Dynamic model atmospheres of AGB stars

Gautschy-Loidl, R.; Höfner, Susanne; Jørgensen, U. G.; Hron, J.

doi:10.1051/0004-6361:20035860

Cited by 103 publications

(188 citation statements)

References 31 publications

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“…L, P,Ṁ, u exp ). In addition, low-resolution synthetic spectra in the visual and IR computed on the basis of model S resemble observed spectra (ISO, KAO) of S Cep fairly well as it was shown by Gautschy-Loidl et al (2004;their Sect. 5.1).…”

Section: The Specific Models Usedsupporting

confidence: 70%

“…For our line profile modelling we used dynamic model atmospheres as described in detail by Höfner et al (2003;DMA3), Gautschy-Loidl et al (2004;DMA4), N05 or Papers I and II. These models represent the scenario of pulsation-enhanced dustdriven winds (cf.…”

Section: General Remarksmentioning

confidence: 99%

“…The first step, calculating opacities based on a given atmospheric structure, was accomplished with the COMA code, a description of which can be found in Aringer (2000), Gautschy-Loidl (2001), or N05. Informations on recent updates and the latest version can be found in Gorfer (2005), Lederer & Aringer (2009.…”

Section: Calculating Synthetic Line Profilesmentioning

confidence: 99%

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Line formation in AGB atmospheres including velocity effects

Nowotny¹,

Höfner

Aringer³

2010

A&A

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145

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Context. Towards the end of the evolutionary stage of the asymptotic giant branch (AGB) the atmospheres of evolved red giants are considerably influenced by radial pulsations of the stellar interiors and developing stellar winds. The resulting complex velocity fields severely affect molecular line profiles (shapes, time-dependent shifts in wavelength, multiple components) observable in near-infrared spectra of long period variables. Time-series high-resolution spectroscopy allows us to probe the atmospheric kinematics and thereby study the mass loss process. Aims. With the help of model calculations the complex line formation process in AGB atmospheres was explored with the focus on velocity effects. Furthermore, we aimed for atmospheric models which are able to quantitatively reproduce line profile variations found in observed spectra of pulsating late-type giants. Methods. Models describing pulsation-enhanced dust-driven winds were used to compute synthetic spectra under the assumptions of chemical equilibrium and LTE. For this purpose, we used molecular data from line lists for the considered species and solved the radiative transfer in spherical geometry including the effects of velocity fields. Radial velocities (RV) derived from Doppler-shifted (components of) synthetic line profiles provide information on the gas velocities in the line-forming region of the spectral features. In addition, we made use of radial optical depth distributions to give estimates for the layers where lines are formed and to illustrate the effects of velocities in the line formation process. Results. Assuming uniform gas velocities for all depth points of an atmospheric model we estimated the conversion factor between gas velocities and measured RVs to p = u gas /RV ≈ 1.2−1.5. On the basis of dynamic model atmospheres and by applying our spectral synthesis codes we investigated in detail the finding that various molecular features in AGB spectra originate at different geometrical depths of the very extended atmospheres of these stars. We show that the models are able to quantitatively reproduce the characteristic line profile variations of lines sampling the deep photosphere (CO Δv = 3, CN) of Mira variables and the corresponding discontinuous, S-shaped RV curve. The global velocity fields (traced by different features) of typical long-period variables are also realistically reproduced. Possible reasons for discrepancies concerning other modelling results (e.g. CO Δv = 2 lines) are outlined. In addition, we present a model showing variations of CO Δv = 3 line profiles comparable to observed spectra of semiregular variables and discuss that the non-occurence of line doubling in these objects may be due to a density effect. Conclusions. The results of our line profile modelling are another indication that the dynamic models studied here are approaching a realistic representation of the outer layers of AGB stars with or without mass loss.

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Section: The Specific Models Usedsupporting

confidence: 70%

Section: General Remarksmentioning

confidence: 99%

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Line formation in AGB atmospheres including velocity effects

Nowotny¹,

Höfner

Aringer³

2010

A&A

Self Cite

145

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“…The star appears larger between 8 and 9 μm. According to Gautschy-Loidl et al (2004) CS affects this wavelength range. Because of this molecular contamination, this region is omitted, and a mean angular diameter of θ = 10.51 ± 0.70 mas is calculated by averaging the diameter from 9 μm to 11.5 μm.…”

Section: Approach 1: Geometric Modelsmentioning

confidence: 99%

“…Distance estimates range from 275 to 315 pc (van Leeuwen 2007;Claussen et al 1987;Bergeat & Chevallier 2005). Different ISO/SWS spectra of TX Psc (Jørgensen et al 2000;Gautschy-Loidl et al 2004) show that there is a difference in the 3 μm feature between 1996 and 1997. With the help of plane-parallel, hydrostatic models Jørgensen et al (2000) interpret this difference as a change in temperature of ∼100 K. The photometry and spectra have been successfully modelled by Gautschy-Loidl et al (2004) with dust-free dynamical models that reproduce the region between 1−5 μm.…”

Section: Introductionmentioning

confidence: 99%

Catching the fish – Constraining stellar parameters for TX Piscium using spectro-interferometric observations

Klotz

Paladini

Hron

et al. 2013

A&A

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Context. Stellar parameter determination is a challenging task when dealing with galactic giant stars. The combination of different investigation techniques has proven to be a promising approach. Aims. We analyse archive spectra obtained with the Short Wavelength Spectrometer (SWS) onboard ISO, and new interferometric observations from the Very Large Telescope MID-infrared Interferometric instrument (VLTI/MIDI) of a very well studied carbon-rich giant: TX Psc. The aim of this work is to determine stellar parameters using spectroscopy and interferometry. Methods. The observations are used to constrain the model atmosphere, and eventually the stellar evolutionary model in the region where the tracks map the beginning of the carbon star sequence. Two different approaches are used to determine stellar parameters: (i) the "classic" interferometric approach where the effective temperature is fixed by using the angular diameter in the N-band (from interferometry) and the apparent bolometric magnitude; (ii) parameters are obtained by fitting a grid of state-of-the-art hydrostatic models to spectroscopic and interferometric observations. Results. We find good agreement between the parameters of the two methods. The effective temperature and luminosity clearly place TX Psc in the carbon-rich AGB star domain in the H-R-diagram. Current evolutionary tracks suggest that TX Psc became a C-star just recently, which means that the star is still in a "quiet" phase compared to the subsequent strong-wind regime. This agrees with the C/O ratio being only slightly greater than one.

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Dust production and mass loss in cool evolved stars

Boyer

2013

Astron Nachr

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Following the red giant branch phase and the subsequent core He-burning phase, the low-to intermediate-mass stars (0.8 < M/M < 8) begin to ascend the asymptotic giant branch (AGB). Pulsations levitate material from the stellar surface and provide density enhancements and shocks, which can encourage dust formation and re-processing. The dust composition depends on the atmospheric chemistry (abundance of carbon relative to oxygen), which is altered by dredging up newly formed carbon to the surface of the star. I will briefly review the current status of models that include AGB mass loss and relate them to recent observations of AGB stars from the Surveying the Agents of Galaxy Evolution (SAGE) Spitzer surveys of the Small and Large Magellanic Clouds, including measures of the total dust input to the interstellar medium from AGB stars.

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Dynamic model atmospheres of AGB stars

Cited by 103 publications

References 31 publications

Line formation in AGB atmospheres including velocity effects

Line formation in AGB atmospheres including velocity effects

Catching the fish – Constraining stellar parameters for TX Piscium using spectro-interferometric observations

Dust production and mass loss in cool evolved stars

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