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K-band High-resolution Spectroscopy of Embedded High-mass Protostars
Abstract A classical paradox in high-mass star formation is that powerful radiation pressure can halt accretion, preventing further growth of a central star. Disk accretion has been proposed to solve this problem, but the disks and the accretion process in high-mass star formation are poorly underst...
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Published in: | The Astrophysical journal 2021-05, Vol.912 (2), p.108 |
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Main Authors: | , , , , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Abstract
A classical paradox in high-mass star formation is that powerful radiation pressure can halt accretion, preventing further growth of a central star. Disk accretion has been proposed to solve this problem, but the disks and the accretion process in high-mass star formation are poorly understood. We executed high-resolution (
R
= 35,000–70,000) iSHELL spectroscopy in
K
-band for 11 high-mass protostars. Br-
γ
emission was observed toward eight sources, and the line profiles for most of these sources are similar to those of low-mass PMS stars. Using an empirical relationship between the Br-
γ
and accretion luminosities, we tentatively estimate disk accretion rates ranging from ≲10
−8
and ∼10
−4
M
⊙
yr
−1
. These low-mass-accretion rates suggest that high-mass protostars gain more mass via episodic accretion as proposed for low-mass protostars. Given the detection limits, CO overtone emission (
v
= 2−0 and 3−1), likely associated with the inner disk region (
r
≪ 100 au), was found toward two sources. This low-detection rate compared with Br-
γ
emission is consistent with previous observations. Ten out of the 11 sources show absorption at the
v
= 0–2 R(7) − R(14) CO R-branch. Most of them are either blueshifted or redshifted, indicating that the absorption is associated with an outflow or an inflow with a velocity of up to ∼50 km s
−1
. Our analysis indicates that the absorption layer is well thermalized (and therefore
cm
−3
) at a single temperature of typically 100–200 K, and located within 200–600 au of the star. |
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ISSN: | 0004-637X 1538-4357 |
DOI: | 10.3847/1538-4357/abee88 |