Transit Spectroscopy with HST/WFC3 January 18, 2012 Exoplanet Transit Spectroscopy with HST/WFC3: Probing H 2 O with New Precision Avi M. Mandell NASA Goddard A Host of Collaborators: Korey Haynes Evan Sinukoff Drake Deming Ashlee Wilkins Sukrit Ranjin David Charbonneau Nikku Madhusudhan Heather Knutson

Transit Spectroscopy with HST/WFC3 January 18, 2012 Wide Field Camera 3 on the Hubble Space Telescope 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 = th Order1 st Order Single Exposure, 512 x 512

Transit Spectroscopy with HST/WFC3 January 18, – 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

Transit Spectroscopy with HST/WFC3 January 18, 2012 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)

Transit Spectroscopy with HST/WFC3 January 18, 2012 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 CoRoT-1 b CoRoT-2 b HAT-P-7 b HAT-P-12 b HAT-P-13 b HD b HD 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 List of Observed/Scheduled Planets WASP-19 WASP-18 WASP-17

Transit Spectroscopy with HST/WFC3 January 18, 2012 Extracting & Correcting the White Light curves 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 Days – Const. WASP-17 Transit: Total Counts Days – Const. WASP-19 Transit: Total Counts

Transit Spectroscopy with HST/WFC3 January 18, 2012 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

Transit Spectroscopy with HST/WFC3 January 18, 2012 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

Transit Spectroscopy with HST/WFC3 January 18, 2012 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?