258 research outputs found
Sulphur-bearing molecules in AGB stars II: Abundances and distributions of CS and SiS
We surveyed 20 AGB stars of different chemical types using the APEX
telescope, and combined this with an IRAM 30 m and APEX survey of CS and SiS
emission towards over 30 S-type stars. For those stars with detections, we
performed radiative transfer modelling to determine abundances and abundance
distributions. We detect CS towards all the surveyed carbon stars, some S-type
stars, and the highest mass-loss rate oxygen-rich stars (
Msol yr). SiS is detected towards the highest mass-loss rate sources of
all chemical types ( Msol yr). We find CS peak
fractional abundances ranging from ~ to ~
for the carbon stars, from ~ to ~ for the
oxygen-rich stars and from ~ to ~ for the
S-type stars. We find SiS peak fractional abundances ranging from ~ to ~ for the carbon stars, from ~ to ~ for the oxygen-rich stars, and from ~ to ~ for the S-type stars. We derived
SiS/SiS = 11.4 for AI Vol, the only star for which we had a
reliable isotopologue detection. Overall, we find that wind density plays an
important role in determining the chemical composition of AGB CSEs. It is seen
that for oxygen-rich AGB stars both CS and SiS are detected only in the highest
density circumstellar envelopes and their abundances are generally lower than
for carbon-rich AGB stars by around an order of magnitude. For carbon-rich and
S-type stars SiS was also only detected in the highest density circumstellar
envelopes, while CS was detected consistently in all surveyed carbon stars and
sporadically among the S-type stars
(Sub)stellar companions shape the winds of evolved stars
Binary interactions dominate the evolution of massive stars, but their role is less clear for low- and intermediate-mass stars. The evolution of a spherical wind from an asymptotic giant branch (AGB) star into a nonspherical planetary nebula (PN) could be due to binary interactions. We observed a sample of AGB stars with the Atacama Large Millimeter/submillimeter Array (ALMA) and found that their winds exhibit distinct nonspherical geometries with morphological similarities to planetary nebulae (PNe). We infer that the same physics shapes both AGB winds and PNe; additionally, the morphology and AGB mass-loss rate are correlated. These characteristics can be explained by binary interaction. We propose an evolutionary scenario for AGB morphologies that is consistent with observed phenomena in AGB stars and PNe
The VLT/SPHERE view of the ATOMIUM cool evolved star sample. I. Overview:Sample characterization through polarization analysis
Aims. Through the ATOMIUM project, based on an ALMA large program, we aim to
present a consistent view of a sample of 17 nearby cool evolved stars
(Aymptotic Giant Branch and red supergiant stars).
Methods. Here we present VLT/SPHERE-ZIMPOL polarimetric maps obtained in the
visible of 14 out of the 17 ATOMIUM sources. They were obtained
contemporaneously with the ALMA high spatial resolution data. To help interpret
the polarized signal, we produced synthetic maps of light scattering by dust,
through 3D radiative transfer simulations with the RADMC3D code.
Results. The degree of linear polarization (DoLP) observed by ZIMPOL spreads
across several optical filters. We infer that it primarily probes dust located
just outside of the point spread function, and in or near the plane of the sky,
with a total optical depth close to unity in the line of sight, representing
only a fraction of the total circumstellar dust. The maximum DoLP ranges from
0.03-0.38 depending on the source, fractions that can be reproduced by our 3D
pilot models for grains composed of common dust species. The spatial structure
of the DoLP shows a diverse set of shapes. Only for three sources do we note a
correlation between the ALMA CO and SiO lines, which trace the gas density, and
the DoLP, which traces the dust.
Conclusion. The clumpiness of the DoLP and the lack of a consistent
correlation between the gas and the dust location show that, in the inner
circumstellar environment (CSE), dust formation occurs at very specific sites.
This has potential consequences for the derived mass-loss rates and dust-to-gas
ratio in the inner region of the CSE. Except for ~Gru and perhaps GY
Aql, we do not detect interactions between the circumstellar wind and the
hypothesized companions that shape the wind at larger scales. This suggests
that the orbits of any other companions are tilted out of the plane of the sky.Comment: Accepted for publication in Astronomy & Astrophysics. 22 pages, 15
figures, 5 table
The VLT/SPHERE view of the ATOMIUM cool evolved star sample. I. Overview: Sample characterization through polarization analysis
Aims. Through the ATOMIUM project, based on an ALMA large program, we aim to
present a consistent view of a sample of 17 nearby cool evolved stars
(Aymptotic Giant Branch and red supergiant stars).
Methods. Here we present VLT/SPHERE-ZIMPOL polarimetric maps obtained in the
visible of 14 out of the 17 ATOMIUM sources. They were obtained
contemporaneously with the ALMA high spatial resolution data. To help interpret
the polarized signal, we produced synthetic maps of light scattering by dust,
through 3D radiative transfer simulations with the RADMC3D code.
Results. The degree of linear polarization (DoLP) observed by ZIMPOL spreads
across several optical filters. We infer that it primarily probes dust located
just outside of the point spread function, and in or near the plane of the sky,
with a total optical depth close to unity in the line of sight, representing
only a fraction of the total circumstellar dust. The maximum DoLP ranges from
0.03-0.38 depending on the source, fractions that can be reproduced by our 3D
pilot models for grains composed of common dust species. The spatial structure
of the DoLP shows a diverse set of shapes. Only for three sources do we note a
correlation between the ALMA CO and SiO lines, which trace the gas density, and
the DoLP, which traces the dust.
Conclusion. The clumpiness of the DoLP and the lack of a consistent
correlation between the gas and the dust location show that, in the inner
circumstellar environment (CSE), dust formation occurs at very specific sites.
This has potential consequences for the derived mass-loss rates and dust-to-gas
ratio in the inner region of the CSE. Except for ~Gru and perhaps GY
Aql, we do not detect interactions between the circumstellar wind and the
hypothesized companions that shape the wind at larger scales. This suggests
that the orbits of any other companions are tilted out of the plane of the sky.Comment: Accepted for publication in Astronomy & Astrophysics. 22 pages, 15
figures, 5 table
(Sub)stellar companions shape the winds of evolved stars
Binary interactions dominate the evolution of massive stars, but their role is less clear for low- and intermediate-mass stars. The evolution of a spherical wind from an asymptotic giant branch (AGB) star into a nonspherical planetary nebula (PN) could be due to binary interactions. We observed a sample of AGB stars with the Atacama Large Millimeter/submillimeter Array (ALMA) and found that their winds exhibit distinct nonspherical geometries with morphological similarities to planetary nebulae (PNe). We infer that the same physics shapes both AGB winds and PNe; additionally, the morphology and AGB mass-loss rate are correlated. These characteristics can be explained by binary interaction. We propose an evolutionary scenario for AGB morphologies that is consistent with observed phenomena in AGB stars and PNe
Constraints on Metal Oxide and Metal Hydroxide Abundances in the Winds of AGB Stars: Potential Detection of FeO in R Dor
Using the Atacama Large Millimeter/submillimeter Array (ALMA), we observed the stellar wind of two oxygen-rich asymptotic giant branch stars, IK Tau and R Dor, between 335 and 362 GHz. One aim was to detect metal oxides and metal hydroxides (AlO, AlOH, FeO, MgO, and MgOH), some of which are thought to be direct precursors of dust nucleation and growth. We report on the potential first detection of FeO (v = 0, Ω = 4, J = 11–10) in R Dor (mass-loss rate M• ~ 1 × 10−7 M ⊙ yr‾¹). The presence of FeO in IK Tau (M• ~ 5 × 10‾⁶ M ⊙ yr‾¹) cannot be confirmed, due to a blend with ²⁹SiS, a molecule that is absent in R Dor. The detection of AlO in R Dor and of AlOH in IK Tau was reported earlier by Decin et al. All other metal oxides and hydroxides, as well as MgS, remain undetected. We derive a column density N(FeO) of 1.1 ± 0.9 × 10¹⁵ cm‾² in R Dor, or a fractional abundance [FeO/H] ~ 1.5 × 10‾⁸ accounting for non-local thermodynamic equilibrium effects. The derived fractional abundance [FeO/H] is a factor ~20 larger than conventional gas-phase chemical-kinetic predictions. This discrepancy may be partly accounted for by the role of vibrationally excited OH in oxidizing Fe, or it may be evidence for other currently unrecognized chemical pathways producing FeO. Assuming a constant fractional abundance w.r.t. H₂, the upper limits for the other metals are [MgO/H₂] < 5.5 × 10‾¹⁰ (R Dor) and <7 × 10‾¹¹ (IK Tau), [MgOH/H₂] < 9 × 10‾⁹ (R Dor) and <1 × 10‾⁹ (IK Tau), [CaO/H₂] < 2.5 × 10‾⁹ (R Dor) and <1 × 10‾¹⁰ (IK Tau), [CaOH/H₂] < 6.5 × 10‾⁹ (R Dor) and <9 × 10‾¹⁰ (IK Tau), and [MgS/H₂] < 4.5 × 10‾¹⁰ (R Dor) and <6 × 10‾¹¹ (IK Tau). The retrieved upper-limit abundances for these latter molecules are in accord with the chemical model predictions
Dust in Supernovae and Supernova Remnants I : Formation Scenarios
Supernovae are considered as prime sources of dust in space. Observations of local supernovae over the past couple of decades have detected the presence of dust in supernova ejecta. The reddening of the high redshift quasars also indicate the presence of large masses of dust in early galaxies. Considering the top heavy IMF in the early galaxies, supernovae are assumed to be the major contributor to these large amounts of dust. However, the composition and morphology of dust grains formed in a supernova ejecta is yet to be understood with clarity. Moreover, the dust masses inferred from observations in mid-infrared and submillimeter wavelength regimes differ by two orders of magnitude or more. Therefore, the mechanism responsible for the synthesis of molecules and dust in such environments plays a crucial role in studying the evolution of cosmic dust in galaxies. This review summarises our current knowledge of dust formation in supernova ejecta and tries to quantify the role of supernovae as dust producers in a galaxy.Peer reviewe
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