4 $\mathsf{\mu}$m spectra of AGB stars I. Observations

Lebzelter, T.; Hinkle, Kenneth H.; Aringer, B.

doi:10.1051/0004-6361:20010994

Cited by 15 publications

(17 citation statements)

References 35 publications

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“…The observed difference between the two cycles indicates that either the accelaration of the H 2 O line forming layer was higher or the deceleration lower. Both possibilities may be connected to a non-continuous mass loss in this star (Lebzelter et al, 2001). A similar behaviour was found in a second star, χ Cyg.…”

Section: Lebzelter and Hinklesupporting

confidence: 78%

Periodic and Nonperiodic Phenomena in AGB Stars

Lebzelter

Hinkle

2002

International Astronomical Union Colloquium

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Section: Lebzelter and Hinklesupporting

confidence: 78%

Periodic and Nonperiodic Phenomena in AGB Stars

Lebzelter

Hinkle

2002

International Astronomical Union Colloquium

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“…The number is φ v of that panel. Column 1 from the left: Time series of an average of 10-20 unblended CO ∆v = 3 lines, using FTS spectra of χ Cyg, taken from Lebzelter et al (2001). Observed heliocentric velocities were converted to systemic velocities RV* using heliocentric centre of mass radial velocity CMRV= −7.5kms −1 from Hinkle et al (1982).…”

Section: Comparison Of Radial Velocity Curvesmentioning

confidence: 99%

Pulsation-induced atmospheric dynamics in M-type AGB stars

Liljegren

Höfner

Eriksson

et al. 2017

A&A

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Context. Wind-driving in asymptotic giant branch (AGB) stars is commonly attributed to a two-step process. First, matter in the stellar atmosphere is levitated by shock waves, induced by stellar pulsation, and second, this matter is accelerated by radiation pressure on dust, resulting in a wind. In dynamical atmosphere and wind models the effects of the stellar pulsation are often simulated by a simplistic prescription at the inner boundary. Aims. We test a sample of dynamical models for M-type AGB stars, for which we kept the stellar parameters fixed to values characteristic of a typical Mira variable but varied the inner boundary condition. The aim was to evaluate the effect on the resulting atmosphere structure and wind properties. The results of the models are compared to observed mass-loss rates and wind velocities, photometry, and radial velocity curves, and to results from 1D radial pulsation models. The goal is to find boundary conditions which give realistic atmosphere and wind properties. Methods. Dynamical atmosphere models are calculated, using the DARWIN code for different combinations of photospheric velocities and luminosity variations. The inner boundary is changed by introducing an offset between maximum expansion of the stellar surface and the luminosity and/or by using an asymmetric shape for the luminosity variation. Ninety-nine different combinations of theses two changes are tested. Results. The model atmospheres are very sensitive to the inner boundary. Models that resulted in realistic wind velocities and massloss rates, when compared to observations, also produced realistic photometric variations. For the models to also reproduce the characteristic radial velocity curve present in Mira stars (derived from CO ∆v = 3 lines), an overall phase shift of 0.2 between the maxima of the luminosity and radial variation had to be introduced. This is a larger phase shift than is found by 1D radial pulsation models. Conclusions. We find that a group of models with different boundary conditions (29 models, including the model with standard boundary conditions) results in realistic velocities and mass-loss rates, and in photometric variations. To achieve the correct line splitting time variation a phase shift is needed.

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“…The strong lines of these species are mainly formed in cool regions far away from the star where the mass loss generates the structure (e.g. Lebzelter et al 2001;Bessell et al 1996;Hinkle et al 1982). …”

Section: Discussionmentioning

confidence: 99%

“…Thus, the absence of the typical SiO bandheads is not really unexpected. In their work on individual SiO lines observed in high resolution FTS spectra of Mira and Semiregular stars Lebzelter et al (2001) find complex and variable profiles indicating strong dynamical effects.…”

Section: Typementioning

confidence: 99%

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H₂O in stellar atmospheres

Aringer¹,

Kerschbaum

Jørgensen³

2002

A&A

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Abstract. We present 26 ISO-SWS spectra taken from a sample of 13 M-type Semiregular, Lb and Mira variables and covering the wavelength range between 2.36 and 5 µm at a medium resolution. All of the studied objects show intense water bands producing a deep absorption dip around 2.5 µm. Features of CO, OH, SiO and CO 2 are also visible. Using the new H 2 O linelist published in the first paper of this series and available opacity data for the other important molecules, we calculated a grid of hydrostatic MARCS atmospheres and the corresponding synthetic ISO-SWS spectra. Based on the comparison with these theoretical results the ISO observations can be divided into four classes. The first two groups include the spectra of the Semiregular (SRb) and Lb variables in our sample. For all of them the region between 2.36 and 4.2 µm can be quite well reproduced by our hydrostatic models. Only the predicted SiO bands above 4 µm are in some cases too strong which is due to known dynamical effects. Depending on the temperature (above or below 3000 K) of the atmosphere, which mainly determines the intensity of the water depression at 2.5 µm, the spectra of the Semiregular and Lb variables fall into the first or second class. The third group consists of observations of Mira stars obtained around maximum light where the range between 2.36 and 4.2 µm can be fitted with our MARCS models except for a strong emission bump appearing in the ISO-SWS data in the region of the SiO features and the slope very close to the short wavelength border. Finally, the last type of spectra corresponds to Mira variables during the phases around the minimum of their visual light curve. For this class the observed water absorption at 2.5 µm is much more intense than in any hydrostatic atmosphere with a realistic choice of effective temperature and surface gravity. Thus, we conclude that dynamical models are needed to explain the ISO-SWS data of Mira stars. For all of the cooler objects from our sample the predicted CO 2 bands between 4.2 and 4.6 µm are too weak which may be due to the opacity data.

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4 $\mathsf{\mu}$m spectra of AGB stars I. Observations

Cited by 15 publications

References 35 publications

Periodic and Nonperiodic Phenomena in AGB Stars

Periodic and Nonperiodic Phenomena in AGB Stars

Pulsation-induced atmospheric dynamics in M-type AGB stars

H₂O in stellar atmospheres

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4 $\mathsf{\mu}$m spectra of AGB stars I. Observations

Cited by 15 publications

References 35 publications

Periodic and Nonperiodic Phenomena in AGB Stars

Periodic and Nonperiodic Phenomena in AGB Stars

Pulsation-induced atmospheric dynamics in M-type AGB stars

H2O in stellar atmospheres

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Product

Resources

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H₂O in stellar atmospheres