Probing the kinematics of FU Orionis objects through high-resolution near-infrared spectroscopy

TL;DR

This study analyzes high-resolution near-infrared spectra of 15 FU Orionis objects to investigate their disk kinematics, revealing double-peaked line profiles in some cases and complexities in line profile origins.

Contribution

It provides the first detailed high-resolution spectral analysis of FUors across multiple bands, highlighting the challenges in identifying Keplerian disk signatures.

Findings

Five targets show double-peaked line profiles in K-band.

Line profiles in J-band correlate with K-band but linewidths do not decrease with wavelength.

CO lines in M-band differ morphologically from K-band lines, indicating different origins.

Abstract

FU Orionis (FUor) objects are thought to be described by a steady-state Keplerian disk. However, the characteristic double-peaked Keplerian line profile is not readily seen in most near-infrared spectra of FUors. In this paper, we measure the near-infrared line profiles of 15 FUors and FUor-like objects by convolving model cool atmosphere spectra with a linear combination of Gaussians. The models are fit to high-resolution spectra obtained with iSHELL on the NASA Infrared Telescope Facility (IRTF). Five of the targets are found to have double-peaked line profiles in K-band, which can also be fitted by a Keplerian line profile. For eight targets that were also observed in J-band, we find that the line profiles are well-correlated to what is observed in K-band, but the linewidth does not clearly appear to decrease with wavelength. We find that a double-peaked line profile can be difficult to see for several reasons, which include blending with extraneous molecular features and potential absorption from a disk wind or infalling material. The CO lines in M-band are morphologically different from their counterparts in K-band, so they are probably of a different origin.