The photodissociation of CO in circumstellar envelopes

Mamon, G. A.; Glassgold, A. E.; Huggins, P. J.

doi:10.1086/166338

Cited by 226 publications

(288 citation statements)

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“…We note that the outer 13 CO radius is practically identical to that of 12 CO (Mamon et al 1988) because, although 13 CO is more easily photodissociated by the interstellar UV field, subsequent fractionation reactions tend to reform 13 CO. To first order, the abundance is kept practically constant up to the photodissociation radius of 12 CO. From this radius, both molecules are dissociated and their abundances drop very fast.…”

Section: Resultsmentioning

confidence: 73%

“…Detailed calculations of the CO photodissociation radius were performed by Mamon et al (1988) for the relevant cases, taking into account the shielding by dust and by the CO molecule itself. The resulting predicted radii were parameterized as a function of the mass loss rate, the expansion velocity, and the relative abundance by Planesas et al (1990), see also Loup et al (1993).…”

Section: Resultsmentioning

confidence: 99%

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Carbon isotopic abundance ratios in S-type stars

Wallerstein

Balick

Alcolea

et al. 2011

A&A

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We have used the IRAM 30 m telescope on Pico de Veleta to observe 11 S-type stars in the J = 1-0 and J = 2-1 transitions of both 12 C 16 O and 13 C 16 O in order to derive the 12 CO/ 13 CO ratio in their circumstellar envelopes. Detections of high signal to noise were achieved for 7 stars. A mean isotope ratio of 35.3 ± 6.2 was found. This ratio fits between the ratio for late M stars of about 12 ± 3 and that of carbon stars of 58 ± 17. Hence, we confirm the often proposed evolutionary sequence from late M through type S to carbon stars. Mass loss rates of 5 × 10 −8 to 3 × 10 −6 M y −1 are derived from the present CO data using a simple uniform outflow model with line-dependent opacities, in very good agreement with previous mass-loss estimates.

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Section: Resultsmentioning

confidence: 73%

Section: Resultsmentioning

confidence: 99%

Carbon isotopic abundance ratios in S-type stars

Wallerstein

Balick

Alcolea

et al. 2011

A&A

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“…Values between parentheses denote refined inner wind abundance values obtained from the new HIFI observations.The fractional abundances for all water isotopologs and isomers are based on the HIFI data presented in this Letter. point out that the line profiles are quite noisy. The 13 CO fractional abundance was obtained assuming the same photodissociation radius as for 12 CO (Mamon et al 1988). However, if the effect of less self-shielding of 13 CO (compared to 12 CO) were more important than estimated by Mamon et al (1988), the photodissocation radius of 13 CO would be smaller, affecting the low excitation rotational transitions more than the higher excitation lines observed by HIFI.…”

Section: Appendix B: Radiative Transfer Modellingmentioning

confidence: 99%

Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tauri as seen byHerschel/HIFI

Decin

Justtanont

Beck

et al. 2010

A&A

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During their asymptotic giant branch evolution, low-mass stars lose a significant fraction of their mass through an intense wind, enriching the interstellar medium with products of nucleosynthesis. We observed the nearby oxygen-rich asymptotic giant branch star IK Tau using the highresolution HIFI spectrometer onboard Herschel. We report on the first detection of H 16 2 O and the rarer isotopologues H 17 2 O and H 18 2 O in both the ortho and para states. We deduce a total water content (relative to molecular hydrogen) of 6.6 × 10 −5 , and an ortho-to-para ratio of 3:1. These results are consistent with the formation of H 2 O in thermodynamical chemical equilibrium at photospheric temperatures, and does not require pulsationally induced non-equilibrium chemistry, vaporization of icy bodies or grain surface reactions. High-excitation lines of 12 CO, 13 CO, 28 SiO, 29 SiO, 30 SiO, HCN, and SO have also been detected. From the observed line widths, the acceleration region in the inner wind zone can be characterized, and we show that the wind acceleration is slower than hitherto anticipated.

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“…The same molecular radius was employed when simultaneously fitting the two carbon isotopologues. Although 13 CO is thought to undergo selective photodissociation because of its lower abundance, this effect tends to be cancelled out by chemical fractionation (e.g., Mamon et al 1988). Thus, assuming the same molecular radii for both species is not unreasonable (also see Schöier & Olofsson 2000).…”

Section: Tablementioning

confidence: 99%

CIRCUMSTELLAR¹²C/¹³C ISOTOPE RATIOS FROM MILLIMETER OBSERVATIONS OF CN AND CO: MIXING IN CARBON- AND OXYGEN-RICH STARS

Milam

Woolf

Ziurys

2008

ApJ

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A survey of the 12 C/ 13 C ratio toward circumstellar envelopes has been conducted at millimeter wavelengths using the facilities of the Arizona Radio Observatory (ARO). The ratios were obtained for a sample of local C-and O-rich asymptotic giant branch and supergiant stars from observations of the 12 C and 13 C isotopologues of CO and CN, respectively. The J = 1 → 0 transitions of both molecules were observed at λ = 3 mm using the ARO 12 m telescope, while the J = 2 → 1 lines of the two species were measured using the ARO Sub-Millimeter Telescope (SMT) at λ = 1 mm. The 12 C/ 13 C ratios were determined from the CO data by modeling both transitions simultaneously with a circumstellar radiative transfer code, which can account for the high opacities present in the emission from this species. In the case of CN, the hyperfine structure was used to evaluate opacity effects. Ratios obtained independently from CO and CN are in good agreement. For the C-rich envelopes, the ratios fall in the range 12 C/ 13 C ∼ 25-90, while the O-rich shells have values of 10-35. Ratios of 12 C/ 13 C ∼ 3-14 are found for the supergiant stars, with the exception of VY CMa, where the values lie in the range 25-46. All ratios obtained in this study are 89, the solar value, suggesting that substantial carbon-13 enrichment may be currently occurring in the local interstellar medium. A qualitative model was constructed based on first and third dredge-up convective mixing that can reproduce the observed ratios. Substantial mixing of H-burning products must occur to explain the ratios in the O-rich objects, while a wide range of 12 C/ 13 C values can be generated by only a few percent mixing of He-burning ashes in the C-rich case. The 12 C/ 13 C ratios obtained in this study should help improve stellar yield models and contribute to the understanding of Galactic chemical evolution.

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The photodissociation of CO in circumstellar envelopes

Cited by 226 publications

References 0 publications

Carbon isotopic abundance ratios in S-type stars

Carbon isotopic abundance ratios in S-type stars

Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tauri as seen byHerschel/HIFI

CIRCUMSTELLAR¹²C/¹³C ISOTOPE RATIOS FROM MILLIMETER OBSERVATIONS OF CN AND CO: MIXING IN CARBON- AND OXYGEN-RICH STARS

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The photodissociation of CO in circumstellar envelopes

Cited by 226 publications

References 0 publications

Carbon isotopic abundance ratios in S-type stars

Carbon isotopic abundance ratios in S-type stars

Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tauri as seen byHerschel/HIFI

CIRCUMSTELLAR12C/13C ISOTOPE RATIOS FROM MILLIMETER OBSERVATIONS OF CN AND CO: MIXING IN CARBON- AND OXYGEN-RICH STARS

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CIRCUMSTELLAR¹²C/¹³C ISOTOPE RATIOS FROM MILLIMETER OBSERVATIONS OF CN AND CO: MIXING IN CARBON- AND OXYGEN-RICH STARS