HST/STIS Transmission Spectral Survey: Probing the Atmospheres of HAT-P-1b and WASP-6b

N. Nikolov, D. K. Sing, F. Pont, A. S. Burrows, J. J. Fortney, G. E. Ballester, T. M. Evans, C. M. Huitson, H. R. Wakeford, P. A. Wilson, S. A. D., N. P. Gibson, G. W. Henry, H. Knutson, A. L. d. Etangs, A. P. Showman, A. Vidal-Madjar, K. Zahnle

Research output: Chapter in Book/Report/Conference proceedingConference contribution


We present optical to near-infrared transmission spectra of HAT-P-1b and WASP-6b, part of a Large HST/STIS hot Jupiter transmission spectral survey (P.I. David Sing). The spectra for each target cover the regimes 2900-5700Å and 5240-10270Å, with resolving power of R = 500. The HAT-P-1b data is coupled with a recent HST/WFC3 transit, spanning the wavelength range 1.087-1.687microns (R=130), acquired in spatial scan mode. The WASP-6b data is complemented with Spritzer/IRAC 3.6 and 4.5 micron transit observations, part of a comparative exoplanetology program (P.I. Jean-Michel Desert). The transmission spectrum of HAT-P-1b shows a strong absorption signature shortward of 5500Å, with a strong blueward slope into the near-UV. We detect atmospheric sodium absorption at a 3.3s significance level, but see no evidence for the potassium feature. The red data implies a marginally flat spectrum with a tentative absorption enhancement at wavelength longer than ~8500Å. The combined STIS and WFC3 optical to NIR spectra differ significantly in absolute radius level (4.3+/-1.6 pressure scale heights), implying strong optical absorption in the atmosphere of HAT-P-1b. The optical to nearinfrared difference cannot be explained by stellar activity, as simultaneous stellar activity monitoring of the G0V HAT-P-1b host star and its identical companion show no significant activity that could explain the result. The red transmission spectrum of WASP-6b is flat with tentative detection of sodium and potassium. We compare both spectra with theoretical atmospheric models, which include haze, sodium and an extra optical absorber in the case of HAT-P-1b. We find that both an optical absorber and a super-solar sodium to water abundance ratio might be a scenario explaining the HAT-P-1b observations.
Original languageEnglish
Title of host publicationSearch for Life Beyond the Solar System. Exoplanets, Biosignatures amp Instruments
EditorsD. Apai, P. Gabor
Publication statusPublished - 01 Mar 2014


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