Viscous Heating and Boundary Layer Accretion in the Disk of Outbursting Star FU Orionis

Abstract

Context. FU Orionis is the archetypal FUor star, a subclass of young stellar object (YSO) that undergo rapid brightening events, often gaining 4-6 magnitudes on timescales of days. This brightening is often associated with a massive increase in accretion; one of the most ubiquitous processes in astrophysics from planets and stars to super-massive black holes. We present multi-band interferometric observations of the FU Ori circumstellar environment, including the first J-band interferometric observations of a YSO. Aims. We investigate the morphology and temperature gradient of the inner-most regions of the accretion disk around FU Orionis. We aim to characterise the heating mechanisms of the disk and comment on potential outburst triggering processes. Methods. Recent upgrades to the MIRC-X instrument at the CHARA array allowed the first dual-band J and H observations of YSOs.Using baselines up to 331 m, we present high angular resolution data of a YSO covering the near-infrared bands J, H, and K. The unprecedented spectral range of the data allows us to apply temperature gradient models to the innermost regions of FU Ori. Results. We spatially resolve the innermost astronomical unit of the disk and determine the exponent of the temperature gradient of the inner disk to $T=r^{-0.74\pm 0.02}$. This agrees with theoretical work that predicts $T=r^{-0.75}$ for actively accreting, steady state disks, a value only obtainable through viscous heating within the disk. We find a disk which extends down to the stellar surface at $0.015\pm 0.007$ au where the temperature is found to be $5800\pm 700$ K indicating boundary layer accretion. We find a disk inclined at $32\pm 4^{\circ }$ with a minor-axis position angle of $34\pm 11^{\circ }$.

arXiv comment10 pages, 6 figures

References in corpus (34)

• emcee: The MCMC Hammer
• Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2
• The Spitzer c2d Legacy Results: Star Formation Rates and Efficiencies; Evolution and Lifetimes
• The VizieR database of Astronomical Catalogues
• Using FU Orionis Outbursts to Constrain Self-Regulated Protostellar Disk Models
• Gaia Data Release 2: Photometric content and validation
• First Results from the CHARA Array. II. A Description of the Instrument
• The PSCz Catalogue
• Flaring vs. self-shadowed disks: the SEDs of Herbig Ae/Be stars
• The Burst Mode of Protostellar Accretion
• PIONIER: a 4-telescope visitor instrument at VLTI
• The Origin of Episodic Accretion Bursts in the Early Stages of Star Formation
• The Palomar Testbed Interferometer
• SearchCal: a Virtual Observatory tool for searching calibrators in optical long baseline interferometry. I: The bright object case
• The Hot Inner Disk of FU Ori
• Fundamental parameters and infrared excesses of Tycho-Gaia stars
• The XMM-Newton serendipitous ultraviolet source survey catalogue
• A triple star system with a misaligned and warped circumstellar disk shaped by disk tearing
• The photometric evolution of FU Orionis objects: disc instability and wind-envelope interaction
• New insights on the AU-scale circumstellar structure of FU Orionis
• FU Orionis resolved by infrared long baseline interferometry at a 2-AU scale
• Resolving the FU Ori System with ALMA: Interacting Twin Disks?
• Long-wavelength excesses of FU Orionis objects: flared outer disks or infalling envelopes?
• Near-Infrared High-Resolution Imaging Polarimetry of FU Ori-Type Objects: Towards A Unified Scheme for Low-Mass Protostellar Evolution
• FU Orionis - The MIDI/VLTI Perspective
• Revealing the sub-AU asymmetries of the inner dust rim in the disk around the Herbig Ae star R CrA
• Surface Geometry of Protoplanetary Disks Inferred From Near-Infrared Imaging Polarimetry
• Irregular dust features around intermediate-mass young stars with GPI: signs of youth or misaligned disks?
• Diagnosing 0.1-10 au scale morphology of the FU\,Ori disk using ALMA and VLTI/GRAVITY
• V346 Normae: First post-outburst observations of an FU Orionis star
• Resolving the Sub-AU-Scale Gas and Dust Distribution in FU Orionis Sources
• Constraining mass ratio and extinction in the FU Orionis binary system with infrared integral field spectroscopy
• Simultaneous spectral energy distribution and near-infrared interferometry modeling of HD 142666
• Low light level CCDs and visibility parameter estimation

Cited by in corpus (11)

• Diagnosing FUor-like Sources: The Parameter Space of Viscously Heated Disks in the Optical and Near-IR
• Millimeter-sized Dust Grains Appear Surviving the Water-sublimating Temperature in the Inner 10 au of the FU Ori Disk
• The young protostellar disk in IRAS16293-2422 B is hot and shows signatures of gravitational instability
• Inferring possible magnetic field strength of accreting inflows in EXor-type objects from scaled laboratory experiments
• Extreme evaporation of planets in hot thermally unstable protoplanetary discs: the case of FU Ori
• The disk of FU Orionis viewed with MATISSE/VLTI: first interferometric observations in $L$ and $M$ bands
• 3-D SPH simulations of the FUOR flares in the clumpy accretion model
• FU Orionis disk outburst: evidence for a gravitational instability scenario triggered in a magnetically dead zone
• Imaging the warped dusty disk wind environment of SU Aurigae with MIRC-X
• The evolution of the flux-size relationship in protoplanetary discs by viscous evolution and radial pebble drift
• Six-telescope integrated optics beam combiner fabricated using ultrafast laser inscription for J- and H-band astronomy