Model for atomic oxygen visible line emissions in Comet C/1995 O1 Hale-Bopp

Raghuram, Susarla; Bhardwaj, Anil

doi:10.1016/j.icarus.2012.11.032

Cited by 17 publications

(39 citation statements)

References 70 publications

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“…The errors correspond to the standard deviation of the 12 spectra. Considering the theoretical production rates of Raghuram & Bhardwaj (2013; see Table 1 of Decock et al (2015), the 1 S/ 1 D ratio corresponding to the G/R ratio), these results confirm that H 2 O is the main parent molecule that photodissociates to produce oxygen atoms when the comet is observed at a heliocentric distance of r ∼ 1 au. This agrees with previous analyses reported for other comets (Cochran 1984(Cochran , 2008Capria et al 2010;Decock et al 2013, and references therein).…”

Section: [Oi] Linessupporting

confidence: 62%

“…The velocity width as well as the flux ratios I 6300 /I 6364 and G/R = I 5577 /(I 6300 + I 6364 ) were measured. The latter permits determining the parent species of oxygen atoms by comparing our results with the theoretical production rates provided by Raghuram & Bhardwaj (2013). However, an accurate measurement of the green line requires decontaminating this line from two C 2 lines that are blended with it at 5577.331 Å and 5577.401 Å.…”

Section: [Oi] Linesmentioning

confidence: 93%

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High-resolution spectra of comet C/2013 R1 (Lovejoy)

Rousselot

Decock

Корсун

et al. 2015

A&A

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Context. High-resolution spectra of comets permit deriving the physical properties of the coma. In the optical range, relative production rates can be computed, and information about isotopic ratios and the origin of oxygen atoms can be obtained. Aims. The main objective of the work presented here was to obtain information about the chemical composition of comet C/2013 R1 (Lovejoy), a bright and long-period comet that passed perihelion (0.81 au) on 22 December 2013. Methods. We used the HARPS-North echelle spectrograph at the 3.5 m telescope TNG to obtain high-resolution spectra of comet C/2013 R1 (Lovejoy) in the optical range immediately after its perihelion passage during four consecutive nights in the period December 23 to 26, 2013.Results. Our results demonstrate the ability of HARPS-North to efficiently obtain cometary spectra. Very faint emission lines, such as those of 15 NH 2 , have been detected, leading to a rough estimate of the 14 N/ 15 N ratio in NH 2 . The 12 C/ 13 C ratio was measured in the C 2 lines and is equal to 80 ± 30. The oxygen lines were studied as well (green to red line intensity ratios and widths), confirming that H 2 O is the main parent molecule that photodissociates to produce oxygen atoms. This suggests that this comet has a high CO 2 abundance. Relative production rates for C 2 and NH 2 were computed, but we found no significant deviation from a typical NH 2 /C 2 ratio.

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Section: [Oi] Linessupporting

confidence: 62%

Section: [Oi] Linesmentioning

confidence: 93%

High-resolution spectra of comet C/2013 R1 (Lovejoy)

Rousselot

Decock

Корсун

et al. 2015

A&A

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“…Since O( 1 S) and O( 1 D) are metastable states, resonance fluorescence by solar photons is not an effective excitation mechanism for populating these states. Dissociative excitation of O-bearing neutrals by photons and photoelectrons, and thermal recombination of atomic oxygen constituted ions are the sources of these metastable states in the cometary coma (Bhardwaj & Haider 2002;Raghuram & Bhardwaj 2013). Most of the comets observed around heliocentric distance of 1 au have H 2 O as the principal constituent in the cometary coma (Bockelée-Morvan et al 2004).…”

Section: Introductionmentioning

confidence: 99%

Photochemistry of atomic oxygen green and red-doublet emissions in comets at larger heliocentric distances

Raghuram

Bhardwaj

2014

A&A

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Context. In comets, the atomic oxygen green (5577 Å) to red-doublet (6300, 6364 Å) emission intensity ratio (G/R ratio) of 0.1 has been used to confirm H 2 O as the parent species producing forbidden oxygen emission lines. The larger (>0.1) value of G/R ratio observed in a few comets is ascribed to the presence of higher CO 2 and CO relative abundances in the cometary coma. Aims. We aim to study the effect of CO 2 and CO relative abundances on the observed G/R ratio in comets observed at large (>2 au) heliocentric distances by accounting for important production and loss processes of O( 1 S) and O( 1 D) atoms in the cometary coma. Methods. Recently we have developed a coupled chemistry-emission model to study photochemistry of O( 1 S) and O( 1 D) atoms and the production of green and red-doublet emissions in comets Hyakutake and Hale-Bopp. In the present work we applied the model to six comets where green and red-doublet emissions are observed when they are beyond 2 au from the Sun. Results. The collisional quenching of O( 1 S) and O( 1 D) can alter the G/R ratio more significantly than that due to change in the relative abundances of CO 2 and CO. In a water-dominated cometary coma and with significant (>10%) CO 2 relative abundance, photodissociation of H 2 O mainly governs the red-doublet emission, whereas CO 2 controls the green line emission. If a comet has equal composition of CO 2 and H 2 O, then ∼50% of red-doublet emission intensity is controlled by the photodissociation of CO 2 . The role of CO photodissociation is insignificant in producing both green and red-doublet emission lines and consequently in determining the G/R ratio. Involvement of multiple production sources in the O( 1 S) formation may be the reason for the observed higher green line width than that of red lines. The G/R ratio values and green and red-doublet line widths calculated by the model are consistent with the observation. Conclusions. Our model calculations suggest that in low gas production rate comets the G/R ratio greater than 0.1 can be used to constrain the upper limit of CO 2 relative abundance provided the slit-projected area on the coma is larger than the collisional zone. If a comet has equal abundances of CO 2 and H 2 O, then the red-doublet emission is significantly (∼50%) controlled by CO 2 photodissociation and thus the G/R ratio is not suitable for estimating CO 2 relative abundance.

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“…The model calculations for comets 103P/Hartley2 and 1P/ Halley have shown that suprathermal electron impact is an important excitation process in the formation of CO(a 3 Π), which is more important than the photodissociation of CO 2 (Bhardwaj & Raghuram 2011;. The model applied to study atomic oxygen emission lines in comets has shown that the collisional quenching in the inner coma can significantly change the observed G/R ratio Raghuram & Bhardwaj 2013, 2014Decock et al 2015). The model calculations in active comets, such as (C/1996 B2) Hyakutake and (C/1995 O1) Hale-Bopp, have shown that the G/R ratio varies as a function of projected distance and depends on the collisions in the cometary comae Raghuram & Bhardwaj 2013).…”

Section: Introductionmentioning

confidence: 99%

“…The model applied to study atomic oxygen emission lines in comets has shown that the collisional quenching in the inner coma can significantly change the observed G/R ratio Raghuram & Bhardwaj 2013, 2014Decock et al 2015). The model calculations in active comets, such as (C/1996 B2) Hyakutake and (C/1995 O1) Hale-Bopp, have shown that the G/R ratio varies as a function of projected distance and depends on the collisions in the cometary comae Raghuram & Bhardwaj 2013). Recently, we have applied our model for the analysis of high-resolution spectroscopic observations made from the ESO very large telescope (VLT) on four comets (viz., C/2002 T7 (LINEAR), 73P-C/SchwassmannWachmann 3, 8P/Tuttle, and 103P/Hartley 2).…”

Section: Introductionmentioning

confidence: 99%

Prediction of Forbidden Ultraviolet and Visible Emissions in Comet 67p/Churyumov–gerasimenko

Raghuram

Bhardwaj

Galand

2016

ApJ

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Remote observation of spectroscopic emissions is a potential tool for the identification and quantification of various species in comets. The CO Cameron band (to trace CO 2 ) and atomic oxygen emissions (to trace H 2 O and/ or CO 2 , CO) have been used to probe neutral composition in the cometary coma. Using a coupled-chemistryemission model, various excitation processes controlling the CO Cameron band and different atomic oxygen and atomic carbon emissions have been modeled in comet 67P/Churyumov-Gerasimenko at 1.29 AU (perihelion) and at 3 AU heliocentric distances, which is being explored by ESAʼs Rosetta mission. The intensities of the CO Cameron band, atomic oxygen, and atomic carbon emission lines as a function of projected distance are calculated for different CO and CO 2 volume mixing ratios relative to water. Contributions of different excitation processes controlling these emissions are quantified. We assess how CO 2 and/or CO volume mixing ratios with respect to H 2 O can be derived based on the observed intensities of the CO Cameron band, atomic oxygen, and atomic carbon emission lines. The results presented in this work serve as baseline calculations to understand the behavior of low out-gassing cometary coma and compare them with the higher gas production rate cases (e.g., comet Halley). Quantitative analysis of different excitation processes governing the spectroscopic emissions is essential to study the chemistry of inner coma and to derive neutral gas composition.

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Model for atomic oxygen visible line emissions in Comet C/1995 O1 Hale-Bopp

Cited by 17 publications

References 70 publications

High-resolution spectra of comet C/2013 R1 (Lovejoy)

High-resolution spectra of comet C/2013 R1 (Lovejoy)

Photochemistry of atomic oxygen green and red-doublet emissions in comets at larger heliocentric distances

Prediction of Forbidden Ultraviolet and Visible Emissions in Comet 67p/Churyumov–gerasimenko

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