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Schonberg, William P.

doi:10.1023/a:1012534626637

Cited by 14 publications

(12 citation statements)

References 75 publications

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“…After modelling the gas kinetic temperature and density distribution of the envelope, the CO emission can be solved through a full radiative transfer code for molecular rotational line emission developed by Schönberg (1988). The details of the current implementation are presented in Justtanont et al (1994Justtanont et al ( , 1996 and Skinner et al (1999).…”

Section: Resultsmentioning

confidence: 99%

Imaging the circumstellar envelope of OH 26.5+0.6

Fong

Justtanont²,

Meixner

et al. 2002

A&A

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Abstract. Using the Berkeley-Illinois-Maryland-Association (BIMA) Millimeter Array, we were able to map the extreme OH/IR star, OH 26.5+0.6, in the 12 CO J = 1-0 line transition. The CO emission is partially resolved with a deconvolved source size of 8.5 × 5.5 . The spectrum shows that the blue-shifted emission is missing, most likely due to interstellar absorption. By modelling the infrared spectral energy distribution, we derive a dust mass loss rate of 1.9 × 10 −6 M yr −1 . From this we are able to place an upper limit on the extent of the dusty envelope of 10 16 cm while our BIMA map shows that the CO photodissociation radius extends out to about 7×10 16 cm. To best fit the BIMA observations and the higher CO rotational transitions using our full radiative transfer code, we needed to include a second, more tenuous AGB wind, outside the high density superwind to account for the observed flux. From our model, we conclude that up to 80% of the CO flux comes from the unresolved superwind.

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Section: Resultsmentioning

confidence: 99%

Imaging the circumstellar envelope of OH 26.5+0.6

Fong

Justtanont²,

Meixner

et al. 2002

A&A

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“…Schönberg (1985) demonstrated that non-local scattering effects cause severe errors in the source function when using the Sobolev approximation (see also J94). Moreover, as demonstrated by Schönberg (1988), part of the line profile of the low-excitation CO transitions is formed under non-LTE circumstances. The decoupling radius (i.e.…”

Section: Line Radiative Transfermentioning

confidence: 91%

Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles

Decin

Hony²,

Koter

et al. 2006

A&A

162

232

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Context. Mass loss plays a dominant role in the evolution of low mass stars while they are on the Asymptotic Giant Branch (AGB). The gas and dust ejected during this phase are a major source in the mass budget of the interstellar medium. Recent studies have pointed towards the importance of variations in the mass-loss history of such objects. Aims. By modelling the full line profile of low excitation CO lines emitted in the circumstellar envelope, we can study the mass-loss history of AGB stars. Methods. We have developed a non-LTE radiative transfer code, which calculates the velocity structure and gas kinetic temperature of the envelope in a self-consistent way. The resulting structure of the envelope provides the input for the molecular line radiative calculations which are evaluated in the comoving frame. The code allows for the implementation of modulations in the mass-loss rate. This code has been benchmarked against other radiative transfer codes and is shown to perform well and efficiently. Results. We illustrate the effects of varying mass-loss rates in case of a superwind phase. The model is applied to the well-studied case of VY CMa. We show that both the observed integrated line strengths as the spectral structure present in the observed line profiles, unambiguously demonstrate that this source underwent a phase of high mass loss (∼3.2 × 10 −4 M yr −1 ) some 1000 yr ago. This phase took place for some 100 yr, and was preceded by a low mass-loss phase (∼1 × 10 −6 M yr −1 ) taking some 800 yr. The current mass-loss rate is estimated to be in the order of 8 × 10 −5 M yr −1 . Conclusions. In this paper, we demonstrate that both the relative strength of the CO rotational line profiles and the (non)-occurrence of spectral structure in the profile offer strong diagnostics to pinpoint the mass-loss history.

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“…The terminal expansion velocity v ∞ can be derived directly from the width of the line profile (Table A.3). The model we use to analyze the CO data is based on a study by Schönberg (1988) and was previously used by Justtanont et al (1994). The interpretation of our observations using this model is discussed in Sect.…”

Section: Physical Conditions In the Outflow: A Modelmentioning

confidence: 99%

“…Line radiation originating from a local region. The size of this region is defined by a velocity which Schönberg (1988) and also Justtanont et al (1994) have referred to as stochastic velocity v sto . The nature of this stochastic velocity is not specified, but physically should consist of a thermal component v therm and a turbulent component v turb , given by…”

Section: Description Of the Modelmentioning

confidence: 99%

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Mass loss and rotational CO emission from Asymptotic Giant Branch stars

Kemper

Stark

Justtanont³

et al. 2003

A&A

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Abstract. We present submillimeter observations of rotational transitions of carbon monoxide from J = 2 → 1 up to 7 → 6 for a sample of Asymptotic Giant Branch stars and red supergiants. It is the first time that the high transitions J = 6 → 5 and 7 → 6 are included in such a study. With line radiative transfer calculations, we aim to determine the mass-loss history of these stars by fitting the CO line intensities. We find that the observed line intensities of the high transitions, including the J = 4 → 3 transition, are significantly lower than the predicted values. We conclude that the physical structure of the outflow of Asymptotic Giant Branch stars is more complex than previously thought. In order to understand the observed line intensities and profiles, a physical structure with a variable mass-loss rate and/or a gradient in stochastic gas velocity is required. A case study of the AGB star WX Psc is performed. We find that the CO line strengths may be explained by variations in mass-loss on time scales similar to those observed in the separated arc-like structures observed around post-AGB stars. In addition, a gradient in the stochastic velocity may play a role. Until this has been sorted out fully, any mass loss determinations based upon single CO lines will remain suspect.

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Untitled

Cited by 14 publications

References 75 publications

Imaging the circumstellar envelope of OH 26.5+0.6

Imaging the circumstellar envelope of OH 26.5+0.6

Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles

Mass loss and rotational CO emission from Asymptotic Giant Branch stars

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