The millimeter IRAM-30 m line survey toward IK Tauri

Velilla-Prieto, L.; Contreras, C. Sánchez; Cernicharo, J.; Agúndez, M.; Quintana-Lacaci, G.; Bujarrabal, V.; Alcolea, J.; Balança, Christian; Herpin, Fabrice; Menten, K. M.; Wyrowski, F.

doi:10.1051/0004-6361/201628776

Cited by 73 publications

(67 citation statements)

References 86 publications

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“…The SO (1 × 10 −6 ), SiO (5 × 10 −6 ), and CS (1 × 10 −6 ; after correcting the 13 CS abundance by the estimated 12 C/ 13 C ≈ 10) abundances all lie in the range reported for AGB CSEs (Danilovich et al 2016;Schöier et al 2013;Velilla Prieto et al 2017), while the H 2 CO abundance (2 × 10 −6 ; assuming an orthoto-para ratio of 3) is about an order of magnitude higher than in IK Tau (Velilla Prieto et al 2017). CH 3 OH has an estimated abundance of 3 × 10 −6 (assuming an E-to-A ratio of 1), almost two orders of magnitude higher than towards the supergiant IRC+10420 (Quintana-Lacaci et al 2016).…”

Section: Chemistrymentioning

confidence: 62%

First detection of methanol towards a post-AGB object, HD 101584

Olofsson

Vlemmings

Bergman

et al. 2017

A&A

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The circumstellar environments of objects on the asymptotic giant branch and beyond are rich in molecular species. Nevertheless, methanol has never been detected in such an object, and is therefore often taken as a clear signpost for a young stellar object. However, we report the first detection of CH 3 OH in a post-AGB object, HD 101584, using ALMA. Its emission, together with emissions from CO, SiO, SO, CS, and H 2 CO, comes from two extreme velocity spots on either side of the object where a high-velocity outflow appears to interact with the surrounding medium. We have derived molecular abundances, and propose that the detected molecular species are the effect of a post-shock chemistry where circumstellar grains play a role. We further provide evidence that HD 101584 was a low-mass, M-type AGB star.

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Section: Chemistrymentioning

confidence: 62%

First detection of methanol towards a post-AGB object, HD 101584

Olofsson

Vlemmings

Bergman

et al. 2017

A&A

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“…H 2 CO has been detected in IK Tau with an abundance between 10 −7 − 10 −8 (Velilla Prieto et al 2017). Our models witḣ M = 10 −6 M yr −1 give a peak abundance similar to the observed range for highly porous one-component outflows.…”

Section: Appendix E: Additional Moleculesmentioning

confidence: 99%

Determining the effects of clumping and porosity on the chemistry in a non-uniform AGB outflow

Sande

Sundqvist

Millar

et al. 2018

A&A

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Publisher rights © 2018 ESO. This work is made available online in accordance with the publisher's policies. Please refer to any applicable terms of use of the publisher. General rightsCopyright for the publications made accessible via the Queen's University Belfast Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. ABSTRACTContext. In the inner regions of asymptotic giant branch (AGB) outflows, several molecules have been detected with abundances much higher than those predicted from thermodynamic equilibrium chemical models. The presence of the majority of these species can be explained by shock-induced non-equilibrium chemical models, where shocks caused by the pulsating star take the chemistry out of equilibrium in the inner region. Moreover, a non-uniform density structure has been detected in several AGB outflows. Both largescale structures, such as spirals and disks, and small-scale density inhomogeneities or clumps have been observed. These structures may also have a considerable impact on the circumstellar chemistry. A detailed parameter study on the quantitative effects of a non-homogeneous outflow has so far not been performed. Aims. We examine the effects of a non-uniform density distribution within an AGB outflow on its chemistry by considering a stochastic, clumpy density structure. Methods. We implement a porosity formalism for treating the increased leakage of light associated with radiation transport through a clumpy, porous medium. We then use this method to examine the effects from the altered UV radiation field penetration on the chemistry, accounting also for the increased reaction rates of two-body processes in the overdense clumps. The specific clumpiness is determined by three parameters: the characteristic length scale of the clumps at the stellar surface, the clump volume filling factor, and the inter-clump density contrast. In this paper, the clumps are assumed to have a spatially constant volume filling factor, which implies that they expand as they move outward in the wind.Results. We present a parameter study of the effect of clumping and porosity on the chemistry throughout the outflow. Both the higher density within the clumps and the increased UV radiation field penetration have an important impact on the chemistry, as they both alter the chemical pathways throughout the outflow. The increased amount of UV radiation in the inner region leads to photodissociation of parent species, releasing the otherwise deficient elements. We find an increased abundance in the inner region of all species not expected to be present assuming thermodynamic equilibrium chemistry, such as HCN in O-rich outflows, H 2 O in C-rich outflows, and NH 3 in both. Conclusions. A non-uniform density distribution directly influences the chemistry throughout the AGB outflow, both through the density structure itself and through its effect on the U...

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“…The angular diameter is estimated around 20 mas (Decin et al 2010a). Currently, a dozen different molecules and some of their isotopologues have been discovered in IK Tau, including CO, HCN, SiO, SiS, SO, SO 2 , NaCl, NS, NO, HCO + , H 2 CO, PO, PN, and H 2 S (Milam et al 2007;Kim et al 2010;Decin et al 2010a,b;De Beck et al 2013Velilla Prieto et al 2017). Some molecules including SiO and SiS are depleted in the circumstellar envelope, possibly owing to condensation onto dust grains.…”

Section: Target Selectionmentioning

confidence: 99%

Study of the aluminium content in AGB winds using ALMA

Decin

Richards

Waters

et al. 2017

A&A

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Context. The condensation of inorganic dust grains in the winds of evolved stars is poorly understood. As of today, it is not yet known which molecular clusters form the first dust grains in oxygen-rich (C/O < 1) asymptotic giant branch (AGB) winds. Aluminium oxides and iron-free silicates are often put forward as promising candidates for the first dust seeds. Aims. We aim to constrain the dust formation histories in the winds of oxygen-rich AGB stars. Methods. We obtained Atacama Large Millimeter/sub-millimeter array (ALMA) observations with a spatial resolution of 120 × 150 mas tracing the dust formation region of the low mass-loss rate AGB star, R Dor, and the high mass-loss rate AGB star, IK Tau. We detected emission line profiles of AlO, AlOH, and AlCl in the ALMA data and used these line profiles to derive a lower limit of atomic aluminium incorporated in molecules. This constrains the aluminium budget that can condense into grains. Results. Radiative transfer models constrain the fractional abundances of AlO, AlOH, and AlCl in IK Tau and R Dor. We show that the gas-phase aluminium chemistry is completely different in both stars with a remarkable difference in the AlO and AlOH abundance stratification. The amount of aluminium locked up in these three molecules is small, ≤1.1 × 10 −7 w.r.t. H 2 , for both stars, i.e. only ≤2% of the total aluminium budget. An important result is that AlO and AlOH, which are the direct precursors of alumina (Al 2 O 3 ) grains, are detected well beyond the onset of the dust condensation, which proves that the aluminium oxide condensation cycle is not fully efficient. The ALMA observations allow us to quantitatively assess the current generation of theoretical dynamical-chemical models for AGB winds. We discuss how the current proposed scenario of aluminium dust condensation for low mass-loss rate AGB stars within a few stellar radii from the star, in particular for R Dor and W Hya, poses a challenge if one wishes to explain both the dust spectral features in the spectral energy distribution (SED) in interferometric data and in the polarized light signal. In particular, the estimated grain temperature of Al 2 O 3 is too high for the grains to retain their amorphous structure. We advocate that large gas-phase (Al 2 O 3 ) n clusters (n > 34) can be the potential agents of the broad 11 µm feature in the SED and in the interferometric data and we propose potential formation mechanisms for these large clusters.

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The millimeter IRAM-30 m line survey toward IK Tauri

Cited by 73 publications

References 86 publications

First detection of methanol towards a post-AGB object, HD 101584

First detection of methanol towards a post-AGB object, HD 101584

Determining the effects of clumping and porosity on the chemistry in a non-uniform AGB outflow

Study of the aluminium content in AGB winds using ALMA

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