Aluminium oxide in the optical spectrum of VY Canis Majoris

Kamiński, T.; Schmidt, M.; Menten, K. M.

doi:10.1051/0004-6361/201220650

Cited by 38 publications

(42 citation statements)

References 46 publications

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“…Our results on gas-phase TiO/TiO 2 indicate that titanium remains in atomic form and in TiO in the inner wind, with some TiO converted into TiO 2 by shock chemistry. Several transitions of molecular TiO and TiO 2 have been observed in the wind of the supergiant VY CMa (Kamiński et al 2013a;De Beck et al 2015), where the TiO 2 emission is extended and not always correlated with the dust continuum emission. These results point out that TiO 2 clusters and grains may not play an important role as condensation seeds.…”

Section: Summary and Discussionmentioning

confidence: 99%

Dust formation in the oxygen-rich AGB star IK Tauri

Gobrecht

Cherchneff

Sarangi

et al. 2015

A&A

185

289

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Aims. We model the synthesis of molecules and dust in the inner wind of the oxygen-rich Mira-type star IK Tau by considering the effects of periodic shocks induced by the stellar pulsation on the gas and by following the non-equilibrium chemistry in the shocked gas layers between 1 R and 10 R . We consider a very complete set of molecules and dust clusters, and combine the nucleation phase of dust formation with the condensation of these clusters into dust grains. We also test the impact of increasing the local gas density. Our derived molecular abundances and dust properties are compared to the most recent observational data. Methods. A semi-analytical formalism based on parameterised fluid equations is used to describe the gas density, velocity, and temperature in the inner wind. The chemistry is described by using a chemical kinetic network of reactions and the condensation mechanism is described by a Brownian formalism. A set of stiff, ordinary, coupled differential equations is solved, and molecular abundances, dust cluster abundances, grain size distributions and dust masses are derived. Results. The shocks drive an active non-equilibrium chemistry in the dust formation zone of IK Tau where the collision destruction of CO in the post-shock gas triggers the formation of C-bearing species such as HCN and CS. Most of the modelled molecular abundances agree well with the latest values derived from Herschel data, except for SO 2 and NH 3 , whose formation may not occur in the inner wind. Clusters of alumina, Al 2 O 3 , are produced within 2 R and lead to a population of alumina grains close to the stellar surface. Clusters of silicates (Mg 2 SiO 4 ) form at larger radii (r > 3 R ), where their nucleation is triggered by the formation of HSiO and H 2 SiO. They efficiently condense and reach their final grain size distribution between ∼6 R and 8 R with a major population of medium size grains peaking at ∼200 Å. This two dust-shell configuration agrees with recent interferometric observations. The derived dust-to-gas mass ratio for IK Tau is in the range 1-6 × 10 −3 and agrees with values derived from observations of O-rich Mira-type stars. Conclusions. Our results confirm the importance of periodic shocks in chemically shaping the inner wind of AGB stars and providing gas conditions conducive to the efficient synthesis of molecules and dust by non-equilibrium processes. They indicate that the wind acceleration will possibly develop in the radius range 4-8 R in IK Tau.

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Section: Summary and Discussionmentioning

confidence: 99%

Dust formation in the oxygen-rich AGB star IK Tauri

Gobrecht

Cherchneff

Sarangi

et al. 2015

A&A

185

289

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“…Indeed, VY CMa displays optical TiO emission whose presence implies non-LTE effects, most likely related to the strong stellar radiation (cf. Kamiński et al 2013). Large scatter of points on a rotational temperature diagram and inability to constrain T rot are problems we have encountered for several other molecules observed in the SMA survey, including NaCl and SiS for which many lines (>15) are observed, all at higher S/N.…”

Section: Analysis Of Rotational-temperature Diagramsmentioning

confidence: 93%

“…Similar narrow molecular emission lines in VY CMa have been attributed to the accelerating wind (e.g., Milam et al 2007). Following Tenenbaum & Ziurys (2009) and Kamiński et al (2013), to better localize the TiO emission region we use the semi-empirical windacceleration model in VY CMa constrained from multi-epoch observations of H 2 O masers (Richards et al 1998). This model assumes linear wind acceleration within 75-440 mas of the star and does not take the inhomogenities of the wind into account on these scales.…”

Section: Localization and Abundances Of The Tio And Tio 2 Gasmentioning

confidence: 99%

“…To compare the rotational profiles of TiO observed at radio and optical wavelengths, we used an optical spectrum of VY CMa obtained in 2001 with the Very Large Telescope (VLT) and reported in Kamiński et al (2013). Referring to the TiO line list of G. J. Phillips 7 , we searched for single-component and wellseparated rotational lines, and chose two examples in the γ (0, 0) band.…”

Section: Tio At Radio and Optical Wavelengthsmentioning

confidence: 99%

“…Simple equilibrium-chemistry models evidently cannot explain the observations of VY CMa. Indeed, molecular abundances calculated for molecular equilibrium have been demonstrated to fail observational tests in AGB stars (Cherchneff 2006) and for some species in VY CMa (Tenenbaum & Ziurys 2009;Kamiński et al 2013). A nonequilibrium approach is needed to explain the circumstellar chemistry of supergiants, but such models do not exist.…”

Section: Ti Oxides and The Formation Of Inorganic Dustmentioning

confidence: 99%

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Pure rotational spectra of TiO and TiO₂in VY Canis Majoris

Kamiński

Gottlieb

Menten

et al. 2013

A&A

Self Cite

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We report the first detection of pure rotational transitions of TiO and TiO 2 at (sub-)millimeter wavelengths towards the red supergiant VY CMa. A rotational temperature, T rot , of about 250 K was derived for TiO 2 . Although T rot was not well constrained for TiO, it is likely somewhat higher than that of TiO 2 . The detection of the Ti oxides confirms that they are formed in the circumstellar envelopes of cool oxygen-rich stars and may be the "seeds" of inorganic-dust formation, but alternative explanations for our observation of TiO and TiO 2 in the cooler regions of the envelope cannot be ruled out at this time. The observations suggest that a significant fraction of the oxides is not converted to dust, but instead remains in the gas phase throughout the outflow.

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Spectroscopy and Photochemistry of [Al, N, C, O, H]: Connectivity to Aluminium‐Bearing Species in the Universe

Wang,

Jiang,

Sun

et al. 2024

Chemistry A European J

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Aluminium is one of the most abundant metals in the universe and impacts the evolution of various astrophysical environments. Currently detected Al‐bearing molecules represent only a small fraction of the aluminium budget, suggesting that aluminium may reside in other species. AlO and AlOH molecules are abundant in the oxygen‐rich supergiant stars such as VY Canis Majoris, a stellar molecular factory with 60+ molecules including the prebiotic NC‐bearing species. Additional Al‐bearing molecules with N, C, O, and H may form in O‐rich environments with radiation‐accelerated chemistry. Here, we present spectroscopic identification of novel aluminium‐bearing molecules composed of [Al, N, C, O, H] and [Al, N, C, O] from the reactions of Al atoms and HNCO in solid argon matrix, which are potential Al‐bearing molecules in space. Photoinduced transformations among six [Al, N, C, O, H] isomers and three [Al, N, C, O] isomers, along with their dissociation reactions forming the known interstellar species, have been disclosed. These results provide new insight into the chemical network of astronomically detected Al‐bearing species in space.

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Aluminium oxide in the optical spectrum of VY Canis Majoris

Cited by 38 publications

References 46 publications

Dust formation in the oxygen-rich AGB star IK Tauri

Dust formation in the oxygen-rich AGB star IK Tauri

Pure rotational spectra of TiO and TiO₂in VY Canis Majoris

Spectroscopy and Photochemistry of [Al, N, C, O, H]: Connectivity to Aluminium‐Bearing Species in the Universe

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Aluminium oxide in the optical spectrum of VY Canis Majoris

Cited by 38 publications

References 46 publications

Dust formation in the oxygen-rich AGB star IK Tauri

Dust formation in the oxygen-rich AGB star IK Tauri

Pure rotational spectra of TiO and TiO2in VY Canis Majoris

Spectroscopy and Photochemistry of [Al, N, C, O, H]: Connectivity to Aluminium‐Bearing Species in the Universe

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Pure rotational spectra of TiO and TiO₂in VY Canis Majoris