Mapping the12CO J = 1−0 andJ = 2−1 emission in AGB and early post-AGB circumstellar envelopes

Castro-Carrizo, A.; Quintana-Lacaci, G.; Neri, R.; Bujarrabal, V.; Schöier, F. L.; Winters, J. M.; Olofsson, H.; Lindqvist, Michael; Lucas, R.; Grewing, M.

doi:10.1051/0004-6361/201014755

Cited by 92 publications

(111 citation statements)

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“…The CO(2-1) polarized emission is detected about 3 (∼800 AU) from the star and that of SiO(5-4) originates within ∼1 (∼250 AU), which could be an indication that, as in the case of the supergiant VX Sgr (Vlemmings et al 2011), the magnetic field has a large-scale component that is preserved throughout the envelope. As the field is then mainly oriented either east-west or north-south, it might be directly related to the slight east-west extent seen in the circumstellar CO envelope (Castro-Carrizo et al 2010, and Fig. 1, right) and the east-west asymmetry in the dust distribution (Weiner et al 2006).…”

Section: The Magnetic Field Of Ik Taumentioning

confidence: 99%

“…The star has a rich circumstellar chemistry, as indicated by the detection of a large number (>20) of different molecular species (see e.g., Kim et al 2010;Decin et al 2010, for the latest results). The circumstellar gas distribution has been mapped in CO(J = 1 → 0), CO(J = 2 → 1) (Castro-Carrizo et al 2010), and CO(J = 3 → 2) (Kim et al 2010) emission. Castro-Carrizo et al (2010 found a western elongation in its innermost region (of ∼1000 AU), and on larger scales a flattened circumstellar envelope that is elongated in the east-west plane over ∼10 000 AU.…”

Section: Introductionmentioning

confidence: 99%

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Polarization of thermal molecular lines in the envelope of IK Tauri

Vlemmings

Ramstedt

Rao³

et al. 2012

A&A

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Molecular line polarization is a unique source of information about the magnetic fields and anisotropies in the circumstellar envelopes of evolved stars. Here we present the first detection of thermal CO(J = 2 → 1) and SiO(J = 5 → 4, ν = 0) polarization, in the envelope of the asymptotic giant branch star IK Tau. The observed polarization direction does not match predictions for circumstellar envelope polarization induced only by an anisotropic radiation field. Assuming that the polarization is purely due to the Goldreich-Kylafis effect, the linear polarization direction is defined by the magnetic field as even the small Zeeman splitting of CO and SiO dominates the molecular collisional and spontaneous emission rates. The polarization was mapped using the Submillimeter Array (SMA) and is predominantly north-south. There is close agreement between the CO and SiO observations, even though the CO polarization arises in the circumstellar envelope at ∼800 AU and the SiO polarization at 250 AU. If the polarization indeed traces the magnetic field, we can thus conclude that it maintains a large-scale structure throughout the circumstellar envelope. We propose that the magnetic field, oriented either east-west or north-south is responsible for the east-west elongation of the CO distribution and asymmetries in the dust envelope. In the future, the Atacama Large Millimeter/submillimeter Array will be able to map the magnetic field using CO polarization for a large number of evolved stars.

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Section: The Magnetic Field Of Ik Taumentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Polarization of thermal molecular lines in the envelope of IK Tauri

Vlemmings

Ramstedt

Rao³

et al. 2012

A&A

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“…Combined with the HIFI observations essentially the full radial range of the CSE can be probed and, if present, modulations in the mass-loss rate and chemical gradients may be identified. The references to this complementary set of molecular line data are given in Table A.1, except for the PdBI CO data that are taken from Castro-Carrizo et al (2010) and the PdBI SiO data from Lucas et al (1992). The calibration of the intensity scale for these data have an uncertainty of ≈±20%…”

Section: Complementary Observationsmentioning

confidence: 99%

“…This procedure is described in more detail in Schöier et al (in prep. ), where a large sample of AGB stars has been mapped in CO line emission at the PdBI as part of the COSAS large survey programme (Castro-Carrizo et al 2010). …”

Section: Co Line Modellingmentioning

confidence: 99%

A chemical inventory of the S-type AGB starχ Cygni based onHerschel/HIFI observations of circumstellar line emission

Schöier

Maercker

Justtanont

et al. 2011

A&A

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Context. S-type AGB stars (C/O ≈ 1) are thought to be transition objects from M-type (O-rich) AGB stars to carbon stars and as such are interesting objects in themselves. Of particular interest is to determine accurate circumstellar properties and molecular abundances, due to their predicted sensitivity to the photospheric C/O-ratio. Aims. Presented here are new sensitive sub-millimetre line observations of molecules towards the S-type AGB star χ Cyg, using the HIFI instrument on-board the Herschel Space Observatory. The observed lines predominantly probe warm gas relatively close to the central star. Methods. Detailed, non-LTE, radiative transfer modelling has been used in order to interpret the circumstellar molecular line observations performed using HIFI, assuming a spherically symmetric, smooth, accelerating wind. Results. Lines from common molecules such as H 2 O, CO and SiO, which are expected to be abundant in an S-type AGB star, are clearly detected (as well as some of their isotopologues) in the HIFI spectra. In addition, we detect lines from carbon-bearing molecules such as HCN and CN. The CO line modelling indicates that the mass-loss rate has not undergone any significant modulations during the past ≈1000 yr. The derived o-H 2 O fractional abundance is ≈7 × 10 −6 , i.e., lower than those obtained for a small sample of M-type AGB stars but higher than what has been derived for a few carbon stars. We further obtain a p-H 2 O fractional abundance of ≈5 × 10 −6 giving an o/p-ratio of ≈1.4. Molecular line cooling is dominated by H 2 O only in a region close to the star ( 6 × 10 14 cm). The SiO abundance is estimated to be ≈1 × 10 −5 . The 12 CO/ 13 CO ratio is 43 ± 6. The high-excitation rotational lines clearly probe the acceleration region of the stellar wind ( 2 × 10 15 cm) and put constraints on dynamical wind models. We are unable to fit consistently the combined ground-based and HIFI data for HCN and CN. Conclusions. The derived H 2 O abundance is reasonably consistent with recent chemical model predictions and so is the SiO abundance. The o/p-ratio of ≈1.4 supports a chemical formation under non-LTE conditions for the H 2 O molecules, and the presence of carbon-bearing molecules at relatively large abundances is also indicative of the importance of non-LTE chemical processes in regulating the circumstellar chemistry. The velocity field derived from the molecular line modelling is consistent with that obtained from solving for the wind dynamics through the coupled momentum equations of the dust and gas particles.

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“…A review of techniques is given by Marengo (2009). Recent advances include millimeter interferometry of the molecular gas (e.g., Castro-Carrizo et al 2010) and imaging of the thermal dust A&A 551, A110 (2013) emission, in the mid-infrared with ground-based observations (e.g., Lagadec et al 2011) and in the far infrared with Herschel (Decin et al 2011). In this paper, we report progress using a different technique: observing the envelopes in dust-scattered Galactic light.…”

Section: Introductionmentioning

confidence: 99%

Deep optical imaging of asymptotic giant branch circumstellar envelopes

Mauron

Huggins

Cheung

2013

A&A

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We report results of a program to image the extended circumstellar envelopes of asymptotic giant branch (AGB) stars in dust-scattered Galactic light. The goal is to characterize the shapes of the envelopes to probe the mass-loss geometry and the presence of hidden binary companions. The observations consist of deep optical imaging of 22 AGB stars with high mass loss rates: 16 with the ESO 3.6 m NTT telescope, and the remainder with other telescopes. The circumstellar envelopes are detected in 15 objects, with mass loss rates > ∼ 2 × 10 −6 M yr −1 . The surface brightness of the envelopes shows a strong decrease with Galactic radius, which indicates a steep radial gradient in the interstellar radiation field. The envelopes range from circular to elliptical in shape, and we characterize them by the ellipticity (E = major/minor axis) of iso-intensity contours. We find that ∼50% of the envelopes are close to circular with E < ∼ 1.1, and others are more elliptical with ∼20% with E > ∼ 1.2. We interpret the shapes in terms of populations of single stars and binaries whose envelopes are flattened by a companion. The distribution of E is qualitatively consistent with expectations based on population synthesis models of binary AGB stars. We also find that ∼50% of the sample exhibit small-scale, elongated features in the central regions. We interpret these as the escape of light from the central star through polar holes, which are also likely produced by companions. Our observations of envelope flattening and polar holes point to a hidden population of binary companions within the circumstellar envelopes of AGB stars. These companions are expected to play an important role in the transition to post-AGB stars and the formation of planetary nebulae.

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Mapping the¹²CO J = 1−0 andJ = 2−1 emission in AGB and early post-AGB circumstellar envelopes

Cited by 92 publications

References 64 publications

Polarization of thermal molecular lines in the envelope of IK Tauri

Polarization of thermal molecular lines in the envelope of IK Tauri

A chemical inventory of the S-type AGB starχ Cygni based onHerschel/HIFI observations of circumstellar line emission

Deep optical imaging of asymptotic giant branch circumstellar envelopes

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