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Arxiv: JWST COMPASS: NIRSpec/G395H Transmission Observations of the Super-Earth TOI-836b Published: 3/29/2024 9:01:34 PM Updated: 3/29/2024 9:01:34 PM

Paper abstract: We present two transit observations of the ~870K, 1.7R_E super-EarthTOI-836b with JWST NIRSpec/G395H, resulting in a 2.8-5.2\mum transmissionspectrum. Using two different reduction pipelines, we obtain a median transitdepth precision of 34ppm for Visit 1 and 36ppm for Visit 2, leading to acombined precision of 25ppm in spectroscopic channels 30 pixels wide(~0.02\mum). We find that the transmission spectrum from both visits is wellfit by a zero-sloped line by fitting zero-sloped and sloped lines, as well asstep functions to our data. Combining both visits, we are able to rule outatmospheres with metallicities <250xSolar for an opaque pressure level of 0.1bar, corresponding to mean molecular weights to <6gmol^{-1}. We thereforeconclude that TOI-836b does not have an H_2-dominated atmosphere, in possiblecontrast with its larger, exterior sibling planet, TOI-836c. We recommend thatfuture proposals to observe small planets exercise caution when requiringspecific numbers of transits to rule out physical scenarios, particularly forhigh metallicities and planets around bright host stars, as PandExo predictionsappear to be more optimistic than that suggested by the gains from additionaltransits implied by our data.