Observing and modeling the dynamic atmosphere of the low mass-loss C-star R Sculptoris at high angular resolution

Sacuto, Stéphane; Aringer, B.; Hron, J.; Nowotny, W.; Paladini, C.; Verhoelst, Tijl; Höfner, Susanne

doi:10.1051/0004-6361/200913786

Cited by 42 publications

(80 citation statements)

References 68 publications

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“…We combined spectroscopic photometric and interferometric observations and hydrostatic and dynamic model atmospheres, as well as simple geometrical models. Until now, the only studies with a similar approach to the one in the present study are those by Sacuto et al (2011) on R Scl and RT Vir Sacuto et al (2013) on RT Vir. While R Scl is a semi-regular pulsating star and RT Vir an M-type star, RU Vir is the first carbon-rich Mira variable for which photometry, spectroscopy, and interferometry are compared to DMAs.…”

Section: Discussionmentioning

confidence: 99%

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Modelling the atmosphere of the carbon-rich Mira RU Virginis

Rau

Paladini

Hron

et al. 2015

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Context. We study the atmosphere of the carbon-rich Mira RU Vir using the mid-infrared high spatial resolution interferometric observations from VLTI/MIDI. Aims. The aim of this work is to analyse the atmosphere of the carbon-rich Mira RU Vir with hydrostatic and dynamic models, in this way deepening the knowledge of the dynamic processes at work in carbon-rich Miras. Methods. We compare spectro-photometric and interferometric measurements of this carbon-rich Mira AGB star with the predictions of different kinds of modelling approaches (hydrostatic model atmospheres plus MOD-More Of Dusty, self-consistent dynamic model atmospheres). A geometric model fitting tool is used for a first interpretation of the interferometric data. Results. The results show that a joint use of different kinds of observations (photometry, spectroscopy, interferometry) is essential for shedding light on the structure of the atmosphere of a carbon-rich Mira. The dynamic model atmospheres fit the ISO spectrum well in the wavelength range λ = [2.9, 25.0] µm. Nevertheless, a discrepancy is noticeable both in the SED (visible) and in the interferometric visibilities (shape and level), which is a possible explanation are intra-/inter-cycle variations in the dynamic model atmospheres, as well as in the observations. The presence of a companion star and/or a disk or a decrease in mass loss within the past few hundred years cannot be excluded, but these explanations are considered unlikely.

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Section: Discussionmentioning

confidence: 99%

“…On the other hand, to date only a few interferometric observations of carbon stars have been compared with model atmospheres (Sacuto et al 2011;Paladini et al 2011;Cruzalèbes et al 2013;Klotz et al 2013;van Belle et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Modelling the atmosphere of the carbon-rich Mira RU Virginis

Rau

Paladini

Hron

et al. 2015

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“…We cannot exclude that the companion is a substellar object orbiting the envelope. There are suggestions in literature that such a situation might be common among AGB stars Höfner et al 2003;Nowotny et al 2010), computed following the approach of Sacuto et al (2011) to artificially impose SiC grains. This dust species was detected in the ISO spectrum of R For (Clément et al 2003).…”

Section: Discussionmentioning

confidence: 99%

Detection of an asymmetry in the envelope of the carbon Mira R Fornacis using VLTI/MIDI

Paladini

Sacuto

Klotz

et al. 2012

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Aims. We present a study of the envelope morphology of the carbon Mira R For with VLTI/MIDI. This object is one of the few asymptotic giant branch (AGB) stars that underwent a dust-obscuration event. The cause of such events is still a matter of discussion. Several symmetric and asymmetric scenarios have been suggested in the literature. Methods. Mid-infrared interferometric observations were obtained separated by two years. The observations probe different depths of the atmosphere and cover different pulsation phases. The visibilities and the differential phases were interpreted using GEM-FIND, a tool for fitting spectrally dispersed interferometric observations with the help of wavelength-dependent geometric models. Results. We report the detection of an asymmetric structure revealed through the MIDI differential phase. This asymmetry is observed at the same baseline and position angle two years later. The observations are best simulated with a model that includes a uniform-disc plus a Gaussian envelope plus a point-source. The geometric model can reproduce both the visibilities and the differential phase signatures. Conclusions. Our MIDI data favour explanations of the R For obscuration event that are based on an asymmetric geometry. We clearly detect a photocentre shift between the star and the strongly resolved dust component. This might be caused by a dust clump or a substellar companion. However, the available observations do not allow us to distinguish between the two options. The finding has strong implications for future studies of the geometry of the envelope of AGB stars: if this is a binary, are all AGB stars that show an obscuration event binaries as well? Or are we looking at asymmetric mass-loss processes (i.e. dusty clumps) in the inner part of a carbon-rich Mira?

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“…Winters et al 2000;Gautschy-Loidl et al 2004;Nowotny et al 2010Nowotny et al , 2011Sacuto et al 2011), some fundamental open questions remain for the case of M-type AGB stars. As shown by Woitke (2006), silicate grains have to be basically iron-free to form and survive in the close vicinity of the star, resulting in insufficient absorption cross sections in the near-infrared to drive an outflow.…”

Section: Introductionmentioning

confidence: 99%

The wind of the M-type AGB star RT Virginis probed by VLTI/MIDI

Sacuto

Ramstedt

Höfner

et al. 2013

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Aims. We study the circumstellar environment of the M-type AGB star RT Vir using mid-infrared high spatial resolution observations from the ESO-VLTI focal instrument MIDI. The aim of this study is to provide observational constraints on theoretical prediction that the winds of M-type AGB objects can be driven by photon scattering on iron-free silicate grains located in the close environment (about 2 to 3 stellar radii) of the star. Methods. We interpreted spectro-interferometric data, first using wavelength-dependent geometric models. We then used a selfconsistent dynamic model atmosphere containing a time-dependent description of grain growth for pure forsterite dust particles to reproduce the photometric, spectrometric, and interferometric measurements of RT Vir. Since the hydrodynamic computation needs stellar parameters as input, a considerable effort was first made to determine these parameters. Results. MIDI differential phases reveal the presence of an asymmetry in the stellar vicinity. Results from the geometrical modeling give us clues to the presence of aluminum and silicate dust in the close circumstellar environment (<5 stellar radii). Comparison between spectro-interferometric data and a self-consistent dust-driven wind model reveals that silicate dust has to be present in the region between 2 to 3 stellar radii to reproduce the 59 and 63 m baseline visibility measurements around 9.8 μm. This gives additional observational evidence in favor of winds driven by photon scattering on iron-free silicate grains located in the close vicinity of an M-type star. However, other sources of opacity are clearly missing to reproduce the 10−13 μm visibility measurements for all baselines.Conclusions. This study is a first attempt to understand the wind mechanism of M-type AGB stars by comparing photometric, spectrometric, and interferometric measurements with state-of-the-art, self-consistent dust-driven wind models. The agreement of the dynamic model atmosphere with interferometric measurements in the 8−10 μm spectral region gives additional observational evidence that the winds of M-type stars can be driven by photon scattering on iron-free silicate grains. Finally, a larger statistical study and progress in advanced self-consistent 3D modeling are still required to solve the remaining problems.

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Observing and modeling the dynamic atmosphere of the low mass-loss C-star R Sculptoris at high angular resolution

Cited by 42 publications

References 68 publications

Modelling the atmosphere of the carbon-rich Mira RU Virginis

Modelling the atmosphere of the carbon-rich Mira RU Virginis

Detection of an asymmetry in the envelope of the carbon Mira R Fornacis using VLTI/MIDI

The wind of the M-type AGB star RT Virginis probed by VLTI/MIDI

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