The Discovery and Follow-up of Four Transiting Short-period Sub-Neptunes Orbiting M dwarfs
The Astronomical Journal(2024)
Abstract
Sub-Neptunes with 2-3R_⊕ are intermediate in size between rocky
planets and Neptune-sized planets. The orbital properties and bulk compositions
of transiting sub-Neptunes provide clues to the formation and evolution of
close-in small planets. In this paper, we present the discovery and follow-up
of four sub-Neptunes orbiting M dwarfs (TOI-782, TOI-1448, TOI-2120, and
TOI-2406), three of which were newly validated by ground-based follow-up
observations and statistical analyses. TOI-782 b, TOI-1448 b, TOI-2120 b, and
TOI-2406 b have radii of R_p = 2.740^+0.082_-0.079 R_⊕,
2.769^+0.073_-0.068 R_⊕, 2.120±0.067 R_⊕, and
2.830^+0.068_-0.066 R_⊕ and orbital periods of P = 8.02, 8.11,
5.80, and 3.08 days, respectively. Doppler monitoring with Subaru/InfraRed
Doppler instrument led to 2σ upper limits on the masses of <19.1M_⊕, <19.5 M_⊕, <6.8 M_⊕, and <15.6 M_⊕ for
TOI-782 b, TOI-1448 b, TOI-2120 b, and TOI-2406 b, respectively. The
mass-radius relationship of these four sub-Neptunes testifies to the existence
of volatile material in their interiors. These four sub-Neptunes, which are
located above the so-called “radius valley”, are likely to retain a
significant atmosphere and/or an icy mantle on the core, such as a water world.
We find that at least three of the four sub-Neptunes (TOI-782 b, TOI-2120 b,
and TOI-2406 b) orbiting M dwarfs older than 1 Gyr, are likely to have
eccentricities of e ∼ 0.2-0.3. The fact that tidal circularization of
their orbits is not achieved over 1 Gyr suggests inefficient tidal dissipation
in their interiors.
MoreTranslated text
Key words
Exoplanets,Mini Neptunes,Radial velocity,Transit photometry,Tides,M dwarf stars
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