SULFUR CHEMISTRY IN THE ENVELOPE OF VY CANIS MAJORIS: DETAILED ANALYSIS OF SO AND SO<sub>2</sub>EMISSION

Adande, G. R.; Edwards, Jessica L.; Ziurys, L. M.

doi:10.1088/0004-637x/778/1/22

Cited by 24 publications

(48 citation statements)

References 34 publications

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“…In order to obtain abundances and envelope radial distributions, the spectra were modeled with the non-LTE radiative transfer code ESCAPADE (Adande et al 2013). The code employs the Sobolev approximation, assuming a uniform expansion velocity, and can be used to model either spherically symmetric or directional, conical outflows.…”

Section: Discussionmentioning

confidence: 99%

“…In the spherical case, the outflow is depicted by finite element shells in which the equations of statistical equilibrium are solved. Collimated outflows are represented as conical sections of the sphere, with a specified orientation (position angle) and cone width (vertex angle; see Adande et al 2013). Rotational levels originating in the ground and first vibrationally excited states are modeled, considering excitation by collisions, as well as by infrared radiation from dust.…”

Section: Discussionmentioning

confidence: 99%

“…Further details are given in Adande et al (2013), and the complete code can be found in Adande (2013).…”

Section: Discussionmentioning

confidence: 99%

“…Our measurements toward IK Tau were conducted before the De Beck et al (2013) work appeared, but concern different transitions, and thus are complementary. These new data have been modeled with the non-LTE circumstellar radiative transfer code ESCAPADE (Adande et al 2013), along with spectra obtained previously for PO and PN toward the supergiant star VY CMa in the ARO 1 mm spectral-line survey of Tenenbaum et al (2010). From this analysis, abundances and radial distributions were determined.…”

Section: Introductionmentioning

confidence: 99%

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New Circumstellar Sources of PO and PN: The Increasing Role of Phosphorus Chemistry in Oxygen-rich Stars

Ziurys

Schmidt

Bernal

2018

ApJ

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PO and PN have been newly identified in several oxygen-rich circumstellar envelopes, using the Submillimeter Telescope of the Arizona Radio Observatory. The J=5→4 and J=6→5 transitions of PN near 235 and 282 GHz, and the lambda doublets originating in the J=5.5→4.5 and J=6.5→5.5 lines of PO at 240 and 284 GHz, have been detected toward the shells of asymptotic giant branch (AGB) stars TX Cam and R Cas. A similar set of lines has been observed toward the supergiant NML Cyg, and new transitions of these two molecules were also measured toward the AGB star IK Tau. Along with the previous data from VY Canis Majoris (VY CMa), these spectral lines were analyzed using the non-local thermodynamic equilibrium (non-LTE) circumstellar modeling code, ESCAPADE. For the AGB stars, peak abundances found for PN and PO were f∼(1-2)×10 −8 and (0.5-1)×10−7 , respectively, while those for the supergiants were f(PN)∼(0.3-0.7)×10 −8 and f(PO)∼(5-7)×10 −8 . PN was well modeled with a spherical radial distribution, suggesting formation near the stellar photosphere, perhaps enhanced by shocks. PO was best reproduced by a shell model, indicating a photochemical origin, except for VY CMa. Overall, the abundance of PO is a factor of 5-20 greater than that of PN. This study suggests that phosphorus-bearing molecules are common in O-rich envelopes, and that a significant amount of phosphorus (>20%) remains in the gas phase.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

“…Further details are given in Adande et al (2013), and the complete code can be found in Adande (2013).…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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New Circumstellar Sources of PO and PN: The Increasing Role of Phosphorus Chemistry in Oxygen-rich Stars

Ziurys

Schmidt

Bernal

2018

ApJ

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“…We note that the abundance of sulphur oxides is yet another mystery in circumstellar chemistry of O-rich stars (e.g. Yamamura et al 1999;Fu et al 2012;Adande et al 2013;Danilovich et al 2016;Velilla Prieto et al 2017). Our results may be indicative of some violent processes, such as shocks, in the formation of NH 3 .…”

Section: Ammonia Chemistrymentioning

confidence: 61%

Circumstellar ammonia in oxygen-rich evolved stars

Wong

Menten

Kamiński

et al. 2018

A&A

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Context. The circumstellar ammonia (NH 3 ) chemistry in evolved stars is poorly understood. Previous observations and modelling showed that NH 3 abundance in oxygen-rich stars is several orders of magnitude above that predicted by equilibrium chemistry. Aims. We would like to characterise the spatial distribution and excitation of NH 3 in the oxygen-rich circumstellar envelopes (CSEs) of four diverse targets: IK Tau, VY CMa, OH 231.8+4.2, and IRC +10420. Methods. We observed NH 3 emission from the ground state in the inversion transitions near 1.3 cm with the Very Large Array (VLA) and submillimetre rotational transitions with the Heterodyne Instrument for the Far-Infrared (HIFI) aboard Herschel Space Observatory from all four targets. For IK Tau and VY CMa, we observed NH 3 rovibrational absorption lines in the ν 2 band near 10.5 µm with the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). We also attempted to search for the rotational transition within the excited vibrational state ( 2 = 1) near 2 mm with the IRAM 30m Telescope. Non-LTE radiative transfer modelling, including radiative pumping to the vibrational state, was carried out to derive the radial distribution of NH 3 in the CSEs of these targets. Results. We detected NH 3 inversion and rotational emission in all four targets. IK Tau and VY CMa show blueshifted absorption in the rovibrational spectra. We did not detect vibrationally excited rotational transition from IK Tau. Spatially resolved VLA images of IK Tau and IRC +10420 show clumpy emission structures; unresolved images of VY CMa and OH 231.8+4.2 indicate that the spatial-kinematic distribution of NH 3 is similar to that of assorted molecules, such as SO and SO 2 , that exhibit localised and clumpy emission. Our modelling shows that the NH 3 abundance relative to molecular hydrogen is generally of the order of 10 −7 , which is a few times lower than previous estimates that were made without considering radiative pumping and is at least 10 times higher than that in the carbon-rich CSE of IRC +10216. NH 3 in OH 231.8+4.2 and IRC +10420 is found to emit in gas denser than the ambient medium. Incidentally, we also derived a new period of IK Tau from its V-band light curve. Conclusions. NH 3 is again detected in very high abundance in evolved stars, especially the oxygen-rich ones. Its emission mainly arises from localised spatial-kinematic structures that are probably denser than the ambient gas. Circumstellar shocks in the accelerated wind may contribute to the production of NH 3 . Future mid-infrared spectroscopy and radio imaging studies are necessary to constrain the radii and physical conditions of the formation regions of NH 3 .

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ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY Canis Majoris

Decin

Richards

Millar

et al. 2016

A&A

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Context. At the end of their lives, most stars lose a significant amount of mass through a stellar wind. The specific physical and chemical circumstances that lead to the onset of the stellar wind for cool luminous stars are not yet understood. Complex geometrical morphologies in the circumstellar envelopes prove that various dynamical and chemical processes are interlocked and their relative contributions are not easy to disentangle. Aims. We aim to study the inner-wind structure (R < 250 R ) of the well-known red supergiant VY CMa, the archetype for the class of luminous red supergiant stars suffering high mass loss. Specifically, the objective is to unravel the density structure in the inner envelope and to examine the chemical interaction between some gas and dust species. Methods. We analyse high spatial resolution (∼ 0 . 24 × 0 . 13) ALMA Science Verification (SV) data in band 7 in which four thermal emission lines of gaseous sodium chloride (NaCl) are present at high signal-to-noise ratio. Results. For the first time, the NaCl emission in the inner wind region of VY CMa is spatially resolved. The ALMA observations reveal the contribution of up to four different spatial regions. The NaCl emission pattern is different compared to the dust continuum and TiO2 emission already analysed from the ALMA SV data. The emission can be reconciled with an axisymmetric geometry, where the lower density polar/rotation axis has a position angle of ∼50• measured from north to east. However, this picture can not capture the full morphological diversity, and discrete mass ejection events need to be invoked to explain localized higher-density regions. The velocity traced by the gaseous NaCl line profiles is significantly lower than the average wind terminal velocity, and much slower than some of the fastest mass ejections, signalling a wide range of characteristic speeds for the mass loss. Gaseous NaCl is detected far beyond the main dust condensation region. Realising the refractory nature of this metal halide, this hints at a chemical process preventing all NaCl from condensing onto dust grains. We show that in the case of the ratio of the surface binding temperature to the grain temperature being ∼50, only some 10% of NaCl remains in gaseous form, while for lower values of this ratio thermal desorption efficiently evaporates NaCl. Photodesorption by stellar photons seems not to be a viable explanation for the detection of gaseous NaCl at 220 R from the central star, and instead, we propose shock-induced sputtering driven by localized mass ejection events as alternative. Conclusions. The analysis of the NaCl lines demonstrate the capabilities of ALMA to decode the geometric morphologies and chemical pathways prevailing in the winds of evolved stars. These early ALMA results prove that the envelopes surrounding evolved stars are far from homogeneous, and that a variety of dynamical and chemical processes dictate the wind structure.

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SULFUR CHEMISTRY IN THE ENVELOPE OF VY CANIS MAJORIS: DETAILED ANALYSIS OF SO AND SO₂EMISSION

Cited by 24 publications

References 34 publications

New Circumstellar Sources of PO and PN: The Increasing Role of Phosphorus Chemistry in Oxygen-rich Stars

New Circumstellar Sources of PO and PN: The Increasing Role of Phosphorus Chemistry in Oxygen-rich Stars

Circumstellar ammonia in oxygen-rich evolved stars

ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY Canis Majoris

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SULFUR CHEMISTRY IN THE ENVELOPE OF VY CANIS MAJORIS: DETAILED ANALYSIS OF SO AND SO2EMISSION

Cited by 24 publications

References 34 publications

New Circumstellar Sources of PO and PN: The Increasing Role of Phosphorus Chemistry in Oxygen-rich Stars

New Circumstellar Sources of PO and PN: The Increasing Role of Phosphorus Chemistry in Oxygen-rich Stars

Circumstellar ammonia in oxygen-rich evolved stars

ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY Canis Majoris

Contact Info

Product

Resources

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SULFUR CHEMISTRY IN THE ENVELOPE OF VY CANIS MAJORIS: DETAILED ANALYSIS OF SO AND SO₂EMISSION