Chapitre 1- Introduction PHY6795O – Chapitres Choisis en Astrophysique Naines Brunes et Exoplanètes Chapitre 1- Introduction PHY6795O - Naines Brunes et Exoplanètes

PHY6795O – Naines brunes et Exoplanètes The grand questions Is there life outside the Solar system? What fraction of stars harbor planets and what fraction are habitable? How do planetary systems form and evolve ? What are the physical properties of exoplanets ? Is our Solar system unique ? PHY6795O – Naines brunes et Exoplanètes Introduction

Your textbook is already obsolete! 2011 First sentence of the book: Exoplanet research is one of the most rapidly developing subjects in astronomy. More than 500 exoplanets are now known, and groups world-wide are actively involved in a broad range of observational and theoretical efforts. 2010 First sentence of the Introduction: One thing is certain about this book: by the time you read it, parts of it will be out of date. The study of exoplanets, planets orbiting around stars other than the sun is a new and fast-moving field. PHY6795O – Naines brunes et Exoplanètes Introduction

Planet definition (Solar system) PHY6795O – Naines brunes et Exoplanètes Introduction

PHY6795O – Naines brunes et Exoplanètes Exoplanet definition PHY6795O – Naines brunes et Exoplanètes Introduction

PHY6795O – Naines brunes et Exoplanètes Naming convention Star name+b,c,d (lower case) in chronological order of discovery Ex: HR8779b, HR8799c, HR8799d Stellar binary systems are specified with capital letters Ex: the WD companion to Sirius A (capital letter) is Sirius B. Should a planetary companion be found around Sirius A, it would be named Sirius Ab. PHY6795O – Naines brunes et Exoplanètes Introduction

PHY6795O – Naines brunes et Exoplanètes Astronomical terms PHY6795O – Naines brunes et Exoplanètes Introduction

20 years of exoplanet research – some results Number Nearly 2000 firm detections, several 1000s of candidates. About half are transiting systems. Most detections restricted to a distance horizon of 50-100 pc (microlensing excluded) For reference, there are about 2000 stars within 25 pc. Diversity Hot-Jupiters (a~a few 0.01 AU) to wide-orbit (a~a few 1000s AU) systems. High-eccentricity systems very common. Super-Earths are the most common planets of the solar neighborhood. Frequency >50% of solar-type stars harbor at least one planet of any mass and with period up to 100 days. The frequency of gas giants is strongly correlated with the host star metallicity. No such correlation for low-mass (< 15 ME) planets. The mass distribution of Super-Earths and Neptune-mass planets (SEN) is strongly increasing between 30 and 15 ME. Low-mass planets appear to be very common. Habitable planets The fraction of low-mass stars with an Earth/super-Earths in the habitable zone (HZ) is significant (at least 10, perhaps as much as 100%). A handful of HZ Earths/super-Earths have been identified. One is transiting but too far (Kepler-186f; 150 pc) for detailed characterization. PHY6795O – Naines brunes et Exoplanètes Introduction

Overview of observational techniques Radial velocity Doppler measurement of host star reflex motion (indirect dynamical method). Yield orbital period (P), semi-major axis (a), eccentricity and mass (m sin i). Second most prolific detection method after transit. PHY6795O – Naines brunes et Exoplanètes Introduction

Overview of observational techniques Astrometry Similar to RV but reflex motion of host star measured in the plane of the sky. Very difficult, requires micro-arcsec accuracy. No system discovered by this technique yet but future space mission GAIA will likely yield many detections. Yield projected semi-major axis (a) and mass if distance to host star is known. PHY6795O – Naines brunes et Exoplanètes Introduction Figure 3.4 de Perryman

Overview of observational techniques Transit Photometric method consisting of measuring the host star flux variation due to the planet primary and secondary eclipses. Most prolific method (largely from the Kepler mission). Works only for systems with an inclination close to 90°. Transit probability is ~1 %. Powerful technique for exoplanet atmosphere caracterization through transit spectroscopy. PHY6795O – Naines brunes et Exoplanètes Introduction

Overview of observational techniques Imaging Photometric method consisting of detecting the planet luminosity directly either in reflected light or thermal emission. Very difficult; first detection in 2008. So far, only the latter has been detected around young stars. In case of thermal emission, the mass of the planet can be inferred from evolutionary models. HR8799, a young (30-60 Myrs) platetary system detected through infrared imaging assisted by adaptive optics. From Marois et al (2010). PHY6795O – Naines brunes et Exoplanètes Introduction

Overview of observational techniques Microlensing Photometric method consisting of detecting the flux amplification induced by the gravitational lensing event of a planet passing in the vicinity of a background star. Cost-effective for building up statistics but not for exoplanet characterization. PHY6795O – Naines brunes et Exoplanètes Introduction

Overview of observational techniques Timing Similar technique to RV but Doppler (timing) measurement is made on a periodic signal intrinsic to the star/system, e.g., pulsars, oscillating stars (WD, sDB) and eclipsing binaries. Specific timing methods for transiting systems: TTV (Transit Time Variation) for detecting multiple systems. TDV (Transit Duration Variation) could be used for detecting exomoons. PHY6795O – Naines brunes et Exoplanètes Introduction

Planet detection methods Doppler variability = relativistic beaming. Ex: Kepler-76b, sole planet deteted by this technique (Faigler et al. 2013). PHY6795O – Naines brunes et Exoplanètes Introduction PHY6795O - Naines Brunes et Exoplanètes

‘’Miscellaneous’’ methods – circumstellar disk http://www.eso.org/public/news/eso1436/ (6 November 2014) PHY6795O – Naines brunes et Exoplanètes Introduction

PHY6795O – Naines brunes et Exoplanètes Discovery status Compilation as of 2010 November 1 (Perryman, Table 1.2, Data from exoplanet.eu). Include 29 brown dwarfs (mass > 13 MJup) PHY6795O – Naines brunes et Exoplanètes Introduction

PHY6795O – Naines brunes et Exoplanètes Discovery status Compilation (red) as of 11 January 2015. Includes 21 brown dwarfs’’ (mass > 13 MJup) 445 656 32 46 13 ? 104 354 2 1 4 591 1179 34 50 18 ? 177 1876 199 18 7 Not the sum of proceeding, since some planets have been detected by more than one technique (principally, transit discoveries with radial velocity follow-up). PHY6795O – Naines brunes et Exoplanètes Introduction

PHY6795O – Naines brunes et Exoplanètes Discovery status PHY6795O – Naines brunes et Exoplanètes Introduction

Chronology of key exoplanet discoveries PHY6795O – Naines brunes et Exoplanètes Introduction

Chronology of key exoplanet discoveries PHY6795O – Naines brunes et Exoplanètes Introduction

Useful on-line references PHY6795O – Naines brunes et Exoplanètes Introduction