V1298 Tauri

V1298 Tauri is a young star (23±4 Myr) in the Taurus Molecular Cloud, classified as a weakly-lined T Tauri star. It belongs to either the Taurus-Auriga association or the slightly older Group 29. The star has a spectral type of K0-K1.5 and a mass of approximately 1.1 M☉. Its youth is confirmed by strong lithium absorption lines and x-ray emission, though it lacks signs of accretion or infrared excess. The star exhibits unpredictable brightness variations due to stellar rotation and starspots, with observed flares. V1298 Tauri hosts four transiting exoplanets discovered in 2019 using Kepler's K2 mission. Planets b, c, and d are near a 1:2:3 resonance, with orbital periods of 8.25, 12.40, and 24.14 days, respectively. Planet e has a longer period (>36 days) and may be in low-order resonance with planet b. The planets range in size between Neptune and Saturn, except for planet b, which is Jupiter-sized. Models suggest the planets have thick envelopes and minimum core masses of 5 ME. Mass constraints indicate planet b is less than 20 Earth masses, while planet c is estimated to be 17+13−6 Earth masses. Planet b’s atmosphere was observed by Hubble, showing water vapor absorption and low metallicity, with a predicted evolution into a sub-Neptune. Planet e may have a water-rich core with a substantial hydrogen envelope, though its status remains uncertain due to varying transit depths. The system is considered young and potentially a precursor to a compact multiplanet system, with resonances suggesting early formation or rapid orbital ...