Detection of CI line emission towards the oxygen-rich AGB star omi Ceti

Saberi, Maryam; Vlemmings, Wouter; Beck, E. De; Montez, Rodolfo; Ramstedt, S.

doi:10.1051/0004-6361/201833080

Cited by 10 publications

(8 citation statements)

References 37 publications

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“…The outflow of Mira A has a mass-loss rate of a few times 10 −7 M yr −1 and contains a bubble-like structure, formed by material blowing from the primary to the secondary (Ramstedt et al 2014). Saberi et al (2018) suggest that the CI emission arises from a more compact region near Mira B and find a CI column density of 1.1 × 10 19 cm −2 . We do not find such large column densities for C in our O-rich models with Ṁ = 10 −7 M yr −1 and a white dwarf companion (Table B.1).…”

Section: Comparison To Observationsmentioning

confidence: 89%

“…CI emission has been detected in a shell-like structure around C-rich AGB stars, where it appears to be formed by interstellar UV photodissociation of CO (Keene et al 1993;van der Veen et al 1998;Olofsson et al 2015;Knapp et al 2000). Saberi et al (2018) detected CI emission in the Mira AB system, where the primary Mira A (omi Cet) is an O-rich AGB star and the secondary Mira B is likely to be a white dwarf with a temperature around 20 000 K (Sokoloski & Bildsten 2010). The outflow of Mira A has a mass-loss rate of a few times 10 −7 M yr −1 and contains a bubble-like structure, formed by material blowing from the primary to the secondary (Ramstedt et al 2014).…”

Section: Comparison To Observationsmentioning

confidence: 99%

“…X-ray observations of AGB stars are correlated with far-UV emission, hinting towards X-ray emission from accretion disks around companions (Ortiz & Guerrero 2021). Additionally, the detection of CI emission towards the known O-rich binary system omi Cet is thought to arise from irra-diation by its white dwarf companion (Saberi et al 2018), while the inner wind of the symbiotic system R Aqr shows evidence of photodissociation caused by its white dwarf (Bujarrabal et al 2021).…”

Section: Introductionmentioning

confidence: 99%

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The Role of Internal Photons on the Chemistry of the Circumstellar Envelopes of AGB Stars

Sande

Millar

2019

ApJ

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Recent high spatial resolution observations of gas and dust in the circumstellar envelopes (CSEs) of AGB stars indicate morphologies much more complex than the smooth density distributions generated by spherically symmetric, constant mass loss rates. In particular, the observation of spiral arcs and disks indicate the likely presence of a binary companion which in some cases give rise to the UV photons detected by GALEX. In this Article, we extend our recent model of the chemistry in a clumpy, porous CSE around an AGB star to include the influence of stellar blackbody photons on the CSE chemistry.Our results indicate that internal photons, in a clumpy, porous CSE, can alter chemistry within a few stellar radii and, for some molecules, alter abundances out to several hundred stellar radii. They further suggest that harder radiation from companion stars or accretion disks will have a substantial impact on chemistry in the dust formation zones and inner CSEs of AGB stars.

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Section: Comparison To Observationsmentioning

confidence: 89%

Section: Comparison To Observationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Role of Internal Photons on the Chemistry of the Circumstellar Envelopes of AGB Stars

Sande

Millar

2019

ApJ

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“…However this likely affects the CSE chemistry (e.g. Saberi et al 2017Saberi et al , 2018Van de Sande & Millar 2019) in the dust formation region, which is beyond the scope of this paper.…”

Section: Influence Of the Isrf On The Co Abundance Distributionmentioning

confidence: 98%

Photodissociation of CO in the outflow of evolved stars

Saberi

Vlemmings

Beck

2019

A&A

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Context. Ultraviolet (UV) photodissociation of carbon monoxide (CO) controls the abundances and distribution of CO and its photodissociation products. This significantly influences the gas-phase chemistry in the circumstellar material around evolved stars. A better understanding of CO photodissociation in outflows also provides a more precise estimate of mass-loss rates. Aims. We aim to update the CO photodissociation rate in an expanding spherical envelope assuming that the interstellar radiation field (ISRF) photons penetrate through the envelope. This will allow us to precisely estimate the CO abundance distributions in circumstellar envelope around evolved stars. Methods. We used the most recent CO spectroscopic data to precisely calculate the depth dependency of the photodissociation rate of each CO dissociating line. We calculated the CO self-and mutual-shielding functions in an expanding envelope. We investigated the dependence of the CO profile on the five fundamental parameters mass-loss rate, the expansion velocity, the CO initial abundance, the CO excitation temperature, and the strength of the ISRF. Results. Our derived CO envelope size is smaller than the commonly used radius derived by Mamon et al. 1988. The difference between results varies from 1% to 39% and depends on the H 2 and CO densities of the envelope. We list two fitting parameters for a large grid of models to estimate the CO abundance distribution. We demonstrate that the CO envelope size can differ between outflows with the same effective content of CO, but different CO abundance, mass-loss rate, and the expansion velocity as a consequence of differing amounts of shielding by H 2 and CO. Conclusions. Our study is based on a large grid of models employing an updated treatment of the CO photodissociation, and in it we find that the abundance of CO close to the star and the outflow density both can have a significant effect on the size of the molecular envelope. We also demonstrate that modest variations in the ISRF can cause measurable differences in the envelope extent.

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“…A white dwarf companion would produce enough dissociating and ionizing photons to significantly alter the circumstellar chemistry and lead to C + deep in the envelope (Millar 2020). Atomic carbon near evolved stars has also been detected for α Ori (Huggins et al 1994) and o Cet (Saberi et al 2018) and interpreted as potentially due to presence of UV radiation from a chromosphere or accretion shocks. In R Scl, atomic carbon was detected from a detached shell, due to dissociation of molecules other than CO (Olofsson et al 2015).…”

Section: Discussionmentioning

confidence: 99%

Ionized carbon around IRC +10216

Reach,

Ruaud,

Wiesemeyer

et al. 2021

Preprint

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Asymptotic giant branch (AGB) stars create a rich inventory of molecules in their envelopes as they lose mass during later stages of their evolution. These molecules cannot survive the conditions in interstellar space, where they are exposed to ultraviolet photons of the interstellar radiation field. As a result, daughter molecules are the ones injected into space, and a halo of those molecules is predicted to exist around cool evolved stars. The most abundant molecule in the envelopes other than H 2 is CO, which dissociates into C that is rapidly ionized into C + in a halo around the star that is optically thin to the interstellar radiation field. We develop the specific predictions of the ionized carbon halo size and column density for the well-studied, nearby star IRC +10216. We compare those models to observations of the [C II] 157.7 µm far-infrared fine-structure line using SOFIA and Herschel. The combination of bright emission toward the star and upper limits to extended [C II] is inconsistent with any standard model. The presence of [C II] toward the star requires some dissociation and ionization in the inner part of the outflow, possibly due to a hot companion star. The lack of extended [C II] emission requires that daughter products from CO photodissociation in

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Detection of CI line emission towards the oxygen-rich AGB star omi Ceti

Cited by 10 publications

References 37 publications

The Role of Internal Photons on the Chemistry of the Circumstellar Envelopes of AGB Stars

The Role of Internal Photons on the Chemistry of the Circumstellar Envelopes of AGB Stars

Photodissociation of CO in the outflow of evolved stars

Ionized carbon around IRC +10216

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