Strong CO<sup>+</sup> and 
	   Emission in Comet C/2016 R2 (Pan-STARRS)<sup>*</sup>

Cochran, A. L.; McKay, Adam

doi:10.3847/2041-8213/aaab57

Cited by 47 publications

(53 citation statements)

References 20 publications

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“…However, large N 2 abundances (>10%) are not expected either, unless there is a cometary outburst during the period of observation. Moreover, different observations have confirmed that the N 2 abundance in this comet is about 7% relative to CO (Cochran & McKay 2018;Biver et al 2018;Opitom et al 2019). Hence, we do not expect this comet to have a large enough N 2 abundance (>10%) to produce the observed [CI]/[NI] emission ratio.…”

Section: Effect Of the Neutral Species Abundancesmentioning

confidence: 68%

Forbidden atomic carbon, nitrogen, and oxygen emission lines in the water-poor comet C/2016 R2 (Pan-STARRS)

Raghuram

Hutsemékers

Opitom

et al. 2020

A&A

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Context. The N 2 and CO-rich and water-depleted comet C/2016 R2 (Pan-STARRS) (hereafter 'C/2016 R2') is a unique comet for detailed spectroscopic analysis. Aims. We aim to explore the associated photochemistry of parent species, which produces different metastable states and forbidden emissions, in this cometary coma of peculiar composition. Methods. We re-analyzed the high-resolution spectra of comet C/2016 R2, which were obtained in February 2018, using the UVES spectrograph of the European Southern Observatory (ESO) Very Large Telescope (VLT). Various forbidden atomic emission lines of [CI], [NI], and [OI] were observed in the optical spectrum of this comet when it was at 2.8 au from the Sun. The observed forbidden emission intensity ratios are studied in the framework of a couple-chemistry emission model. Results. The model calculations show that CO 2 is the major source of both atomic oxygen green and red-doublet emissions in the coma of C/2016 R2 (while for most comets it is generally H 2 O), whereas, CO and N 2 govern the atomic carbon and nitrogen emissions, respectively. Our modelled oxygen green to red-doublet and carbon to nitrogen emission ratios are higher by a factor of 3, when compared to the observations. These discrepancies can be due to uncertainties associated with photon cross sections or unknown production/loss sources. Our modelled oxygen green to red-doublet emission ratio is close to the observations, when we consider an O 2 abundance with a production rate of 30% relative to the CO production rate. We constrained the mean photodissociation yield of CO producing C( 1 S) as about 1%, a quantity which has not been measured in the laboratory. The collisional quenching is not a significant loss process for N( 2 D) though its radiative lifetime is significant (∼10 hrs). Hence, the observed [NI] doublet-emission ratio ([NI] 5198/5200) of 1.22, which is smaller than the terrestrial measurement by a factor 1.4, is mainly due to the characteristic radiative decay of N( 2 D).

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Section: Effect Of the Neutral Species Abundancesmentioning

confidence: 68%

Forbidden atomic carbon, nitrogen, and oxygen emission lines in the water-poor comet C/2016 R2 (Pan-STARRS)

Raghuram

Hutsemékers

Opitom

et al. 2020

A&A

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“…This fits with recent estimates of the CO snowline in the TW Hya disk (Zhang et al 2017). Appreciable amounts of N 2 in comets are rare (Cochran et al 2000;Cochran 2002;Rubin et al 2015), though a N 2 /CO ratio of 0.15 was recently reported in one comet (Cochran & McKay 2018), and the majority of comets therefore likely formed interior to the N 2 snowline, placing the N 2 snowline in the outer range of the proposed comet-forming region of 5 and 35 au (Mumma & Charnley 2011). Finally, Pluto appears to be rich in N 2 , which would be consistent with formation exterior to the N 2 snowline, though other explanations have been given as well (Stern et al 2018).…”

Section: Density and Temperature Structurementioning

confidence: 99%

Jupiter's Composition Suggests its Core Assembled Exterior to the N₂ Snowline

2019

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Jupiter's atmosphere is enriched in C, N, S, P, Ar, Kr and Xe with respect to solar abundances by a factor of ∼3. Gas Giant envelopes are mainly enriched through the dissolution of solids in the atmosphere, and this constant enrichment factor is puzzling since several of the above elements are not expected to have been in the solid phase in Jupiter's feeding zone; most seriously, Ar and the main carrier of N, N 2 , only condense at the very low temperatures, 21-26 K, associated with the outer solar nebula. We propose that a plausible solution to the enigma of Jupiter's uniform enrichment pattern is that Jupiter's core formed exterior to the N 2 and Ar snowlines, beyond 30 au, resulting in a Solar composition core in all volatiles heavier than Ne. During envelope accretion and planetesimal bombardment, some of the core mixed in with the envelope causing the observed enrichment pattern. We show that this scenario naturally produces the observed atmosphere composition, even with substantial pollution from N-poor pebble and planetesimal accretion in Jupiter's final feeding zone. We note that giant core formation at large nebular radii is consistent with recent models of gas giant core formation through pebble accretion, which requires the core to form exterior to Jupiter's current location to counter rapid inward migration during the core and envelope formation process. If this scenario is common, gas giant core formation may account for many of the gaps observed in protoplanetary disks between 10s and 100 au.

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“…The CN and UC images exhibited extended, filamentary structures similar to those seen with the CO + filter. Although the filters were designed to isolate gas (CN) or to be a nearly emission-free continuum area (UC), the CN bandpass includes N + 2 emission (Cochran and McKay 2018;Opitom et al 2019) and both bandpasses contain emissions from CO + ions (Pearse and Gaydon 1976, and references therein). For most comets, these ions are much fainter than the intended gas and/or continuum and can be safely ignored but this is not the case for R2 PanSTARRS.…”

Section: Dct-lmimentioning

confidence: 99%

“…d Due to the lack of observations of N2 in comets, the mean mixing ratios compared to H2O and CO are not meaningful to calculate. Therefore the number included is based on past observations discussed in Cochran and McKay (2018) and has very large uncertainty (indicated by the "?"). e Derived from our NH2 upper limit assuming all NH2 is released via NH3 photodissociation (i.e.…”

Section: Cometary Populationmentioning

confidence: 99%

“…Comet C/2016 R2 (PanSTARRS) was observed to have a peculiar optical spectrum when it was at a heliocentric distance of 3.1 AU, dominated by emissions from CO + and N + 2 with a lack of emission from other species such as CN and C 2 typically observed at these wavelengths (Cochran and McKay 2018). From these observations, it was derived that N 2 /CO ∼ 0.06, among the highest values observed in a comet.…”

Section: Introductionmentioning

confidence: 95%

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