Dave Charbonneau: why transits are cool
Kicking off afternoon session is Josh Winn on transit uses and abuses.
Then Gaspar Bakos on ground based transits.
you get masses, and planetary radii.
Can go to low masses and close in planets, and working to earth masses in habitable zone – Real Soon Now
as Dave says, it will be a current or near future graduate student who gets the first peek at a true Earth
also, transiting planets offer quick opportunity for spectra through differential transiting spectra of the host star.
Should work for Neptunes, then waterworld Super-Earths.
Dave beats up theorists.
Why don’t we understand Puffy Planets. Its just H/He – can’t we do EoS for simple gases?!
Only one real normal giant transiting planet – Corot-9b – and it does fit the Jupiter like M-R curve with a core mass in the expected range (0-20 Earth mass core)
HD 17156 – 1 R_Jupiter planet in 20 day orbit
FGS astroseismology Gilliland et al and Nutman et al 2010 in prep
measurement of stellar density from transit and from astroseismology, independently, agree
so we know something about what we are doing
astroseismology gives independent concurrent high precison stellar density which locks in the transit calibrations and gives a stellar age estimate
luvly spectra of giant planetary photospheres. seen that…
methane, water, clouds
good complementary use of ground based and space based capabiltiies
need to make sure we keep the space based assets and tie in observations
recently claims of ground based detection of differential spectral detection of transiting planets – same game played from ground
hard, because of foreground and variability, but it is being done from 4m class telescopes, right now
up next – density of super-earths – do they have H/He envelopes and are migrated low mass Neptunes? Or are they Si/Fe balls? Or, Ice worlds with deep H2O over rock?
Ballard et al 2010 on GJ436 – less than 1.5 R_Earth, IF it transits – not known to transit
Corot and Kepler results later this week.
Bean et al 2009 – NH3 cell for near IR detection around M stars
getting to 3-5 m/sec right now
MEarth project – 2000 nearest low mass stars
using 8 16″ telescopes at Mt Hopkins
cool movie of them in operation, interesting approach to fish for transits. Operational
GJ1214b – Rogers and Seager 2009 – illustrated H/He envelope vs H2O vs H2 over Fe/Si
Miller-Ricci method to measure scale height and abundances
Spitzer data scheduled to be taken, want some HST data, please.
Looks intriguing. Ought to see if there is lots of Hydrogen, or rule it out.
Everybody wants to do M dwarfs next…
Winn: check slides for the master list of things you can and may be able to observe or infer from transit observations, now or eventually.
Lots of stuff – why are hot giant planets eccentric in some cases?
Are they really eccentric, or are just messing up?
measure oblateness, spin precession, stellar obliquity etc
common theme – need high precision photometry over long baselines, multiple transits, lots of careful followups
choke point is the followups
Holt-Schlesinger effect – never heard it called that, eh, life is not fair Rossiter-McLaughlin it is…
Sun has anomalously high obliquity? Hmm. Or are the hot giants’ orbital plane coming into alignment with the spin axis of the star? Gas coupling during migration?
Well, except for XO-3 which has λ ~ 37 degrees
Use R-M on 80606 to find λ ~ 60 degrees – proof of Kozai pumping?
HAT P-7 – λ ~ 180 degrees – retrograde, maybe, or close to orthogonal but projected
Four more misaligned hot giants soon to be announced!!!
Bunch of λ ~ 0, then some outliers – doesn’t look uniform, but not enough data yet. Two modes of migration (per Fabrycky and Winn ’09)? ie data is consistent with two separate distributions, hence inference of two physical processes
apsidal lock, outer planet eccentric
measure concentration of planet (k2) from residual eccentricity
cf Wu and Goldreich 2002 and Mardling 2007, 2010
if mutually inclined, eccentricity circulates
check obliquity, λ ~ 1 degree +/- 1 – consistent with small relative inclination
Probably a 3rd planet in HAT P-13 system – long period residuals
planet HAT P-13c due to tranist April 21 – May 5, if coplanar – someone look
Good question: are the high λ planets correlated with Puffyness?
What abour RV vs transit discovered planets; is there an orbital period correlations.
Someone look, quick.
Bakos: 68 transiting planets now, 13 space based, so far.
6 were discovered first through RV
Transitsearch.org – follow it on twitter…
also AXA – Amateur Exoplanet Archive – go find your own transits
also TRESCA – for variable star observers wanting to dip their toes into the planet game
eg HAT has found over 1000 transit candidates
half are triples, others errors from giants, blends, rotators and crap photometry
5% make it to be real candidates and go to big glass for spectrographic followup and RV confirmation
efficient followup since phasing is known
good movie at the end on transit discoveries with time