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

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${}_{\mathrm{eff}}$ = 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.

Accepted for Publication in the Astronomical Journal