Transcript Friday, Oct. 11

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Lecture 16: Exoplanets, Brown Dwarfs,
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This class
Exoplanets Chapt 15
brown dwarfs
Read before coming to class
The Sun Chapt 16
Stars Chapt 17
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flux, luminosity, magnitudes, spectra
Hertzsprung-Russell Diagram
• Full Moon by Michael Light
• negatives by astronauts.
News! Oct 19th
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Named after Siding
Spring Observatory
• Comet Siding Spring, will pass within
~139,500 kilometers of the Red Planet
• dist < 1/2 dist between Earth & Luna
• dist < 1/10 dist of any known comet
flyby of Earth.
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Exoplanets and their planetary systems:
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David Lafreniere, Ray
Jayawardhana, Marten H. van
Kerkwijk (University of Toronto,
Gemini Observatory)
This image could be the first
direct image of a planet (upper
left) around another Sun-like
star (center).
• Extra-solar planets == exoplanets
• How different from those in our SS (Solar
System)?
• Are our theories about SS formation
applicable to other systems?
Atacama Larger
Millimeter/submillimeter Array
(ALMA)
•5000 m
•64 antennas
•22 countries (incl. Canada)
• molecular emission lines
 Molecular gas distribution,
T, density & motions.
Proplyd disk around HD 21997
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DUST RING
(Hershel Space
Obs. & ALMA)
CO gas
(ALMA)
Gas rotating around host
star (ALMA)
• ~10 million years old
• “hybrid disk”  both planetesimals
(dust) and gas
• dust more extended
Exoplanets: Characteristics MASSES
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• Roughly 1822 planets detected (this week).
• Interactive catalogue at http://exoplanet.eu/
# of
planets
Mass Super-Earths
Earth
Mass
Uranus
Mass
Uranus
masses in Jupiter’s mass (Mjup: 318 x Mearth).
• maximum mass ~ 50 x Mjup
• gas giants
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Exoplanets: Characteristics DISTANCES
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• Roughly 1822 planets detected.
• Interactive catalogue at http://exoplanet.eu/
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# of
planets
Distance
Earth
Distance
Neptune
distance from host star in AU
• maximum distance a few thousand AU
• most are closer than Earth
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Exoplanets: Characteristics
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• small mass planets rare?
or
• was our observational method
biased?
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Exoplanets: Radial Velocity Method
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Movie
• Radial Velocity == velocity along
our line of sight.
• Fgrav between star + planet causes
star to be pulled towards planet.
•  star wobbles  Star’s motion is
Doppler Shifted.
• shift correlates with Fgrav
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Exoplanets: Radial Velocity Method
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• If m (==planet mass) large, then F large 
radial velocity large.
• If r (== star – planet distance) small, then F
large  radial velocity large.
 Easier to detect massive planet close to star.
Review
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Most exoplanets detected to ~2013 had
masses similar to Jovians & orbit
closer to their star than Jupiter does
to ours.
Exoplanets: Doppler Shift Method
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• Period Jupiter (5 AU) = 12 yrs.
• long time for one person to observe one star! note
Saturn’s Period vs career length.
 Easier to detect planets close to star.
• Currently team work  longer time.
Exoplanets
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Artist’s impression:
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The star Gliese 667 C, which belongs to a
triple system – 2 of the stars seen in the
background. The 6 Earth-mass exoplanet
circulates around its low-mass host star at a
distance equal to only 1/20th of the EarthSun distance.
Planet around alpha Centauri B! Sun-like star.
•4.3 ly distant, 3 stars.
•Earth mass planet
• P~3 days closer than Mercury
• High Accuracy Radial Velocity Planet Searcher (HARPS)
spectrograph, on ESO's 3.6-metre telescope, discovery
of 150 exoplanets Sept 12/11.
• at that time HARPS helped discover most of the
planets of mass < 20 Earth masses -> super-Earths and
small gas giants. (About 40).
• most low-mass candidates in multi-planet systems.
Exoplanets -- Kepler 78b
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HARPS &
HIRES
spectrograph on
Keck I
• r = 1.2 x Earth & M = 1.7 x Earth 
density ~ Earth => same density
• orbit’s every 8.5 hrs => 2000K hotter
• tidal forces will break it apart
Exoplanets
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• CoRoT- 7b (HARPS on ESO 3.6m)
– 5 earth-masses
– Density Earth-like  rocky.
– 23 * closer to star than Mercury to Sun
• Gliese 581g ((aka Zaramina’s World) (HIRES on Keck)
– red dwarf star
– in habitable zone (.15 AU) – distance for liquid H2O
– 3* earth-mass; 1.5* earth-diameter
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Exoplanets: Transit Method
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movie
summary
• method for Canada's space telescope
called MOST
• Produces a light curve (Intensity vs Time)
as the planet orbits.
• larger planets  larger dips in light curve.
• closer planets  shorter time between
dips (e.g. within career).
 Easier to detect large planets close to their
star.
There are earth-sized planets but harder to
detect.
Exoplanets
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• NASA’s Kepler Mission
• Launched March 2009 - now finished.
• This is a test on a known planet.
Exoplanets -- Kepler 78b
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How do we get
planet radius for
density? Transit
method.
• r = 1.2 x Earth & M = 1.7 x Earth 
density ~ Earth => same density
Combine Spectroscopy and Transit method
 Temperature Maps
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• Tidally locked Hot Jupiter WASP-43b
• too distant to be photographed
• T and H2O abundance at different
longitudes
Exoplanets: Imaging Technique
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low
resolution
high
resolution
Recall resolution.
Resolved and Unresolved:
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• Resolved galaxies in background.
• Generally structure of stars cannot be
distinguished  unresolved.
Exoplanets: Imaging Technique
summary
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David Lafreniere, Ray
Jayawardhana, Marten H. van
Kerkwijk (University of Toronto,
Gemini Observatory)
This image could be the first
direct image of a planet (upper
left) around another Sun-like
star (center).
• Resolve the planet from its host star.
• Do not resolve surface of either star or planet.
Imaging Technique  birth of a giant planet!
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HST: protoplanetary disk
ESO: protoplanet candidate
• ESO’s Very Large Telescope on right
with adaptive optics and coronograph.
Exoplanets: Imaging Technique
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• Found 51 planets, all but 2 have
M >= 3*Mjup, up to 32*Mjup
• Fomalhaut planet < 3 Earth masses.
Review
There
was an observational bias systems with Hot Jupiters
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summary
• mass
 stronger Doppler Shift in radial velocity
method
 larger light dip in transit method
• proximity
 shorter time in radial velocity method
shorter time in transit method
– but there are super-Earths.
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Summary
• There are planets smaller than Jupiter
– Harder to detect them.
– Now have 405 planetary systems with
planets M<10*M_Earth. (333 multiple
planet systems)
– 885 planets
• Other planetary systems are different than
ours
– massive planets close to star
Exoplanets: planets close to host stars
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• Migration while there is still the gas disk:
• E.g. friction between the gas disk and the
protoplanets cause the protoplanets to lose
energy and spiral inwards.
• Gap blown by proto-star’s wind.
• Particularly effective for “Hot Jupiters”.
Later Migration:
The Nice Model
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• In the era of planetesimal ejection
• Neptune moves outside orbit of
Uranus.