Spitzer observations of acetylene bands in carbon-rich AGB stars in the Large Magellanic Cloud

Abstract

We investigate the molecular bands in carbon-rich AGB stars in the Large Magellanic Cloud (LMC), using the InfraRed Spectrograph (IRS) on board the Spitzer Space Telescope (SST) over the 5--38 micron range. All 26 low-resolution spectra show acetylene (C2H2) bands at 7 and 14 micron. The hydrogen cyanide (HCN) bands at these wavelengths are very weak or absent. This is consistent with low nitrogen abundances in the LMC. The observed 14 micron C2H2 band is reasonably reproduced by an excitation temperature of 500 K. There is no clear dilution of the 14 micron band by circumstellar dust emission. This 14 micron band originates from molecular gas in the circumstellar envelope in these high mass-loss rate stars, in agreement with previous findings for Galactic stars. The C2H2,column density, derived from the 13.7 micron band, shows a gas mass-loss rate in the range 3x10^-6 to 5x10^{-5} Msun yr-1. This is comparable with the total mass-loss rate of these stars estimated from the spectral energy distribution. Additionally, we compare the line strengths of the 13.7 micron C2H2 band of our LMC sample with those of a Galactic sample. Despite the low metallicity of the LMC, there is no clear difference in the C2H2 abundance among LMC and Galactic stars. This reflects the effect of the 3rd dredge-up bringing self-produced carbon to the surface, leading to high C/O ratios at low metallicity.

arXiv comment7 pages, accepted by MNRAS

References in corpus (7)

• The Infrared Spectrograph on the Spitzer Space Telescope
• The carrier of the "30" micron emission feature in evolved stars. A simple model using magnesium sulfide
• Classification of 2.4-45.2 Micron Spectra from the ISO Short Wavelength Spectrometer
• Chemical Abundances in Twelve Red Giants of the Large Magellanic Cloud from High-Resolution Infrared Spectroscopy
• Three-micron spectra of AGB stars and supergiants in nearby galaxies
• The time variation in infrared water-vapour bands in Mira variables
• Very Large Telescope three micron spectra of dust-enshrouded red giants in the Large Magellanic Cloud

Cited by in corpus (39)

• The global gas and dust budget of the Large Magellanic Cloud: AGB stars and supernovae, and the impact on the ISM evolution
• Luminosities and mass-loss rates of SMC and LMC AGB stars and Red Supergiants
• ExoMol molecular line lists -- XXXVII: spectra of acetylene
• The Brightest Galaxies in the Dark Ages: Galaxies' Dust Continuum Emission During the Reionization Era
• 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
• Molecules and dust production in the Magellanic Clouds
• Spitzer Space Telescope spectra of post-AGB stars in the Large Magellanic Cloud ---polycyclic aromatic hydrocarbons at low metallicities
• Physical Characterization of an Unlensed Dusty Star-Forming Galaxy at $z=5.85$
• Spitzer spectroscopy of carbon stars in the Small Magellanic Cloud
• Luminosities and mass-loss rates of Local Group AGB stars and Red Supergiants
• Carbonaceous molecules in the oxygen-rich circumstellar environment of binary post-AGB stars: C_{60} fullerenes and polycyclic aromatic hydrocarbons
• The Spitzer-IRS spectrum of SMP LMC 11
• A Spitzer Space Telescope far-infrared spectral atlas of compact sources in the Magellanic Clouds. I. The Large Magellanic Cloud
• Effects of Metallicity on the Chemical Composition of Carbon Stars
• The trigger of the AGB superwind: the importance of carbon
• Spitzer Space Telescope spectral observations of AGB stars in the Fornax dwarf spheroidal galaxy
• AGB stars of the intermediate-age LMC cluster NGC 1846 II. Dredge up along the AGB
• The infrared spectral properties of Magellanic carbon stars
• The circumbinary disc around the J-type C-star IRAS 18006-3213
• Carbon star wind models at solar and sub-solar metallicities: a comparative study. I. Mass loss and the properties of dust-driven winds
• The Role of Acetylene in the Chemical Evolution of Carbon Complexity
• The LMC's Top 250: Classification of the Most Luminous Compact 8 micron Sources in the Large Magellanic Cloud
• Probing the dusty stellar populations of the Local Volume Galaxies with JWST/MIRI
• The mass-loss return from evolved stars to the Large Magellanic Cloud III. Dust properties for carbon-rich asymptotic giant branch stars
• Understanding the evolution and dust formation of carbon stars in the LMC with a look at the JWST
• Metal-rich carbon stars in the Sagittarius Dwarf Spheroidal galaxy
• AKARI's infrared view on nearby stars : Using AKARI Infrared Camera All-Sky Survey, 2MASS, and Hipparcos catalog
• AKARI's infrared view on nearby stars : Using AKARI Infrared Camera All-Sky Survey, 2MASS, and Hipparcos catalog
• A multiwavelength analysis of planetary nebulae in the Large Magellanic Cloud
• The chemistry of extragalactic carbon stars
• The dust and gas content of carbon stars toward the Galactic Halo
• Stellar Pulsation and the Production of Dust and Molecules in Galactic Carbon Stars
• Oxygen-rich dust production in IC 10
• Abundant hydrocarbons in a buried galactic nucleus with signs of carbonaceous grain and polycyclic aromatic hydrocarbon processing
• Carbon stars in the X-Shooter Spectral Library: II. Comparison with models
• Spitzer observations of molecules and dust in evolved stars in nearby galaxies
• Dust Production around Carbon-Rich Stars: The Role of Metallicity
• Observational studies of mass loss from AGB stars