New maser species tracing spiral-arm accretion flows in a high-mass young stellar object

Abstract

Numerical simulations have predicted that substructures such as spiral arms can be produced through a gravitationally unstable disk around high-mass young stellar objects (HMYSOs)1,2,3,4,5. Recent high-resolution observations from the Atacama Large Millimeter/submillimeter Array have investigated these substructures at a spatial resolution of ~100 au (refs. 6,7,8,9,10). An accretion burst, which is a manifestation of an increase in the accretion rate caused by a gravitational instability in the disk1,11,12, can result in luminosity outbursting phenomena—as has been seen in several HMYSOs13,14. However, no clear relationship between the accretion bursts and disk substructures has been established. Here we report the detections of three new molecular maser species, HDO, HNCO and 13CH3OH, from the direction of the HMYSO G358.93-0.03 during a 6.7 GHz methanol maser flaring event15. High-quality imaging of the three new maser species exhibits consistent observational evidence that these masers closely trace the spiral-arm substructures around this HMYSO. The rapid decay of the spectral lines emitted from these molecules suggests that these are transient phenomena (for only ~1 month), probably associated with rapid changes in radiation field due to an accretion burst. Therefore, these new maser species provide evidence linking the spiral-arm substructure with an accretion burst, both expected from massive disk instabilities.

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Fig. 1: Spatial distribution and spectra of multiple molecular maser transitions detected in the direction of G358.93-0.03 with the VLA.
Fig. 2: Kinematic model results for a two-arm spiral structure traced by HDO, HNCO and 13CH3OH masers.
Fig. 3: The expected brightness temperatures under a radiative–radiative pumping.
Fig. 4: The decay in the peak flux density of HDO, HNCO and 13CH3OH maser features obtained from VLA and TMRT observations.

Data availability

The data from both TMRT and VLA that support the plots within this paper and other findings of this study are available from X.C. on reasonable request. Source data are provided with this paper.

Code availability

The code for the pumping model of HDO and HNCO masers is available at https://github.com/ParfenovS/LVG_LRT

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Acknowledgements

We thank TMRT and VLA staff for their assistance in obtaining the data presented in this paper. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under agreement by the Associated Universities, Inc. X.C. was supported by the National Natural Science Foundation of China (grant numbers 11590781, 11873002, 12011530065 and 11590780), Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme (2019), Astronomy Science and Technology Research Laboratory of Department of Education of Guangdong Province, and Key Laboratory for Astronomical Observation and Technology of Guangzhou. A.M.S. and S.P. were supported by the Russian Science Foundation (grant number 18-12-00193). S.P.E. acknowledges the support of an ARC Discovery Project (project number DP180101061).

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Authors

Contributions

X.C. and A.M.S. wrote the initial manuscript, obtained and reduced the data, and led the initial observing proposals. Z.-Y.R. carried out the kinematic model analysis for the maser spots. S.P. performed the pumping model calculations for the masers. S.L.B., S.P.E. Z.-Q.S. and B.L. were involved in the initial observing proposal of the VLA and TMRT and helped to improve the manuscript. G.C.M., W.B., C.B., T.H., T.R.H., H.L., K.M., K.S., B.S., Y.G. and X.Z. are members of the M2O group and helped improve to the text.

Corresponding authors

Correspondence to Xi Chen or Andrej M. Sobolev.

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Extended data

Extended Data Fig. 1 The damping factor γ/γ0 as a function of distance from center protostar.

The vertical dashed line denotes the position of turning point (r0 =410 au).

Supplementary information

Supplementary Information

Supplementary Tables 1–6.

Source data

Source Data Fig. 3

Pumping model data.

Source Data Fig. 4

Maser monitoring data.

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Chen, X., Sobolev, A.M., Ren, Z. et al. New maser species tracing spiral-arm accretion flows in a high-mass young stellar object. Nat Astron (2020). https://doi.org/10.1038/s41550-020-1144-x

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