The radio continuum spectrum of Mira A and Mira B up to submillimeter wavelengths

Planesas, P.; Alcolea, J.; Bachiller, R.

doi:10.1051/0004-6361/201527833

Cited by 15 publications

(15 citation statements)

References 24 publications

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“…The spectral index in the radio wavelengths is found to be 1.86(≈2), close to the Rayleigh-Jeans law at low frequencies of an optically thick blackbody (Reid & Menten 1997a). Matthews et al (2015) and Planesas et al (2016) found that this spectral index can also fit well the submillimetre flux densities of o Cet at 338 GHz in ALMA Band 7 and at 679 GHz in ALMA Band 9, respectively.…”

Section: Previous Observationssupporting

confidence: 63%

Resolving the extended atmosphere and the inner wind of Mira (oCeti) with long ALMA baselines

Wong

Kamiński

Menten

et al. 2016

A&A

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Context. High angular resolution (sub)millimetre observations of asymptotic giant branch (AGB) stars, now possible with the Atacama Large Millimeter/submillimeter Array (ALMA), allow direct imaging of these objects' photospheres. The physical properties of the molecular material around these regions, which until now has only been studied by imaging of maser emission and spatially unresolved absorption spectroscopy, can be probed with radiative transfer modelling and compared to hydrodynamical model predictions. The prototypical Mira variable, o Cet (Mira), was observed as a Science Verification target in the 2014 ALMA Long Baseline Campaign, offering the first opportunity to study these physical conditions in detail. Aims. With the longest baseline of 15 km, ALMA produces clearly resolved images of the continuum and molecular line emission/absorption at an angular resolution of ∼30 mas at 220 GHz. Models are constructed for Mira's extended atmosphere to investigate the physics and molecular abundances therein. Methods. We imaged the data of 28 SiO = 0, 2 J = 5−4 and H 2 O v 2 = 1 J Ka,Kc = 5 5,0 −6 4,3 transitions and extracted spectra from various lines of sight towards Mira's extended atmosphere. In the course of imaging the emission/absorption, we encountered ambiguities in the resulting images and spectra that appear to be related to the performance of the CLEAN algorithm when applied to a combination of extended emission, and compact emission and absorption. We addressed these issues by a series of tests and simulations. We derived the gas density, kinetic temperature, molecular abundance, and outflow/infall velocities in Mira's extended atmosphere by modelling the SiO and H 2 O lines. Results. We resolve Mira's millimetre continuum emission and our data are consistent with a radio photosphere with a brightness temperature of 2611 ± 51 K. In agreement with recent results obtained with the Very Large Array, we do not confirm the existence of a compact region (<5 mas) of enhanced brightness. Our modelling shows that SiO gas starts to deplete beyond 4 R and at a kinetic temperature of 600 K. The inner dust shells are probably composed of grain types other than pure silicates. During this ALMA observation, Mira's atmosphere generally exhibited infall motion with a shock front of velocity 12 km s −1 outside the radio photosphere. Despite the chaotic nature of Mira's atmosphere, the structures predicted by the hydrodynamical model, codex, can reproduce the observed spectra in astonishing detail, while some other models fail when confronted with the new data. Conclusions. For the first time, millimetre-wavelength molecular absorption against the stellar continuum has been clearly imaged. Combined with radiative transfer modelling, the ALMA data successfully demonstrates the ability to reveal the physical conditions of the extended atmospheres and inner winds of AGB stars in unprecedented detail. Long-term monitoring of oxygen-rich evolved stars will be the key to understanding the unsolved problem of dust ...

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Section: Previous Observationssupporting

confidence: 63%

Resolving the extended atmosphere and the inner wind of Mira (oCeti) with long ALMA baselines

Wong

Kamiński

Menten

et al. 2016

A&A

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“…Recently, the short distance environment of Mira A+B has been observed using the Atacama Large Millimetre/submillimetre Array (ALMA). Continuum emission has been observed at 1, 3 and 7 mm wavelength and its analysis (Vlemmings et al 2015;Planesas et al 2016), in particular in association with JVLA observations (Matthews et al 2015), has resolved Mira A photosphere with unprecedented spatial resolution. The 12 CO(3-2) line emission has been mapped with an also unprecedented spatial resolution of ∼0.5 ′′ up to a distance of ∼10 ′′ from the central star by Ramstedt et al (2014).…”

Section: Introductionmentioning

confidence: 77%

Morphology and kinematics of the gas envelope of Mira Ceti

Nhung¹,

Hoai²,

Diep³

et al. 2016

Mon. Not. R. Astron. Soc.

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Observations of 12 CO(3-2) emission of the circumbinary envelope of Mira Ceti, made by ALMA are analysed. The observed Doppler velocity distribution is made of three components: a blue-shifted south-eastern arc, which can be described as a ring in slow radial expansion, ∼1.7 km s −1 , making an angle of ∼50 • with the plane of the sky and born some 2000 years ago; a few arcs, probably born at the same epoch as the blueshifted arc, all sharing Doppler velocities red-shifted by approximately 3±2 km s −1 with respect to the main star; the third, central region dominated by the circumbinary envelope, displaying two outflows in the south-western and north-eastern hemispheres. At short distances from the star, up to ∼1.5 ′′ , these hemispheres display very different morphologies: the south-western outflow covers a broad solid angle, expands radially at a rate between 5 and 10 km s −1 and is slightly red shifted; the north-eastern outflow consists of two arms, both blue-shifted, bracketing a broad dark region where emission is suppressed. At distances between ∼1.5 ′′ and ∼2.5 ′′ the asymmetry between the two hemispheres is significantly smaller and detached arcs, particularly spectacular in the north-eastern hemisphere are present. Close to the stars, we observe a mass of gas surrounding Mira B, with a size of a few tens of AU, and having Doppler velocities with respect to Mira B reaching ±1.5 km s −1 , which we interpret as gas flowing from Mira A toward Mira B.

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“…32 in the combined data. The observations are described in Planesas et al (2016). Four spectral ranges were observed: 330.4−330.7 and 345.6−345.9 GHz − at a velocity resolution of 0.1 km s −1 − and 331.1−332.8 and 343.7−345.5 GHz, at a velocity resolution of about 13.6 km s −1 .…”

Section: Almamentioning

confidence: 99%

An observational study of dust nucleation in Mira (o Ceti)

Kamiński

Wong

Schmidt

et al. 2016

A&A

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Context. Dust is efficiently produced by cool giant stars, but the condensation of inorganic dust is poorly understood. Observations of key aluminum bearing molecules around evolved stars has enabled us to investigate the nucleation of alumina (Al 2 O 3 ) dust in the gas. Aims. We aim to identify and characterize aluminum bearing species in the circumstellar gas of Mira (o Ceti) in order to elucidate their role in the production of Al 2 O 3 dust. Methods. We used multiepoch spectral line observations at (sub-)millimeter, far-infrared, and optical wavelengths including: maps with ALMA that probe the gas distribution in the immediate vicinity of the star at ∼30 mas; observations with ALMA, APEX, and Herschel in 2013−2015 for studying cycle and inter-cycle variability of the rotational lines of Al-bearing molecules; optical records as far back as 1965 to examine variations in electronic transitions over time spans of days to decades; and velocity measurements and excitation analysis of the spectral features that constrain the physical parameters of the gas.Results. Three diatomic molecules AlO, AlOH, and AlH, and atomic Al i are the main observable aluminum species in Mira, although a significant fraction of aluminum might reside in other species that have not yet been identified. Strong irregular variability in the (sub-)millimeter and optical features of AlO (possibly the direct precursor of Al 2 O 3 ) indicates substantial changes in the excitation conditions, or varying abundance that is likely related to shocks in the star. The inhomogeneous distribution of AlO might influence the spatial and temporal characteristics of dust production. Conclusions. We are unable to quantitatively trace aluminum depletion from the gas, but the rich observational material constrains time-dependent chemical networks. Future improvements should include spectroscopic characterization of higher aluminum oxides, coordinated observations of dust and gas species at different variability phases, and tools to derive abundances in shock-excited gas.

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The radio continuum spectrum of Mira A and Mira B up to submillimeter wavelengths

Cited by 15 publications

References 24 publications

Resolving the extended atmosphere and the inner wind of Mira (oCeti) with long ALMA baselines

Resolving the extended atmosphere and the inner wind of Mira (oCeti) with long ALMA baselines

Morphology and kinematics of the gas envelope of Mira Ceti

An observational study of dust nucleation in Mira (o Ceti)

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