1. Lecture 16: Exoplanets, Brown Dwarfs,
This class
Exoplanets Chapt 15
brown dwarfs
Read before coming to class
The Sun Chapt 16
Stars Chapt 17
flux, luminosity, magnitudes, spectra
Hertzsprung-Russell Diagram
Full Moon by Michael Light
negatives by astronauts.
ALL NOTES COPYRIGHT JAYANNE ENGLISH

2. dist < 1/2 dist between Earth & Luna
News! Oct 19th
dist == distance
Discovered by:Robert H. McNaught at Siding Spring Observatory in Australia
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.
Named after Siding Spring Observatory

3. Exoplanets and their planetary systems:
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?
We’ve described our solar system in general.

4. Atacama Larger Millimeter/submillimeter Array (ALMA)
64 antennas
22 countries (incl. Canada)
molecular emission lines
 Molecular gas distribution, T, density & motions.

5. “hybrid disk”  both planetesimals (dust) and gas dust more extended
Proplyd disk around HD 21997
DUST RING
(Hershel Space Obs. & ALMA)
CO gas
(ALMA)
Gas rotating around host star (ALMA)
If it had T Tauri stage at a few million years the gas would have been cleared by now but nuclear fusion doesn’t turn on until 10 million years so perhaps this is ok.
~10 million years old
“hybrid disk”  both planetesimals (dust) and gas
dust more extended

6. Exoplanets: Characteristics MASSES
Roughly 1822 planets detected (this week).
Interactive catalogue at
# of
planets
Mass Uranus
Mass Earth
Super-Earths
Mj == Jupiter Masses. Earth is Mj.
SuperEarths are mass of Earth
last year’s histograms on this page
This is quite different from the solar system!
When have a mass orbiting a central mass, we can determine the central mass.
Mass Uranus
masses in Jupiter’s mass (Mjup: 318 x Mearth).
maximum mass ~ 50 x Mjup
 gas giants

7. Exoplanets: Characteristics DISTANCES
Roughly 1822 planets detected.
Interactive catalogue at
# of
planets
This year’s histogram
Mj == Jupiter Masses. Earth is Mj.
This is quite different from the solar system!
Can get radius of orbit from Kepler’s 3rd law.
Distance Earth
Distance
Neptune
distance from host star in AU
maximum distance a few thousand AU
 most are closer than Earth

8. Exoplanets: Characteristics
Note that by 2009 only 23 planets found with masses less than Jupiter.
small mass planets rare? or
was our observational method biased?

9. Exoplanets: Radial Velocity Method
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
See our class’s public website for animations.
Movie

10. Exoplanets: Radial Velocity Method
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.
See the class’s public website for animations.

11. Review
Most exoplanets detected to ~2013 had masses similar to Jovians & orbit closer to their star than Jupiter does to ours.

12. Exoplanets: Doppler Shift Method
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.

13. most low-mass candidates in multi-planet systems.
Artist’s impression:
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 Earth-Sun distance.
Exoplanets
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.

14. r = 1.2 x Earth & M = 1.7 x Earth  density ~ Earth => same density
Exoplanets -- Kepler 78b
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
HARPS & HIRES spectrograph on Keck I

15. Exoplanets 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
Could just do Gliese 581g

16. Exoplanets: Transit Method
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.
movie
Now there are1147 planets discovered by this method (i.e. Kepler Mission)
There are earth-sized planets but harder to detect.

17. Launched March 2009 - now finished. This is a test on a known planet.
Exoplanets
Kepler made it easier to detect smaller planets.
NASA’s Kepler Mission
Launched March now finished.
This is a test on a known planet.

18. r = 1.2 x Earth & M = 1.7 x Earth  density ~ Earth => same density
Exoplanets -- Kepler 78b
The equations for the derivation of a planet’s mass, radius, and density were given in lecture.
How do we get planet radius for density? Transit method.
r = 1.2 x Earth & M = 1.7 x Earth  density ~ Earth => same density

19. Combine Spectroscopy and Transit method  Temperature Maps
WASP-43b is too distant to be photographed, but because its orbit is observed edge-on to Earth, astronomers detected it by observing regular dips in the light of its parent star as the planet passes in front of it.The planet is about the same size as Jupiter, but is nearly twice as massive. The planet is so close to its orange dwarf host star that it completes an orbit in just 19 hours. The planet is also gravitationally locked so that it keeps one hemisphere facing the star, just as our moon keeps one face toward Earth.The scientists combined two previous methods of analyzing exoplanets and put them together in one for the first time to study the atmosphere of WASP-43b. Spectroscopy allowed them to determine the water abundance and temperature structure of the atmosphere. By observing the planet’s rotation, the astronomers were also able to measure the water abundances and temperatures at different longitudes.
Tidally locked Hot Jupiter WASP-43b
too distant to be photographed
T and H2O abundance at different longitudes

20. Exoplanets: Imaging Technique
low resolution
high resolution
Recall resolution.

21. Resolved and Unresolved:
These are generalizations. Some galaxies are so far away that they are unresolved. Some stars are becoming resolved using new technologies and observing techniques. We will talk more about this in the section on stars later in the term.
Resolved galaxies in background.
Generally structure of stars cannot be distinguished  unresolved.

22. Exoplanets: Imaging Technique
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.

23. Imaging Technique  birth of a giant planet!
This composite image shows a view from the NASA/ESA Hubble Space Telescope (left) and from the NACO system on ESO’s Very Large Telescope (right) of the gas and dust around the young star HD The Hubble visible-light image shows the outer disc of gas and dust around the star. The new infrared VLT picture of a small part of the disc shows a candidate protoplanet. Both pictures were taken with a special coronagraph that suppresses the light from the brilliant star. The position of the star is marked with a red cross in both panels.
HST: protoplanetary disk
ESO: protoplanet candidate
ESO’s Very Large Telescope on right with adaptive optics and coronograph.

24. Exoplanets: Imaging Technique
Other techniques are microlensing and pulsar timing.
Found 51 planets, all but 2 have
M >= 3*Mjup, up to 32*Mjup
Fomalhaut planet < 3 Earth masses.

25. Review There was an observational bias systems with Hot Jupiters
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.

26. There are planets smaller than Jupiter Harder to detect them.
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
but both condensation and instabilty theories predict gas giants in outer solar system

27. Exoplanets: planets close to host stars
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”.
Hot Jupiters are planets close to their host star.
Perhaps even Jupiter formed out in the Kuiper Belt and migrated in.

28. Later Migration: The Nice Model
Got to here.
In the era of planetesimal ejection
Neptune moves outside orbit of Uranus.