UNIVERSITÀ' DEGLI STUDI DI TRIESTE XXV CICLO DEL DOTTORATO DI RICERCA IN FISICA Photometric transit search for planets around cool stars from thè Western Italian Alps: thè APACHE survey Ph.D. program Di.rector: Prof. Paolo Camerini The.sis Supervisori*: Ph. D. student: -fit-—' Prof. Mario G. Lattauzzi IU+*i. {. fat)tfto Paolo Giacobbe Prof .essa Francesea Matteucci Dr. Alessandro Bozzetti ANNO ACCADEMICO 2012/2013 UNIVERSITA' DEGLI STUDI DI TRIESTE XXV CICLO DEL DOTTORATO DI RICERCA IN FISICA Photometric transit search for planets around cool stars from the Western Italian Alps: the APACHE survey Ph.D. program Director: Prof. Paolo Camerini Ph.D. student: Thesis Supervisors: Paolo Giacobbe Prof. Mario G. Lattanzi Prof.essa Francesca Matteucci Dr. Alessandro Sozzetti ANNO ACCADEMICO 2012/2013 You find out that life is just a game of inches. Al Pacino's Inch By Inch speech in `Any Given Sunday' UNIVERSITY OF TRIESTE Abstract Photometric transit search for planets around cool stars from the Western Italian Alps: the APACHE survey by Paolo Giacobbe Small-size ground-based telescopes can effectively be used to look for transiting rocky planets around nearby low-mass M stars using the photometric transit method. Since 2008, a consortium of the Astrophysical Observatory of Torino (OATo-INAF) and the Astronomical Observatory of the Autonomous Region of Aosta Valley (OAVdA) have been preparing for the long-term photometric survey APACHE (A PAthway toward the Characterization of Habitable Earths), aimed at finding transiting small-size plan- ets around thousands of nearby early and mid-M dwarfs. APACHE uses an array of five dedicated and identical 40-cm Ritchey-Chretien telescopes and its routine science operations started at the beginning of summer 2012. Here I present the results of the `pilot study', a year-long photometric monitoring cam- paign of a sample of 23 nearby dM stars, and of the APACHE survey first year data. In these studies, I set out to (i) demonstrate the sensitivity to > 2R⊕ transiting plan- ets with periods of up to a few days around our programme stars, through a two-fold approach that combines a characterization of the statistical noise properties of our pho- tometry with the determination of transit detection probabilities via simulations; and (ii), where possible, improves our knowledge of some astrophysical properties (e.g. ac- tivity, rotation) of our targets by combining our differential photometric measurements with spectroscopic information from the long-term programme GAPS with the HARPS- N spectrograph on the Telescopio Nazionale Galileo. Furthermore, cool M dwarfs within a few tens of parsecs from the Sun are becoming the focus of dedicated observational programs in the realm of exoplanet astrophysics that will make use of astrometric measurements. I present numerical simulations to gauge the Gaia potential for precision astrometry of exoplanets orbiting a sample of known dM stars within ∼ 30 pc from the Sun. I then investigate some aspects of the synergy between the astrometric data expected from the Gaia mission on nearby M dwarfs and the APACHE program. Contents Abstract ii List of Figures vi List of Tablesx 1 Introduction1 1.1 A personal prospect..............................1 1.2 Scientific motivations..............................2 1.3 Chapter Summaries..............................6 2 Detection and characterization of extrasolar planets8 2.1 The radial velocity method..........................8 2.2 The transit method............................... 10 2.2.1 Exoplanet atmospheres........................ 11 2.2.1.1 Transmission spectroscopy................. 11 2.2.1.2 Infrared Emission...................... 12 2.2.2 The Rossiter-McLaughlin effect.................... 12 2.2.3 Transit Timing Variation (TTV)................... 13 2.3 The astrometric method............................ 13 2.4 The direct imaging method.......................... 15 2.5 The gravitational microlensing method.................... 16 3 The physical properties of extrasolar planets 18 3.1 Introduction................................... 18 3.2 A brief overview of observations........................ 19 3.2.1 Lessons from our Solar System.................... 19 3.2.2 Observed properties of exoplanets.................. 20 3.3 Planet formation................................ 21 3.3.1 Core-accretion model.......................... 21 3.3.2 Gravitational instability........................ 23 3.3.3 Core-accretion versus gravitational instability............ 24 3.4 Interior structure properties.......................... 24 3.4.1 Earth-like to super-Earth planets (< 10M⊕)............. 25 3.4.2 Neptune-like to super-Jupiter planets (> 10M⊕).......... 25 3.5 Atmospheric properties............................ 26 3.5.1 Biosignatures.............................. 26 iii Contents iv 3.6 Star-planet interaction. Tidal effects...................... 27 4 The path to the APACHE survey 29 4.1 The M-dwarfs opportunity........................... 30 4.2 The site characterization study........................ 33 4.3 Pilot study................................... 34 4.3.1 Instrumentation and methodology.................. 36 4.3.2 Stellar sample.............................. 39 4.3.3 Results................................. 39 4.3.3.1 Photometric precision.................... 39 4.3.3.2 Global analysis........................ 41 4.3.3.3 Correlated (red) noise analysis............... 44 4.3.3.4 On the choice of the comparison stars........... 46 4.3.4 Photometric variability: periodicity analysis............. 50 4.3.4.1 Characterizing stellar rotation............... 50 4.3.5 Photometric variability: starspots analysis.............. 56 4.3.6 Photometric variability: flares analysis................ 58 4.3.7 Limits to transiting companions................... 59 4.3.8 Summary and conclusions....................... 70 5 The APACHE survey architecture 72 5.1 Instrumentation and methodology: hardware setup............. 72 5.2 Instrumentation and methodology: software interface for the hardware setup....................................... 73 5.2.1 Weather Monitoring.......................... 76 5.2.2 Operations' monitoring........................ 76 5.2.3 Observational strategy......................... 76 5.3 Instrumentation and methodology: data reduction............. 78 5.3.1 Image calibration............................ 78 5.3.2 Image aperture photometry...................... 80 5.3.3 Differential photometry........................ 81 5.4 Input catalogue................................. 82 5.4.1 Mass and radius estimation...................... 85 6 Results from the first year of APACHE survey 88 6.1 Summary of observations........................... 89 6.2 Photometric precision............................. 90 6.2.1 Global analysis............................. 90 6.2.2 Correlated (red) noise analysis.................... 92 6.3 Photometric variability: periodicity analysis................. 94 6.3.1 Searching for transit-like events.................... 95 6.3.2 Characterizing stellar rotation.................... 96 6.3.3 Photometric variability: flares analysis................ 99 6.4 Limits to transiting companions........................ 103 6.4.1 APACHE's Ensemble Sensitivity................... 103 6.4.2 Transit Probabilities = ηtra;i(R; P ).................. 103 6.4.3 Transit Detection Efficiencies = ηdet;i(R; P )............. 104 Contents v 6.4.3.1 Transit Detection Efficiencies from the raw light curves. 106 6.4.4 APACHE's Ensemble Sensitivity: results............... 107 6.5 Summary and Conclusion........................... 109 7 Astrometric detection of giant planets around nearby M dwarfs: the Gaia potential 111 7.1 Introduction................................... 111 7.2 Simulation Scheme............................... 113 7.3 Statistical and Numerical Analysis Tools................... 115 7.4 Results...................................... 116 7.4.1 Detection Probabilities......................... 116 7.4.2 Orbit Determination.......................... 118 7.4.3 Expected Planet Yield......................... 122 7.4.4 Measuring Transiting Systems Configurations............ 124 7.4.5 Predicting Giant Planets' Location and Brightness......... 127 7.5 Summary and Conclusions........................... 130 8 On the synergies between GAIA and transits survey 134 8.1 Simulation Scheme............................... 134 8.2 Statistical and Numerical Analysis Tools................... 136 8.3 Predicting the transit epochs......................... 136 8.4 Summary and Conclusions........................... 142 9 Summary and future steps 143 9.1 The APACHE survey............................. 144 9.2 Astrometric detection of giant planets around nearby M dwarfs: the Gaia potential..................................... 146 Bibliography 149 List of Figures 3.1 Mass VS Year of discovery diagram...................... 19 3.2 Mass of known extra-solar planets (in Mearth) as a function of orbital distance (in AU)................................ 21 3.3 Mass-radius diagram for transiting planets.................. 22 4.1 The distribution of seeing measurements over the whole period of obser- vation. The small black stars show 7864 individual data points (many of them overlapping due to the seeing values having been approximated to the first significant digit), each corresponding to an average seeing value over a 1 min interval, rounded to 0:1. The large filled circles indicate the median seeing value for each night...................... 34 4.2 Photometric errors (RMS) VS instrumental mean magnitude