to the Ursa Major Group , 1987 .

[77]  Avi M. Mandell,et al.  Observable consequences of planet formation models in systems with close-in terrestrial planets , 2007, 0711.2015.

[78]  N. Santos,et al.  Metallicity of M dwarfs - I. A photometric calibration and the impact on the mass-luminosity relation at the bottom of the main sequence , 2005, astro-ph/0503260.

[79]  J. Eaton,et al.  Starspot areas and temperatures in nine binary systems with late-type components , 1985 .

[80]  The First Direct Measurements of Surface Magnetic Fields on Very Low Mass Stars , 2006, astro-ph/0610365.

[81]  David Charbonneau,et al.  Design Considerations for a Ground-Based Transit Search for Habitable Planets Orbiting M Dwarfs , 2007, 0709.2879.

[82]  Sara Seager,et al.  THE OPTICAL AND NEAR-INFRARED TRANSMISSION SPECTRUM OF THE SUPER-EARTH GJ 1214b: FURTHER EVIDENCE FOR A METAL-RICH ATMOSPHERE , 2011, 1109.0582.

[83]  K. Apps,et al.  ON THE METAL RICHNESS OF M DWARFS WITH PLANETS , 2009, 0904.3092.

[84]  Marc Ollivier,et al.  The CoRoT space mission : early results Special feature The CoRoT-7 planetary system : two orbiting super-Earths , 2009 .

[85]  Tsevi Mazeh,et al.  Correcting systematic effects in a large set of photometric light curves , 2005, astro-ph/0502056.

[86]  K. Horne,et al.  AN OPTIMAL EXTRACTION ALGORITHM FOR CCD SPECTROSCOPY. , 1986 .

[87]  G. Laughlin,et al.  A physically-motivated photometric calibration of M dwarf metallicity , 2010, 1006.2850.

[88]  Gautam Vasisht,et al.  The presence of methane in the atmosphere of an extrasolar planet , 2008, Nature.

[89]  S. Seager,et al.  THREE POSSIBLE ORIGINS FOR THE GAS LAYER ON GJ 1214b , 2009, 0912.3243.

[90]  William H. Press,et al.  Numerical Recipes in C, 2nd Edition , 1992 .

[91]  Michel Mayor,et al.  ELODIE metallicity-biased search for transiting Hot Jupiters. II. A very hot Jupiter transiting the bright K star HD 189733 , 2005 .