JWST COMPASS: NIRSpec/G395H Transmission Observations of the Super-Earth TOI-776b

TL;DR

This study presents JWST NIRSpec/G395H transmission spectra of super-Earth TOI-776b, demonstrating the capability to constrain atmospheric metallicity and highlighting observational challenges and consistency across independent data reductions.

Contribution

First JWST transmission observations of TOI-776b, providing atmospheric metallicity constraints and analyzing data reduction consistency and detector offsets.

Findings

Ruled out metallicities up to 100× solar in one visit and beyond 350× solar in another.

Achieved 34ppm median transit depth precision in spectroscopic channels.

Identified differences in spectral structure between independent reductions and visits.

Abstract

We present two transit observations of the $\sim$520K, 1.85R$_\oplus$, 4.0M$_\oplus$ super-Earth TOI-776b with JWST NIRSpec/G395H, resulting in a 2.8-5.2$\mu$m transmission spectrum. Producing reductions using the ExoTiC-JEDI and Eureka! pipelines, we obtain a median transit depth precision of 34ppm for both visits and both reductions in spectroscopic channels 30 pixels wide ($\sim$0.02$\mu$m). We find that our independent reductions produce consistent transmission spectra, however, each visit shows differing overall structure. For both reductions, a flat line is preferred for Visit 1 while a flat line with an offset between the NRS1 and NRS2 detectors is preferred for Visit 2; however, we are able to correct for this offset during our modeling analysis following methods outlined in previous literature. Using picaso forward models, we can rule out metallicities up to at least 100$\times$ solar with an opaque pressure of 10$^{-3}$ bar to $\geq$3$\sigma$ in all cases, however, the exact lower limit varies between the visits, with Visit 1 ruling out $\lesssim$100$\times$ solar while the lower limits for Visit 2 extend beyond $\sim$350$\times$ solar. Our results add to the growing list of super-Earth atmospheric constraints by JWST, which provide critical insight into the diversity and challenges of characterizing terrestrial planets.