Evidence for Very Extended Gaseous Layers around O‐rich Mira Variables and M Giants

Mennesson, Bertrand; Perrin, G.; Chagnon, Gilles; Foresto, V. Coudé du; Ridgway, Stephen T.; Mérand, A.; Salomé, P.; Bordé, P.; Cotton, W. D.; Morel, S.; Kervella, P.; Traub, Wesley A.; Lacasse, M. G.

doi:10.1086/342671

Cited by 90 publications

(162 citation statements)

References 22 publications

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“…For o Cet and W Aql, the maximum optical depths reach ∼ 3.5 for the models given in Table 2 (which have the maximum possible optical depths and gas masses, see below). The extent of the WML derived from our models are comparable to those derived for 14 AGB stars from measurements of angular sizes in the K and L bands (Mennesson et al 2002). Our results are also in good agreement with those of Perrin et al (2004) who derive radii of about 2.2 R and temperatures ranging from 1500-2100 K for the WMLs of a sample of five Mira stars by using CO and H 2 O lines from near-infrared spectra.…”

Section: Discussionsupporting

confidence: 88%

“…In this context, empirically characterising the properties of the gas from which dust forms is paramount. This region is usually studied through spectroscopic observations of molecular bands (see, e.g., Tsuji et al 1997;Mennesson et al 2002;Perrin et al 2004;Ohnaka et al 2012) and of resolved molecular lines (see, e.g., Hinkle et al 1982;Lebzelter et al 2005;Nowotny et al 2010) in the near-infrared. By using different molecules and transitions, authors are able to constrain the kinematEmail: theokhouri@gmail.com ics and the column densities of gas in the WML, even as a function of the distance from the star.…”

Section: Introductionmentioning

confidence: 99%

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ALMA observations of the vibrationally excited rotational CO transition v = 1, J = 3 − 2 towards five AGB stars

Khouri

Vlemmings

Ramstedt

et al. 2016

Monthly Notices of the Royal Astronomical Society: Letters

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ALMA observations of the vibrationally-excited rotational CO transition v = 1, J = 3 − 2 towards five AGB stars ABSTRACTWe report the serendipitous detection with ALMA of the vibrationally-excited purerotational CO transition v = 1, J = 3 − 2 towards five asymptotic giant branch (AGB) stars, o Cet, R Aqr, R Scl, W Aql, and π 1 Gru. The observed lines are formed in the poorly-understood region located between the stellar surface and the region where the wind starts, the so-called warm molecular layer. We successfully reproduce the observed lines profiles using a simple model. We constrain the extents, densities, and kinematics of the region where the lines are produced. R Aqr and R Scl show inverse P-Cygni line profiles which indicate infall of material onto the stars. The line profiles of o Cet and R Scl show variability. The serendipitous detection towards these five sources shows that vibrationally-excited rotational lines can be observed towards a large number of nearby AGB stars using ALMA. This opens a new possibility for the study of the innermost regions of AGB circumstellar envelopes.

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Section: Discussionsupporting

confidence: 88%

Section: Introductionmentioning

confidence: 99%

ALMA observations of the vibrationally excited rotational CO transition v = 1, J = 3 − 2 towards five AGB stars

Khouri

Vlemmings

Ramstedt

et al. 2016

Monthly Notices of the Royal Astronomical Society: Letters

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“…Mennesson et al 2002;Perrin et al 2004;Ireland et al 2004d;Woodruff et al 2004;and Fedele et al 2005) and C-rich (e.g. Hron et al 1998;) AGB stars, as well as for RSG stars (e.g.…”

Section: Discussion and Interpretationmentioning

confidence: 99%

“…Therefore it is difficult to measure a continuum diameter, while these opaque molecular layers can easily have radii twice the continuum radius (e.g. Mennesson et al 2002;Tej et al 2003;and Ohnaka 2004) with temperatures of 1000 to 2000 K, i.e. below the temperature of the continuum-forming surface of the star, but higher than the temperature of the surrounding circumstellar dust envelope.…”

Section: Introductionmentioning

confidence: 99%

The mid-infrared diameter of W Hydrae

Zhao-Geisler

Quirrenbach

Köhler

et al. 2011

A&A

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Aims. Asymptotic giant branch (AGB) stars are among the largest distributors of dust into the interstellar medium, and it is therefore important to understand the dust formation process and sequence in their strongly pulsating extended atmosphere. By monitoring the AGB star W Hya interferometrically over a few pulsations cycles, the upper atmospheric layers can be studied to obtain information on their chemical gas and dust composition and their intracycle and cycle-to-cycle behavior. Methods. Mid-infrared (8-13 μm) interferometric data of W Hya were obtained with MIDI/VLTI between April 2007 and September 2009, covering nearly three pulsation cycles. The spectrally dispersed visibility data of all 75 observations were analyzed by fitting a circular fully limb-darkened disk (FDD) model to all data and individual pulsation phases. Asymmetries were studied with an elliptical FDD. Results. Modeling results in an apparent angular FDD diameter of W Hya of about (80 ± 1.2) mas (7.8 AU) between 8 and 10 μm, which corresponds to an about 1.9 times larger diameter than the photospheric one. The diameter gradually increases up to (105 ± 1.2) mas (10.3 AU) at 12 μm. In contrast, the FDD relative flux fraction decreases from (0.85 ± 0.02) to (0.77 ± 0.02), reflecting the increased flux contribution from a fully resolved surrounding silicate dust shell. The asymmetric character of the extended structure could be confirmed. An elliptical FDD yields a position angle of (11 ± 20) • and an axis ratio of (0.87 ± 0.07). A weak pulsation dependency is revealed with a diameter increase of (5.4 ± 1.8) mas between visual minimum and maximum, while detected cycle-to-cycle variations are smaller. Conclusions. W Hya's diameter shows a behavior that is very similar to the Mira stars RR Sco and S Ori and can be described by an analogous model. The constant diameter part results from a partially resolved stellar disk, including a close molecular layer of H 2 O, while the increase beyond 10 μm can most likely be attributed to the contribution of a spatially resolved nearby Al 2 O 3 dust shell. Probably due to the low mass-loss rate, close Fe-free silicate dust could not be detected. The results suggest that the formation of amorphous Al 2 O 3 occurs mainly at visual minimum. A possible close Al 2 O 3 dust shell has now been revealed in a few objects calling for self-consistent dynamic atmospheric models including dust formation close to the star. The asymmetry might be explained by an enhanced dust concentration along an N-S axis.

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“…Mennesson et al (2002) and Perrin et al (2004) showed that the opacity A&A 576, A70 (2015) of a putative envelope at about 2 R cannot be neglected in order to interpret visibility curves. Observations in specific narrow-band filters pointed to CO and H 2 O vapors as potential major contributors to the opacity in K band, with water vapor being the main contributor.…”

Section: Near-infraredmentioning

confidence: 99%

High-resolution IR and radio observations of AGB stars

Perrin

Cotton

Millan-Gabet

et al. 2015

A&A

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Aims. We present the results of observations with interferometers of a sample of pulsating asymptotic giant branch (AGB) stars in the infrared and at radio wavelengths. The goal of these observations is to explore the extended stellar atmospheres and to establish links between the spatial scales of molecular envelopes and of the dust shell. This is the key to better understand the process of dust formation and therefore of mass loss. Methods. We used the ESO VLTI/MIDI interferometer in the N band, the Keck Interferometer in the K band, and NRAO VLBA observations of SiO masers at 7 mm wavelength of a sample of AGB stars: U Ari, W Cnc, RX Tau, RT Tau, RT Aql, S Ser, and V Mon. The various instruments probe different altitudes of the atmosphere of the AGB stars. They are sensitive to regions below the silicate dust condensation distance and provide the opportunity of finding hints about how dust and its precursors form in the extended atmosphere of an AGB star. The K-band observations are sensitive to water and carbon-monoxyde vapors. Unfortunately, we were only able to observe S Ser in this wavelength range. Results. We find a ratio of 2.2 between the molecular envelope radius and the photospheric size, which is consistent with previous results. The N-band observations are mostly sensitive to vapors of SiO and water and to dust (alumina and silicate). The silicate dust shell is fully resolved, and no precise parameters can be deduced from the N-band observations other than a spatial extension of at least 12-16 R for our sample. The sizes found for the SiO region are consistent with the radii of the SiO maser rings provided by the VLBA observations. The sizes of the alumina and water vapor regions are systematically found to be larger. There is clear evidence that SiO is absent from regions farther from the star where silicate dust condenses. Conclusions. These observations support a possible scenario in which SiO is adsorbed by species such as corundum. An alternative explanation could be that SiO has chemically disappeared at this range of distances.

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Evidence for Very Extended Gaseous Layers around O‐rich Mira Variables and M Giants

Cited by 90 publications

References 22 publications

ALMA observations of the vibrationally excited rotational CO transition v = 1, J = 3 − 2 towards five AGB stars

ALMA observations of the vibrationally excited rotational CO transition v = 1, J = 3 − 2 towards five AGB stars

The mid-infrared diameter of W Hydrae

High-resolution IR and radio observations of AGB stars

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