Spectroscopic Time-series Performance of JWST/NIRSpec from Commissioning Observations

Néstor Espinoza, Leonardo Úbeda, Stephan M. Birkmann, Pierre Ferruit, Jeff A. Valenti, David K. Sing, Zafar Rustamkulov, Michael Regan, Sarah Kendrew, Elena Sabbi, Everett Schlawin, Thomas Beatty, Loïc Albert, Thomas P. Greene, Nikolay Nikolov, Diane Karakla, Charles Keyes, Nimisha Kumari, Catarina Alves de Oliveira, Torsten Böker, Maria Peña-Guerrero, Giovanna Giardino, Elena Manjavacas, Charles Proffitt, Timothy Rawle

Submitted on 2 November 2022


We report on JWST commissioning observations of the transiting exoplanet HAT-P-14 b, obtained using the Bright Object Time Series (BOTS) mode of the NIRSpec instrument with the G395H/F290LP grating/filter combination (35μm). While the data were used primarily to verify that the NIRSpec BOTS mode is working as expected, and to enable it for general scientific use, they yield a precise transmission spectrum which we find is featureless down to the precision level of the instrument, consistent with expectations given HAT-P-14~b's small scale-height and hence expected atmospheric features. The exquisite quality and stability of the \emph{JWST/NIRSpec} transit spectrum -- almost devoid of any systematic effects -- allowed us to obtain median uncertainties of 50-60 ppm in this wavelength range at a resolution of R=100 in a single exposure, which is in excellent agreement with pre-flight expectations and close to the (or at the) photon-noise limit for a J=9.094, F-type star like HAT-P-14. These observations showcase the ability of NIRSpec/BOTS to perform cutting-edge transiting exoplanet atmospheric science, setting the stage for observations and discoveries to be made in Cycle 1 and beyond.


Comment: 16 pages, 14 figures; part of the PASP Focus Issue "JWST Time-Series Observations: Commissioning Performance". Paper after the first round of referee comments; inputs welcome

Subjects: Astrophysics - Earth and Planetary Astrophysics; Astrophysics - Instrumentation and Methods for Astrophysics