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arXiv · 2303.07381

LRG-BEASTS: Evidence for clouds in the transmission spectrum of HATS-46 b

E. Ahrer·P. J. Wheatley·S. Gandhi·J. Kirk·G. W. King·T. Louden·L. Welbanks
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Abstract

We have performed low-resolution ground-based spectroscopy of HATS-46 b in transmission, using the EFOSC2 instrument on the ESO New Technology Telescope (NTT). HATS-46 b is a highly-inflated exoplanet that is a prime target for transmission spectroscopy, having a Jupiter-like radius (0.95 R$_\textrm{Jup}$) but a much lower mass (0.16 M$_\textrm{Jup}$). It orbits a G-type star with a 4.7 d period, giving an equilibrium temperature of 1100 K. We observed one transit of HATS-46 b with the NTT, with the time-series spectra covering a wavelength range of 3900 - 9000 Angstrom at a resolution of $R \sim 380$. We achieved a remarkably precise transmission spectrum of 1.03 $\times$ photon noise, with a median uncertainty of $357$ ppm for $\sim 200$ Angstrom wide bins, despite the relative faintness of the host star with $V_{\mathrm{mag}} = 13.6$. The transmission spectrum does not show strong absorption features and retrievals favour a cloudy model, ruling out a clear atmosphere with $3.0σ$ confidence. We also place a conservative upper limit on the sodium abundance under the alternative scenario of a clear atmosphere. This is the eighth planet in the LRG-BEASTS survey, which uses 4m-class telescopes such as the NTT to obtain low-resolution transmission spectra of hot Jupiters with precisions of around one atmospheric scale height.

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E. Ahrer, P. J. Wheatley, S. Gandhi, J. Kirk, G. W. King, T. Louden, L. Welbanks. 2023-03-13. LRG-BEASTS: Evidence for clouds in the transmission spectrum of HATS-46 b. https://doi.org/10.1093/mnras%2Fstad779

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