Evidence of Accretion Burst: The Viscously Heated Inner Disk of the Embedded Protostar IRAS 16316-1540

Kavli Affiliate: Gregory J. Herczeg

| First 5 Authors: Sung-Yong Yoon, Jeong-Eun Lee, Seokho Lee, Gregory J. Herczeg, Sunkyung Park

| Summary:

Outbursts of young stellar objects occur when the mass accretion rate
suddenly increases. However, such outbursts are difficult to detect for deeply
embedded protostars due to their thick envelope and the rarity of outbursts.
The near-IR spectroscopy is a useful tool to identify ongoing outburst
candidates by the characteristic absorption features that indicate a disk
origin. However, without high-resolution spectroscopy, the spectra of outburst
candidates can be confused with the late-type stars since they have similar
spectral features. For the protostar IRAS 16316-1540, the near-IR spectrum has
line equivalent widths that are consistent with M-dwarf photospheres. However,
our high-resolution IGRINS spectra reveal that the absorption lines have boxy
and/or double-peaked profiles, as expected from a disk and not the star. The
continuum emission source is likely the hot, optically thick disk, heated by
viscous accretion. The projected disk rotation velocity of 41$pm$5 km s$^{-1}$
corresponds to $sim 0.1$ AU. Based on the result, we suggest IRAS 16316-1540
as an ongoing outburst candidate. Viscous heating of disks is usually
interpreted as evidence for ongoing bursts, which may be more common than
previously estimated from low-resolution near-IR spectra.

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