We have used the Infrared Spectrograph (IRS) on the Spitzer Space Telescope to observe stars in the Small Magellanic Cloud (SMC) selected from the Point Source Catalog of the Midcourse Space Experiment (MSX). We concentrate on the dust properties of the oxygen-rich evolved stars. The dust composition has smaller contributions from alumina compared to the Galaxy. This difference may arise from the lower metallicity in the SMC, but it could be a selection effect, as the SMC sample includes more stars that are brighter and thus more massive. The distribution of the SMC stars along the silicate sequence looks more like the Galactic sample of red supergiants than asymptotic giant branch stars (AGBs). While many of the SMC stars are definitively on the AGB, several also show evidence of hot bottom burning. Three of the supergiants show PAH emission at 11.3 mu m. Two other sources show mixed chemistry, with both carbon-rich and oxygen-rich spectral features. One, MSX SMC 134, may be the first confirmed silicate/carbon star in the SMC. The other, MSX SMC 049, is a candidate post-AGB star. MSX SMC 145, previously considered a candidate OH/IR star, is actually an AGB star with a background galaxy at z. =. 0.16 along the same line of sight. We consider the overall characteristics of all the MSX sources, the most infrared-bright objects in the SMC, in light of the higher sensitivity and resolution of Spitzer, and compare them with the object types expected from the original selection criteria. This population represents what will be seen in more distant galaxies by the upcoming James Webb Space Telescope (JWST). Color-color diagrams generated from the IRS spectra and the mid-infrared filters on JWST show how one can separate evolved stars from young stellar objects (YSOs) and distinguish among different classes of YSOs.

We present observations of newly discovered 24 micron circumstellar structures detected with the Multiband Imaging Photometer for Spitzer (MIPS) around three evolved stars in the Cygnus-X star forming region. One of the objects, BD+43 3710, has a bipolar nebula, possibly due to an outflow or a torus of material. A second, HBHA 4202-22, a Wolf-Rayet candidate, shows a circular shell of 24 micron emission suggestive of either a limb-brightened shell or disk seen face-on. No diffuse emission was detected around either of these two objects in the Spitzer 3.6-8 micron Infrared Array Camera (IRAC) bands. The third object is the luminous blue variable candidate G79.29+0.46. We resolved the previously known inner ring in all four IRAC bands. The 24 micron emission from the inner ring extends ~1.2 arcmin beyond the shorter wavelength emission, well beyond what can be attributed to the difference in resolutions between MIPS and IRAC. Additionally, we have discovered an outer ring of 24 micron emission, possibly due to an earlier episode of mass loss. For the two shell stars, we present the results of radiative transfer models, constraining the stellar and dust shell parameters. The shells are composed of amorphous carbon grains, plus polycyclic aromatic hydrocarbons in the case of G79.29+0.46. Both G79.29+0.46 and HBHA 4202-22 lie behind the main Cygnus-X cloud. Although G79.29+0.46 may simply be on the far side of the cloud, HBHA 4202-22 is unrelated to the Cygnus-X star formation region.

In previous work we have demonstrated the ability of the algorithm developed by Magain, Courbin, and Sohy (MCS, ApJ 2008 (1)) to resolve point sources and filamentary extended sources that have positions closer than the traditional 1.22λ/D diffraction limit of an optical system. The efficacy of the technique depends on a number of factors, including the signal-to-noise-ratio (SNR), the 'blackness' of the overall image, knowledge of the original system point response function, etc. In this paper we explore the effect of these parameters on the results of the algorithm to determine the point at which the positions and amplitudes of sources reconstructed using the MCS algorithm become unreliable.

Millimeter and mid-infrared observations have been made of the dense clumps of dust and gas and of young stellar objects (YSOs) associated with the bright, compact submillimeter source G79.3+0.3 P1 in the relatively nearby MSX infrared-dark cloud G79.3+0.3. The Gemini mid-infrared observations reported here indicate the presence of three YSOs within the cloud. BIMA 3 mm continuum observations show that the brightest of the YSOs is likely to be a Herbig Ae/Be star. High-angular-resolution molecular-line observations suggest that a wind from this star may be triggering collapse in the adjacent molecular cloud. The submillimeter source G79.3+0.3 P1 itself does not contain infrared sources and may represent an earlier stage of star formation. Subject headings: stars: formation — stars: pre-main sequence — ISM: clouds — dust, extinction

Super-resolution of images, particularly the separation of point sources within the Rayleigh limit of an optical system, has been empirically and theoretically proved. Issues remain, however, around the ability to perform true super-resolution of structure within extended objects. Puschmann and Kneer (1) conclude that "super-resolution cannot be achieved for extended objects which are not band limited." They do find that sharpening by contrast enhancement was possible in extended images. Examination of the theoretical work of Donoho (2) suggests the possibility of resolving linear structures under certain conditions. The resolution enhancement is only possible in the direction normal to the feature's length vector. I discuss here the required conditions for super-resolution of these objects and propose a modification of the Magain, Courbin and Sohy (MCS) method (3) that allows super-resolved reconstruction of linear features.

We have produced an atlas of Spitzer Infrared Spectrograph (IRS) spectra of mass-losing, evolved stars in the Large Magellanic Cloud. These stars were selected to have high mass-loss rates and so contribute significantly to the return of processed materials to the ISM. Our high-quality spectra enable the determination of the chemistry of the circumstellar envelope from the mid-IR spectral features and continuum. We have classified the spectral types of the stars and show that the spectral types separate clearly in infrared color-color diagrams constructed from 2MASS data and synthetic IRAC/MIPS fluxes derived from our IRS spectra. We present diagnostics to identify and classify evolved stars in nearby galaxies with high confidence levels using Spitzer and 2MASS photometry. Comparison of the spectral classes determined using IRS data with the IR types assigned based on NIR colors also revealed a significant number of mis-classifications and enabled us to refine the NIR color criteria resulting in more accurate NIR color classifications of dust-enshrouded objects.

To ascertain the nature of the brightest compact mid-infrared (mid-IR) sources in the Large Magellanic Cloud (LMC), we have applied an updated version of Buchanan et al.'s Two Micron All Sky Survey (2MASS)-Midcourse Space Experiment (MSX) color classification system, which is based on the results of Spitzer Space Telescope spectroscopy, to a mid-IR (8 mu m) flux-limited sample of 250 LMC objects for which 2MASS and MSX photometry is available. The resulting 2MASS-MSX ("JHK8") color-based classifications of these sources, which constitute the most mid-IR-luminous objects in the LMC, were augmented, cross-checked, and corrected where necessary via a variety of independent means, such that only 46 sources retain tentative classifications and only 10 sources cannot be classified at all. The sample is found to consist primarily of carbon-rich asymptotic giant branch (AGB) stars (35%), red supergiants (RSGs) (18%), and compact HII regions (32%), with additional, small populations of oxygen-rich AGB stars (similar to 5%), dusty, early-type emission-line stars (similar to 3%), and foreground, O-rich AGB stars in the Milky Way (similar to 3%). The very large ratio of C-rich to O-rich objects among the luminous and heavily dust-enshrouded AGB stars in our LMC IR source sample is consistent with the hypothesis that carbon stars form easily in lower metallicity environments. We demonstrate that very luminous C-rich and O-rich AGB stars and RSGs, identified here primarily on the basis of their JHK8 colors, also appear as distinct clusters in Spitzer Infrared Array Camera (IRAC)/Multiband Imaging Photometer for Spitzer (MIPS) color-color diagrams. Thus, in principle, the infrared spectrograph (IRS)-based IR photometric classification techniques applied here to the LMC can be applied to any external galaxy whose most luminous IR point sources are detectable and resolvable by 2MASS and Spitzer.

Magain, Courbin, and Sohy (MCS, 1998) [1] proposed a two-channel (separable point source plus extended background) method for astronomical image deconvolution. Unlike the two-channel Richardson-Lucy algorithm [2], [3], the MCS method does not require prior knowledge of point source amplitudes and positions. MCS claim that their method produces accurate astrometry and photometry in crowded fields and in the presence of variable backgrounds. This paper compares Midcourse Space Experiment (MSX) 8 μm Galactic plane images [4] deconvolved via the MCS method to Spitzer Space Telescope Glimpse Survey [5] 8 μm images of the same fields. The improved sampling and final image point spread function (PSF) for the deconvolved MSX image is chosen to match the Spitzer observation. In the parlance of MCS, this determines the light distribution from an 85 cm telescope (Spitzer) by deconvolving data taken with a 33 cm space telescope (MSX). Results are presented for varying degrees of background complexity and examine the limitations of the MCS method for use on infrared data in regions of high source density and bright complex backgrounds. 1. DECONVOLUTION WITH CORRECT SAMPLING Starck, Pantin, and Murtagh [6] in their 2002 review of deconvolution methods define super resolution as “recovering object spatial frequency information outside the spatial bandwidth of the image formation system.” Their review of the theoretical literature admits that true super-resolution is possible if the object to be resolved is nearly black – that is, most pixels in the data have zero values and the non-zero elements are well-spaced [7]. This is certainly true in many astronomical images, though it leads to difficulties in areas with structured backgrounds. While true super-resolution is not possible for extended objects that are not band-limited, the super-resolution techniques will provide image sharpening and contrast enhancement. [8] We may write the observed distribution of light from a source, d(x), as measured by a given instrument, as ) ( ) ( * ) ( ) ( x x x x n f p d + = where p(x) is the total system point response function (PRF), f(x) is the true light distribution, and n(x) is the noise inherent in the measured data. Deconvolution is the effort to remove the effect of the point response function, and our recovery of the higher spatial resolution image consistent with the true light distribution yields a superresolution image. Typical deconvolution algorithms seek to minimize the function

The IRAS focal plane contained a slitless spectrometer, the Low Resolution Spectrometer (LRS). Several regions in the Rosette nebula HII region are nearly unresolved in the in-scan direction, permitting extraction of LRS spectra. The spectral coverage of the LRS includes some of the unidentified infrared (UIR) bands, associated with PAHs by some authors. The extracted spectra include three clearly defined regimes: low density ionized material, of order 30 cm−3, non-ionized material of the same density, and denser material with equivalent luminosity of an embedded early B star. Only the last exhibit UIR emission bands in our data.

We present an atlas of Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of highly luminous, compact mid-infrared sources in the Large Magellanic Cloud. Sources were selected on the basis of infrared colors and 8 micron (MSX) 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 HII 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 ~1.0E4 L_sun) have C-rich envelopes, while the O-rich objects are predominantly luminous RSGs with L_IR ~ 1.0E5 L_sun. We determine mean bolometric corrections to the stellar K-band flux densities and find that for carbon stars, the bolometric corrections depend on the infrared color, whereas for RSGs, the bolometric correction is independent of IR color. Our results reveal that objects previously classified as PNe on the basis of IR colors are in fact compact HII regions with very red IRS spectra that include strong atomic recombination lines and PAH emission features. We demonstrate that the IRS spectral classes in our sample separate clearly in infrared color-color diagrams that use combinations of 2MASS data and synthetic IRAC/MIPS 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 HII regions in nearby galaxies using Spitzer and near-infrared photometry.

We present an atlas of Spitzer Space Telescope Infrared Spectrograph (IRS ) spectra of highly luminous, compact mid-infrared sources in the Large Magellanic Cloud. Sources were selected on the basis of infrared colors and 8 μm (MSX ) fluxes indicative of highly evolved, intermediateto 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 ∼ 10 L⊙) have C-rich envelopes, while the O-rich objects are predominantly luminous RSGs with LIR ∼ 10 5 L⊙. For both classes of evolved star (C-rich AGB stars and RSGs), we use the nearto mid-infrared spectral energy distributions to determine mean bolometric corrections to the stellar K-band flux densities. For carbon stars, the bolometric corrections depend on the infrared color, whereas for RSGs, the bolometric correction is independent of IR color. Our results reveal that objects previously classified as PNe on the basis of IR colors are in fact compact H II regions with Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester NY 14623. Email: clbsps,jhk@cis.rit.edu Department of Physics & Astronomy, University of Rochester, Bausch & Lomb Hall, P.O. Box 270171, Rochester, NY 14627-0171 Dept. of Physics and Astronomy, Valparaiso University, Valparaiso, IN 46383 NASA/JPL, 4800 Oak Grove Drive, Pasadena, CA 91109 Air Force Research Laboratory; OASD (NII) Space Programs, Suite 7000, 1851 S. Bell St., Arlington, VA 22202 Valdosta University, 1500 N Patterson Street, Valdosta, GA 31698

We have observed a sample of 36 objects in the Small Magellanic Cloud (SMC) with the Infrared Spectrometer on the Spitzer Space Telescope. Nineteen of these sources are carbon stars. An examination of the near- and mid-infrared photometry shows that the carbon-rich and oxygen-rich dust sources follow two easily separated sequences. A comparison of the spectra of the 19 carbon stars in the SMC to spectra from the Infrared Space Observatory (ISO) of carbon stars in the Galaxy reveals significant differences. The absorption bands at 7.5 um and 13.7 um due to C2H2 are stronger in the SMC sample, and the SiC dust emission feature at 11.3 um is weaker. Our measurements of the MgS dust emission feature at 26-30 um are less conclusive, but this feature appears to be weaker in the SMC sample as well. All of these results are consistent with the lower metallicity in the SMC. The lower abundance of SiC grains in the SMC may result in less efficient carbon-rich dust production, which could explain the excess C2H2 gas seen in the spectra. The sources in the SMC with the strongest SiC dust emission tend to have redder infrared colors than the other sources in the sample, which implies more amorphous carbon, and they also tend to show stronger MgS dust emission. The weakest SiC emission features tend to be shifted to the blue; these spectra may arise from low-density shells with large SiC grains.