TOI-1696 and TOI-2136: Constraining the Masses of Two Mini-Neptunes with HPF

TL;DR

This study validates two mini-Neptune exoplanets orbiting M dwarf stars, providing refined orbital and size data, and highlights TOI-2136b as a prime target for atmospheric studies with JWST.

Contribution

The paper presents the validation and characterization of two mini-Neptune planets around M dwarfs using multi-method observations, including radial velocities and high-contrast imaging.

Findings

TOI-1696b has a radius of 3.24 R⊕ and an upper mass limit of 56.6 M⊕.

TOI-2136b has a radius of 2.09 R⊕ and an upper mass limit of 15.0 M⊕.

TOI-2136b is an excellent candidate for atmospheric follow-up with JWST.

Abstract

We present the validation of two planets orbiting M dwarfs, TOI-1696b and TOI-2136b. Both planets are mini-Neptunes orbiting nearby stars, making them promising prospects for atmospheric characterization with the James Webb Space Telescope. We validated the planetary nature of both candidates using high contrast imaging, ground-based photometry, and near-infrared radial velocities. Adaptive Optics images were taken using the ShARCS camera on the 3 m Shane Telescope. Speckle images were taken using the NN-Explore Exoplanet Stellar Speckle Imager on the WIYN 3.5 m telescope. Radii and orbital ephemerides were refined using a combination of TESS, the diffuser-assisted ARCTIC imager on the 3.5m ARC telescope at Apache Point Observatory, and the 0.6 m telescope at Red Buttes Observatory. We obtained radial velocities using the Habitable-Zone Planet Finder on the 10 m Hobby-Eberly Telescope, which enabled us to place upper limits on the masses of both transiting planets. TOI-1696b (P = 2.5 days; R$_{p}$ = 3.24 R$_{\oplus}$; M$_{p}$ $<$ 56.6 M$_{\oplus}$) falls into a sparsely-populated region of parameter space considering its host star's temperature (T$_{\rm{eff}}$ = 3168 K, M4.5), as planets of its size are quite rare around mid to late M dwarfs. On the other hand, TOI-2136b (P = 7.85 days; R$_{p}$ = 2.09 R$_{\oplus}$; M$_{p}$ $<$ 15.0 M$_{\oplus}$) is an excellent candidate for atmospheric follow-up with JWST.