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Carbon stars dominate the measured dust production in nearby metal-poor galaxies. The details of how they die will strongly influence both the dust ecosystem and the chemical evolution of galaxies in their quiescent phases. Recent spectroscopic observations with SOFIA, along with photometry from Spitzer and WISE, reveal a close link between the pulsational behavior of carbon stars and the quantity and nature of the dust they produce. If carbon stars are forming significant quantities of carbon-rich dust, then that dust is amorphous carbon, and they are pulsating as Miras, that is with both strong amplitudes and in the fundamental mode. This clue points us to the key moment in the evolution of star, when it enters that final phase of high mass loss and dust production that will strip its core bare and reveal a white dwarf within a planetary nebula., {"references":["Kraemer, K.E., Sloan, G.C., Keller, L.D., et al. 2019, ApJ, 887, 82","Sloan, G.C., Kraemer, K.E., McDonald, I., et al. 2016, 826, 44"]}

The Infrared Spectrograph (IRS) on the {\em Spitzer Space Telescope} observed nearly 800 point sources in the Large Magellanic Cloud (LMC), taking over 1,000 spectra. 197 of these targets were observed as part of the Sage-Spec Spitzer Legacy program; the remainder are from a variety of different calibration, guaranteed time and open time projects. We classify these point sources into types according to their infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership, and variability information, using a decision-tree classification method. We then refine the classification using supplementary information from the astrophysical literature. We find that our IRS sample is comprised substantially of YSO and H\,{\sc ii} regions, post-Main Sequence low-mass stars: (post-)AGB stars and planetary nebulae and massive stars including several rare evolutionary types. Two supernova remnants, a nova and several background galaxies were also observed. We use these classifications to improve our understanding of the stellar populations in the Large Magellanic Cloud, study the composition and characteristics of dust species in a variety of LMC objects, and to verify the photometric classification methods used by mid-IR surveys. We discover that some widely-used catalogues of objects contain considerable contamination and others are missing sources in our sample., Comment: Accepted for publication in MNRAS

The Optical Gravitational Lensing Experiment identified over 1,800 carbon-rich Mira and semi-regular variables in the Small Magellanic Cloud. Multi-epoch infrared photometry reveals that the semi-regulars and Miras follow different sequences in color-color space when using colors sensitive to molecular absorption bands. The dustiest Miras have the strongest pulsation amplitudes and longest periods. Efforts to determine bolometric magnitudes reveal possible systematic errors with published bolometric corrections., Comment: 5 pages, 7 figures, contributed talk at "Why Galaxies Care About AGB Stars III", Vienna, July 2014, http://www.univie.ac.at/galagb/ Revised arXiv submission includes editorial corrections by R. Wing

International audience; Massive stars shape galaxy evolution and nearby star formation through feedback mechanisms, yet many aspects of how they form and how they evolve towards the zero-age-main-sequence are still a mystery. The Cygnus-X region contains many massive young stellar objects (YSOs), and at only a distance of 1.7 kpc, this complex is ideal for studying massive star formation. We have observed a list of 25 sources with the IRS, basing our source selection on candidates previously identified in the Cygnus-X Spitzer Legacy Survey using the MIPS and IRAC instruments, the IRAM 1.2 mm survey of the region, and combining these with some older infrared surveys. Common features in the spectra include molecular hydrogen lines tracing shocks at the HII region boundary, polycyclic aromatic hydrocarbon emission in the HII region, and carbon dioxide ice absorption in the envelope. Silicate absorption is also present, allowing us to determine interstellar extinction to the sources. Neon and sulfur forbidden emission lines from ionized gas were also detected. Using the objects' spectral energy distributions, along with line flux ratios derived from the new IRS spectra, we fit models of YSOs to derive stellar mass, age, and temperature, as well as total luminosity of the system, envelope accretion rate of mass onto the stars, and other physical parameters. This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 0754568 and by the Smithsonian Institution.

We present the classification of 197 point sources observed with the Infrared Spectrograph in the SAGE-Spec Legacy program on the Spitzer Space Telescope. We introduce a decision-tree method of object classification based on infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership, and variability information, which is used to classify the SAGE-Spec sample of point sources. The decision tree has a broad application to mid-infrared spectroscopic surveys, where supporting photometry and variability information are available. We use these classifications to make deductions about the stellar populations of the Large Magellanic Cloud and the success of photometric classification methods. We find 90 asymptotic giant branch (AGB) stars, 29 young stellar objects, 23 post-AGB objects, 19 red supergiants, eight stellar photospheres, seven background galaxies, seven planetary nebulae, two HII regions and 12 other objects, seven of which remain unclassified., (43 pages, 21 figures, 4 tables including one large table out of order; to be published in MNRAS)

The Infrared Spectrograph (IRS) on the Spitzer Space Telescope observed nearly 800 point sources in the Large Magellanic Cloud (LMC), taking over 1000 spectra. 197 of these targets were observed as part of the SAGE-Spec Spitzer Legacy program; the remainder are from a variety of different calibration, guaranteed time and open time projects. We classify these point sources into types according to their infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership and variability information, using a decision-tree classification method. We then refine the classification using supplementary information from the astrophysical literature. We find that our IRS sample is comprised substantially of YSO and H ii regions, post-main-sequence low-mass stars: (post-)asymptotic giant branch stars and planetary nebulae and massive stars including several rare evolutionary types. Two supernova remnants, a nova and several background galaxies were also observed. We use these classifications to improve our understanding of the stellar populations in the LMC, study the composition and characteristics of dust species in a variety of LMC objects, and to verify the photometric classification methods used by mid-IR surveys. We discover that some widely used catalogues of objects contain considerable contamination and others are missing sources in our sample.