Exoplanet Transit Spectroscopy with HST/WFC3: Probing H 2 O with New Precision

1. Exoplanet Transit Spectroscopy with HST/WFC3: Probing H2O with New Precision Avi M. Mandell NASA Goddard A Host of Collaborators: Korey Haynes Evan Sinukoff Drake Deming Ashlee Wilkins SukritRanjin David Charbonneau NikkuMadhusudhan Heather Knutson

2. Wide Field Camera 3 on the Hubble Space Telescope Single Exposure, 512 x 512 • New IR camera installed on the HST in May of 2009 • Two channels: optical (200 – 1000 nm) and IR (800 – 1700 nm) • IR Channel: 1024 x 1024 pixels covering 2.3 x 2.1 arcmin • Slitless grism spectroscopy provides two options for IR spectra • G102: λ= 0.8 – 1.15 μm, R = 210 • G141: λ= 1.1 – 1.7 μm, R = 130 0th Order 1st Order

3. 1.1 – 1.7 Microns: Measuring Water Absorption • Wavelength range samples both the strong water bands at 1.15 and 1.4 μm as well as continuum regions on either side • Contrast between the water features and continuum regions can reveal both the chemical composition as well as information on the temperature structure

4. Multiple Exoplanet Campaigns with HST/WFC3 • Berta et al. 2011: Transmission spectrum of GJ 1214 b • Examined instrument systematics in detail, identifying a characteristic single-orbit ramp in counts • Combined three transits to produce a well-constrained spectrum showing no water absorption within uncertainties • Heavy-element atmosphere or clouds? • Other programs are ongoing… • Gibson et al. (poster) • Swain et al. • Deming et al. (this talk, poster by Sukrit Ranjin)

5. Deming et al. Cycle 18 Program • Large collaboration focused on hot giant exoplanets • Sample of 16 objects • Most planets in the sample have radii significantly larger than expected from formation models • A number of planets may have upper-atmosphere temperature inversions • This talk will focus on 3 interesting cases: • WASP-17: Ultra-low density, retrograde orbit • WASP-18: Very massive planet in a 0.94-hr orbit (extremely hot!) • WASP-19: Shortest-period planet known (P ~ 19 hr) but no temperature inversion List of Observed/Scheduled Planets CoRoT-1 b CoRoT-2 b HAT-P-7 b HAT-P-12 b HAT-P-13 b HD189733 b HD209458 b TrES-2 b TrES-3 b TrES-4 b WASP-4 b WASP-12 b WASP-17 b WASP-18 b WASP-19 b XO-1 b WASP-18 WASP-19 WASP-17

6. Extracting & Correcting the White Light curves WASP-17 Transit: Total Counts • Tested several extraction methods (direct extraction vs. the STScI pipeline algorithm aXe) and various extraction box sizes • Similar to Berta et al., a ramp-up in measured counts is observed between each read-out of the buffer • Due to persistent charge build-up • However, characteristic shape of ramp is different for each object – unclear whether it is due to exposure level or differences in the buffer read-out options • As noted by Berta et al., ramp pattern can be removed extremely well by dividing by a mean of the out-of-transit data (divide-oot method) • Additional improvements can be made by subtracting a background-level spectrum derived from off-spectrum data 0.05 0.10 0.15 0.20 0.25 0.30 0.35 Days – Const. WASP-19 Transit: Total Counts 0.05 0.10 0.15 0.20 0.25 0.30 Days – Const.

7. Fitting Light curves With MCMC • We fit the data using a Markov Chain Monte Carlo (MCMC) analysis (Ford 2005) • Light curve model from Mandel & Agol (2002) • Priors for orbital and transit parameters taken from previous results • Additional components for linear trend over multi-orbit observational period (e.g. Berta et al.) as well as a possible sinusoidal component due to thermal emission • We compare our MCMC results with results from the TAP (Transit Analysis Package) program developed by Gazak et al. • Uncertainties are estimated from distribution of MCMC parameters; we test several types of restrictions on priors

8. Preliminary Results • First: No Spectroscopic Results Yet! Sorry! • Resolving some issues with spectral drift on the detector… • White-light photometry for the three transits matches up well with previous data at optical wavelengths (as we expected) – and the uncertainties are extremely small! • The white-light photometry for the WASP-19 eclipse data can be compared directly to models constrained by Spitzer (Anderson et al. 2012), and seems to be consistent with C/O ~ 1.0 Preliminary Results Removed Preliminary Results Removed

9. Next Steps • Finish correcting the data for motion across the chip, and fit binned sections of the spectra to determine the change in effective planetary radius across the spectrum • Fit the spectral extractions with models -- Madhusudhan et al., Burrows et al., etc. – to constrain the molecular composition, C/O ratio, and the temperature structure • Address the sample as a whole: what trends do we see in planets with similar equilibrium temperature, stellar type, mass/radius, stellar activity, etc?