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Peer-reviewedCC BY 4.0The Astrophysical Journal

Episodic Accretion Drives an Ultrafast Outflow and CH ₃ CN Shock Chemistry in G24.33+0.14

  • Xiaoyun Xu1
  • Xi Chen1
  • Yang Yang2
  • Gregory Herczeg3
  • Andrej M. Sobolev4
4 affiliations
  1. 1Guangzhou University
  2. 2Changsha Normal University
  3. 3Peking University
  4. 4Chinese Academy of Sciences
Open at sourcePDFDOICite

Abstract

We present the Atacama Large Millimeter/submillimeter Array (ALMA) and the NOrthern Extended Millimeter Array (NOEMA) observations of the molecular outflow from the high-mass young stellar object (HMYSO) G24.33+0.14, which has recently undergone an accretion burst. CO (2–1) and SiO (5–4) reveal a bipolar outflow with pronounced asymmetry and multiple shells, indicating episodic mass ejection. CO reaches projected velocities up to ∼150 km s ⁻¹ , placing the outflow in the extremely high-velocity (EHV) regime. Position–velocity (PV) diagrams show distinct Hubble-wedge structures, and high-velocity CO knots cluster into two separate wedges, supporting nonsteady, multiepoch ejection. Crucially, CH ₃ CN ( J = 12–11, K = 0–4) emission is detected along the outflow axis and spatially coincides with SiO (5–4). Its velocity gradient aligns with the outflow, rather than the disk, and the derived rotational temperatures have a median value of 135 K, which, together with its spatial and kinematic association with SiO, supports a shock-related origin of the CH ₃ CN emission. Comparison of burst-phase (ALMA 2019) and postburst (NOEMA 2020) data shows significant intensity variations in CO and CH ₃ OH masers, confirming that accretion bursts modify outflow physical conditions on observable timescales. These results support a possible connection between episodic accretion, shock chemistry, and extreme-velocity mass ejection in a massive protostar.

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Cite

BibTeXRIS
BibTeX
@article{xu2026episodic,
  title = {{Episodic Accretion Drives an Ultrafast Outflow and CH ₃ CN Shock Chemistry in G24.33+0.14}},
  author = {Xiaoyun Xu and Xi Chen and Yang Yang and Gregory Herczeg and Andrej M. Sobolev},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-4357/aea6c1},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea6c1},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Episodic Accretion Drives an Ultrafast Outflow and CH ₃ CN Shock Chemistry in G24.33+0.14
AU  - Xiaoyun Xu
AU  - Xi Chen
AU  - Yang Yang
AU  - Gregory Herczeg
AU  - Andrej M. Sobolev
PY  - 2026
DA  - 2026/10/09
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/aea6c1
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/aea6c1
AB  - We present the Atacama Large Millimeter/submillimeter Array (ALMA) and the NOrthern Extended Millimeter Array (NOEMA) observations of the molecular outflow from the high-mass young stellar object (HMYSO) G24.33+0.14, which has recently undergone an accretion burst. CO (2–1) and SiO (5–4) reveal a bipolar outflow with pronounced asymmetry and multiple shells, indicating episodic mass ejection. CO reaches projected velocities up to ∼150 km s ⁻¹ , placing the outflow in the extremely high-velocity (EHV) regime. Position–velocity (PV) diagrams show distinct Hubble-wedge structures, and high-velocity CO knots cluster into two separate wedges, supporting nonsteady, multiepoch ejection. Crucially, CH ₃ CN ( J = 12–11, K = 0–4) emission is detected along the outflow axis and spatially coincides with SiO (5–4). Its velocity gradient aligns with the outflow, rather than the disk, and the derived rotational temperatures have a median value of 135 K, which, together with its spatial and kinematic association with SiO, supports a shock-related origin of the CH ₃ CN emission. Comparison of burst-phase (ALMA 2019) and postburst (NOEMA 2020) data shows significant intensity variations in CO and CH ₃ OH masers, confirming that accretion bursts modify outflow physical conditions on observable timescales. These results support a possible connection between episodic accretion, shock chemistry, and extreme-velocity mass ejection in a massive protostar.
SN  - 0004-637X
SN  - 1538-4357
ER  -