TOI-1696: A Nearby M4 Dwarf with a 3 R _⊕ Planet in the Neptunian Desert

Abstract

We present the discovery and validation of a temperate sub-Neptune around the nearby mid-M dwarf TIC 470381900 (TOI-1696), with a radius of 3.09 ± 0.11 R ⊕ and an orbital period of 2.5 days, using a combination of Transiting Exoplanets Survey Satellite (TESS) and follow-up observations using ground-based telescopes. Joint analysis of multiband photometry from TESS, Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets (MuSCAT), MuSCAT3, Sinistro, and KeplerCam confirmed the transit signal to be achromatic as well as refined the orbital ephemeris. High-resolution imaging with Gemini/’Alopeke and high-resolution spectroscopy with the Subaru InfraRed Doppler (IRD) confirmed that there are no stellar companions or background sources to the star. The spectroscopic observations with IRD and Infrared Telescope Facility SpeX were used to determine the stellar parameters, and it was found that the host star is an M4 dwarf with an effective temperature of T eff = 3185 ± 76 K and a metallicity of [Fe/H] = 0.336 ± 0.060 dex. The radial velocities measured from IRD set a 2σ upper limit on the planetary mass to be 48.8 M ⊕. The large radius ratio (R p/R ⋆ ∼ 0.1) and the relatively bright near-infrared magnitude (J = 12.2 mag) make this planet an attractive target for further follow-up observations. TOI-1696 b is one of the planets belonging to the Neptunian desert with the highest transmission spectroscopy metric discovered to date, making it an interesting candidate for atmospheric characterizations with JWST.

Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Transmission Spectroscopy

“…Furthermore, the constrained impact parameter (b  0.9 at 3σ; see Section 4.5 and Table 2) and boxy transit shape (see Figure 7) eliminate the possibility of grazing transit geometries. We simulated eclipses for a range of plausible HEBs following the method of Mori et al (2022), which was based on Bouma et al (2020). Our simulations provided no configuration that can match the transit depth and transit shape observed in multiple bands with TESS and MuSCAT series.…”

The Discovery and Follow-up of Four Transiting Short-period Sub-Neptunes Orbiting M Dwarfs

“…We estimated the metallicity ([Fe/H]) and the effective temperature (T eff ) of four host stars using the IRD spectra following the procedure described in Mori et al (2022). For TOI-782 b, TOI-1448 b, and TOI-2120 b, we used the template spectra identical to those used for the RV analysis, but for TOI-2406 b, we used a combined spectrum before deconvolving the instrument profile to avoid amplifying the additional noise due to the low S/N.…”

“…We aim to compute the eclipse depths for a range of plausible HEBs in the bluest and reddest bandpasses where they are expected to vary significantly. We adopt the method presented in Mori et al (2022), which is based on Bouma et al (2020), to perform the calculation over a grid of eclipsing companions. 62 Comparing the simulated eclipse depth with the observed one (Section 3.4.2) in each band, we find that no plausible HEB configuration explored in our simulation can reproduce the observed transit depths in the multiple bands simultaneously as well as the transit shape.…”

M dwarfs found in the first Byurakan spectral sky survey database. Gaia EDR3 and TESS data. Some preliminary results

“…TESS data have been used in many studies devoted to detecting exoplanets around dwarf stars (Bryant & Bayliss 2022;Espinoza et al 2022;Gilbert et al 2022;Gan et al 2022;Giacalone et al 2022;Mori et al 2022;Vach et al 2022;Yee et al 2022). We here apply the same methodology in the search of planets around FBS M dwarfs.…”