HD 179949b: A Close Orbiting Extrasolar Giant Planet with a stratosphere?

TL;DR

This study used high-resolution near-infrared spectroscopy to search for atmospheric signatures of the close-orbiting exoplanet HD 179949b, setting new limits on its contrast ratio and atmospheric composition.

Contribution

First to place deep near-infrared contrast limits on HD 179949b, testing models of atmospheric emission and absorption signatures with phase-dependent spectroscopic techniques.

Findings

No planetary signal detected in the observed spectral region.

Ruled out absorption-dominated atmospheres at contrast ratio ~1/3350.

Set the deepest contrast limits yet for a close-orbiting exoplanet.

Abstract

We have carried out a search for the 2.14 micron spectroscopic signature of the close orbiting extrasolar giant planet, HD 179949b. High cadence time series spectra were obtained with the CRIRES spectrograph at VLT1 on two closely separated nights. Deconvolution yielded spectroscopic profiles with mean S/N ratios of several thousand, enabling the near infrared contrast ratios predicted for the HD 179949 system to be achieved. Recent models have predicted that the hottest planets may exhibit spectral signatures in emission due to the presence of TiO and VO which may be responsible for a temperature inversion high in the atmosphere. We have used our phase dependent orbital model and tomographic techniques to search for the planetary signature under the assumption of an absorption line dominated atmospheric spectrum, where T and V are depleted from the atmospheric model, and an emission line dominated spectrum, where TiO and VO are present. We do not detect a planet in either case, but the 2.120 - 2.174 micron wavelength region covered by our observations enables the deepest near infrared limits yet to be placed on the planet/star contrast ratio of any close orbiting extrasolar giant planet system. We are able to rule out the presence of an atmosphere dominated by absorption opacities in the case of HD 179949b at a contrast ratio of F_p/F_* ~ 1/3350, with 99 per cent confidence.