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

Abstract

The early K-type T-Tauri star, V1298 Tau ($V=10\mathrm{mag}$, $\mathrm{age}\approx 20-30\mathrm{Myr}$) hosts four transiting planets with radii ranging from $4.9-9.6R_{\oplus }$. The three inner planets have orbital periods of $\approx 8-24\mathrm{d}$ while the outer planet's period is poorly constrained by single transits observed with \emph{K2} and \emph{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) modelling analysis, which includes recently obtained \emph{TESS} photometry and MAROON-X RV measurements. Assuming circular orbits, we obtain a low-significance ($\approx 2\ddot{I}ƒ$) RV detection of planet c implying a mass of $19.8_{-8.9}^{+9.3}{M}_{\oplus }$ and a conservative $2\ddot{I}ƒ$ upper limit of $<39M_{\oplus }$. For planets b and d, we derive $2\ddot{I}ƒ$ upper limits of $M_{\mathrm{b}}<159M_{\oplus }$ and $M_{\mathrm{d}}<41M_{\oplus }$. For planet e, plausible discrete periods of $P_{\mathrm{e}}>55.4\mathrm{d}$ are ruled out at a $3\ddot{I}ƒ$ level while seven solutions with $43.3<P_{\mathrm{e}}/\mathrm{d}<55.4$ are consistent with the most probable $46.768131\pm 000076\mathrm{d}$ solution within $3\ddot{I}ƒ$. Adopting the most probable solution yields a $2.6\ddot{I}ƒ$ RV detection with mass a of $0.66\pm 0.26M_{\mathrm{Jup}}$. 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 ($\sim 5\%$ by mass) H${}_2$ envelope.

18 pages, 13 figures, accepted for publication in AJ