Download Chap1-Introduction - Groupe d`astrophysique de UdeM

PHY6795O – Chapitres Choisis en Astrophysique
Naines Brunes et Exoplanètes
Chapitre 1- Introduction
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
2
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parts of it will be out of date.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 fastmoving field.
PHY6795O – Naines brunes et Exoplanètes
Introduction
3
Planet definition (Solar system)
PHY6795O – Naines brunes et Exoplanètes
Introduction
4
Exoplanet definition
PHY6795O – Naines brunes et Exoplanètes
Introduction
5
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
6
Astronomical terms
PHY6795O – Naines brunes et Exoplanètes
Introduction
7
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
8
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
9
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
10
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
11
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
12
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
13
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
14
Planet detection methods
PHY6795O – Naines brunes et Exoplanètes
Introduction
15
‘’Miscellaneous’’ methods – circumstellar disk
http://www.eso.org/public/news/eso1436/ (6 November 2014)
PHY6795O – Naines brunes et Exoplanètes
Introduction
16
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
17
Discovery status
Compilation (red) as of 11 January 2015. Includes 21 brown
dwarfs’’ (mass > 13 MJup)
445
656
32
46
13
?
177
7
104
354
2
1
4
18
591
1179
34
50
18
?
1876
199
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
18
Discovery status
PHY6795O – Naines brunes et Exoplanètes
Introduction
19
Chronology of key exoplanet discoveries
PHY6795O – Naines brunes et Exoplanètes
Introduction
20
Chronology of key exoplanet discoveries
PHY6795O – Naines brunes et Exoplanètes
Introduction
21
Useful on-line references
PHY6795O – Naines brunes et Exoplanètes
Introduction
22