Gas infall and possible circumstellar rotation in R Leonis

Fonfría, J. P.; Santander-García, M.; Cernicharo, J.; Velilla-Prieto, L.; Agúndez, M.; Marcelino, N.; Quintana-Lacaci, G.

doi:10.1051/0004-6361/201834840

Cited by 10 publications

(14 citation statements)

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“…In recent years there has been a strong focus on investigating the isotropy of the mass-loss process in low-to intermediate mass evolved stars, which was partly expedited by the superior imaging capabilities of ALMA. Several AGB sources with previously known complex circumstellar dynamics and/or binary companions have been mapped in detail (e.g., Decin et al 2015;Maercker et al 2016;Doan et al 2017;Kim et al 2017;Homan et al 2018;Fonfría et al 2019). With the DEATHSTAR project, the aim is to get an overview of how widespread and significant the detected asymmetrical features are, from the perspective of measuring the amount of circumstellar wind material.…”

Section: Discussion and Summarymentioning

confidence: 99%

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DEATHSTAR: Nearby AGB stars with the Atacama Compact Array

Ramstedt

Vlemmings

Doan

et al. 2020

A&A

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Context. This is the first publication from the DEATHSTAR project. The overall goal of the project is to reduce the uncertainties of the observational estimates of mass-loss rates from evolved stars on the Asymptotic Giant Branch (AGB). Aim. The aim in this first publication is to constrain the sizes of the 12CO emitting region from the circumstellar envelopes around 42 mostly southern AGB stars, of which 21 are M-type and 21 are C-type, using the Atacama Compact Array (ACA) at the Atacama Large Millimeter/submillimeter Array. The symmetry of the outflows is also investigated. Methods. Line emission from 12CO J = 2→1 and 3→2 from all of the sources were mapped using the ACA. In this initial analysis, the emission distribution was fit to a Gaussian distribution in the uv-plane. A detailed radiative transfer analysis will be presented in a future publication. The major and minor axis of the best-fit Gaussian at the line center velocity of the 12CO J = 2→1 emission gives a first indication of the size of the emitting region. Furthermore, the fitting results, such as the Gaussian major and minor axis, center position, and the goodness of fit across both lines, constrain the symmetry of the emission distribution. For a subsample of sources, the measured emission distribution is compared to predictions from previous best-fit radiative transfer modeling results. Results. We find that the CO envelope sizes are, in general, larger for C-type than for M-type AGB stars, which is as expected if the CO/H2 ratio is larger in C-type stars. Furthermore, the measurements show a relation between the measured (Gaussian) 12CO J = 2→1 size and circumstellar density that, while in broad agreement with photodissociation calculations, reveals large scatter and some systematic differences between the different stellar types. For lower mass-loss-rate irregular and semi-regular variables of both M- and C-type AGB stars, the 12CO J = 2→1 size appears to be independent of the ratio of the mass-loss rate to outflow velocity, which is a measure of circumstellar density. For the higher mass-loss-rate Mira stars, the 12CO J = 2→1 size clearly increases with circumstellar density, with larger sizes for the higher CO-abundance C-type stars. The M-type stars appear to be consistently smaller than predicted from photodissociation theory. The majority of the sources have CO envelope sizes that are consistent with a spherically symmetric, smooth outflow, at least on larger scales. For about a third of the sources, indications of strong asymmetries are detected. This is consistent with what was found in previous interferometric investigations of northern sources. Smaller scale asymmetries are found in a larger fraction of sources. Conclusions. These results for CO envelope radii and shapes can be used to constrain detailed radiative transfer modeling of the same stars so as to determine mass-loss rates that are independent of photodissociation models. For a large fraction of the sources, observations at higher spatial resolution will be necessary to deduce the nature and origin of the complex circumstellar dynamics revealed by our ACA observations.

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Section: Discussion and Summarymentioning

confidence: 99%

“…Instead, these line profiles are anomalous. Some are previously known to be anomalous, for example, L 2 Pup (e.g., Kervella et al 2016) and R Leo (Fonfría et al 2019), while others have not been studied with a focus on the detailed structure of the CSE, for example, R Hya and SS Vir.…”

Section: Indications Of Circumstellar Anisotropic Structurementioning

confidence: 99%

DEATHSTAR: Nearby AGB stars with the Atacama Compact Array

Ramstedt

Vlemmings

Doan

et al. 2020

A&A

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“…morpho-kinematics than had been originally anticipated. It has been the case with Mira for now many years, recent examples are QX Pup (Sánchez Contreras et al 2018;Olofsson et al 2019), R Aqr (Ramstedt et al 2018) and R Leo (Fonfria et al 2019), raising new questions that are still awaiting an answer. In the present case of R Dor, several such questions are present: the motor of the inner rotation providing the required angular momentum is unknown; Vlemmings et al (2018) and Homan et al (2018) argue for the presence of a close by companion but we have no evidence for its existence and a magnetic field origin is an-other possibility (Matt et al 2000); a detailed study of the strong absorption observed in the blue-shifted hemisphere, in particular for the SiO emission line, possibly including a contribution from in-falling gas, needs still to be done; the dynamics underlying the emission of the radial outflows revealed in the present work is not understood; the nature of the high Doppler velocity components, apparently unrelated to other observations, is unknown.…”

Section: Discussionmentioning

confidence: 99%

The nascent wind of AGB star R doradus: evidence for a recent episode of enhanced mass loss

Nhung

Hoai

Tuan-Anh

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We analyse ALMA observations of the SO(J K = 6 5 − 5 4 ) emission of the circumstellar envelope of oxygen-rich AGB star R Dor, probing distances between 20 and 100 au from the star where the nascent wind is building up. We give evidence for the slow wind to host, in addition to a previously observed rotating disc, a radial outflow covering very large solid angles and displaying strong inhomogeneity both in direction and radially: the former takes the form of multiple cores and the latter displays a radial dependence suggesting an episode of enhanced mass loss having occurred a century or so ago.

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“…Second, the low gravity of AGB stars causes the extended atmosphere to be affected by convective processes that lead to asymmetric structures, hot spots, and highdensity clumps. This complex morphology is predicted by 3D hydrodynamical simulations (Freytag et al 2017) and is starting to be characterized in detail with high angular resolution observations at infrared and (sub-)millimeter wavelengths (e.g., Khouri et al 2016;Vlemmings et al 2017;Fonfría et al 2019).…”

Section: Radial Profiles Of Temperature and Pressurementioning

confidence: 96%

Chemical equilibrium in AGB atmospheres: successes, failures, and prospects for small molecules, clusters, and condensates

Agúndez

Martínez

Andrés

et al. 2020

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Chemical equilibrium has proven extremely useful for predicting the chemical composition of AGB atmospheres. Here we use a recently developed code and an updated thermochemical database that includes gaseous and condensed species involving 34 elements to compute the chemical equilibrium composition of AGB atmospheres of M-, S-, and C-type stars. We include for the first time Ti x C y clusters, with x = 1-4 and y = 1-4, and selected larger clusters ranging up to Ti 13 C 22 , for which thermochemical data are obtained from quantum-chemical calculations. Our main aims are to systematically survey the main reservoirs of each element in AGB atmospheres, review the successes and failures of chemical equilibrium by comparing it with the latest observational data, identify potentially detectable molecules that have not yet been observed, and diagnose the most likely gas-phase precursors of dust and determine which clusters might act as building blocks of dust grains. We find that in general, chemical equilibrium reproduces the observed abundances of parent molecules in circumstellar envelopes of AGB stars well. There are, however, severe discrepancies of several orders of magnitude for some parent molecules that are observed to be anomalously overabundant with respect to the predictions of chemical equilibrium. These are HCN, CS, NH 3 , and SO 2 in M-type stars, H 2 O and NH 3 in S-type stars, and the hydrides H 2 O, NH 3 , SiH 4 , and PH 3 in C-type stars. Several molecules have not yet been observed in AGB atmospheres but are predicted with nonnegligible abundances and are good candidates for detection with observatories such as ALMA. The most interesting ones are SiC 5 , SiNH, SiCl, PS, HBO, and the metal-containing molecules MgS, CaS, CaOH, CaCl, CaF, ScO, ZrO, VO, FeS, CoH, and NiS. In agreement with previous studies, the first condensates predicted to appear in C-rich atmospheres are found to be carbon, TiC, and SiC, while Al 2 O 3 is the first major condensate expected in O-rich outflows. According to our chemical equilibrium calculations, the gas-phase precursors of carbon dust are probably acetylene, atomic carbon, and/or C 3 , while for silicon carbide dust, the most likely precursors are the molecules SiC 2 and Si 2 C. In the case of titanium carbide dust, atomic Ti is the major reservoir of this element in the inner regions of AGB atmospheres, and therefore it is probably the main supplier of titanium during the formation of TiC dust. However, chemical equilibrium predicts that large titanium-carbon clusters such as Ti 8 C 12 and Ti 13 C 22 become the major reservoirs of titanium at the expense of atomic Ti in the region where condensation of TiC is expected to occur. This suggests that the assembly of large Ti x C y clusters might be related to the formation of the first condensation nuclei of TiC. In the case of Al 2 O 3 dust, chemical equilibrium indicates that atomic Al and the carriers of Al-O bonds AlOH, AlO, and Al 2 O are the most likely gas-phase precursors.

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Gas infall and possible circumstellar rotation in R Leonis

Cited by 10 publications

References 38 publications

DEATHSTAR: Nearby AGB stars with the Atacama Compact Array

DEATHSTAR: Nearby AGB stars with the Atacama Compact Array

The nascent wind of AGB star R doradus: evidence for a recent episode of enhanced mass loss

Chemical equilibrium in AGB atmospheres: successes, failures, and prospects for small molecules, clusters, and condensates

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