JWST COMPASS: NIRSpec/G395H Transmission Observations of the Super-Earth TOI-836b

• Main Authors: Alderson, Lili, Batalha, Natasha E, Wakeford, Hannah R, Wallack, Nicole L, Aguichine, Artyom, Teske, Johanna, Redai, Jea Adams, Alam, Munazza K, Batalha, Natalie M, Gao, Peter, Kirk, James, Lopez-Morales, Mercedes, Moran, Sarah E, Scarsdale, Nicholas, Wogan, Nicholas F, Wolfgang, Angie
• Format: Journal Article
• Language: English
• Published: 29-03-2024
• Subjects: Physics - Earth and Planetary Astrophysics
• DOI: 10.48550/arxiv.2404.00093

We present two transit observations of the ~870K, 1.7R$_E$ super-Earth
TOI-836b with JWST NIRSpec/G395H, resulting in a 2.8-5.2$\mu$m transmission
spectrum. Using two different reduction pipelines, we obtain a median transit
depth precision of 34ppm for Visit 1 and 36ppm for Visit 2, leading to a
combined precision of 25ppm in spectroscopic channels 30 pixels wide
(~0.02$\mu$m). We find that the transmission spectrum from both visits is well
fit by a zero-sloped line by fitting zero-sloped and sloped lines, as well as
step functions to our data. Combining both visits, we are able to rule out
atmospheres with metallicities <250xSolar for an opaque pressure level of 0.1
bar, corresponding to mean molecular weights to <6gmol$^{-1}$. We therefore
conclude that TOI-836b does not have an H$_2$-dominated atmosphere, in possible
contrast with its larger, exterior sibling planet, TOI-836c. We recommend that
future proposals to observe small planets exercise caution when requiring
specific numbers of transits to rule out physical scenarios, particularly for
high metallicities and planets around bright host stars, as PandExo predictions
appear to be more optimistic than that suggested by the gains from additional
transits implied by our data.