Spitzer spectroscopy of carbon stars in the Small Magellanic Cloud

Abstract

We present Spitzer Space telescope spectroscopic observations of 14 carbon-rich AGB stars in the Small Magellanic Cloud. SiC dust is seen in most of the carbon-rich stars but it is weak compared to LMC stars. The SiC feature is strong only for stars with significant dust excess, opposite to what is observed for Galactic stars. We argue that in the SMC, SiC forms at lower temperature than graphite dust, whereas the reverse situation occurs in the Galaxy where SiC condenses at higher temperatures and forms first. Dust input into the interstellar medium by AGB stars consists mostly of carbonaceous dust, with little SiC or silicate dust. Only the two coolest stars show a 30-micron band due to MgS dust. We suggest that this is due to the fact that, in the SMC, mass-losing AGB stars generally have low circumstellar (dust) optical depth and therefore effective heating of dust by the central star does not allow temperatures below the 650 K necessary for MgS to exist as a solid. Gas phase C${}_2$H${}_2$ bands are stronger in the SMC than in the LMC or Galaxy. This is attributed to an increasing C/O ratio at low metallicity. We present a colour-colour diagram based on Spitzer IRAC and MIPS colours to discriminate between O- and C-rich stars. We show that AGB stars in the SMC become carbon stars early in the thermal-pulsing AGB evolution, and remain optically visible for $\sim 6\times 10^5$ yr. For the LMC, this lifetime is $\sim 3\times 10^5$ yr. The superwind phase traced with Spitzer lasts for $\sim 10^4$ yr. Spitzer spectra of a K supergiant and a compact HII region are also given.

17 pages, 17 figures

References in corpus (24)

• The Spitzer Space Telescope Mission
• The Infrared Spectrograph on the Spitzer Space Telescope
• A large stellar evolution database for population synthesis studies. II. Stellar models and isochrones for an alpha-enhanced metal distribution
• Improved HCN/HNC linelist, model atmospheres and synthetic spectra for WZ Cas
• Bump Cepheids in the Magellanic Clouds: Metallicities, the Distances to the LMC and SMC, and the Pulsation-Evolution Mass Discrepancy
• Too little radiation pressure on dust in the winds of oxygen-rich AGB stars
• Spitzer SAGE survey of the Large Magellanic Cloud II: Evolved Stars and Infrared Color Magnitude Diagrams
• A step toward the calibration of the RGB Tip as a Standard Candle
• Near-Infrared Photometry of Carbon Stars
• The carrier of the "30" micron emission feature in evolved stars. A simple model using magnesium sulfide
• A Spitzer mid-infrared spectral survey of mass-losing carbon stars in the Large Magellanic Cloud
• AGB stars in the Magellanic Clouds. I. The C/M ratio
• Mid-infrared spectroscopy of carbon stars in the Small Magellanic Cloud
• MSX, 2MASS, and the LMC: A Combined Near and Mid Infrared View
• Dust-enshrouded giants in clusters in the Magellanic Clouds
• Spitzer observations of acetylene bands in carbon-rich AGB stars in the Large Magellanic Cloud
• Low-mass supernovae in the early Galactic halo: source of the double r/s-process enriched halo stars?
• A Spitzer IRS Spectral Atlas of Luminous 8 micron Sources in the Large Magellanic Cloud
• Three-micron spectra of AGB stars and supergiants in nearby galaxies
• Fe emission and ionized excess absorption in the luminous quasar 3C109 with XMM-Newton
• Long Period Variables detected by ISO in the SMC
• The effect of stellar evolution on SiC dust grain sizes
• Very Large Telescope three micron spectra of dust-enshrouded red giants in the Large Magellanic Cloud
• Catalogue of candidate emission-line objects in the Small Magellanic Cloud

Cited by in corpus (54)

• Evolution of asymptotic giant branch stars II. Optical to far-infrared isochrones with improved TP-AGB models
• Evolution, nucleosynthesis and yields of low mass AGB stars at different metallicities (II): the FRUITY database
• The global gas and dust budget of the Large Magellanic Cloud: AGB stars and supernovae, and the impact on the ISM evolution
• Production of dust by massive stars at high redshift
• Luminosities and mass-loss rates of SMC and LMC AGB stars and Red Supergiants
• Surveying the Agents of Galaxy Evolution in the Tidally-Stripped, Low Metallicity Small Magellanic Cloud (SAGE-SMC) II. Cool Evolved Stars
• The nature of star formation in distant ultraluminous infrared galaxies selected in a remarkably narrow redshift range
• The Dust Budget of the SMC: Are AGB Stars the Primary Dust Source at Low Metallicity?
• The SAGE-Spec Spitzer Legacy program: The life-cycle of dust and gas in the Large Magellanic Cloud. Point source classification I
• The Magellanic zoo: Mid-infrared Spitzer spectroscopy of evolved stars and circumstellar dust in the Magellanic Clouds
• Optically visible post-AGB/RGB stars and young stellar objects in the Small Magellanic Cloud: candidate selection, spectral energy distributions and spectroscopic examination
• Carbon-rich dust past the asymptotic giant branch: aliphatics, aromatics, and fullerenes in the Magellanic Clouds
• Molecules and dust production in the Magellanic Clouds
• Unusual Dust Emission from Planetary Nebulae in the Magellanic Clouds
• Luminosities and mass-loss rates of Local Group AGB stars and Red Supergiants
• An Infrared Census of DUST in Nearby Galaxies with Spitzer (DUSTiNGS), II. Discovery of Metal-poor Dusty AGB Stars
• Silicon carbide absorption features: dust formation in the outflows of extreme carbon stars
• Spitzer Infrared Spectrographic point source classification in the Small Magellanic Cloud
• Intense Mass Loss from C-rich AGB Stars at low Metallicity?
• Optical properties of silicon carbide for astrophysical applications I. New laboratory infrared reflectance spectra and optical constants
• Effects of Metallicity on the Chemical Composition of Carbon Stars
• Discovery of Extreme Carbon Stars in the Large Magellanic Cloud
• The trigger of the AGB superwind: the importance of carbon
• Spitzer Space Telescope spectral observations of AGB stars in the Fornax dwarf spheroidal galaxy
• The infrared spectral properties of Magellanic carbon stars
• The mass-loss, expansion velocities and dust production rates of carbon stars in the Magellanic Clouds
• Optical constants of silicon carbide for astrophysical applications. II. Extending optical functions from IR to UV using single-crystal absorption spectra
• Condensation of MgS in outflows from carbon stars
• An Infrared Census of DUST in Nearby Galaxies with Spitzer (DUSTiNGS). IV. Discovery of High-Redshift AGB Analogs
• Carbon star wind models at solar and sub-solar metallicities: a comparative study. I. Mass loss and the properties of dust-driven winds
• The First Fluorine Abundance Determinations in Extragalactic AGB Carbon Stars
• The Spitzer Spectroscopic Survey of S-type Stars
• The LMC's Top 250: Classification of the Most Luminous Compact 8 micron Sources in the Large Magellanic Cloud
• Synthetic photometry for carbon-rich giants. III. Tracing the sequence of mass-losing galactic C-type Miras
• On the nature of the most obscured C-rich AGB stars in the Magellanic Clouds
• Dust mass-loss rates from AGB stars in the Fornax and Sagittarius dwarf Spheroidal galaxies
• The mass-loss return from evolved stars to the Large Magellanic Cloud III. Dust properties for carbon-rich asymptotic giant branch stars
• Observations of the Planetary Nebula SMP LMC 058 with the JWST MIRI Medium Resolution Spectrometer
• The VLTI/MIDI view on the inner mass loss of evolved stars from the Herschel MESS sample
• Carbon enrichment of the evolved stars in the Sagittarius dwarf spheroidal
• The low wind expansion velocity of metal-poor carbon stars in the Halo and the Sagittarius stream
• Metal-rich carbon stars in the Sagittarius Dwarf Spheroidal galaxy
• Characterizing the Population of Bright Infrared Sources in the Small Magellanic Cloud
• A dearth of OH/IR stars in the Small Magellanic Cloud
• Classification Study of WISE Infrared Sources: Identification of Candidate Asymptotic Giant Branch Stars
• The chemistry of extragalactic carbon stars
• Stellar Pulsation and the Production of Dust and Molecules in Galactic Carbon Stars
• The dust and gas content of carbon stars toward the Galactic Halo
• The 21 micron and 30 micron circumstellar dust features in evolved C-rich objects
• Stellar dust production and composition in the Magellanic Clouds
• Post-AGB nebular studies
• Molecular processes from the AGB to the PN stage
• Observational studies of mass loss from AGB stars
• Revealing infrared populations of nearby galaxies using the Spitzer Space Telescope