Broad-band spectrophotometry of the hot Jupiter HAT-P-12b from the near-UV to the near-IR

TL;DR

This study uses broad-band spectrophotometry over a wide wavelength range to analyze the atmosphere of exoplanet HAT-P-12b, finding a flat spectrum indicative of clouds and refining transit parameters without detecting additional planets.

Contribution

First comprehensive broad-band spectrophotometry of HAT-P-12b from near-UV to near-IR, revealing a flat spectrum and constraining atmospheric properties and transit parameters.

Findings

No Rayleigh slope detected, spectrum is flat suggesting clouds.

Refined transit parameters and ephemeris with no evidence of additional planets.

Host star shows mild variability but no clear rotation period.

Abstract

The detection of trends or gradients in the transmission spectrum of extrasolar planets is possible with observations at very low spectral resolution. Transit measurements of sufficient accuracy using selected broad-band filters allow for an initial characterization of the atmosphere of the planet. We obtained time series photometry of 20 transit events and analyzed them homogeneously, along with eight light curves obtained from the literature. In total, the light curves span a range from 0.35 to 1.25 microns. During two observing seasons over four months each, we monitored the host star to constrain the potential influence of starspots on the derived transit parameters. We rule out the presence of a Rayleigh slope extending over the entire optical wavelength range, a flat spectrum is favored for HAT-P-12b with respect to a cloud-free atmosphere model spectrum. A potential cause of such gray absorption is the presence of a cloud layer at the probed latitudes. Furthermore, in this work we refine the transit parameters, the ephemeris and perform a TTV analysis in which we found no indication for an unseen companion. The host star showed a mild non-periodic variability of up to 1%. However, no stellar rotation period could be detected to high confidence.