The disk of FU Orionis viewed with MATISSE/VLTI

Abstract

Aims. We studied the accretion disk of the archetypal eruptive young star FU Orionis with the use of mid-infrared interferometry, which enabled us to resolve the innermost regions of the disk down to a spatial resolution of 3 milliarcseconds (mas) in the L band, that is, within 1 au of the protostar. Methods. We used the interferometric instrument MATISSE/VLTI to obtain observations of FU Ori’s disk in the L, M, and N bands with multiple baseline configurations. We also obtained contemporaneous photometry in the optical (UBVRIr′i′; SAAO and Konkoly Observatory) and near-infrared (JHKs; NOT). Our results were compared with radiative transfer simulations modeled by RADMC-3D. Results. The disk of FU Orionis is marginally resolved with MATISSE, suggesting that the region emitting in the thermal infrared is rather compact. An upper limit of ~1.3 ± 0.1 mas (in L) can be given for the diameter of the disk region probed in the L band, corresponding to 0.5 au at the adopted Gaia EDR3 distance. This represents the hot, gaseous region of the accretion disk. The N-band data indicate that the dusty passive disk is silicate-rich. Only the innermost region of said dusty disk is found to emit strongly in the N band, and it is resolved at an angular size of ~5 mas, which translates to a diameter of about 2 au. The observations therefore place stringent constraints for the outer radius of the inner accretion disk. Dust radiative transfer simulations with RADMC-3D provide adequate fits to the spectral energy distribution from the optical to the submillimeter and to the interferometric observables when opting for an accretion rate M ~ 2 × 10−5 M⊙ yr−1 and assuming M* = 0.6 M⊙, Most importantly, the hot inner accretion disk’s outer radius can be fixed at 0.3 au. The outer radius of the dusty disk is placed at 100 au, based on constraints from scattered-light images in the literature. The dust mass contained in the disk is 2.4 × 10−4 M⊙, and for a typical gas-to-dust ratio of 100, the total mass in the disk is approximately 0.02 M⊙. We did not find any evidence for a nearby companion in the current interferometric data, and we tentatively explored the case of disk misalignment. For the latter, our modeling results suggest that the disk orientation is similar to that found in previous imaging studies by ALMA. Should there be an asymmetry in the very compact, inner accretion disk, this might be resolved at even smaller spatial scales (≤1 mas).

Modeling the Multiwavelength Evolution of the V960 Mon System

“…We vary the η and β flaring parameters and find that the flaring law that best matches the decrease in K band, the sudden rise at L band, and the flat M band, is given by = 0.08 h a a a 1.0 i ( ) . This is in good agreement with the flaring law found for FU Ori by Lykou et al (2022), though they find a shallower power-law index of 0.13. The final model is shown in Figure 13.…”

The Gaia alerted fading of the FUor-type star Gaia21elv

“…Following the method of Connelley & Reipurth ( 2018 ), we used the X-SHOOTER spectrum to estimate the visual extinction toward the source by comparing it to the spectrum of FU Ori, which has a low and well-known extinction ( A V = 1.7 ± 0.1 mag; e.g. Siwak et al 2018, Lykou et al 2022. We dereddened the spectrum of Gaia21elv with increasing A V until it matched the scaled, flux calibrated spectrum of FU Ori.…”

Photometric and Spectroscopic Study of the EXor-like Eruptive Young Star Gaia19fct

“…We estimated an extinction (A V ) by comparing the spectrum of Gaia19fct to that of FU Ori as done in Connelley & Reipurth (2018). FU Ori is known to have a low extinction (A V = 1.7 mag; Siwak et al 2018;Green et al 2019;Lykou et al 2022), making it a good comparison target. This method is valid for eruptive young stars whose optical and NIR spectra are dominated by an active accretion disk rather than the stellar photosphere (Hartmann & Kenyon 1996;Connelley & Reipurth 2018;Fischer et al 2022).…”