Multi-colour light variation of AGB stars observed with ISO

Kerschbaum, F.; Lebzelter, T.; Lázaro, C.

doi:10.1051/0004-6361:20010889

Cited by 44 publications

(63 citation statements)

References 22 publications

(26 reference statements)

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“…Thus, only some indications can be listed here. Kerschbaum et al (2001;their Fig. 5) found that their lightcurve in the K-filter of the C-rich Mira T Dra lags behind the visual data (AAVSO) by 0.06 in phase.…”

Section: Discussionmentioning

confidence: 92%

Line formation in AGB atmospheres including velocity effects

Nowotny¹,

Höfner

Aringer³

2010

A&A

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: Discussionmentioning

confidence: 92%

Line formation in AGB atmospheres including velocity effects

Nowotny¹,

Höfner

Aringer³

2010

A&A

145

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“…Percy & Fleming 1992) for which Hipparcos found variations with an amplitude of 0.1 mag and a period of only 6.3 days (Koen & Eyer 2002). However, more recently, samples of these Hipparcos short-period SRs have been the subject of other dedicated photometric surveys, such as those performed by and Kerschbaum et al (2001), which could not confirm the presence of any variability with a period below 35 days in any of their targets. Kerschbaum et al (2001) suggest some instrumental artefact of Hipparcos.…”

Section: The Calibrator Star: Hr 5512mentioning

confidence: 96%

“…However, more recently, samples of these Hipparcos short-period SRs have been the subject of other dedicated photometric surveys, such as those performed by and Kerschbaum et al (2001), which could not confirm the presence of any variability with a period below 35 days in any of their targets. Kerschbaum et al (2001) suggest some instrumental artefact of Hipparcos. We are therefore confident that the brightness of our calibrator HR 5512 has not changed significantly during the observing run.…”

Section: The Calibrator Star: Hr 5512mentioning

confidence: 99%

Is Arcturus a well-understood K giant?

Verhoelst

Bordé

Perrin

et al. 2005

A&A

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Abstract. We present near-IR interferometric measurements of the K1.5 giant Arcturus (α Bootis), obtained at the IOTA interferometer with the FLUOR instrument, in four narrow filters with central wavelengths ranging from 2.03 µm to 2.39 µm. These observations were expected to allow us to quantify the wavelength dependence of the diameter of a typical K giant. They are compared to predictions from both plane-parallel and spherical model atmospheres. Unexpectedly, neither can explain the observed visibilities. We show that these data suggest the presence of a companion, in accordance with the Hipparcos data on this star, and discuss this solution with respect to Arcturus' single star status.

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“…They are also important for stellar and galactic evolution, especially in connection with the formation of planetary nebulae. For reviews on AGB envelopes and their properties see, e.g., Habing & Olofsson (2004) and Kerschbaum et al (2011).…”

Section: Introductionmentioning

confidence: 99%

Deep optical imaging of asymptotic giant branch circumstellar envelopes

Mauron

Huggins

Cheung

2013

A&A

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We report results of a program to image the extended circumstellar envelopes of asymptotic giant branch (AGB) stars in dust-scattered Galactic light. The goal is to characterize the shapes of the envelopes to probe the mass-loss geometry and the presence of hidden binary companions. The observations consist of deep optical imaging of 22 AGB stars with high mass loss rates: 16 with the ESO 3.6 m NTT telescope, and the remainder with other telescopes. The circumstellar envelopes are detected in 15 objects, with mass loss rates > ∼ 2 × 10 −6 M yr −1 . The surface brightness of the envelopes shows a strong decrease with Galactic radius, which indicates a steep radial gradient in the interstellar radiation field. The envelopes range from circular to elliptical in shape, and we characterize them by the ellipticity (E = major/minor axis) of iso-intensity contours. We find that ∼50% of the envelopes are close to circular with E < ∼ 1.1, and others are more elliptical with ∼20% with E > ∼ 1.2. We interpret the shapes in terms of populations of single stars and binaries whose envelopes are flattened by a companion. The distribution of E is qualitatively consistent with expectations based on population synthesis models of binary AGB stars. We also find that ∼50% of the sample exhibit small-scale, elongated features in the central regions. We interpret these as the escape of light from the central star through polar holes, which are also likely produced by companions. Our observations of envelope flattening and polar holes point to a hidden population of binary companions within the circumstellar envelopes of AGB stars. These companions are expected to play an important role in the transition to post-AGB stars and the formation of planetary nebulae.

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Multi-colour light variation of AGB stars observed with ISO

Cited by 44 publications

References 22 publications

Line formation in AGB atmospheres including velocity effects

Line formation in AGB atmospheres including velocity effects

Is Arcturus a well-understood K giant?

Deep optical imaging of asymptotic giant branch circumstellar envelopes

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