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arXiv · 1310.0083

HST hot Jupiter Transmission Spectral Survey: A detection of Na and strong optical absorption in HAT-P-1b

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. Aigrain·D. Deming·N. P. Gibson·G. W. Henry·H. Knutson·A. Lecavelier des Etangs·A. P. Showman·A. Vidal-Madjar·K. Zahnle
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Abstract

We present an optical to near-infrared transmission spectrum of the hot Jupiter HAT-P-1b, based on HST observations, covering the spectral regime from 0.29 to 1.027{\mu}m with STIS, which is coupled with a recent WFC3 transit (1.087 to 1.687{\mu}m). We derive refined physical parameters of the HAT-P-1 system, including an improved orbital ephemeris. The transmission spectrum shows a strong absorption signature shortward of 0.55{\mu}m, with a strong blueward slope into the near-ultraviolet. We detect atmospheric sodium absorption at a 3.3{\sigma} significance level, but find no evidence for the potassium feature. The red data implies a marginally flat spectrum with a tentative absorption enhancement at wavelength longer than ~0.85{\mu}m. The STIS and WFC3 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 near-infrared difference cannot be explained by stellar activity, as simulta- neous stellar activity monitoring of the G0V HAT-P-1b host star and its identical companion show no significant activity that could explain the result. We compare the complete STIS and WFC3 transmission spectrum with theoretical atmospheric mod- els which include haze, sodium and an extra optical absorber. We find that both an optical absorber and a super-solar sodium to water abundance ratio might be a sce- nario explaining the HAT-P-1b observations. Our results suggest that strong optical absorbers may be a dominant atmospheric feature in some hot Jupiter exoplanets.

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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. Aigrain, D. Deming, N. P. Gibson, G. W. Henry, H. Knutson, A. Lecavelier des Etangs, A. P. Showman, A. Vidal-Madjar, K. Zahnle. 2013-09-30. HST hot Jupiter Transmission Spectral Survey: A detection of Na and strong optical absorption in HAT-P-1b. https://doi.org/10.1093/mnras/stt1859

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