The circumstellar environments of EP Aqr  and Y CVn  probed by the H I emission at 21 cm

Bertre, T. Le; Gérard, E.

doi:10.1051/0004-6361:20035797

Cited by 25 publications

(29 citation statements)

References 28 publications

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“…The H i spectra obtained on V1942 Sgr are very similar to those obtained by Le Bertre & Gérard (2004) and Libert et al (2007) on Y CVn, a well-documented carbon star with a detached shell discovered by IRAS (Young et al 1993a) and imaged by ISO (Izumiura et al 1996). At the central position, we detect a pedestal of width 10 km s −1 , twice the expansion velocity measured for the narrow CO components.…”

Section: V1942 Sgrsupporting

confidence: 74%

Circumstellar H I and CO around the carbon stars V1942 Sagittarii and V Coronae Borealis

Libert¹,

Gérard

Thum

et al. 2010

A&A

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Context. The majority of stars that leave the main sequence are undergoing extensive mass loss, in particular during the asymptotic giant branch (AGB) phase of evolution. Observations show that the rate at which this phenomenon develops differs widely from source to source, so that the time-integrated mass loss as a function of the initial conditions (mass, metallicity, etc.) and of the stage of evolution is presently not well understood. Aims. We investigate the mass loss history of AGB stars by observing the molecular and atomic emission of their circumstellar envelopes. Methods. We selected two stars that are on the thermally pulsing phase of the AGB (TP-AGB) for which high quality data in both the CO rotation lines and the atomic hydrogen line at 21 cm could be obtained. Results. A carbon star of the irregular variability type, V1942 Sgr, has a complex CO line profile that may originate in a long-lived wind of rate ∼10 −7 M yr −1 , and from a young ( < ∼ 10 4 years) fast outflow of rate ∼5 × 10 −7 M yr −1 . The intense H i emission is indicative of a detached shell with 0.044 M of hydrogen. This shell probably results from the slowing-down, by surrounding matter, of the same long-lived wind observed in CO that has been active for ∼6 × 10 5 years. On the other hand, the carbon Mira V CrB is presently undergoing mass loss at a rate of 2 × 10 −7 M yr −1 , but was not detected in the H i data. The wind is mostly molecular and has been active for at most 3 × 10 4 years, with an integrated mass loss of at most 6.5 × 10 −3 M . Conclusions. Although both sources are carbon stars on the TP-AGB, they appear to develop mass loss in very different conditions, and a high rate of mass loss may not imply a high integrated mass loss.

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Section: V1942 Sgrsupporting

confidence: 74%

Circumstellar H I and CO around the carbon stars V1942 Sagittarii and V Coronae Borealis

Libert¹,

Gérard

Thum

et al. 2010

A&A

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“…Using the Very Large Array (VLA), Matthews & Reid (2007) have detected arcminute-scale H i emission features at velocities consistent with the H i emission profile reported by Le Bertre & Gérard (2004). However, they cannot unambiguously conclude on the relation between these clumps and EP Aqr.…”

Section: Presentation Of the Sourcementioning

confidence: 71%

“…From Hipparcos, its distance is derived Delgado et al (2003); (2) Knapp et al (1998); (3) Paper I; (4) Le Bertre & Gérard (2004).…”

Section: Presentation Of the Sourcementioning

confidence: 99%

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Mass loss from dusty, low outflow-velocity AGB stars

Winters¹,

Bertre

Pety

et al. 2007

A&A

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Context. CO rotational lines are frequently used to trace the outflows from AGB stars. Some profiles are composite, with a narrow component super-imposed on a broader one. These profiles have been interpreted in different ways, calling for episodic mass loss, a bipolar flow, or a circumstellar disk. Aims. To investigate the structure of one of these outflows, we have obtained detailed 12 CO(2-1) and 12 CO(1-0) maps of EP Aqr, a prototypical source with composite CO profiles. Methods. Interferometric data were acquired with the IRAM interferometer and combined with on-the-fly maps obtained at the IRAM 30-m. The resulting maps in 12 CO(2-1) and 12 CO(1-0) cover a field of 100 × 100 with a spectral resolution of 0.1 km s −1 and with beams of 1.7 × 1.0 and 3.5 × 1.8 , respectively. Results. The source is clearly resolved with a size of about 15 (FWHM). We do not observe any obvious departure from circular symmetry, but there is evidence of a ringed structure in the CO(2-1) map with enhanced intensity at ∼3.5 and 7.5 from the central star. The continuum level at 1.3 and 2.6 mm is consistent with the star's photospheric emission. We modeled the spatio-kinematic structure with Monte-Carlo radiative transfer simulations assuming spherical symmetry. We reached a reasonable fit to the mapintegrated spectra, but not to the imaging data, possibly because the circumstellar shell of EP Aqr presents inhomogeneities on a scale that is not, or is only barely, resolved in our maps. EP Aqr may be a proto-typical oxygen-rich source for the class of theoretical models exhibiting mass loss variations on a ∼100 yr timescale discovered by Winters et al. (2000), which show a layered structure in their extended circumstellar shells.

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“…These are difficult observations to perform because of the omnipresence of this emission. Thanks to some dedicated work, however, considerable progress has been made in this area (Le Bertre and Gérard 2004;Matthews et al 2013Matthews et al , 2015. In general, the data do not contradict a largely isotropic mass loss, although there is evidence of circumstellar-interstellar media interactions at large distances from the stars.…”

Section: Circumstellar Morphologymentioning

confidence: 96%

Mass loss of stars on the asymptotic giant branch

Höfner

Olofsson

2018

Astron Astrophys Rev

471

376

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As low-and intermediate-mass stars reach the asymptotic giant branch (AGB), they have developed into intriguing and complex objects that are major players in the cosmic gas/dust cycle. At this stage, their appearance and evolution are strongly affected by a range of dynamical processes. Large-scale convective flows bring newlyformed chemical elements to the stellar surface and, together with pulsations, they trigger shock waves in the extended stellar atmosphere. There, massive outflows of gas and dust have their origin, which enrich the interstellar medium and, eventually, lead to a transformation of the cool luminous giants into white dwarfs. Dust grains forming in the upper atmospheric layers play a critical role in the wind acceleration process, by scattering and absorbing stellar photons and transferring their outward-directed momentum to the surrounding gas through collisions. Recent progress in high-angularresolution instrumentation, from the visual to the radio regime, is leading to valuable new insights into the complex dynamical atmospheres of AGB stars and their windforming regions. Observations are revealing asymmetries and inhomogeneities in the photospheric and dust-forming layers which vary on time-scales of months, as well as more long-lived large-scale structures in the circumstellar envelopes. High-angularresolution observations indicate at what distances from the stars dust condensation occurs, and they give information on the chemical composition and sizes of dust grains in the close vicinity of cool giants. These are essential constraints for building B Susanne Höfner

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The circumstellar environments of EP Aqr and Y CVn probed by the H I emission at 21 cm

Cited by 25 publications

References 28 publications

Circumstellar H I and CO around the carbon stars V1942 Sagittarii and V Coronae Borealis

Circumstellar H I and CO around the carbon stars V1942 Sagittarii and V Coronae Borealis

Mass loss from dusty, low outflow-velocity AGB stars

Mass loss of stars on the asymptotic giant branch

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