2025ApJ...990L...9C

Excellent (<25 mas) Hα images of the star TYC 5709-354-1 led to the discovery of a rare Hα protoplanet. This star was discovered by the WISPIT survey to have a large multi-ring transitional disk, and is hereafter WISPIT 2. Our Hα images of 2025 April 13 and 16 discovered an accreting (Hα in emission) protoplanet: WISPIT 2b (r = 309.43 ± 1.56 mas; (∼54 au deprojected), PA = 242$\mathop{.}\limits^{\unicode{x000b0}}$21 ± 0$\mathop{.}\limits^{\unicode{x000b0}}$41) likely clearing a dust-free gap between the two brightest dust rings in the transitional disk. Our signal-to-noise ratio of 12.5 detection gave an Hα ASDI contrast of (6.5 ± 0.5) × 10^–4 and an Hα line flux of (1.29 ± 0.28) × 10^–15 erg s^–1 cm^–2. We also present L' photometry from LBT/LMIRcam of the planet (L' = 15.30 ± 0.05 mag), which, when coupled with an age of $5.{1}_{-1.3}^{+2.4}$ Myr, yields a planet mass estimate of 5.3 ± 1.0 M_jup from the DUSTY evolutionary models. WISPIT 2b is accreting at $2.{25}_{-0.17}^{+3.75}$ × 10^–12M_Sun yr^–1. WISPIT 2b is very similar to the other Hα protoplanets in terms of mass, age, flux, and accretion rate. The inclination of the system (i = 44°) is also, surprisingly, very similar to the other known Hα protoplanet systems, which all cluster from 37° ≤ i ≤ 52°. We argue this clustering has only a ∼1.0% (2.6σ) probability of occurring randomly, and so we speculate that magnetospherical accretion might have a preferred inclination range (∼37°-52°) for the direct (cloud free, low extinction) line of sight to the Hα line formation/shock region. We also find at 110 mas (∼15 au deprojected) a close companion candidate (CC1) that may be consistent with an inner dusty 9 ± 4 M_jup planet.