Silicon Carbide Absorption Features: Dust Formation in the Outflows of Extreme Carbon Stars

Speck, A. K.; Corman, Adrian; Wakeman, Kristina; Wheeler, Caleb; Thompson, G. D.

doi:10.1088/0004-637x/691/2/1202

Cited by 71 publications

(106 citation statements)

References 86 publications

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“…Simple energy-balance estimates suggest that amorphous carbon dust should form within a few stellar radii . A lower limit of about 1.3 R in is suggested for SiC formation in extreme carbon stars by Speck et al (2009). The range considered here also agrees with observations of Galactic carbon stars (e.g., IRC+10216; Danchi et al 1995) and results from RT modeling of LMC stars (e.g., van Loon et al 1999).…”

Section: Shell Geometrysupporting

confidence: 89%

“…It is not easy, however, to constrain T cond as it depends on many factors such as the C/O ratio and the gas pressure (e.g., Sect. 3.4 of Speck et al 2009, and references therein). A detailed treatment of T cond is beyond the scope of our work.…”

Section: Preparationmentioning

confidence: 97%

“…A detailed treatment of T cond is beyond the scope of our work. Speck et al (2009) suggest that carbon dust can form at temperatures above 1400 K even at low mass-loss rates. They also find that for high C/O ratios, graphite grains can form at temperatures of ∼1800 K. While our current models only consider amorphous carbon dust grains, we are interested in as few constraints on the output parameters as possible so as to be able to extend our treatment by including more grain types in the future if required.…”

Section: Preparationmentioning

confidence: 99%

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

Srinivasan

Sargent

Meixner

2011

A&A

110

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Context. Outflows from asymptotic giant branch (AGB) and red supergiant (RSG) stars inject dust into the interstellar medium. The total rate of dust return provides an important constraint to galactic chemical evolution models. However, this requires detailed radiative transfer (RT) modeling of individual stars, which becomes impractical for large data sets. An alternative approach is to select the best-fit spectral energy distribution (SED) from a grid of dust shell models, allowing for a faster determination of the luminosities and mass-loss rates for entire samples. Aims. We have developed the Grid of RSG and AGB ModelS (GRAMS) to measure the mass-loss return from evolved stars. The models span the range of stellar, dust shell and grain properties relevant to evolved stars. The GRAMS model database will be made available to the scientific community. In this paper we present the carbon-rich AGB model grid and compare our results with photometry and spectra of Large Magellanic Cloud (LMC) carbon stars from the SAGE (Surveying the Agents of Galaxy Evolution) and SAGE-Spec programs. Methods. We generate models for spherically symmetric dust shells using the 2Dust code, with hydrostatic models for the central stars. The model photospheres have effective temperatures between 2600 and 4000 K and luminosities from ∼2000 L to ∼40 000 L . Assuming a constant expansion velocity, we explore five values of the inner radius R in of the dust shell (1.5, 3, 4.5, 7 and 12 R star ). We fix the outer radius at 1000 R in . Based on the results from our previous study, we use amorphous carbon dust mixed with 10% silicon carbide by mass. The grain size distribution follows a power-law and an exponential falloff at large sizes. The models span twenty-six values of 11.3 μm optical depth, ranging from 0.001 to 4. For each model, 2Dust calculates the output SED from 0.2 to 200 μm. Results. Over 12 000 models have dust temperatures below 1800 K. For these, we derive synthetic photometry in optical, nearinfrared and mid-infrared filters for comparison with available data. We find good agreement with magnitudes and colors observed for LMC carbon-rich and extreme AGB star candidates from the SAGE survey, as well as spectroscopically confirmed carbon stars from the SAGE-Spec study. Our models reproduce the IRAC colors of most of the extreme AGB star candidates, consistent with the expectation that a majority of these enshrouded stars have carbon-rich dust. Finally, we fit the SEDs of some well-studied carbon stars and compare the resulting luminosities and mass-loss rates with those from previous studies.

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Section: Shell Geometrysupporting

confidence: 89%

Section: Preparationmentioning

confidence: 97%

Section: Preparationmentioning

confidence: 99%

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

Srinivasan

Sargent

Meixner

2011

A&A

110

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“…The SiC feature falls in the S 9W-band (see Fig. 1), and it is usually found in emission: only a few carbon stars are known to have the SiC feature in absorption (Speck et al 1997;Pitman et al 2006;Gruendl et al 2008;Speck et al 2009). Thus carbon stars tend to increase monotonously in both (S 9W − L18W) and (J − L18W) colors.…”

Section: (S9w -L18w) Vs (J -L18w)mentioning

confidence: 99%

AKARI's infrared view on nearby stars

Ita

Matsuura

Ishihara

et al. 2010

A&A

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Context. The AKARI, a Japanese infrared space mission, has performed an All-Sky Survey in six infrared-bands from 9 to 180 μm with higher spatial resolutions and better sensitivities than IRAS. Aims. We investigate the mid-infrared (9 and 18 μm) point source catalog (PSC) obtained with the infrared camera (IRC) onboard AKARI, in order to understand the infrared nature of the known objects and to identify previously unknown objects. Methods. Color-color diagrams and a color-magnitude diagram were plotted with the AKARI-IRC PSC and other available all-sky survey catalogs. We combined the Hipparcos astrometric catalog and the 2MASS all-sky survey catalog with the AKARI-IRC PSC. We furthermore searched literature and SIMBAD astronomical database for object types, spectral types, and luminosity classes. We identified the locations of representative stars and objects on the color−magnitude and color−color diagram schemes. The properties of unclassified sources can be inferred from their locations on these diagrams. Results. We found that the (B − V) vs. (V − S 9W) color−color diagram is useful for identifying the stars with infrared excess emerged from circumstellar envelopes or disks. Be stars with infrared excess are separated well from other types of stars in this diagram. Whereas (J − L18W) vs. (S 9W − L18W) diagram is a powerful tool for classifying several object types. Carbon-rich asymptotic giant branch (AGB) stars and OH/IR stars form distinct sequences in this color−color diagram. Young stellar objects (YSOs), pre-main sequence (PMS) stars, post-AGB stars, and planetary nebulae (PNe) have the largest mid-infrared color excess and can be identified in the infrared catalog. Finally, we plot the L18W vs. (S 9W − L18W) color−magnitude diagram, using the AKARI data together with Hipparcos parallaxes. This diagram can be used to identify low-mass YSOs and AGB stars. We found that this diagram is comparable to the [24] vs. ([8.0] − [24]) diagram of Large Magellanic Cloud sources using the Spitzer Space Telescope data. Our understanding of Galactic objects will be used to interpret color-magnitude diagram of stellar populations in the nearby galaxies that Spitzer Space Telescope observed. Conclusions. Our study of the AKARI color−color and color−magnitude diagrams will be used to explore properties of unknown objects in the future. In addition, our analysis highlights a future key project to understand stellar evolution with a circumstellar envelope, once the forthcoming astronometrical data with GAIA are available.

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“…3.1.5) suggest at best a moderate 11.3 μm optical depth. Based on this information, LPV 28579 would not be considered an extreme carbon star (Speck et al 2009). …”

Section: Observationsmentioning

confidence: 99%

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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Silicon Carbide Absorption Features: Dust Formation in the Outflows of Extreme Carbon Stars

Cited by 71 publications

References 86 publications

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

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

AKARI's infrared view on nearby stars

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

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