TOI-1743 b, TOI-5799 b, TOI-5799 c and TOI-6223 b: TESS discovery and validation of four super-Earth to Neptune-sized planets around M dwarfs

TL;DR

This study reports the discovery and validation of four transiting planets around bright M-dwarf stars using TESS data complemented by extensive ground-based photometry, high-resolution imaging, and spectroscopy. By combining DV tests, SHERLOCK/sector analyses, and TRICERATOPS statistics with global modeling in EXOFASTv2 and SED fitting, the authors derive precise planetary radii ($R_p \approx$ 1.7–1.8 $R_\oplus$ for three planets and $\sim5.1\,R_\oplus$ for TOI-6223 b) and temperatures, and identify TOI-5799 c as a temperate super-Earth near the inner edge of the HZ. The planets lie in key regions of the period-radius plane: TOI-1743 b, TOI-5799 b, and TOI-5799 c near the radius valley for low-mass stars, while TOI-6223 b sits on the Neptunian ridge, offering constraints on migration and atmospheric retention. The targets are excellent for radial velocity follow-up and JWST atmospheric characterization, with simulations indicating detectable molecular signatures and favorable transmission spectroscopy metrics, particularly for TOI-5799 c, making these systems valuable for understanding planet formation and the evolution of sub-Neptunes around M dwarfs.

Abstract

We present the discovery by the TESS mission of one transiting Neptune-sized planet, TOI-6223 b and two transiting super-Earths, TOI-1743 b and TOI-5799 b. We validate these planets using a statistical validation method, multi-color light curves and other ancillary observations. We combined TESS and ground-based photometric data to constrain the physical properties of the planets. TOI-6223-b is slightly larger than Neptune ($R_p=5.12^{+0.24}_{-0.25}$ $R_\oplus$) orbiting an early M dwarf in 3.86 days, and it has an equilibrium temperature of $T_{\rm eq}=714\pm14$ K. TOI-1743 b orbits its M4V star every 4.27 days. It has a radius of $R_p=1.83^{+0.11}_{-0.10}$ $R_\oplus$ and an equilibrium temperature of $T_{\rm eq}=485^{+14}_{-13}$ K. TOI-5799 b has a radius of $R_p=1.733^{+0.096}_{-0.090}$ $R_\oplus$, and an equilibrium temperature of $T_{\rm eq}=505\pm16$ K orbits an M2 dwarf in 4.17 days. We also present the discovery of an additional transiting planet, TOI-5799 c, that we identified in the TESS data and validated using the SHERLOCK pipeline. TOI-5799 c is a super-Earth with a radius of $R_p=1.76^{+0.11}_{-0.10}$ $R_\oplus$. Its orbital period and its equilibrium temperature are 14.01 days and $T_{\rm eq}=337\pm11$ K, which place it near the inner edge of the habitable zone of its star.We show that these planets are suitable for both radial velocity follow-up and atmospheric characterization. They orbit bright (< 11 $K_{mag}$) early M dwarfs, making them accessible for precise mass measurements. The combination of the planet sizes and stellar brightness of their host stars also make them suitable targets for atmospheric exploration with the JWST. Such studies may provide insights into planet formation and evolution, as TOI-1743-b, TOI-5799-b, and TOI-5799-c lie within the so-called radius valley, while TOI-6223-b is located on the Neptunian ridge in the period-radius plane.

Figures (19)

• Figure 1: Contaminating sources within the SPOC aperture (red mask) overlaid on the heat map from TESS observations of the target stars: TOI-1743 (left panel), TOI-5799 (middle panel) and TOI-6223 (right panel). The sizes of the target and nearby stars are scaled according to their relative fluxes in the TESS filter. The pixel scale is 21$\arcsec$ per pixel. This plot was generated using TESS-cont2024AA...691A.233C.
• Figure 2: Phase-folded TESS transit light curves (gray circles) of TOI-1743.01 (top) and TOI-6223.01 (bottom). Global transit model (with limb darkening for TESS filter) for each system are shown with a red line. For clarity, binned light curves are shown with black dots.
• Figure 3: Same as Fig. \ref{['fig:TESS1']} but for inner (top) and outer (bottom) planets of TOI-5799 system.
• Figure 4: Black lines show the normalized (at 7400 Å) Shane/Kast optical spectra of (from top to bottom): TOI-1743, TOI-5799, and TOI-6223. Best-fit SDSS standard templates 2007AJ....133..531B are shown with magenta lines. The key spectral features between 4200--8900 Å are labeled, including the location of the (corrected) O$_2$ telluric A-band at 7500 Å ($\oplus$). Zoomed regions around 6563 Å H$\alpha$ and 6708 Å Li I lines are shown in inset boxes. The 5600–5900 Å gap due to the dichroic separation between the blue and red channels of the Kast spectrograph.
• Figure 5: The Baade/MagE spectrum of TOI-5799 (black line) is shown in comparison with the M2 SDSS template from 2007AJ....133..531B. The spectra are normalized at 7400 Å, and prominent spectral features between 4300--8100 Å are labeled, including regions affected by uncorrected telluric oxygen and water absorption ($\oplus$). 6555–6585 Å region is shown in inset box to highlight H$\alpha$ and Ca I features.