Updated Planetary Mass Constraints of the Young V1298 Tau System Using MAROON-X

Abstract

The early K-type T-Tauri star, V1298 Tau ( V = 10 mag, age ≈ 20–30 Myr) hosts four transiting planets with radii ranging from 4.9 to 9.6 R ⊕ . The three inner planets have orbital periods of ≈8–24 days while the outer planet’s period is poorly constrained by single transits observed with K2 and the Transiting Exoplanet Survey Satellite (TESS). Planets b, c, and d are proto–sub-Neptunes that may be undergoing significant mass loss. Depending on the stellar activity and planet masses, they are expected to evolve into super-Earths/sub-Neptunes that bound the radius valley. Here we present results of a joint transit and radial velocity (RV) modeling analysis, which includes recently obtained TESS photometry and MAROON-X RV measurements. Assuming circular orbits, we obtain a low-significance (≈2 σ ) RV detection of planet c, implying a mass of 19.8 − 8.9 + 9.3 M ⊕ and a conservative 2 σ upper limit of <39 M ⊕ . For planets b and d, we derive 2 σ upper limits of M b < 159 M ⊕ and M d < 41 M ⊕ , respectively. For planet e, plausible discrete periods of P e > 55.4 days are ruled out at the 3 σ level while seven solutions with 43.3 < 55.4 are consistent with the most probable 46.768131 ± 000076 days solution within 3 σ . Adopting the most probable solution yields a 2.6 σ RV detection with a mass of 0.66 ± 0.26 M Jup . Comparing the updated mass and radius constraints with planetary evolution and interior structure models shows that planets b, d, and e are consistent with predictions for young gas-rich planets and that planet c is consistent with having a water-rich core with a substantial (∼5% by mass) H 2 envelope.