TESS discovery of two super-Earths orbiting the M-dwarf stars TOI-6002 and TOI-5713 near the radius valley (2408.00709v4)

Abstract: We present the validation of two TESS super-Earth candidates transiting the mid-M dwarfs TOI-6002 and TOI-5713 every 10.90 and 10.44 days, respectively. The first star (TOI-6002) is located $32.038\pm0.019$ pc away, with a radius of $0.2409^{+0.0066}_{-0.0065}$ \rsun, a mass of $0.2105^{+0.0049}_{-0.0048}$ \msun, and an effective temperature of $3229^{+77}_{-57}$ K. The second star (TOI-5713) is located $40.946\pm0.032$ pc away, with a radius of $0.2985^{+0.0073}_{-0.0072}$ \rsun, a mass of $0.2653\pm0.0061$ \msun, and an effective temperature of $3225^{+41}_{-40}$ K. We validated the planets using TESS data, ground-based multi-wavelength photometry from many ground-based facilities, as well as high-resolution AO observations from Keck/NIRC2. TOI-6002 b has a radius of $1.65^{+0.22}_{-0.19}$ \re\ and receives $1.77^{+0.16}_{-0.11} S_\oplus$. TOI-5713 b has a radius of $1.77_{-0.11}^{+0.13} \re$ and receives $2.42\pm{0.11} S_\oplus$. Both planets are located near the radius valley and near the inner edge of the habitable zone of their host stars, which makes them intriguing targets for future studies to understand the formation and evolution of small planets around M-dwarf stars.

• The paper validates and characterizes two TESS-discovered super-Earths orbiting M-dwarfs TOI-6002 and TOI-5713, highlighting their proximity to the "radius valley."
• With radii around 1.65 and 1.77 R{0010}{0008} respectively, these planets' location near the radius valley provides crucial data for understanding planetary formation and evolution processes around M dwarfs.
• These super-Earths are promising targets for future atmospheric characterization with JWST and radial velocity measurements to determine mass, offering insights into habitability and composition.

Discovery and Characterization of Two Super-Earths Near the Radius Valley

The paper presents the validation and characterization of two super-Earths discovered by TESS, orbiting the M-dwarf stars TOI-6002 and TOI-5713. This paper provides insights into planetary formation and the potential for habitability in small planets around M-dwarfs, focusing on their location near the so-called "radius valley."

Stellar and Planetary Parameters

TOI-6002 and TOI-5713 are mid-M dwarfs, residing at roughly 32 and 41 parsecs away, respectively. TOI-6002 has a radius and mass of 0.2409 $\mathrm{R_{\odot}}$ and 0.2105 $\mathrm{M_{\odot}}$, with an effective temperature of about 3229 K. TOI-5713 is slightly larger and more massive, with a radius of 0.2985 $\mathrm{R_{\odot}}$ and a mass of 0.2653 $\mathrm{M_{\odot}}$, and an effective temperature also near 3225 K.

The planets, TOI-6002 b and TOI-5713 b, have orbital periods of approximately 10.90 and 10.44 days. TOI-6002 b has a radius of 1.65 $\mathrm{R_{\oplus}}$ and receives an insolation of 1.77 $S_{\oplus}$, while TOI-5713 b has a radius of 1.77 $\mathrm{R_{\oplus}}$ and receives 2.42 $S_{\oplus}$.

Validation and Observation Techniques

The validation of these exoplanets relied on multiple datasets from TESS, supplemented by ground-based observations and high-resolution adaptive optics imaging which ruled out potential false positives from nearby stars or bound eclipsing binaries. The detailed spectroscopic characterization using instruments like IRTF/SpeX provided spectral types and metallicity estimates which aligned with single star models. The statistical tool TRICERATOPS confirmed the planetary nature of the transit signals through the computed low false positive probabilities.

Implications and Theoretical Context

Both exoplanets reside near the "radius valley," a notable feature in the distribution of small planets that is hypothesized to stem from evolutionary processes like photoevaporation or core-powered mass loss. The differing slopes of the radius valley for FGK and M dwarfs highlight a transitional region for small planets, where TOI-6002 b and TOI-5713 b reside. This makes them pivotal for understanding whether similar processes shape planetary systems across diverse stellar environments.

The finding of the paper aligns with the narrative that small planets around M dwarfs are crucial for an in-depth understanding of exoplanet atmospheric evolution and the stability of super-Earth-sized planets. The potential density measurements and radial velocity follow-up could further refine models of planetary formation, especially in distinguishing between rocky compositions and those with substantial volatile envelopes.

Potential for Future Research and Observations

The paper hints at the possibility of further observations, particularly those targeting atmospheric characterization using JWST. The planets' positions near the radius valley make them suitable candidates to paper the transition from a potentially temperate climate to a Venus-like runaway greenhouse effect. Thus, they might provide insights into habitability limits and atmospheric chemistry.

TOI-6002 b and TOI-5713 b's prospects for radial velocity detections are promising, especially with high precision instruments capable of detecting the hypothetical reflex motion predicted at approximately 3 m/s. This would help refine their masses and infer denser rocky or volatile-rich compositions.

In summary, this research enriches the current understanding of exoplanet populations around M dwarfs, contributing to our grasp of planetary system architecture and evolution. The analysis presented serves as a cornerstone for future observational campaigns, aiming to unravel the complex interplay of physical processes governing super-Earths and their atmospheres.