Spitzer spectroscopy of carbon stars in the Small Magellanic Cloud

Lagadec, E.; Zijlstra, A. A.; Sloan, G. C.; Matsuura, M.; Wood, P. R.; Loon, Jacco Th. van; Harris, G. J.; Blommaert, J. A. D. L.; Hony, S.; Groenewegen, M. A. T.; Feast, M. W.; Whitelock, P. A.; Menzies, John; Cioni, M. R. L.

doi:10.1111/j.1365-2966.2007.11517.x

Cited by 73 publications

(147 citation statements)

References 59 publications

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“…4.1), reflecting the growing importance of circumstellar dust. Similar CMDs were documented by Zijlstra et al (2006) and Lagadec et al (2007;their Fig. 2) for the Magellanic Clouds and the C stars observed in these systems with the Spitzer Space Telescope.…”

Section: The Models In the Context Of A Stellar Populationsupporting

confidence: 84%

Synthetic photometry for carbon-rich giants

Nowotny¹,

Aringer²,

Höfner

et al. 2013

A&A

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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.

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Section: The Models In the Context Of A Stellar Populationsupporting

confidence: 84%

Synthetic photometry for carbon-rich giants

Nowotny¹,

Aringer²,

Höfner

et al. 2013

A&A

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“…The theoretical work of Mattsson et al (2008) and Wachter et al (2008) showed that the mass-loss rates of carbon stars may not be sensitive to metallicity. Numerous recent studies using Spitzer spectra of AGB stars in low-metallicity Local Group galaxies (e.g., Sloan et al 2006;Zijlstra et al 2006;Lagadec et al 2007;Matsuura et al 2007;Sloan et al 2008) seem to support this claim. Similar results were obtained by Groenewegen et al (2007), who found in their modeling of the IRS spectra of 60 carbon stars in the Magellanic Clouds that the trend of mass-loss rates with period of luminosity was comparable to that of Galactic sources.…”

Section: Introductionmentioning

confidence: 90%

The mass-loss return from evolved stars to the Large Magellanic Cloud

Srinivasan

Sargent

Matsuura

et al. 2010

A&A

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We present a radiative transfer model for the circumstellar dust shell around a Large Magellanic Cloud (LMC) long-period variable (LPV) previously studied as part of the Optical Gravitational Lensing Experiment (OGLE) survey of the LMC. OGLE LMC LPV 28579 (SAGE J051306.40-690946.3) is a carbon-rich asymptotic giant branch (AGB) star for which we have Spitzer broadband photometry and spectra from the SAGE and SAGE-Spec programs along with broadband UBVIJHK s photometry. By modeling this source, we obtain a baseline set of dust properties to be used in the construction of a grid of models for carbon stars. We reproduce the spectral energy distribution of the source using a mixture of amorphous carbon and silicon carbide with 15% SiC by mass. The grain sizes are distributed according to the KMH model, with γ = 3.5, a min = 0.01 μm and a 0 = 1.0 μm. The best-fit model produces an optical depth of 0.28 for the dust shell at the peak of the SiC feature (11.3 μm), with an inner radius of about 1430 R or 4.4 times the stellar radius. The temperature at this inner radius is 1310 K. Assuming an expansion velocity of 10 km s −1 , we obtain a dust mass-loss rate of 2.5 × 10 −9 M yr −1 . We calculate a 15% variation in this mass-loss rate by testing the sensitivity of the fit to variation in the input parameters. We also present a simple model for the molecular gas in the extended atmosphere that could give rise to the 13.7 μm feature seen in the spectrum. We find that a combination of CO and C 2 H 2 gas at an excitation temperature of about 1000 K and column densities of 3 × 10 21 cm −2 and 10 19 cm −2 respectively are able to reproduce the observations. Given that the excitation temperature is close to the temperature of the dust at the inner radius, most of the molecular contribution probably arises from this region. The luminosity corresponding to the first epoch of SAGE observations is 6580 L . For an effective temperature of about 3000 K, this implies a stellar mass of 1.5−2 M and an age of 1−2.5 Gyr for OGLE LMC LPV 28579. We calculate a gas mass-loss rate of 5.0 × 10 −7 M yr −1 assuming a gas:dust ratio of 200. This number is comparable to the gas mass-loss rates estimated from the period, color and 8 μm flux of the source.

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“…To analyze the carbon-rich spectra, we applied the Manchester method introduced by Sloan et al (2006b) and also applied by Zijlstra et al (2006) and Lagadec et al (2007). These papers (Sloan & Price 1995, and the dotted line is a power law: F 10 /F 12 ¼ 1:32(F 10 /F 11 ) 1:77 .…”

Section: The Manchester Methodsmentioning

confidence: 99%

“…Fortunately, other programs produced a surplus of carbon stars, which has resulted in a series of papers on carbon stars in the SMC (Sloan et al 2006b;Lagadec et al 2007) and the LMC Leisenring et al 2008). Three of the peak-up failures resulted in serendipitous observations.…”

Section: Sample Selectionmentioning

confidence: 99%

“…Program 3505 (PI Wood) spanned a range of mass-loss rates in the LMC and the SMC. It included a young stellar object (YSO;van Loon et al 2005b), but nearly all of the rest are carbon stars Matsuura et al 2006;Groenewegen et al 2007;Lagadec et al 2007). The other three programs also observed more carbon stars than initially planned, with sources classified photometrically as OH/IR stars turning out to be carbon stars instead.…”

Section: Introductionmentioning

confidence: 99%

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The Magellanic Zoo: Mid‐InfraredSpitzerSpectroscopy of Evolved Stars and Circumstellar Dust in the Magellanic Clouds

Sloan

Kraemer

Wood

et al. 2008

Astrophysical Journal

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101

170

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We observed a sample of evolved stars in the Large and Small Magellanic Clouds (LMC and SMC) with the Infrared Spectrograph on the Spitzer Space Telescope. Comparing samples from the SMC, LMC, and the Galaxy reveals that the dust production rate depends on metallicity for oxygen-rich stars, but carbon stars with similar pulsation properties produce similar quantities of dust, regardless of their initial metallicity. Other properties of the oxygen-rich stars also depend on metallicity. As the metallicity decreases, the fraction of naked (i.e., dust-free) stars increases, and among the naked stars, the strength of the 8 m absorption band from SiO decreases. Our sample includes several massive stars in the LMC with long pulsation periods that produce significant amounts of dust, probably because they are young and relatively metal-rich. Little alumina dust is seen in circumstellar shells in the SMC and LMC, unlike in Galactic samples. Three oxygen-rich sources also show emission from magnesium-rich crystalline silicates. Many also show an emission feature at 14 m. The one S star in our sample shows a newly detected emission feature centered at 13.5 m. At lower metallicity, carbon stars with similar amounts of amorphous carbon in their shells have stronger absorption from molecular acetylene (C 2 H 2 ) and weaker emission from SiC and MgS dust, as discovered in previous studies.

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Spitzer spectroscopy of carbon stars in the Small Magellanic Cloud

Abstract: ???The definitive version is available at www.blackwell-synergy.com.??? Copyright Blackwell Publishing DOI: 10.1111/j.1365-2966.2007.11517.

Cited by 73 publications

References 59 publications

Synthetic photometry for carbon-rich giants

Synthetic photometry for carbon-rich giants

The mass-loss return from evolved stars to the Large Magellanic Cloud

The Magellanic Zoo: Mid‐InfraredSpitzerSpectroscopy of Evolved Stars and Circumstellar Dust in the Magellanic Clouds

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