Stellar Pulsation and the Production of Dust and Molecules in Galactic Carbon Stars

Abstract

New infrared spectra of 33 Galactic carbon stars from FORCAST on SOFIA reveal strong connections between stellar pulsations and the dust and molecular chemistry in their circumstellar shells. A sharp boundary in overall dust content, which predominantly measures the amount of amorphous carbon, separates the semi-regular and Mira variables, with the semi-regulars showing little dust in their spectra and the Miras showing more. In semi-regulars, the contribution from SiC dust increases rapidly as the overall dust content grows, but in Miras, the SiC dust feature grows weaker as more dust is added. A similar dichotomy is found with the absorption band from CS at $\sim$7.3 $\mu$m, which is generally limited to semi-regular variables. Observationally, these differences make it straightforward to distinguish semi-regular and Mira variables spectroscopically without the need for long-term photometric observations or knowledge of their distances. The rapid onset of strong SiC emission in Galactic carbon stars in semi-regulars variables points to a different dust-condensation process before strong pulsations take over. The break in the production of amorphous carbon between semi-regulars and Miras seen in the Galactic sample is also evident in Magellanic carbon stars, linking strong pulsations in carbon stars to the strong mass-loss rates which will end their lives as stars across a wide range of metallicities.

22 pages, 13 figures, accepted by ApJ

References in corpus (17)

• Early Science with SOFIA, the Stratospheric Observatory for Infrared Astronomy
• Near-Infrared Photometry of Carbon Stars
• The VMC Survey - XIV. First results on the look-back time star-formation rate tomography of the Small Magellanic Cloud
• A Spitzer mid-infrared spectral survey of mass-losing carbon stars in the Large Magellanic Cloud
• The Magellanic zoo: Mid-infrared Spitzer spectroscopy of evolved stars and circumstellar dust in the Magellanic Clouds
• Spitzer spectroscopy of carbon stars in the Small Magellanic Cloud
• Luminosities and mass-loss rates of Local Group AGB stars and Red Supergiants
• Spitzer observations of acetylene bands in carbon-rich AGB stars in the Large Magellanic Cloud
• Synthetic photometry for carbon-rich giants. IV. An extensive grid of dynamic atmosphere and wind models
• Effects of Metallicity on the Chemical Composition of Carbon Stars
• The trigger of the AGB superwind: the importance of carbon
• The mass-loss, expansion velocities and dust production rates of carbon stars in the Magellanic Clouds
• Carbon star wind models at solar and sub-solar metallicities: a comparative study. I. Mass loss and the properties of dust-driven winds
• The onset of the AGB wind tied to a transition between sequences in the period-luminosity diagram
• AGB dust and gas ejecta in extremely metal-poor environments
• Interplay between pulsation, mass loss, and third dredge-up: More about Miras with and without technetium
• Circumstellar CO J = 3-2 detected around the evolving metal-poor ([Fe/H] ~ -1.15 dex) AGB star RU Vulpeculae

Cited by in corpus (7)

• The OGLE Collection of Variable Stars. Nearly 66,000 Mira stars in the Milky Way
• Carbon stars as standard candles: I. The luminosity function of carbon stars in the Magellanic Clouds
• Multiwavelength properties of Miras
• Where have all the interstellar silicon carbides gone?
• Charting Circumstellar Chemistry of Carbon-rich AGB Stars: I. ALMA 3 mm spectral surveys
• The Dustiest Galactic S Stars: Mid-Infrared Spectra from SOFIA/FORCAST
• Temporal Changes in the Infrared Spectra of Magellanic Carbon Stars