ASpitzer Space TelescopeInfrared Spectrograph Spectral Atlas of Luminous 8 μm Sources in the Large Magellanic Cloud

Abstract

We present an atlas of Spitzer Space Telescope Infrared Spectrograph ( IRS) spectra of highly luminous, compact, mid-IR sources in the Large Magellanic Cloud. Sources were selected on the basis of IR colors and 8 m (Midcourse Space Experiment) fluxes indicative of highly evolved, intermediate-to-high-mass stars with current or recent mass loss at large rates. We determine the chemistry of the circumstellar envelope from the mid-IR continuum and spectral features and classify the spectral types of the stars. In the sample of 60 sources, we find 21 red supergiants (RSGs), 16 C-rich asymptotic giant branch (AGB) stars, 11 H ii regions, 4 likely O-rich AGB stars, 4 Galactic O-rich AGB stars, 2 OH /IR stars, and 2 B[e] supergiants with peculiar IR spectra. We find that the overwhelming majority of the sample AGB stars (with typical IR luminosities of $10 4 L ) have C-rich envelopes, while the O-rich objects are predominantly luminous RSGs with L IR $ 10 5 L . For both classes of evolved star (C-rich AGB stars and RSGs), we use the near-to-mid-IR spectral energy distributions to determine mean bolometric corrections to the stellar K-band flux densities. For carbon stars, the bolometric corrections depend on the IR color, whereas for RSGs, the bolometric correction is independent of IR color. Our results reveal that objects previously classified as planetary nebulae on the basis of IR colors are, in fact, compact H ii regions with very red IRS spectra that include strong atomic recombination lines and polycyclic aromatic hydrocarbon emission features. We demonstrate that the IRS spectral classes in our sample separate clearly in IR color-color diagrams that use combinations of Two Micron All Sky Survey data and synthetic Spitzer Infrared Array Camera and Multiband Imaging Photometer for Spitzer fluxes derived from the IRS spectra. On this basis we suggest diagnostics to identify and classify, with high confidence levels, IR-luminous evolved stars and compact H ii regions in nearby galaxies using Spitzer and near-IR photometry.

Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73

“…However, the investigations of Oksala et al (2013) revealed that the chemical composition of the ejecta, in particular the enrichment in 13 C, better agrees with a pre-RSG scenario. This is also the case for LHA 120-S 73, although it shows the strongest enrichment in 13 C. Additional support for a less evolved state is provided by the spectral energy distribution of the dust, which is clearly distinct from those of (post-)RSGs (see, e.g., Buchanan et al 2006). Furthermore, LHA 120-S 73 is a point source in Spitzer IRAC/MIPS images without any diffuse nebulosity (Kastner et al 2010).…”

Luminosities and mass-loss rates of Local Group AGB stars and red supergiants

“…Only the EROs from Program 40650 (Gruendl et al 2008) are affected. Sloan et al (2008) Evolved stars in the LMC and SMC 1094 F. Kemper AGB evolution in the LMC (and Galaxy) 3277 M. P. Egan Sloan et al (2006), Kraemer et al (2016) Infrared-bright sample in the SMC 3426 J. H. Kastner Buchanan et al (2006) Infrared-bright sample in the LMC 3505 P. R. Wood Zijlstra et al (2006), Lagadec et al (2007) AGB stars in the LMC and SMC 3591 F. Kemper Leisenring et al (2008) Evolved O-rich stars in the LMC 30155 J. R. Houck…”

New Magellanic Cloud R Coronae Borealis and DY Persei type stars from the EROS-2 database: the connection between RCBs, DYPers, and ordinary carbon stars

“…They were all obtained in 2008; individual epochs are listed in Table 2. Alcock et al 2001 and 5 in the SMC 2 , Tisserand et al 2004) as well as 5 RCB candidates selected either from their optical spectra (Morgan et al 2003) 3 or their mid-infrared featureless spectra (Kraemer et al 2005;Buchanan et al 2006). The EROS-2 light curves of all these objects, if catalogued, are available at the following URL: http://eros.in2p3.fr/ Variables/RCB/RCB-LMC.html…”