Mancini, L and Giordano, M and Molliere, P and Southworth, J and Brahm, R and Ciceri, S and Henning, T (2016) An optical transmission spectrum of the transiting hot Jupiter in the metal-poor WASP-98 planetary system. Monthly Notices of the Royal Astronomical Society, 461 (1). 1053 - 1061. ISSN 1365-2966

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Abstract

The WASP-98 planetary system represents a rare case of a hot Jupiter hosted by a metal-poor main-sequence star. We present a follow-up study of this system based on multiband photometry and high-resolution spectroscopy. Two new transit events of WASP-98 b were simultaneously observed in four passbands (g′, r′, i′, z′), using the telescope-defocusing technique, yielding eight high-precision light curves with point-to-point scatters of less than 1 mmag. We also collected three spectra of the parent star with a high-resolution spectrograph, which we used to remeasure its spectral characteristics, in particular its metallicity. We found this to be very low, [Fe/H] = −0.49 ± 0.10, but larger than was previously reported, [Fe/H] = −0.60 ± 0.19. We used these new photometric and spectroscopic data to refine the orbital and physical properties of this planetary system, finding that the stellar and planetary mass measurements are significantly larger than those in the discovery paper. In addition, the multiband light curves were used to construct an optical transmission spectrum of WASP-98 b and probe the characteristics of its atmosphere at the terminator. We measured a lower radius at z′ compared with the other three passbands. The maximum variation is between the r′ and z′ bands, has a confidence level of roughly 6σ and equates to 5.5 pressure scale heights. We compared this spectrum to theoretical models, investigating several possible types of atmospheres, including hazy, cloudy, cloud-free, and clear atmospheres with titanium and vanadium oxide opacities. We could not find a good fit to the observations, except in the extreme case of a clear atmosphere with TiO and VO opacities, in which the condensation of Ti and V was suppressed. As this case is unrealistic, our results suggest the presence of an additional optical-absorbing species in the atmosphere of WASP-98 b, of unknown chemical nature.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: techniques, photometric, spectroscopic, stars, fundamental parameters, individual, WASP-98, planetary systems
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Faculty of Natural Sciences > School of Physical and Geographical Sciences
Related URLs:
Depositing User: Symplectic
Date Deposited: 01 Nov 2016 14:40
Last Modified: 19 Sep 2017 13:06
URI: http://eprints.keele.ac.uk/id/eprint/2394

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