Using FU Orionis outbursts to constrain self-regulated protostellar disk models

TLDR

FU Orionis outbursts in young stellar objects are attributed to a large‑scale, self‑regulated thermal ionization instability in their protostellar accretion disks. The study tests the hypothesis that such outbursts occur only in systems where inward mass transport ionizes hydrogen in the inner disk. The authors combine one‑dimensional convective vertical‑structure and radial‑diffusion disk models, fitting their time‑dependent evolution to observed FU Orionis timescales to estimate the effective viscous stress (α≈10⁻⁴–10⁻³) in the inner disk. They find a critical mass flux of 5×10⁻⁷ M☉ yr⁻¹ (independent of α) for a one‑solar‑mass, three‑solar‑radius star, and that infall rates of 1–10×10⁻⁶ M☉ yr⁻¹ reproduce observed FU Orionis timescales consistent with core collapse rates. Published in The Astrophysical Journal (June 1994, DOI 10.1086/174206).

Abstract

view Abstract Citations (681) References (68) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Using FU Orionis Outbursts to Constrain Self-regulated Protostellar Disk Models Bell, K. R. ; Lin, D. N. C. Abstract One dimensional, convective, vertical structure models and one dimensional, time dependent, radial diffusion models are combined to create a self-consistent picture in which FU~Orionis outbursts occur in young stellar objects (YSOs) as the result of a large scale, self-regulated, thermal ionization instability in the surrounding protostellar accretion disk. By fitting the results of time dependent disk models to observed time scales of FU~Orionis events, we estimate the magnitude of the effeciency of the effective viscous stress in the inner disk (r < 1 AU) to be, in accordance with the ad hoc ``alpha'' prescription, 10^{-4} where hydrogen is neutral and 10^{-3} where hydrogen is ionized. We hypothesize that all YSOs receive infall onto their outer disks which is steady (or slowly declining with time) and that FU~Orionis outbursts are self-regulated, disk outbursts which occur only in systems which transport matter inward at a rate sufficiently high to cause hydrogen to be ionized in the inner disk. We estimate a critical mass flux of 5x10^{-7} solar masses / year {\it independent of the magnitude of alpha} for systems with one solar mass, three solar radius central objects. Infall accretion rates in the range of (1-10)x10^{-6} solar masses per year produce observed FU~Orionis time scales consistent with estimates of spherical molecular cloud core collapse rates. Publication: The Astrophysical Journal Pub Date: June 1994 DOI: 10.1086/174206 arXiv: arXiv:astro-ph/9312015 Bibcode: 1994ApJ...427..987B Keywords: Accretion Disks; Ionization; Protostars; Star Formation; Stellar Mass Accretion; Stellar Models; Thermal Stability; Hydrogen Clouds; Radial Flow; Stellar Mass Ejection; Astrophysics; ACCRETION; ACCRETION DISKS; STARS: FORMATION; STARS: PRE--MAIN-SEQUENCE; STARS: VARIABLES: OTHER FU ORIONIS; Astrophysics E-Print: 38 pages, 9 figures, uucompressed postscript: beware! remove stray blank lines, 000 full text sources arXiv | ADS | data products SIMBAD (11)