A transiting, temperate mini-Neptune orbiting the M dwarf TOI-1759 unveiled by TESS

Abstract

We report the discovery and characterization of TOI-1759 b, a temperate (400 K) sub-Neptune-sized exoplanet orbiting the M dwarf TOI-1759 (TIC 408636441). TOI-1759 b was observed by TESS to transit on sectors 16, 17 and 24, with only one transit observed per sector, creating an ambiguity on the orbital period of the planet candidate. Ground-based photometric observations, combined with radial-velocity measurements obtained with the CARMENES spectrograph, confirm an actual period of 18.85019±0.00014 d. A joint analysis of all available photometry and radial velocities reveal a radius of 3.17 ± 0.10 R ⊕ and a mass of 10.8 ± 1.5 M ⊕ . Combining this with the stellar properties derived for TOI-1759 (R = 0.597 ± 0.015 R ; M = 0.606 ± 0.020 M ; T eff = 4065 ± 51 K), we compute a transmission spectroscopic metric (TSM) value of over 80 for the planet, making it a good target for transmission spectroscopy studies. TOI-1759 b is among the top five temperate, small exoplanets (T eq < 500 K, R p < 4 R ⊕ ) with the highest TSM discovered to date. Two additional signals with periods of 80 d and > 200 d seem to be present in our radial velocities. While our data suggest both could arise from stellar activity, the later signal's source and periodicity are hard to pinpoint given the ∼ 200 d baseline of our radial-velocity campaign with CARMENES. Longer baseline radial-velocity campaigns should be performed in order to unveil the true nature of this long period signal.

The HD 260655 system: Two rocky worlds transiting a bright M dwarf at 10 pc

“…The presence of haze also damps the spectral features, especially at shorter wavelengths, and more severely in case of enhanced metallicity. Similar trends with enhanced metallicity or haze were also observed in simulations made for other planets (e.g., Nowak et al 2020;Trifonov et al 2021;Espinoza et al 2022). We conclude that a single transit observation with any of these JWST and HST modes would be sufficient for robust detection of the molecular features in the H/He-dominated scenarios, otherwise placing tight constraints on the presence of such species and/or of an H/He envelope.…”

GJ 806 (TOI-4481): A bright nearby multi-planetary system with a transiting hot, low-density super-Earth

“…The presence of haze significantly dampens the spectral features at wavelengths shorter than 2 µm, but some features remain detectable with just one transit observation even in case of enhanced metallicity and haze. Similar trends with enhanced metallicity or haze were also observed in simulations made for other planets (e.g., Espinoza et al 2022). Interestingly, the spectrum for the H 2 O-dominated atmosphere presents absorption features of ∼60 ppm, that might be detected with high significance by combining a few visits.…”