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Title: ALMA Images of the Orion Hot Core at 349 GHz

Abstract

We present ALMA images of the dust and molecular line emission in the Orion Hot Core at 349 GHz. At 0.″2 angular resolution the images reveal multiple clumps in an arc ∼1″ east of Orion Source I, the protostar at the center of the Kleinmann–Low Nebula, and another chain of peaks from IRc7 toward the southwest. The molecular line images show narrow filamentary structures at velocities >10 km s{sup −1} away from the heavily resolved ambient cloud velocity ∼5 km s{sup −1}. Many of these filaments trace the SiO outflow from Source I, and lie along the edges of the dust emission. Molecular line emission at excitation temperatures 300–2000 K, and velocities >10 km s{sup −1} from the ambient cloud, suggest that the Hot Core may be heated in shocks by the outflow from Source I or from the Becklin–Neugebauer (BN)/SrcI explosion. The spectral line observations also reveal a remarkable molecular ring, ∼2″ south of SrcI, with a diameter ∼600 au. The ring is seen in high-excitation transitions of HC{sub 3}N, HCN v 2 = 1, and SO{sub 2}. An impact of ejecta from the BN/SrcI explosion with a dense dust clump could result in the observed ring of shockedmore » material.« less

Authors:
;  [1]
  1. Radio Astronomy Laboratory, University of California, Berkeley, CA 94720 (United States)
Publication Date:
OSTI Identifier:
22663425
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 843; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BORON NITRIDES; CLOUDS; COSMIC DUST; EMISSION; EXCITATION; EXPLOSIONS; GHZ RANGE; HYDROCYANIC ACID; INTERSTELLAR SPACE; NEBULAE; NITRILES; PROTOSTARS; RESOLUTION; SILICON OXIDES; STARS; SULFUR DIOXIDE

Citation Formats

Wright, M. C. H., and Plambeck, R. L., E-mail: wright@astro.berkeley.edu. ALMA Images of the Orion Hot Core at 349 GHz. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA72E6.
Wright, M. C. H., & Plambeck, R. L., E-mail: wright@astro.berkeley.edu. ALMA Images of the Orion Hot Core at 349 GHz. United States. doi:10.3847/1538-4357/AA72E6.
Wright, M. C. H., and Plambeck, R. L., E-mail: wright@astro.berkeley.edu. Mon . "ALMA Images of the Orion Hot Core at 349 GHz". United States. doi:10.3847/1538-4357/AA72E6.
@article{osti_22663425,
title = {ALMA Images of the Orion Hot Core at 349 GHz},
author = {Wright, M. C. H. and Plambeck, R. L., E-mail: wright@astro.berkeley.edu},
abstractNote = {We present ALMA images of the dust and molecular line emission in the Orion Hot Core at 349 GHz. At 0.″2 angular resolution the images reveal multiple clumps in an arc ∼1″ east of Orion Source I, the protostar at the center of the Kleinmann–Low Nebula, and another chain of peaks from IRc7 toward the southwest. The molecular line images show narrow filamentary structures at velocities >10 km s{sup −1} away from the heavily resolved ambient cloud velocity ∼5 km s{sup −1}. Many of these filaments trace the SiO outflow from Source I, and lie along the edges of the dust emission. Molecular line emission at excitation temperatures 300–2000 K, and velocities >10 km s{sup −1} from the ambient cloud, suggest that the Hot Core may be heated in shocks by the outflow from Source I or from the Becklin–Neugebauer (BN)/SrcI explosion. The spectral line observations also reveal a remarkable molecular ring, ∼2″ south of SrcI, with a diameter ∼600 au. The ring is seen in high-excitation transitions of HC{sub 3}N, HCN v 2 = 1, and SO{sub 2}. An impact of ejecta from the BN/SrcI explosion with a dense dust clump could result in the observed ring of shocked material.},
doi = {10.3847/1538-4357/AA72E6},
journal = {Astrophysical Journal},
number = 2,
volume = 843,
place = {United States},
year = {Mon Jul 10 00:00:00 EDT 2017},
month = {Mon Jul 10 00:00:00 EDT 2017}
}
  • We present sensitive high angular resolution (∼0.″1–0.″3) continuum Atacama Large Millimeter/Submillimeter Array (ALMA) observations of the archetypal hot core located in the Orion Kleinmann-Low (KL) region. The observations were made in five different spectral bands (bands 3, 6, 7, 8, and 9) covering a very broad range of frequencies (149–658 GHz). Apart from the well-known millimeter emitting objects located in this region (Orion Source I and BN), we report the first submillimeter detection of three compact continuum sources (ALMA1–3) in the vicinities of the Orion-KL hot molecular core. These three continuum objects have spectral indices between 1.47 and 1.56, andmore » brightness temperatures between 100 and 200 K at 658 GHz, suggesting that we are seeing moderate, optically thick dust emission with possible grain growth. However, as these objects are not associated with warm molecular gas, and some of them are farther out from the molecular core, we thus conclude that they cannot heat the molecular core. This result favors the hypothesis that the hot molecular core in Orion-KL core is heated externally.« less
  • We investigated the ALMA science verification data of Orion KL and found a spectral signature of the vibrationally excited H{sub 2}O maser line at 232.68670 GHz ({nu}{sub 2} = 1, 5{sub 5,0}-6{sub 4,3}). This line has been detected previously in circumstellar envelopes of late-type stars but not in young stellar objects such as Orion KL. Thus, this is the first detection of the 232 GHz vibrationally excited H{sub 2}O maser in star-forming regions. The distribution of the 232 GHz maser is concentrated at the position of the radio Source I, which is remarkably different from other molecular lines. The spectrummore » shows a double-peak structure at the peak velocities of -2.1 and 13.3 km s{sup -1}. It appears to be consistent with the 22 GHz H{sub 2}O masers and 43 GHz SiO masers observed around Source I. Thus, the 232 GHz H{sub 2}O maser around Source I would be excited by the internal heating by an embedded protostar, being associated with either the root of the outflows/jets or the circumstellar disk around Source I, as traced by the 22 GHz H{sub 2}O masers or 43 GHz SiO masers, respectively.« less
  • We have observed a cluster forming clump (MM3) associated with the infrared dark cloud G34.43+00.24 in the 1.3 mm continuum and the CH{sub 3}OH, CS, {sup 13}CS, SiO, CH{sub 3}CH{sub 2}CN, and HCOOCH{sub 3} lines with the Atacama Large Millimeter/submillimeter Array and in K-band with the Keck telescope. We have found a young outflow toward the center of this clump in the SiO, CS, and CH{sub 3}OH lines. This outflow is likely driven by a protostar embedded in a hot core, which is traced by the CH{sub 3}CH{sub 2}CN, HCOOCH{sub 3}, {sup 13}CS, and high excitation CH{sub 3}OH lines. Themore » size of the hot core is about 800 × 300 AU in spite of its low mass (<1.1 M {sub ☉}), suggesting a high accretion rate or the presence of multiple star system harboring a few hot corinos. The outflow is highly collimated, and the dynamical timescale is estimated to be less than 740 yr. In addition, we have also detected extended emission of SiO, CS, and CH{sub 3}OH, which is not associated with the hot core and the outflow. This emission may be related to past star formation activity in the clump. Although G34.43+00.24 MM3 is surrounded by a dark feature in infrared, it has already experienced active formation of low-mass stars in an early stage of clump evolution.« less
  • We report the first detection of a hot molecular core outside our Galaxy based on radio observations with ALMA toward a high-mass young stellar object (YSO) in a nearby low metallicity galaxy, the Large Magellanic Cloud (LMC). Molecular emission lines of CO, C{sup 17}O, HCO{sup +}, H{sup 13}CO{sup +}, H{sub 2}CO, NO, SiO, H{sub 2}CS, {sup 33}SO, {sup 32}SO{sub 2}, {sup 34}SO{sub 2}, and {sup 33}SO{sub 2} are detected from a compact region (∼0.1 pc) associated with a high-mass YSO, ST11. The temperature of molecular gas is estimated to be higher than 100 K based on rotation diagram analysis ofmore » SO{sub 2} and {sup 34}SO{sub 2} lines. The compact source size, warm gas temperature, high density, and rich molecular lines around a high-mass protostar suggest that ST11 is associated with a hot molecular core. We find that the molecular abundances of the LMC hot core are significantly different from those of Galactic hot cores. The abundances of CH{sub 3}OH, H{sub 2}CO, and HNCO are remarkably lower compared to Galactic hot cores by at least 1–3 orders of magnitude. We suggest that these abundances are characterized by the deficiency of molecules whose formation requires the hydrogenation of CO on grain surfaces. In contrast, NO shows a high abundance in ST11 despite the notably low abundance of nitrogen in the LMC. A multitude of SO{sub 2} and its isotopologue line detections in ST11 imply that SO{sub 2} can be a key molecular tracer of hot core chemistry in metal-poor environments. Furthermore, we find molecular outflows around the hot core, which is the second detection of an extragalactic protostellar outflow. In this paper, we discuss the physical and chemical characteristics of a hot molecular core in the low metallicity environment.« less