Extrasolar Planets

Optical Transmission Spectroscopy of the Terrestrial Exoplanet LHS 3844b from 13 Ground-Based Transit Observations

By Keith Cowing
Press Release
astro-ph.EP
August 12, 2020
Filed under
Optical Transmission Spectroscopy of the Terrestrial Exoplanet LHS 3844b from 13 Ground-Based Transit Observations
Transmission spectrum of LHS 3844b compared to model atmospheres. The observed transmission spectrum (1-σ black error bars) is constructed from the inverse-variance weighted mean transit depths across the 13 data sets used in this analysis. They are the same 1-σ black error bars as in Figure 5, and the transit depth values are provided in the grey columns of Table 5. We test two sets of clear atmospheric models: 1) solar composition, and 2) 100% H2O steam. For each model case we test surface pressures from 0.01 - 10 bar. The σ values in the legend are the confidence to which we can rule out each model. We also compare the observed transmission spectrum to a flat line, which is more consistent with the observations.
astro-ph.EP

Atmospheric studies of spectroscopically accessible terrestrial exoplanets lay the groundwork for comparative planetology between these worlds and the Solar System terrestrial planets.

LHS 3844b is a highly-irradiated terrestrial exoplanet (R=1.303+/-0.022R_Earth) orbiting a mid-M dwarf 15 parsecs away. Work based on near-infrared Spitzer phase curves ruled out atmospheres with surface pressures >/=10 bars on this planet. We present 13 transit observations of LHS 3844b taken with the Magellan Clay telescope and the LDSS3C multi-object spectrograph covering 620-1020 nm.

We analyze each of the 13 data sets individually using a Gaussian process regression, and present both white and spectroscopic light curves. In the combined white light curve we achieve an RMS precision of 65 ppm when binning to 10-minutes. The mean white light curve value of (Rp/Rs)^2 is 0.4170+/-0.0046%. To construct the transmission spectrum, we split the white light curves into 20 spectrophotometric bands, each spanning 20 nm, and compute the mean values of (Rp/Rs)^2 in each band.

We compare the transmission spectrum to two sets of atmospheric models. We disfavor a clear, solar composition atmosphere (mu=2.34) with surface pressures >/=0.1 bar to 5.2-sigma confidence. We disfavor a clear, H2O steam atmosphere (mu=18) with surface pressures >/=0.1 bar to low confidence (2.9-sigma).

Our observed transmission spectrum favors a flat line. For solar composition atmospheres with surface pressures >/=1 bar we rule out clouds with cloud-top pressures of 0.1 bar (5.3-sigma), but we cannot address high-altitude clouds at lower pressures. Our results add further evidence that LHS 3844b is devoid of an atmosphere.

Hannah Diamond-Lowe, David Charbonneau, Matej Malik, Eliza M.-R. Kempton, Yuri Beletsky
Comments: 16 pages; 8 figures; accepted to AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2008.05444 [astro-ph.EP] (or arXiv:2008.05444v1 [astro-ph.EP] for this version)
Submission history
From: Hannah Diamond-Lowe
[v1] Wed, 12 Aug 2020 17:12:07 UTC (1,774 KB)
https://arxiv.org/abs/2008.05444
Astrobiology

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