Affiliation:
1. School of Physics and Astronomy, University of Leicester , Leicester LE1 7RH UK
2. Fakultät für Physik, Universität Duisburg-Essen , Lotharstraße 1, D-47057 Duisburg , Germany
Abstract
ABSTRACT
Accretion luminosity of young star FU Ori (FUOR) increased from undetectable levels to hundreds of L⊙ in 1937 and remains nearly as high at the present time. In a recent paper, we showed how Extreme Evaporation (EE) of a young gas giant planet that migrated to a ∼10 d orbit around the star may power FUOR. However, our model assumed a power-law mass–radius relation for the evaporating planet. Here, we employ a stellar evolution code to model mass losing planets. We find that adiabatic planets expand rapidly, which results in runaway FUOR bursts. Superadiabatic planets contract while losing mass; their outbursts are dimming with time. Long steadily declining bursts such as FUOR require relatively fine-tuned internal planetary structure, which may be rare. More commonly we find that superadiabatic planets contract too rapidly and their EE falters, leading to FUOR burst stutter. This stutter allows a single planet to produce many short repeating bursts, which may be relevant to bursts observed in V346 Nor, V899, and V1647. We compute broad-band spectra of our best-fitting scenario for FUOR. Since the outburst is triggered behind the planet location, the mid-infrared (mid-IR) emission rises many months before the optical, similar to bursts in Gaia-17bpi and Gaia-18dvy. We show that in outbursts powered by the classic thermal instability, mid-IR lags the optical, whereas the dead zone activation models predict mid-IR light precede the optical burst by many years to decades. We comment on the stellar flyby scenario for FUOR.
Publisher
Oxford University Press (OUP)
Subject
Space and Planetary Science,Astronomy and Astrophysics