Evolution of the Circumstellar Molecular Envelope. I. A BIMA CO Survey of Evolved Stars

Fong, D.; Meixner, Margaret; Sutton, E. C.; Zalucha, Angela M.; Welch, W. J.

doi:10.1086/508127

Cited by 65 publications

(84 citation statements)

References 105 publications

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“…The PACS images show the complex circumstellar dust distribution with several large arcs surrounding the system. Previous images of the CO emission show a wide bipolar structure with the north part approaching and the south receding (Planesas et al 1990;Josselin et al 2000;Fong et al 2006), that is perpendicular to the north and south stream. The higher resolution (2.…”

Section: Introductionmentioning

confidence: 89%

The wonderful complexity of the Mira AB system

Ramstedt

Mohamed

Vlemmings

et al. 2014

A&A

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We have mapped the 12 CO(3-2) line emission around the Mira AB system at 0. 5 resolution using the Atacama Large Millimeter/submillimeter Array (ALMA). The CO map shows amazing complexity. The circumstellar gas has been shaped by different dynamical actors during the evolution of the system, and several morphological components can be identified. The companion is marginally resolved in continuum emission and is currently at 0. 487 ± 0. 006 separation. In the main line component, centered on the stellar velocity, spiral arcs around Mira A are found. The spiral appears to be relatively flat and oriented in the orbital plane. An accretion wake behind the companion is clearly visible, and the projected arc separation is about 5 . In the blue wing of the line emission, offset from the main line, several large (∼5-10 ) opposing arcs are found. We tentatively suggest that this structure is created by the wind of Mira B blowing a bubble in the expanding envelope of Mira A.

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Section: Introductionmentioning

confidence: 89%

The wonderful complexity of the Mira AB system

Ramstedt

Mohamed

Vlemmings

et al. 2014

A&A

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“…For instance, Huggins et al (1988) detected CO emission out to ∼210 in the J = 1−0 line and 180 in the J = 2−1 line. Later, the J = 1−0 line was detected out to 190 (Fong et al 2003(Fong et al , 2006. Recently, Cernicharo et al (priv.…”

Section: Radius Of Peak Abundancementioning

confidence: 94%

Photodissociation and chemistry of N₂in the circumstellar envelope of carbon-rich AGB stars

Millar

Walsh

et al. 2014

A&A

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Context. The envelopes of asymptotic giant branch (AGB) stars are irradiated externally by ultraviolet photons; hence, the chemistry is sensitive to the photodissociation of N 2 and CO, which are major reservoirs of nitrogen and carbon, respectively. The photodissociation of N 2 has recently been quantified by laboratory and theoretical studies. Improvements have also been made for CO photodissociation. Aims. For the first time, we use accurate N 2 and CO photodissociation rates and shielding functions in a model of the circumstellar envelope of the carbon-rich AGB star, IRC +10216. Methods. We use a state-of-the-art chemical model of an AGB envelope, the latest CO and N 2 photodissociation data, and a new method for implementing molecular shielding functions in full spherical geometry with isotropic incident radiation. We compare computed column densities and radial distributions of molecules with observations. Results. The transition of N 2 → N (also, CO → C → C + ) is shifted towards the outer envelope relative to previous models. This leads to different column densities and radial distributions of N-bearing species, especially those species whose formation/destruction processes largely depend on the availability of atomic or molecular nitrogen, for example, C n N (n = 1, 3, 5), C n N − (n = 1, 3, 5), HC n N (n = 1, 3, 5, 7, 9), H 2 CN and CH 2 CN. Conclusions. The chemistry of many species is directly or indirectly affected by the photodissociation of N 2 and CO, especially in the outer shell of AGB stars where photodissociation is important. Thus, it is important to include N 2 and CO shielding in astrochemical models of AGB envelopes and other irradiated environments. In general, while differences remain between our model of IRC +10216 and the observed molecular column densities, better agreement is found between the calculated and observed radii of peak abundance.

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“…Certain authors suggested that this object has evolved off the red giant branch (RGB) and is now a post-AGB star (Bujarrabal et al 2007;Fong et al 2006), while others reported that this is a high-latitude F-supergiant, possibly a binary (Luck et al 1990). The spectra measured here reveal two components, also found in high-resolution interferometer maps (Bujarrabal et al 2007), one being a narrow, spatially-confined component with T K ∼ 600 K and the other a more extended, possible bipolar, nebula.…”

Section: Individual Objectsmentioning

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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Evolution of the Circumstellar Molecular Envelope. I. A BIMA CO Survey of Evolved Stars

Cited by 65 publications

References 105 publications

The wonderful complexity of the Mira AB system

The wonderful complexity of the Mira AB system

Photodissociation and chemistry of N₂in the circumstellar envelope of carbon-rich AGB stars

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

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Evolution of the Circumstellar Molecular Envelope. I. A BIMA CO Survey of Evolved Stars

Cited by 65 publications

References 105 publications

The wonderful complexity of the Mira AB system

The wonderful complexity of the Mira AB system

Photodissociation and chemistry of N2in the circumstellar envelope of carbon-rich AGB stars

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

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Photodissociation and chemistry of N₂in the circumstellar envelope of carbon-rich AGB stars

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