The First Mid-infrared Detection of HNC in the Interstellar Medium: Probing the Extreme Environment toward the Orion Hot Core

Nickerson, Sarah; Rangwala, Naseem; Colgan, Sean W. J.; DeWitt, Curtis; Huang, Xinchuan; Acharyya, Kinsuk; Drozdovskaya, M. N.; Fortenberry, Ryan C.; Herbst, Eric; Lee, Timothy J.

doi:10.3847/1538-4357/abca36

Cited by 19 publications

(27 citation statements)

References 141 publications

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“…Our results build on previous 12.96-13.33 μm SOFIA/ EXES observations toward IRc2 (Rangwala et al 2018), and a segment of this survey was previously published covering HCN and the first MIR detections of HNC and H CN 13 in the interstellar medium (Nickerson et al 2021). This work complements EXES and TEXES observations toward the conventional protostar-harboring hot cores AFGL 2591, AFGL 2136 (4-13 μm; Indriolo et al 2015;Barr et al 2020Barr et al , 2022Indriolo et al 2020), NGC 7538 IRS 1 (7.6-13.7 μm; Knez et al 2009), and Mon R2 (7.23-7.38 μm;Dungee et al 2018).…”

Section: Introductionsupporting

confidence: 85%

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The Mid-infrared Molecular Inventory toward Orion IRc2

Nickerson

Rangwala

Colgan

et al. 2023

ApJ

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We present the first high spectral resolution mid-infrared survey in the Orion BN/KL region, covering 7.2–28.3 μm. With SOFIA/EXES, we target the enigmatic source Orion IRc2. While this is in the most prolifically studied massive star-forming region, longer wavelengths and molecular emission lines dominated previous spectral surveys. The mid-infrared observations in this work access different components and molecular species in unprecedented detail. We unambiguously identify two new kinematic components, both chemically rich with multiple molecular absorption lines. The “blue clump” has v LSR = −7.1 ± 0.7 km s−1, and the “red clump” has 1.4 ± 0.5 km s−1. While the blue and red clumps have similar temperatures and line widths, molecular species in the blue clump have higher column densities. They are both likely linked to pure rotational H2 emission also covered by this survey. This work provides evidence for the scenario that the blue and red clumps are distinct components unrelated to the classic components in the Orion BN/KL region. Comparison to spectroscopic surveys toward other infrared targets in the region show that the blue clump is clearly extended. We analyze, compare, and present in-depth findings on the physical conditions of C2H2, 13CCH2, CH4, CS, H2O, HCN, H 13 CN , HNC, NH3, and SO2 absorption lines and an H2 emission line associated with the blue and red clumps. We also provide limited analysis of H2O and SiO molecular emission lines toward Orion IRc2 and the atomic forbidden transitions [Fe ii], [S i], [S iii], and [Ne ii].

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Section: Introductionsupporting

confidence: 85%

“…We normalize the EXES data following the procedure detailed in Nickerson et al (2021). Here we summarize it briefly.…”

Section: Flux Preparationmentioning

confidence: 99%

The Mid-infrared Molecular Inventory toward Orion IRc2

Nickerson

Rangwala

Colgan

et al. 2023

ApJ

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“…Furthermore, Crockett et al (2014a) conclude that H 2 S emission, which is pumped by far-IR radiation, in the Hot Core region signals the presence of a hidden source of luminosity. Another hybrid hypothesis is that the Hot Core might have been a typical hot core around Source I prior to Orion's explosive event, and that, as a result of this, even the dense gas of the Hot Core were spatially separated from the protostars, especially Source I (Nickerson et al 2021), giving us the enigmatic molecular core we observe today.…”

Section: Hot Corementioning

confidence: 99%

Mapping physical parameters in Orion KL at high spatial resolution

Wilkins,

Carroll,

Blake

2021

Preprint

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The Orion Kleinmann-Low nebula (Orion KL) is notoriously complex and exhibits a range of physical and chemical components. We conducted high angular resolution (sub-arcsecond) observations of 13 CH 3 OH ν = 0 (∼0. 3 and ∼0. 7) and CH 3 CN ν 8 = 1 (∼0. 2 and ∼0. 9) line emission with the Atacama Large Millimeter/submillimeter Array (ALMA) to investigate Orion KL's structure on small spatial scales (≤350 au). Gas kinematics, excitation temperatures, and column densities were derived from the molecular emission via a pixel-by-pixel spectral line fitting of the image cubes, enabling us to examine the small-scale variation of these parameters. Sub-regions of the Hot Core have a higher excitation temperature in a 0. 2 beam than a 0. 9 beam, indicative of possible internal sources of heating. Furthermore, the velocity field includes a bipolar ∼7−8 km s −1 feature with a southeastnorthwest orientation against the surrounding ∼4−5 km s −1 velocity field, which may be due to an outflow. We also find evidence of a possible source of internal heating toward the Northwest Clump, since the excitation temperature there is higher in a smaller beam versus a larger beam. Finally, the region southwest of the Hot Core (Hot Core-SW) presents itself as a particularly heterogeneous region bridging the Hot Core and Compact Ridge. Additional studies to identify the (hidden) sources of luminosity and heating within Orion KL are necessary to better understand the nebula and its chemistry.

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“…The ongoing investigations of HNC/HCN in OMC-1 make clear the ratio's potential as a temperature probe for cold molecular gas (Schilke et al 1992;Graninger et al 2014;Hacar et al 2020). Studies of dark cloud cores (Hirota et al 1998;Nickerson et al 2021), prestellar cores (Padovani et al 2011), star-forming Hii regions (Jin et al 2015) and galaxies (Cañameras et al 2021), the protoplanetary disk orbiting TW Hya (Graninger et al 2015;Long et al 2021), and even low-mass protostars and young brown dwarfs (Riaz et al 2018) reveal the utility of HNC/HCN ratio measurements across environments ranging from molecular clouds through the early stages of stellar evolution. The interplay between the two molecules appears to be governed primarily by the reaction HNC + H → HCN + H. At temperatures above ∼100 K, this process favors conversion of HNC to HCN, thus decreasing the HNC/HCN ratio as protostellar evolution proceeds (Jin et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Sampling molecular gas in the Helix planetary nebula: Variation in HNC/HCN with UV flux

Bublitz

Kastner

Hily-Blant

et al. 2022

A&A

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Context. Observations of molecular clouds, prestellar cores, and protoplanetary disks have established that the HNC/HCN ratio may be a potent diagnostic of molecular gas physical conditions. The processes that govern the relative abundances of these molecules nevertheless remain poorly understood. Aims. We seek to exploit the wide range of UV irradiation strengths within the ∼pc diameter Helix planetary nebula to explore the potential role of UV radiation in driving HNC/HCN. Methods. We performed IRAM 30 m and APEX 12 m radio line observations across six positions within the Helix Nebula, making use of radiative transfer and photodissociation modeling codes to interpret the results for line intensities and line ratios in terms of the molecular gas properties. Results. We have obtained the first detections of the plasma-embedded Helix molecular knots (globules) in HCN, HNC, HCO+, and other trace molecules. Analysis of the HNC/HCN integrated line intensity ratio reveals an increase with radial distance from the Helix central star. In the context of molecular line ratios of other planetary nebulae from the literature, the HNC/HCN ratio appears to be anticorrelated with UV emission over four orders of magnitude in incident flux. Models of the photodissociation regions within the Helix using the RADEX and Meudon codes reveal strong constraints on the column density (1.5–2.5 × 1012 cm−2) of the molecular gas, as well as pressure and temperature. Analysis of the molecular ion HCO+ across the Helix indicates that X-ray irradiation is likely driving HCO+ production in the outer regions of planetary nebulae, where photodissociation is limited but cold gas and ionized molecules are abundant. Conclusions. Although the observational results clearly indicate that UV irradiation is important in determining the HNC/HCN ratio, our photodissociation region modeling indicates that the UV flux gradient alone cannot reproduce the observed variation in HNC/HCN across the Helix Nebula. Instead, HNC/HCN appears to be dependent on both UV irradiation and gas pressure and density.

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The First Mid-infrared Detection of HNC in the Interstellar Medium: Probing the Extreme Environment toward the Orion Hot Core

Cited by 19 publications

References 141 publications

The Mid-infrared Molecular Inventory toward Orion IRc2

The Mid-infrared Molecular Inventory toward Orion IRc2

Mapping physical parameters in Orion KL at high spatial resolution

Sampling molecular gas in the Helix planetary nebula: Variation in HNC/HCN with UV flux

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