ATOMIUM: A high-resolution view on the highly asymmetric wind of the AGB star<i>π</i><sup>1</sup>Gruis

Homan, W.; Montargès, M.; Pimpanuwat, Bannawit; Richards, A. M. S.; Wallström, Sofia; Kervella, P.; Decin, L.; Zijlstra, A. A.; Danilovich, T.; Koter, A. de; Menten, K. M.; Sahai, Raghvendra; Plane, J. M. C.; Lee, Kelvin; Waters, Rens; Baudry, A.; Wong, K. T.; Millar, T. J.; Sande, M. Van de; Lagadec, E.; Gobrecht, David; Yates, J.; Price, Daniel J.; Cannon, Emily; Bolte, John; Ceuster, Frederik De; Herpin, Fabrice; Nuth, J. A.; Sindel, Jan Philip; Kee, Dylan; Grey, Malcolm D.; Etoka, S.; Jeste, Manali; Gottlieb, C. A.; Gottlieb, Elaine; McDonald, Iain; Mellah, I. El; Müller, H. S. P.

doi:10.1051/0004-6361/202039185

Cited by 27 publications

(48 citation statements)

References 88 publications

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“…Such a structure had already been found in the S-type star π 1 Gru (Sahai 1992), which was later confirmed by higher spatial resolution observations using ALMA (Doan et al 2017). This object has a G0V companion (Feast 1953) and possibly a second, much closer companion (Homan et al 2020). In Hoai et al (2014), we reported for RS Cnc the possible presence of a companion seen in the 12 CO(1-0) channel maps at velocities around 6.6 km s −1 and located about 1 west-northwest of the continuum source.…”

Section: Cosupporting

confidence: 65%

Molecules, shocks, and disk in the axi-symmetric wind of the MS-type AGB star RS Cancri

Winters

Hoai

Wong

et al. 2022

A&A

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Context. The latest evolutionary phases of low- and intermediate-mass stars are characterized by complex physical processes like turbulence, convection, stellar pulsations, magnetic fields, condensation of solid particles, and the formation of massive outflows that inject freshly produced heavy elements and dust particles into the interstellar medium. Aims. By investigating individual objects in detail, we wish to analyze and disentangle the effects of the interrelated physical processes on the structure of the wind-forming regions around them. Methods. We use the Northern Extended Millimeter Array to obtain spatially and spectrally resolved observations of the semi-regular asymptotic giant branch (AGB) star RS Cancri and apply detailed 3D reconstruction modeling and local thermodynamic equilibrium radiative transfer calculations in order to shed light on the morpho-kinematic structure of its inner, wind-forming environment. Results. We detect 32 lines of 13 molecules and isotopologs (CO, SiO, SO, SO2, H2O, HCN, PN), including several transitions from vibrationally excited states. HCN, H13CN, and millimeter vibrationally excited H2O, SO, 34SO, SO2, and PN are detected for the first time in RS Cnc. Evidence for rotation is seen in HCN, SO, SO2, and SiO(v = 1). From CO and SiO channel maps, we find an inner, equatorial density enhancement, and a bipolar outflow structure with a mass-loss rate of 1 × 10−7 M⊙yr−1 for the equatorial region and of 2 × 10−7 M⊙yr−1 for the polar outflows. The 12CO/13CO ratio is measured to be ~20 on average, 24 ± 2 in the polar outflows and 19 ± 3 in the equatorial region. We do not find direct evidence of a companion that might explain this kind of kinematic structure, and explore the possibility that a magnetic field might be the cause of it. The innermost molecular gas is influenced by stellar pulsation and possibly by convective cells that leave their imprint on broad wings of certain molecular lines, such as SiO and SO. Conclusions. RS Cnc is one of the few nearby, low-mass-loss-rate, oxygen-rich AGB stars with a wind displaying both an equatorial disk and bipolar outflows. Its orientation with respect to the line of sight is particularly favorable for a reliable study of its morpho-kinematics. Nevertheless, the mechanism causing early spherical symmetry breaking remains uncertain, calling for additional high spatial- and spectral-resolution observations of the emission of different molecules in different transitions, along with more thorough investigation of the coupling among the different physical processes at play.

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Section: Cosupporting

confidence: 65%

Molecules, shocks, and disk in the axi-symmetric wind of the MS-type AGB star RS Cancri

Winters

Hoai

Wong

et al. 2022

A&A

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“…AlF, AlCl, NaCl, KCl) were detected towards π 1 Gru, the only other S-type star in the ATOMIUM survey. This may be partly because the unusual torus + bipolar structure of the CSE of π 1 Gru (Doan et al 2017;Homan et al 2020) could make it harder to detect less abundant molecules or might even interfere with molecule formation. We are not aware of any other detections of halide molecules towards S-type stars with ALMA.…”

Section: S-type Agb Starsmentioning

confidence: 99%

ATOMIUM: halide molecules around the S-type AGB star W Aquilae

Danilovich

Sande

Plane

et al. 2021

A&A

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Context. S-type asymptotic giant branch (AGB) stars are thought to be intermediates in the evolution of oxygen- to carbon-rich AGB stars. The chemical compositions of their circumstellar envelopes are also intermediate but have not been studied in as much detail as their carbon- and oxygen-rich counterparts. W Aql is a nearby S-type star, with well-known circumstellar parameters, making it an ideal object for in-depth study of less common molecules. Aims. We aim to determine the abundances of AlCl and AlF from rotational lines, which have been observed for the first time towards an S-type AGB star. In combination with models based on PACS observations, we aim to update our chemical kinetics network based on these results. Methods. We analyse ALMA observations towards W Aql of AlCl in the ground and first two vibrationally excited states and AlF in the ground vibrational state. Using radiative transfer models, we determine the abundances and spatial abundance distributions of Al35Cl, Al37Cl, and AlF. We also model HCl and HF emission and compare these models to PACS spectra to constrain the abundances of these species. Results. AlCl is found in clumps very close to the star, with emission confined within 0′′.1 of the star. AlF emission is more extended, with faint emission extending 0′′.2 to 0′′.6 from the continuum peak. We find peak abundances, relative to H2, of 1.7 × 10−7 for Al35Cl, 7 × 10−8 for Al37Cl, and 1 × 10−7 for AlF. From the PACS spectra, we find abundances of 9.7 × 10−8 and ≤10−8, relative to H2, for HCl and HF, respectively. Conclusions. The AlF abundance exceeds the solar F abundance, indicating that fluorine synthesised in the AGB star has already been dredged up to the surface of the star and ejected into the circumstellar envelope. From our analysis of chemical reactions in the wind, we conclude that AlF may participate in the dust formation process, but we cannot fully explain the rapid depletion of AlCl seen inthe wind.

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“…These values are also typical of the line data cubes in each configuration. The procedure for constructing the final cubes of CO and SiO is identical to what is described by Homan et al (2020b), with a few minor variations, notably in weighting (see next paragraph) during imaging to produce the desired resolutions as given in Table 2.…”

Section: Data Acquisition and Reductionmentioning

confidence: 99%

“…Considering that the void in R Hya consistently appears in approximately the same channels and at the same place in different molecules observed in the atomium survey, the presence of a photodissociating companion (i.e., either a cool WD or hot main-sequence star) cannot be immediately excluded. Depending on its properties, such a companion could easily remain hidden in spectra or SEDs, as was the case for the WD companion of EP Aqr (Homan et al 2020a), or the companion of π 1 Gruis (Homan et al 2020b). It must be noted, however, that it is unlikely that R Hya possesses two companions of significant mass within a radius of 50 au, since this would make the system highly unstable, implying that it would probably not have survived up to the AGB phase.…”

Section: Compact Emission Voidmentioning

confidence: 99%

ATOMIUM: The astounding complexity of the near circumstellar environment of the M-type AGB star R Hydrae

Homan

Pimpanuwat

Herpin

et al. 2021

A&A

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Evolved low- to intermediate-mass stars are known to shed their gaseous envelope into a large, dusty, molecule-rich circumstellar nebula which typically develops a high degree of structural complexity. Most of the large-scale, spatially correlated structures in the nebula are thought to originate from the interaction of the stellar wind with a companion. As part of the ATOMIUM large programme, we observed the M-type asymptotic giant branch (AGB) star R Hydrae with the Atacama Large Millimeter/submillimeter Array. The morphology of the inner wind of R Hya, which has a known companion at ∼3500 au, was determined from maps of CO and SiO obtained at high angular resolution. A map of the CO emission reveals a multi-layered structure consisting of a large elliptical feature at an angular scale of ∼10″ that is oriented along the north–south axis. The wind morphology within the elliptical feature is dominated by two hollow bubbles. The bubbles are on opposite sides of the AGB star and lie along an axis with a position angle of ∼115°. Both bubbles are offset from the central star, and their appearance in the SiO channel maps indicates that they might be shock waves travelling through the AGB wind. An estimate of the dynamical age of the bubbles yields an age of the order of 100 yr, which is in agreement with the previously proposed elapsed time since the star last underwent a thermal pulse. When the CO and SiO emission is examined on subarcsecond angular scales, there is evidence for an inclined, differentially rotating equatorial density enhancement, strongly suggesting the presence of a second nearby companion. The position angle of the major axis of this disc is ∼70° in the plane of the sky. We tentatively estimate that a lower limit on the mass of the nearby companion is ∼0.65 M⊙ on the basis of the highest measured speeds in the disc and the location of its inner rim at ∼6 au from the AGB star.

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ATOMIUM: A high-resolution view on the highly asymmetric wind of the AGB starπ¹Gruis

Cited by 27 publications

References 88 publications

Molecules, shocks, and disk in the axi-symmetric wind of the MS-type AGB star RS Cancri

Molecules, shocks, and disk in the axi-symmetric wind of the MS-type AGB star RS Cancri

ATOMIUM: halide molecules around the S-type AGB star W Aquilae

ATOMIUM: The astounding complexity of the near circumstellar environment of the M-type AGB star R Hydrae

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ATOMIUM: A high-resolution view on the highly asymmetric wind of the AGB starπ1Gruis

Cited by 27 publications

References 88 publications

Molecules, shocks, and disk in the axi-symmetric wind of the MS-type AGB star RS Cancri

Molecules, shocks, and disk in the axi-symmetric wind of the MS-type AGB star RS Cancri

ATOMIUM: halide molecules around the S-type AGB star W Aquilae

ATOMIUM: The astounding complexity of the near circumstellar environment of the M-type AGB star R Hydrae

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ATOMIUM: A high-resolution view on the highly asymmetric wind of the AGB starπ¹Gruis