Planets In Transit:Planets In Transit:The Shadow Knows!The Shadow Knows!

David CharbonneauDavid Charbonneau

California InstituteCalifornia Institute

of Technologyof Technology

www.astro.caltech.edu/~dcwww.astro.caltech.edu/~dc

STScI May Symposium – 3 May 2004

Overview: Transits and AtmospheresOverview: Transits and Atmospheres

By making use of the transiting geometry of one system, By making use of the transiting geometry of one system, HST has enabled the first direct studies of an extrasolar HST has enabled the first direct studies of an extrasolar planet, including:planet, including: Accurate determination of the planetary radiusAccurate determination of the planetary radius Searches for planetary moons and ringsSearches for planetary moons and rings Studies of the planetary atmosphere and exosphereStudies of the planetary atmosphere and exosphere

These studies also serve to develop these HST-based These studies also serve to develop these HST-based techniques, in anticipation of planets yet-to-be-discovered:techniques, in anticipation of planets yet-to-be-discovered: Wide-field, ground-based surveysWide-field, ground-based surveys The Kepler MissionThe Kepler Mission

HST is also being used to search for new transiting planets HST is also being used to search for new transiting planets

The Radial Velocity SurveysThe Radial Velocity Surveys

Transit CharacteristicsTransit Characteristics

ProbabilityProbabilitypptt = R = Rstarstar / a / a = 0.1= 0.1

DepthDepthI / I = (RI / I = (Rplpl / R / Rstarstar))22

= 0.01= 0.01

PeriodPeriodP = 3 – 7 daysP = 3 – 7 days

DurationDurationt = 3 hourst = 3 hours

The First Transiting Planet:The First Transiting Planet:HD 209458bHD 209458b

Numerous groups (Henry et al.; Numerous groups (Henry et al.; Charbonneau et al.; Jha et al.; Charbonneau et al.; Jha et al.; Deeg et al. ) have presented Deeg et al. ) have presented ground-based photometry (~0.2%)ground-based photometry (~0.2%)

Uncertainty in RUncertainty in Rpp is dominated by is dominated by uncertainty in Runcertainty in Rss

Charbonneau et al. (2000)

The First Transiting Planet:The First Transiting Planet:HD 209458bHD 209458b

Numerous groups (Henry et al.; Numerous groups (Henry et al.; Charbonneau et al.; Jha et al.; Charbonneau et al.; Jha et al.; Deeg et al. ) have presented Deeg et al. ) have presented ground-based photometry (~0.2%)ground-based photometry (~0.2%)

Uncertainty in RUncertainty in Rpp is dominated by is dominated by uncertainty in Runcertainty in Rss

HST photometry (~0.01%) breaks HST photometry (~0.01%) breaks this degeneracythis degeneracy

Best estimates are:Best estimates are:

Brown et al. (2001)

Jup06.035.1 RRp Jup 05.069.0 MMp

Charbonneau et al. (2000)

Understanding the Understanding the Planetary RadiiPlanetary Radii

Radius results from slowing of Radius results from slowing of contraction, not due to “puffing contraction, not due to “puffing up” (Burrows et al. 2000)up” (Burrows et al. 2000)

Initial models assumed energy Initial models assumed energy was deposited deep in the was deposited deep in the atmosphereatmosphere

““Colder” models require Colder” models require additional energy sourceadditional energy source tidal circularization tidal circularization

(Bodenheimer et al. 2001)(Bodenheimer et al. 2001) atmospheric circulation atmospheric circulation

(Showman & Guillot 2002)(Showman & Guillot 2002) Discrepancy is increased if a Discrepancy is increased if a

large planetary core is large planetary core is includedincluded

Showman & Guillot (2002)

Bodenheimer et al. (2001)

HST STIS PhotometryHST STIS Photometryof HD 209458of HD 209458

Unphased HST STIS PhotometryUnphased HST STIS Photometryof HD 209458of HD 209458

Planetary SatellitesPlanetary Satellitesfrom Photometric Residualsfrom Photometric Residuals

Planetary SatellitesPlanetary Satellitesfrom Transit Timingfrom Transit Timing

FGS Transit TimingFGS Transit Timing

Schultz et al. (2002) Schultz et al. (2002) have observed several have observed several transits with HST Fine transits with HST Fine Guidance SensorsGuidance Sensors

FGS provide very rapid FGS provide very rapid cadence (S/N = 80 in cadence (S/N = 80 in 0.025 s)0.025 s)

These data target times These data target times of ingress and egressof ingress and egress

Schultz et al. (2002)

Atmospheric Transmission Atmospheric Transmission SpectroscopySpectroscopy

Compare transit depth at various wavelengths (Seager & Sasselov; Compare transit depth at various wavelengths (Seager & Sasselov; Hubbard et al.; Brown)Hubbard et al.; Brown)

Where strong atmospheric opacity is present, the planet will appear Where strong atmospheric opacity is present, the planet will appear larger, and hence the transit will seem deeperlarger, and hence the transit will seem deeper

Brown (2001)

Detection of anDetection of anExtrasolar Planet AtmosphereExtrasolar Planet Atmosphere

Detection of Sodium AbsorptionDetection of Sodium Absorption The transit appears deeper by The transit appears deeper by

2.3 x 102.3 x 10-4-4 when observed at the when observed at the sodium resonance lines near sodium resonance lines near 589nm589nm

This is ~1/3 the expected value for This is ~1/3 the expected value for a cloudless atmosphere with a a cloudless atmosphere with a solar abundance of sodium in solar abundance of sodium in atomic formatomic form

Charbonneau, Brown, Gilliland, & Noyes (2002)

HST/STIS Transmission SpectrumHST/STIS Transmission SpectrumNEAR FUTURENEAR FUTURE

Charbonneau et al. (2002)

New STIS New STIS ObservationsObservations

(290 – 1020 nm) (290 – 1020 nm)

Charbonneau, Brown, Gilliland, & Noyes (2003)

Detection of an Evaporating Detection of an Evaporating Atmosphere of HydrogenAtmosphere of Hydrogen

Vidal-Madjar et al. (2003) detect Vidal-Madjar et al. (2003) detect a very large (15%) transit depth a very large (15%) transit depth at Ly at Ly

At this radius, hydrogen atoms At this radius, hydrogen atoms are no longer gravitationally are no longer gravitationally bound – planet is losing massbound – planet is losing mass

Liang et al. (2003) model the Liang et al. (2003) model the photochemical processes and photochemical processes and determine that photolysis of Hdetermine that photolysis of H22O O could result in a concentration of could result in a concentration of atomic H 3x greater than Jovian atomic H 3x greater than Jovian atmosphereatmosphere

More recently, Vidal-Madjar et al. More recently, Vidal-Madjar et al. (2004) have claimed a detection (2004) have claimed a detection of C & O in the exosphereof C & O in the exosphere

Vidal-Madjar et al. (2003)

NICMOS NICMOS Search for Search for Water in Water in

HD209458bHD209458b

3 visits of 5 orbits each; 3 visits of 5 orbits each; 11stst visit has occurred visit has occurred

Search for water features Search for water features in 1.1 – 1.9 in 1.1 – 1.9 m bandpassm bandpass

Orbit-to-orbit sensitivity Orbit-to-orbit sensitivity could reach S/N ~ 36,000 could reach S/N ~ 36,000 (if instrumental effects (if instrumental effects can be corrected)can be corrected)

Brown (2003)

Gilliland (2004)

A Second Transiting Planet:A Second Transiting Planet:OGLE-TR-56 bOGLE-TR-56 b

First extrasolar planet discovered First extrasolar planet discovered by its photometric transit (2 by its photometric transit (2 additional OGLE planets have additional OGLE planets have recently been announced)recently been announced)

1.2 day orbital period1.2 day orbital period This system is at a much greater This system is at a much greater

distance, hence it is much fainter distance, hence it is much fainter and follow-up is more difficultand follow-up is more difficult

HST/ACS multi-color follow-up in HST/ACS multi-color follow-up in progress to determine accurate progress to determine accurate planetary radius (Sasselov et al. planetary radius (Sasselov et al. 2004)2004)

Best ground-based estimates are:Best ground-based estimates are:

Torres et al. (2003)

Jup16.023.1 RRp

Jup23.045.1 MMp

Sleuth: The Palomar Planet FinderSleuth: The Palomar Planet Finder

There is only a single known system that is bright enough to study – we need more targets in a hurry to apply these HST-based techniques

SLEUTH delivers high-cadence time series photometry on roughly 10,000 stars (9 < V < 15) in a typical field centered on the galactic plane.

We obtain sufficient precision on 4,000 stars to detect a close-in Jupiter-sized companion.

The Search Is On:The Search Is On:There are roughly a dozen similar wide-field surveys for There are roughly a dozen similar wide-field surveys for

transiting planets circling bright stars (8 < V < 12)transiting planets circling bright stars (8 < V < 12)

G. Mandushev (Lowell Obs.)

HST Search for Planets in 47 TucHST Search for Planets in 47 Tuc 34,000 main-sequence 34,000 main-sequence

stars were monitored for stars were monitored for 8.3 days8.3 days

Benefit of a cluster: Benefit of a cluster: apparent magnitude apparent magnitude implies a stellar (and implies a stellar (and hence planetary) radiushence planetary) radius

No planets were No planets were detected, whereas 17 detected, whereas 17 would have been would have been expected based on radial expected based on radial velocity surveysvelocity surveys

Implies that planets Implies that planets cannot form and survive cannot form and survive in this environment, likely in this environment, likely due to crowding and low-due to crowding and low-metallicitymetallicity

Gilliland et al. (2000)

New HST Survey New HST Survey Toward Galactic BulgeToward Galactic Bulge

Bulge is not affected by low-Bulge is not affected by low-metallicity or high stellar densitymetallicity or high stellar density

Sahu et al. monitored field in Sahu et al. monitored field in Sgr-I window for 7 days (Feb Sgr-I window for 7 days (Feb 2004), with additional epoch in 2004), with additional epoch in cycle 14 (proper motion)cycle 14 (proper motion)

100,000 stars to V=23, so 100,000 stars to V=23, so several dozen planets could be several dozen planets could be detecteddetected

Possibility of studying planet rate Possibility of studying planet rate as a function of stellar type and as a function of stellar type and metallicitymetallicity

Blends that mimic planetary Blends that mimic planetary transits are a concern, but effect transits are a concern, but effect can be mitigated by 2-color can be mitigated by 2-color photometry, centroiding, and, for photometry, centroiding, and, for brightest candidates, RV workbrightest candidates, RV work

Sahu et al. (2004)

The Kepler-HST ConnectionThe Kepler-HST Connection Kepler will monitor 100,000 Kepler will monitor 100,000

stars in a 10 deg square f.o.v. stars in a 10 deg square f.o.v. with a precision of better than with a precision of better than ~ 5 x 10~ 5 x 10-5-5

Primary goal: Determine the Primary goal: Determine the rate of occurrence of terrestrial rate of occurrence of terrestrial planets around Sun-like starsplanets around Sun-like stars

Kepler could uncover dozens of Kepler could uncover dozens of transiting gas giants during the transiting gas giants during the first year of operation: These first year of operation: These would be great targets for HST would be great targets for HST follow-up studyfollow-up study

Kepler could uncover dozens of Kepler could uncover dozens of transiting Earth-like planets. transiting Earth-like planets. HST/STIS would be the HST/STIS would be the onlyonly instrument capable of instrument capable of confirming these candidatesconfirming these candidates

Summary: Summary: The Future of HST & Transiting PlanetsThe Future of HST & Transiting Planets

HST enabled the first direct studies of an extrasolar HST enabled the first direct studies of an extrasolar planet, including an accurate determination of the radius, planet, including an accurate determination of the radius, a search for satellites, and a study of the atmospherea search for satellites, and a study of the atmosphere

This work allowed the community to develop these HST-This work allowed the community to develop these HST-based techniques, but we are in need of new targetsbased techniques, but we are in need of new targets

We need to encourage the numerous wide-field ground-We need to encourage the numerous wide-field ground-based surveys to deliver more transiting planets while based surveys to deliver more transiting planets while HST remains availableHST remains available

HST may soon produce transiting planets of its own via HST may soon produce transiting planets of its own via the survey of the Galactic bulgethe survey of the Galactic bulge

If HST can last into the Kepler Mission timescale, it could If HST can last into the Kepler Mission timescale, it could enable detailed studies of dozens of gas giant planets enable detailed studies of dozens of gas giant planets (2007), and the confirmation of terrestrial planet (2007), and the confirmation of terrestrial planet candidates (2010)candidates (2010)