Transmission Spectroscopy of WASP-79b from 0.6 to 5.0 $\mu$m

TL;DR

This study presents a comprehensive transmission spectroscopy analysis of hot Jupiter WASP-79b across 0.6 to 5.0 micrometers, constraining its water abundance and atmospheric composition, and highlighting its suitability for JWST observations.

Contribution

First combined multi-instrument spectroscopic study of WASP-79b, constraining water abundance and atmospheric composition, and updating its ephemeris for future JWST observations.

Findings

Water abundance constrained to --2.20 to --1.55 in log scale.

Atmospheric retrieval favors FeH and H- inclusion.

WASP-79b is a prime target for JWST ERS and Panchromatic Transmission programs.

Abstract

As part of the PanCET program, we have conducted a spectroscopic study of WASP-79b, an inflated hot Jupiter orbiting an F-type star in Eridanus with a period of 3.66 days. Building on the original WASP and TRAPPIST photometry of Smalley et al (2012), we examine HST/WFC3 (1.125 - 1.650 $\mu$m), Magellan/LDSS-3C (0.6 - 1 $\mu$m) data, and Spitzer data (3.6 and 4.5 $\mu$m). Using data from all three instruments, we constrain the water abundance to be --2.20 $\leq$ log(H$_2$O) $\leq$ --1.55. We present these results along with the results of an atmospheric retrieval analysis, which favor inclusion of FeH and H$^-$ in the atmospheric model. We also provide an updated ephemeris based on the Smalley, HST/WFC3, LDSS-3C, Spitzer, and TESS transit times. With the detectable water feature and its occupation of the clear/cloudy transition region of the temperature/gravity phase space, WASP-79b is a target of interest for the approved JWST Director's Discretionary Early Release Science (DD ERS) program, with ERS observations planned to be the first to execute in Cycle 1. Transiting exoplanets have been approved for 78.1 hours of data collection, and with the delay in the JWST launch, WASP-79b is now a target for the Panchromatic Transmission program. This program will observe WASP-79b for 42 hours in 4 different instrument modes, providing substantially more data by which to investigate this hot Jupiter.