Molecular abundances in IRC + 10216

McCabe, Eithne M.; Smith, Robert C.; Clegg, R. E. S.

doi:10.1038/281263a0

Cited by 76 publications

(25 citation statements)

References 40 publications

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“…As long as chemical reactions are faster than the dynamical time scale, the molecular abundances are thought to be well described by equilibrium values, but -as the density drops -at some point in the outflow the reactions become inefficient and abundances do not change any more being fixed at a certain level corresponding to some equilibrium values. Following McCabe et al (1979), we estimate that such freezing-out should occur in the outflow of VY CMa at densities of about n H = 10 10 cm −3 , which are expected at a distance of few R (Decin et al 2006). Such a "freezing out" scenario in VY CMa would be supported for AlO by its abundance being close to the maximal value predicted by equilibrium models (and indeed those maximal abundances correspond to distances of a few R ).…”

Section: The Origin Of the Alo Emissionmentioning

confidence: 59%

Aluminium oxide in the optical spectrum of VY Canis Majoris

Kamiński

Schmidt

Menten

2012

A&A

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We report the first identification of the optical bands of the B 2 Σ + -X 2 Σ + system of AlO in the red supergiant VY CMa. In addition to TiO, VO, ScO, and YO, which were recognized in the optical spectrum of the star long time ago, AlO is another refractory molecule which displays strong emission bands in this peculiar star. Simulating the bands of AlO, we derive a rotational temperature of the circumstellar gas of T rot = 700 K. By resolving individual rotational components of the bands, we derive the kinematical characteristics of the gas, finding that the emission is centred at the stellar radial velocity and its intrinsic width is 13.5 km s −1 (full width at half maximum). It is the narrowest emission among all (thermal) features observed in VY CMa so far. The temperature and line widths suggest that the emission arises in gas located within ∼20 stellar radii, where the outflow is still being accelerated. This result contradicts equilibrium-chemistry models which predict substantial AlO abundances only to within a few stellar radii. We argue that non-equilibrium models involving propagation of shocks are needed to explain the observations.

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Section: The Origin Of the Alo Emissionmentioning

confidence: 59%

Aluminium oxide in the optical spectrum of VY Canis Majoris

Kamiński

Schmidt

Menten

2012

A&A

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“…This temperature implies formation at a radius of ∼ for VY CMa and 5R * ∼ for IK Tau, given the assumed dependence and the Ϫ0.7 3R r * stellar temperatures of 3368 K (VY CMa) and 2100 K (IK Tau). Presumably, these LTE abundances "freeze out" as the molecules flow from the hotter regions, as predicted by chemical models (McCabe et al 1979), thus explaining the observed source sizes of ∼ (VY CMa) and ∼ (IK Tau). Ro-40R 30R * * tational temperatures of 70-92 K are consistent with this scenario as well, considering the high dipole moment of NaCl (9.0 D).…”

Section: ϫ9mentioning

confidence: 80%

Oxygen-rich Mass Loss with a Pinch of Salt: NaCl in the Circumstellar Gas of IK Tauri and VY Canis Majoris

Milam

Apponi

Woolf

et al. 2007

ApJ

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The NaCl molecule has been observed in the circumstellar envelopes of VY Canis Majoris (VY CMa) and IK Tauri (IK Tau)-the first identifications of a metal refractory in oxygen-rich shells of evolved stars. Five rotational transitions of NaCl at 1 and 2 mm were detected toward VY CMa and three 1 mm lines were observed toward IK Tau, using the telescopes of the Arizona Radio Observatory. In both objects, the line widths of the NaCl profiles were extremely narrow relative to those of other molecules, indicating that sodium chloride has not reached the terminal outflow velocity in either star, likely a result of early condensation onto grains. Modeling the observed spectra suggests abundances, relative to H 2 , of in VY CMa and in IK Tau, with source Ϫ9 Ϫ9f ∼ 5 # 10 f ∼ 4 # 10 sizes of 0.5Љ and 0.3Љ, respectively. The extent of these sources is consistent with the size of the dust acceleration zones in both stars. NaCl therefore appears to be at least as abundant in O-rich shells as compared to C-rich envelopes, where, although it appears to condense out earlier in the O-rich case. Chemical Ϫ9f ∼ (0.2-2) # 10 equilibrium calculations indicate that NaCl is the major carrier of sodium at K for oxygen-rich stars, with T ∼ 1100 predicted fractional abundances in good agreement with the observations. These measurements suggest that crystalline salt may be an important condensate for sodium in both C-and O-rich circumstellar shells.

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“…Infrared spectroscopy has demonstrated that stable, closed-shell species such as CS, NH 3 , HCN, and HCCH have high abundances in the inner envelope of IRCϩ10216 (Ϸ10 Ϫ3 to 10 Ϫ6 , relative to H 2 ). As molecules flow outward, some abundances freeze out at intermediate radii, HCN and CO, for example (15,16). At the outer regions, photons and cosmic rays initiate an active photochemistry that creates radicals (11,12).…”

Section: The Chemical Environment Of Circumstellar Shellsmentioning

confidence: 99%