High Resolution Optical and NIR Spectra of HBC 722

TL;DR

This study presents high-resolution optical and near-IR spectra of HBC 722, revealing the dynamics of its accretion disk and wind during its 2010 outburst, with evidence of disk rotation and wind-disk anti-correlation.

Contribution

It provides detailed spectroscopic analysis of HBC 722's accretion and wind features, highlighting the anti-correlation and disk rotation, and models the disk temperature distribution.

Findings

Wind features are anti-correlated with disk features over time.

Optical and near-IR spectra trace different disk radii with distinct rotation velocities.

Disk temperature distribution follows a power-law with index 0.8.

Abstract

We present the results of high resolution (R$\ge$30,000) optical and near-IR spectroscopic monitoring observations of HBC 722, a recent FU Orionis object that underwent an accretion burst in 2010. We observed HBC 722 in optical/near-IR with the BOES, HET-HRS, and IGRINS spectrographs, at various points in the outburst. We found atomic lines with strongly blueshifted absorption features or P Cygni profiles, both evidence of a wind driven by the accretion. Some lines show a broad double-peaked absorption feature, evidence of disk rotation. However, the wind-driven and disk-driven spectroscopic features are anti-correlated in time; the disk features became strong as the wind features disappeared. This anti-correlation might indicate that the rebuilding of the inner disk was interrupted by the wind pressure during the first two years. The Half-Width at Half-Depth (HWHD) of the double-peaked profiles decreases with wavelength, indicative of the Keplerian rotation; the optical spectra with the disk feature are fitted by a G5 template stellar spectrum convolved with a rotation velocity of 70 km s$^{-1}$ while the near-IR disk features are fitted by a K5 template stellar spectrum convolved with a rotation velocity of 50 km s$^{-1}$. Therefore, the optical and near-IR spectra seem to trace the disk at 39 and 76 $\textit{R}_{\odot}$, respectively. We fit a power-law temperature distribution in the disk, finding an index of 0.8, comparable to optically thick accretion disk models.