Abstract
We present the discovery of a transiting mini-Neptune around TOI-1201, a relatively bright and moderately young early M dwarf (J ≈ 9.5 mag, ~600–800 Myr) in an equal-mass ~8 arcsecond-wide binary system, using data from the Transiting Exoplanet Survey Satellite, along with follow-up transit observations. With an orbital period of 2.49 d, TOI-1201 b is a warm mini-Neptune with a radius of Rb = 2.415 ± 0.090 R⊕. This signal is also present in the precise radial velocity measurements from CARMENES, confirming the existence of the planet and providing a planetary mass of Mb = 6.28 ± 0.88 M⊕ and, thus, an estimated bulk density of 2.45−0.42+0.48 g cm−3. The spectroscopic observations additionally show evidence of a signal with a period of 19 d and a long periodic variation of undetermined origin. In combination with ground-based photometric monitoring from WASP-South and ASAS-SN, we attribute the 19 d signal to the stellar rotation period (Prot = 19–23 d), although we cannot rule out that the variation seen in photometry belongs to the visually close binary companion. We calculate precise stellar parameters for both TOI-1201 and its companion. The transiting planet is anexcellent target for atmosphere characterization (the transmission spectroscopy metric is 97−16+21) with the upcoming James Webb Space Telescope. It is also feasible to measure its spin-orbit alignment via the Rossiter-McLaughlin effect using current state-of-the-art spectrographs with submeter per second radial velocity precision.
Highlights
Results from the Kepler (Borucki et al 2010; Mathur et al 2017) and K2 (Howell et al 2014) missions have revealed that M dwarfs (Teff 4000 K) host on average ∼2.5 planets with radii below 4 R⊕ and with periods of less than 200 d (e.g., Dressing & Charbonneau 2013, 2015)
In the case of core-powered mass loss, the planet’s heating originates from infrared (IR) radiation coming from the cooling planetary interior, while photo-evaporation is due to extreme ultraviolet photons from the host star
We find ourselves in an era in which the ongoing Transiting Exoplanet Survey Satellite (TESS; Ricker et al 2015) mission is set to find such targets that will be suitable for transmission spectroscopy using the future James Webb Space Telescope (JWST; Gardner et al 2009)
Summary
Results from the Kepler (Borucki et al 2010; Mathur et al 2017) and K2 (Howell et al 2014) missions have revealed that M dwarfs (Teff 4000 K) host on average ∼2.5 planets with radii below 4 R⊕ and with periods of less than 200 d (e.g., Dressing & Charbonneau 2013, 2015). Within the Tess Follow-up Observing Program (TFOP) “Seeing-limited Photometry” SG1 subgroup, the first follow-up transit photometric data immediately indicated that TOI-1201 was the correct stellar host and not TOI-393 Sector 4 light curve into three chunks, which we shifted using a sinusoidal signal with a period of 20.5 ± 0.5 d and amplitude variations of ∼6.7 ppt (Fig. D.1) These data support the 21 d signal, though yet again, the TESS pixel (21 arcsec) contains both objects. Establish the rotational period of TOI-1201 to be 19–23 d
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