FUOr-Aur 0544+3330: A New YSO Outburst in the Outskirts of Auriga OB1, Viewed Face-On

TL;DR

This paper reports the discovery and analysis of a new FU Ori-type outburst in a young stellar object in Auriga, characterized by significant brightening, spectral features indicative of a face-on accretion disk, and detailed modeling of its accretion parameters.

Contribution

It presents the first detailed observation and modeling of FUOr-Aur 0544+3330, a new FU Ori outburst, including spectral analysis and accretion disk parameter estimation.

Findings

Brightening of over 5 magnitudes in optical wavelengths.

Spectral features consistent with FU Ori class and face-on disk orientation.

Accretion rate estimated at 10^{-5.48} M_sun/yr.

Abstract

We present a newly appreciated FU Ori outburst event that began in 2019 and reached a peak in early 2021. Suspected young stellar object WISE J054452.25+333009.6 experienced substantial brightening, in excess of $-5$ mag at optical wavelengths and $-2.5$ mag at mid-infrared wavelengths. The time from near-quiescence to peak brightness was approximately 24 months. Optical and near-infrared spectra confirm that the outbursting source (hereby designated FUOr-Aur 0544+3330) shows all the hallmarks of the FU Ori class, including the Li I indicator of stellar youth. The mix of ionized and neutral atomic lines, alongside prominent molecular absorption features, is consistent with the expected change in spectral type from earlier in the optical to later-type in the near-infrared. The closest analog among well-studied FU Ori objects is V1515 Cyg. Both sources have unusually narrow-lined absorption spectra that can be explained by a face-on disk orientation, such that disk-broadening is minimized and wind-induced blueshift (in e.g. H$\alpha$, NaD, Ca II) is maximized. Both the optical through infrared spectral energy distribution and high-resolution spectrum are well-fit by a pure-accretion disk model. Adopting a distance of $d=1.5$ kpc, the accretion and central star parameters are: $\dot{M} = 10^{-5.48}$ $M_\odot$ yr$^{-1}$, $M_* = 0.17 \ M_\odot$, and $R_\mathrm{inner} = 1.04 \ R_\odot$. Other fitted values are disk inclination $i=5.9$ deg and source extinction $A_V=1.83$ mag. These parameters yield accretion luminosity $L_\mathrm{acc} = 8.4\ L_\odot$ and maximum disk temperature $T_{\rm{max}} = 6218$ K.