Interferometric properties of pulsating C-rich AGB stars

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

doi:10.1051/0004-6361/200911938

Cited by 26 publications

(37 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Simulations with dust-free model atmospheres show that the effect of pulsation on the N-band UD-radius is less than 0.1 mas at 1 kpc (Paladini et al 2009). This would be ∼0.3 mas for a star at the distance of TX Psc.…”

Section: Interferometric and Spectroscopic Variabilitymentioning

confidence: 94%

See 1 more Smart Citation

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

Klotz

Paladini

Hron

et al. 2013

A&A

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Interferometric and Spectroscopic Variabilitymentioning

confidence: 94%

“…This profile is used to calculate a synthetic visibility profile in the mid-IR for a subset of the models in the grid. A detailed description of the computation of the visibility profiles is given in Paladini et al (2009).…”

Section: Hydrostatic Modelsmentioning

confidence: 99%

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

Klotz

Paladini

Hron

et al. 2013

A&A

Self Cite

View full text Add to dashboard Cite

show abstract

“…Model R was adopted from Höfner et al (2003), while models T and S were taken from Gautschy-Loidl et al (2004). The latter model was also used in various other studies (Nowotny et al 2005a(Nowotny et al ,b, 2010(Nowotny et al , 2011aPaladini et al 2009). Computed specifically for this study were the last two models, C1 and C2.…”

Section: Combined Atmosphere and Wind Modelsmentioning

confidence: 99%

Synthetic photometry for carbon-rich giants

Nowotny¹,

Aringer²,

Höfner

et al. 2013

A&A

Self Cite

View full text Add to dashboard Cite

Late-type giant stars in the evolutionary stage of the asymptotic giant branch increasingly lose mass via comparatively slow but dense stellar winds. Not only do these evolved red giants contribute in this way to the enrichment of the surrounding interstellar medium, but the outflows also have a substantial influence on the spectro-photometric appearance of such objects. In the case of carbon-rich atmospheric chemistries, the developing cool circumstellar envelopes contain dust grains mainly composed of amorphous carbon. With increasing mass-loss rates, this leads to more and more pronounced circumstellar reddening. With the help of model calculations we aim at reproducing the observational photometric findings for a large sample of well-characterised galactic C-type Mira variables losing mass at different rates. We used dynamic model atmospheres, describing the outer layers of C-rich Miras, which are severly affected by dynamic effects. Based on the resulting structures and under the assumptions of chemical equilibrium as well as LTE, we computed synthetic spectra and synthetic broad-band photometry (Johnson-Cousins-Glass BVRIJHKL M). A set of five representative models with different stellar parameters describes a sequence from less to more evolved objects with steadily increasing mass-loss rates. This allowed us to study the significant influence of circumstellar dust on the spectral energy distributions and the (amplitudes of) lightcurves in different filters. We tested the photometric properties (mean NIR magnitudes, colours, and amplitudes) and other characteristics of the models (mass-loss rates, periods, and bolometric corrections) by comparing these with the corresponding observational data adopted from the literature. Using different kinds of diagrams we illustrate where the models are located in a supposed evolutionary sequence defined by observed C-type Mira samples. Based on comparisons of galactic targets with empirical relations derived for C stars in the Large Magellanic Cloud we discuss the relevance of metallicity and excess carbon (C-O) for the development of dust-driven winds. Having investigated the dynamic model atmospheres from different (mainly photometric) perspectives, we conclude that our modelling approach (meaning the combination of numerical method and a suitable choice of model parameters) is able to describe C-rich long-period variables over a wide range of mass-loss rates, i.e., from moderately pulsating objects without any dusty wind to highly dust-enshrouded Carbon Miras. Thus, we can trace the observed sequence of C-type Miras, which is mainly determined by the mass loss.

show abstract

“…Unfortunately, for V Hya, only H and K-band observations have been published. Diameter determinations for C-stars in these bands are mainly influenced by the presence of molecular shells consisting of C 2 H 2 , HCN, CN and CO (Gautschy-Loidl et al 2004;Paladini et al 2009). …”

Section: Wavelength Dependence Of the Diametermentioning

confidence: 99%

Dust and molecular shells in asymptotic giant branch stars

Zhao-Geisler

Quirrenbach

Köhler

et al. 2012

A&A

View full text Add to dashboard Cite

Context. Asymptotic giant branch (AGB) stars are one of the largest distributors of dust into the interstellar medium. However, the wind formation mechanism and dust condensation sequence leading to the observed high mass-loss rates have not yet been constrained well observationally, in particular for oxygen-rich AGB stars. Aims. The immediate objective in this work is to identify molecules and dust species which are present in the layers above the photosphere, and which have emission and absorption features in the mid-infrared (IR), causing the diameter to vary across the N-band, and are potentially relevant for the wind formation. Methods. Mid-IR (8-13 μm) interferometric data of four oxygen-rich AGB stars (R Aql, R Aqr, R Hya, and W Hya) and one carbonrich AGB star (V Hya) were obtained with MIDI/VLTI between April 2007 and September 2009. The spectrally dispersed visibility data are analyzed by fitting a circular fully limb-darkened disk (FDD). Results. The FDD diameter as function of wavelength is similar for all oxygen-rich stars. The apparent size is almost constant between 8 and 10 μm and gradually increases at wavelengths longer than 10 μm. The apparent FDD diameter in the carbon-rich star V Hya essentially decreases from 8 to 12 μm. The FDD diameters are about 2.2 times larger than the photospheric diameters estimated from K-band observations found in the literature. The silicate dust shells of R Aql, R Hya and W Hya are located fairly far away from the star, while the silicate dust shell of R Aqr and the amorphous carbon (AMC) and SiC dust shell of V Hya are found to be closer to the star at around 8 photospheric radii. Phase-to-phase variations of the diameters of the oxygen-rich stars could be measured and are on the order of 15% but with large uncertainties. Conclusions. From a comparison of the diameter trend with the trends in RR Sco and S Ori it can be concluded that in oxygen-rich stars the overall larger diameter originates from a warm molecular layer of H 2 O, and the gradual increase longward of 10 μm can be most likely attributed to the contribution of a close Al 2 O 3 dust shell. The chromatic trend of the Gaussian FWHM in V Hya can be explained with the presence of AMC and SiC dust. The observations suggest that the formation of amorphous Al 2 O 3 in oxygenrich stars occurs mainly around or after visual minimum. However, no firm conclusions can be drawn concerning the mass-loss mechanism. Future modeling with hydrostatic and self-consistent dynamical stellar atmospheric models will be required for a more certain understanding.

show abstract

Interferometric properties of pulsating C-rich AGB stars

Cited by 26 publications

References 29 publications

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

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

Synthetic photometry for carbon-rich giants

Dust and molecular shells in asymptotic giant branch stars

Contact Info

Product

Resources

About