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We present complicated dust structures within multiple regions of the candidate supernova remnant (SNR) the `Tornado' (G357.7-0.1) using observations with Spitzer and Herschel. We use Point Process Mapping, PPMAP, to investigate the distribution of dust in the Tornado at a resolution of 8", compared to the native telescope beams of 5-36". We find complex dust structures at multiple temperatures within both the head and the tail of the Tornado, ranging from 15 to 60K. Cool dust in the head forms a shell, with some overlap with the radio emission, which envelopes warm dust at the X-ray peak. Akin to the terrestrial sandy whirlwinds known as `Dust Devils', we find a large mass of dust contained within the Tornado. We derive a total dust mass for the Tornado head of 16.7 solar masses, assuming a dust absorption coefficient of kappa_300 =0.56m^2 kg^1, which can be explained by interstellar material swept up by a SNR expanding in a dense region. The X-ray, infra-red, and radio emission from the Tornado head indicate that this is a SNR. The origin of the tail is more unclear, although we propose that there is an X-ray binary embedded in the SNR, the outflow from which drives into the SNR shell. This interaction forms the helical tail structure in a similar manner to that of the SNR W50 and microquasar SS433., 16 pages, 10 figures + 3 appendix figures. Accepted to be published in MNRAS

Optical and infrared polarization mapping and recent Planck observations of the filamentary cloud L1495 in Taurus show that the large-scale magnetic field is approximately perpendicular to the long axis of the cloud. We use the HAWC+ polarimeter on SOFIA to probe the complex magnetic field in the B211 part of the cloud. Our results reveal a dispersion of polarization angles of $36^\circ$, about five times that measured on a larger scale by Planck. Applying the Davis-Chandrasekhar-Fermi (DCF) method with velocity information obtained from IRAM 30m C$^{18}$O(1-0) observations, we find two distinct sub-regions with magnetic field strengths differing by more than a factor 3. The quieter sub-region is magnetically critical and sub-Alfv\'enic; the field is comparable to the average field measured in molecular clumps based on Zeeman observations. The more chaotic, super-Alfv\'enic sub-region shows at least three velocity components, indicating interaction among multiple substructures. Its field is much less than the average Zeeman field in molecular clumps, suggesting that the DCF value of the field there may be an underestimate. Numerical simulation of filamentary cloud formation shows that filamentary substructures can strongly perturb the magnetic field. DCF and true field values in the simulation are compared. Pre-stellar cores are observed in B211 and are seen in our simulation. The appendices give a derivation of the standard DCF method that allows for a dispersion in polarization angles that is not small, present an alternate derivation of the structure function version of the DCF method, and treat fragmentation of filaments., Comment: 27 pages, 12 figures

We present near-infrared and optical observations of the Type Ic Supernova (SN) 2020oi in the galaxy M100 and the broad-lined Type Ic SN2020bvc in UGC 9379, using Gemini, LCO, SOAR, and other ground-based telescopes. The near-IR spectrum of SN2020oi at day 63 since the explosion shows strong CO emissions and a rising K-band continuum, which is the first unambiguous dust detection from a Type Ic SN. Non-LTE CO modeling shows that CO is still optically thick, and that the lower limit to the CO mass is 0.001 Msun. The dust temperature is 810 K, and the dust mass is ~10^(-5) Msun. We explore the possibilities that the dust is freshly formed in the ejecta, heated dust in the pre-existing circumstellar medium, and an infrared echo. The light curves of SN2020oi are consistent with a STELLA model with canonical explosion energy, 0.07 Msun Ni mass, and 0.7 Msun ejecta mass. A model of high explosion energy of ~10^(52) erg, 0.4 Msun Ni mass, 6.5 Msun ejecta mass with the circumstellar matter, reproduces the double-peaked light curves of SN2020bvc. We observe temporal changes of absorption features of the IR Ca~II triplet, S~I at 1.043 micron, and Fe~II at 5169 Angstrom. The blue-shifted lines indicate high velocities, up to 60,000 km/s for SN2020bvc and 20,000 km/s for SN2020oi, and the expansion velocity rapidly declines before the optical maximum. We present spectral signatures and diagnostics of CO and SiO molecular bands between 1.4 and 10 microns., accepted for the ApJ; data files are available for Figures 1 and 4

N49 (LHA 120-N49) is a bright X-ray supernova remnant (SNR) in the Large Magellanic Cloud. We present new $^{12}$CO($J$ = 1-0, 3-2), HI, and 1.4 GHz radio-continuum observations of the SNR N49 using Mopra, ASTE, ALMA, and ATCA. We have newly identified three HI clouds using ATCA with an angular resolution of ~20": one associated with the SNR and the others located in front of the SNR. Both the CO and HI clouds in the velocity range from 280-291 km s$^{-1}$ are spatially correlated with both the soft X-rays (0.2-1.2 keV) and the hard X-rays (2.0-7.0 keV) of N49 on a ~10 pc scale. CO 3-2/1-0 intensity ratios indicate higher values of the CO cloud toward the SNR shell with an angular resolution of ~45", and thus a strong interaction was suggested. Using the ALMA, we have spatially resolved CO clumps embedded within or along the southeastern rim of N49 with an angular resolution of ~3''. Three of the CO clumps are rim-brightened on a 0.7-2 pc scale in both hard X-rays and the radio continuum$:$ this provides further evidence for dynamical interactions between the CO clumps and the SNR shock wave. The enhancement of the radio synchrotron radiation can be understood in terms of magnetic-field amplification around the CO clumps via a shock-cloud interaction. We also present a possible scenario in which the recombining plasma that dominates the hard X-rays from N49 was formed via thermal conduction between the SNR shock waves and the cold$/$dense molecular clumps., 28 pages, 12 figures, 1 table, accepted for publication in The Astrophysical Journal (ApJ)

We search for far-infrared (FIR) counterparts of known supernova remnants (SNRs) in the Galactic plane (10 deg, Comment: 33 pages and 39 figures. Accepted in MNRAS. Appendix figures are available here: https://github.com/hanchawn/Arxiv (includes full catalogue of Herschel images from this sample)

Theoretical models predict that core-collapse supernovae (CCSNe) can be efficient dust producers (0.1-1.0 Msun), potentially accounting for most of the dust production in the early Universe. Observational evidence for this dust production efficiency is however currently limited to only a few CCSN remnants (e.g., SN1987A, Crab Nebula). In this paper, we revisit the dust mass produced in Cassiopeia A (Cas A), a ~330-year old O-rich Galactic supernova remnant (SNR) embedded in a dense interstellar foreground and background. We present the first spatially resolved analysis of Cas A based on Spitzer and Herschel infrared and submillimetre data at a common resolution of ~0.6 arcmin for this 5 arcmin diameter remnant following a careful removal of contaminating line emission and synchrotron radiation. We fit the dust continuum from 17 to 500 micron with a four-component interstellar medium (ISM) and supernova (SN) dust model. We find a concentration of cold dust in the unshocked ejecta of Cas A and derive a mass of 0.3-0.5 Msun of silicate grains freshly produced in the SNR, with a lower limit of >=0.1-0.2 Msun. For a mixture of 50% of silicate-type grains and 50% of carbonaceous grains, we derive a total SN dust mass between 0.4 Msun and 0.6 Msun. These dust mass estimates are higher than from most previous studies of Cas A and support the scenario of supernova dominated dust production at high redshifts. We furthermore derive an interstellar extinction map for the field around Cas A which towards Cas A gives average values of A_V=6-8 mag, up to a maximum of A_V=15 mag., 37 pages, 24 figures, Manuscript published in MNRAS, including minor corrections. Accepted on 01/11/2016. Deposited on 08/01/2017

We used the Spitzer Space Telescope's Infrared Spectrograph to map nearly the entire extent of Cassiopeia A between 5-40 micron. Using infrared and Chandra X-ray Doppler velocity measurements, along with the locations of optical ejecta beyond the forward shock, we constructed a 3-D model of the remnant. The structure of Cas A can be characterized into a spherical component, a tilted thick disk, and multiple ejecta jets/pistons and optical fast-moving knots all populating the thick disk plane. The Bright Ring in Cas A identifies the intersection between the thick plane/pistons and a roughly spherical reverse shock. The ejecta pistons indicate a radial velocity gradient in the explosion. Some ejecta pistons are bipolar with oppositely-directed flows about the expansion center while some ejecta pistons show no such symmetry. Some ejecta pistons appear to maintain the integrity of the nuclear burning layers while others appear to have punched through the outer layers. The ejecta pistons indicate a radial velocity gradient in the explosion. In 3-D, the Fe jet in the southeast occupies a "hole" in the Si-group emission and does not represent "overturning", as previously thought. Although interaction with the circumstellar medium affects the detailed appearance of the remnant and may affect the visibility of the southeast Fe jet, the bulk of the symmetries and asymmetries in Cas A are intrinsic to the explosion., Comment: Accepted to ApJ. 54 pages, 21 figures. For high resolution figures and associated mpeg movie and 3D PDF files, see http://homepages.spa.umn.edu/~tdelaney/paper

We present the Spitzer Atlas of Stellar Spectra, which includes 159 stellar spectra (5-32 μm; R ~ 100) taken with the Infrared Spectrograph on the Spitzer Space Telescope. This Atlas gathers representative spectra of a broad section of the Hertzsprung-Russell diagram, intended to serve as a general stellar spectral reference in the mid-infrared. It includes stars from all luminosity classes, as well as Wolf-Rayet (WR) objects. Furthermore, it includes some objects of intrinsic interest, such as blue stragglers and certain pulsating variables. All of the spectra have been uniformly reduced, and all are available online. For dwarfs and giants, the spectra of early-type objects are relatively featureless, characterized by the presence of hydrogen lines in A spectral types. Besides these, the most noticeable photospheric features correspond to water vapor and silicon monoxide in late-type objects and methane and ammonia features at the latest spectral types. Most supergiant spectra in the Atlas present evidence of circumstellar gas and/or dust. The sample includes five M supergiant spectra, which show strong dust excesses and in some cases polycyclic aromatic hydrocarbon features. Sequences of WR stars present the well-known pattern of lines of He I and He II, as well as forbidden lines of ionized metals. The characteristic flat-top shape of the [Ne III] line is evident even at these low spectral resolutions. Several Luminous Blue Variables and other transition stars are present in the Atlas and show very diverse spectra, dominated by circumstellar gas and dust features. We show that the [8]-[24] Spitzer colors (IRAC and MIPS) are poor predictors of spectral type for most luminosity classes.

The interaction of the Puppis A supernova remnant (SNR) with a neighboring molecular cloud provides a unique opportunity to measure the amount of grain destruction in an SNR shock. Spitzer Space Telescope MIPS imaging of the entire SNR at 24, 70, and 160 μm shows an extremely good correlation with X-ray emission, indicating that the SNR’s IR radiation is dominated by the thermal emission of swept-up interstellar dust, collisionally heated by the hot shocked gas. Spitzer IRS spectral observations targeted both the Bright Eastern Knot (BEK) of the SNR where a small cloud has been engulfed by the supernova blast wave and outlying portions of the associated molecular cloud that are yet to be hit by the shock front. Modeling the spectra from both regions reveals the composition and the grain size distribution of the interstellar dust, both in front of and behind the SNR shock front. The comparison shows that the ubiquitous polycyclic aromatic hydrocarbons of the interstellar medium are destroyed within the BEK, along with nearly 25% of the mass of graphite and silicate dust grains.

We present Spitzer Infrared Spectrograph and Infrared Array Camera observations of the young supernova remnant E0102 (SNR 1E0102-7219) in the Small Magellanic Cloud. The infrared spectra show strong lines of Ne and O, with the [Ne II] line at 12.8 μm having a large velocity dispersion of 2000-4500 km s^(–1) indicative of fast-moving ejecta. Unlike the young Galactic SNR Cas A, E0102 lacks emission from Ar and Fe. Diagnostics of the observed [Ne III] line pairs imply that [Ne III] emitting ejecta have a low temperature of 650 K, while [Ne V] line pairs imply that the infrared [Ne V] emitting ejecta have a high density of ~10^4 cm^(–3). We have calculated radiative shock models for various velocity ranges including the effects of photoionization. The shock model indicates that the [Ne V] lines come mainly from the cooling zone, which is hot and dense, whereas [Ne II] and [Ne III] come mainly from the photoionization zone, which has a low temperature of 400-1000 K. We estimate an infrared-emitting Ne ejecta mass of 0.04 M_⊙ from the infrared observations, and discuss implications for the progenitor mass. The spectra also have a dust continuum feature peaking at 18 μm that coincides spatially with the ejecta, providing evidence that dust formed in the expanding ejecta. The 18 μm peak dust feature is fitted by a mixture of MgSiO_3 and Si dust grains, while the rest of the continuum requires either carbon or Al2O3 grains. We measure the total dust mass formed within the ejecta of E0102 to be ~0.014 M_⊙. The dust mass in E0102 is thus a factor of a few smaller than that in Cas A. The composition of the dust is also different, showing relatively less silicate and likely no Fe-bearing dust, as is suggested by the absence of Fe-emitting ejecta.

Extremely red objects, identified in the early Spitzer Space Telescope observations of the bright-rimmed globule IC 1396A and photometrically classified as Class I protostars Class II T Tauri stars based on their mid-infrared colors, were observed spectroscopically at 5.5 to 38 microns (IRS), at the 22 GHz water maser frequency (GBT), and in the optical (Palomar). The sources photometrically identified as Class I are confirmed as objects dominated by accretion luminosity from dense envelopes, with accretion rates 1e-5 to 1e-6 Msun/yr. The ice/silicate absorption ratio in the envelope is exceptionally low for the IC 1396A protostars, compared to those in nearby star-forming regions, suggesting the envelope chemistry is altered by the radiation field or globule pressure. Only one 22 GHz water maser was detected in IC 1396A; its infrared counterpart has luminosity, accepted to the Astrophysical Journal

We report the X-ray detection of the Type II-plateau supernova SN 2004et in the spiral galaxy NGC 6946, using the Chandra X-Ray Observatory. The position of the X-ray source was found to agree with the optical position within ~0.4 arcsec. Chandra also surveyed the region before the 2004 event, finding no X-ray emission at the location of the progenitor. For the post-explosion observations, a total of 202, 151, and 158 photons were detected in three pointings, each ~29 ks in length, on 2004 October 22, November 6, and December 3, respectively. The spectrum of the first observation is best fit by a thermal model with a temperature of kT=1.3 keV and a line-of-sight absorption of N_H=1.0 x 10^{22} cm^{-2}. The inferred unabsorbed luminosity (0.4-8 keV) is ~4x10^{38} erg/s, adopting a distance of 5.5 Mpc. A comparison between hard and soft counts on the first and third epochs indicates a softening over this time, although there is an insufficient number of photons to constrain the variation of temperature and absorption by spectral fitting. We model the emission as arising from the reverse shock region in the interaction between the supernova ejecta and the progenitor wind. For a Type IIP supernova with an extended progenitor, the cool shell formed at the time of shock wave breakout from the star can affect the initial evolution of the interaction shell and the absorption of radiation from the reverse shock. The observed spectral softening might be due to decreasing shell absorption. We find a pre-supernova mass loss rate of (2-2.5)x 10^{-6} M_{\odot} /yr for a wind velocity of 10 kms, which is in line with expectations for a Type IIP supernova., Comment: total 19 pages including 7 figures. ApJ, in press. See http://spider.ipac.caltech.edu/staff/rho/preprint/SN2004etms.ps for the paper including full resolution images

We present near-infrared narrow-band images of the supernova remnant W49B, taken with the WIRC instrument on the Hale 200 inch telescope on Mt. Palomar. The 1.64 micron [Fe II] image reveals a barrel-shaped structure with coaxial rings, which is suggestive of bipolar wind structures surrounding massive stars. The 2.12 micron shocked molecular hydrogen image extends 1.9 pc outside of the [Fe II] emission to the southeast. We also present archival Chandra data, which show an X-ray jet-like structure along the axis of the [Fe II] barrel, and flaring at each end. Fitting single temperature X-ray emission models reveals: an enhancement of heavy elements, with particularly high abundances of hot Fe and Ni, and relatively metal-rich core and jet regions. We interpret these findings as evidence that W49B originated inside a wind-blown bubble (R ~ 5 pc) interior to a dense molecular cloud. This suggests that W49B's progenitor was a supermassive star, that could significantly shape its surrounding environment. We also suggest two interpretations for the jet morphology, abundance variations and molecular hydrogen emission: (1) the explosion may have been jet-driven and interacting with the molecular cavity (i.e. a Gamma-ray burst); or (2) the explosion could have been a traditional supernova, with the jet structure being the result of interactions between the shock and an enriched interstellar cloud., Comment: 9 pages with embedded figures Accepted by the Astrophysical Journal

High resolution millimeter-wave and near-infrared observations of the supernova remnants W28 and W44 reveal extensive shocked molecular gas where supernova blast waves are propagating into giant molecular clouds. New CO observations were carried out with the IRAM 30-m and ARO 12-m telescopes, and the near-infrared observations were with Palomar 200-inch telescope. The near-infrared observations reveal shocked H2 emission from both supernova remnants, showing intricate networks of filaments on arcsec scales, following the bright ridges of the radio shells. The CO and CS linewidths, indicative of the shock speed, are 20-30 km/s. Both the near-infrared and millimeter-wave emission are attributed to shocks into gas with density >1e3 cm-3. Individual shock structures are resolved in the H2 emission, with inferred edge-on shock thickness ~1e17 cm, consistent with non-dissociative shocks into gas densities of 1e3-1e4 cm-3. Bright 1720 MHz OH masers are located within the shocked H2 gas complexes and highlight only localized areas where the conditions for masing are optimal. The Halpha and X-ray emission, have morphologies very different from the radio. We find a detailed correlation of the radio and H2 emission for some long filaments, indicating cosmic ray acceleration or re-acceleration due to the shocks into moderately dense gas. The different morphologies of these two remnants at different wavelengths is explained by a highly nonuniform structure for giant molecular clouds., ApJ, in press; several figures in jpg form

We present new images of the supernova remnant (SNR) Cas A observed in the 24 and 70 μm bands of the Spitzer Space Telescope (Spitzer). The IR emission correlates well with the Si X-ray and optical [S II] emission but poorly with either the synchrotron-dominated radio structure or the continuum X-ray emission. The IR is therefore dominated by thermal emission from dust within the SNR and associated with emission-line gas inside the reverse shock region, confirming earlier IRAS and Infrared Space Observatory results. Supplemented by new photometric measurements from archived Midcourse Space Experiment images, we suggest stochastic heating to model the overall mid- to far-IR spectral energy distribution. The 24 and 70 μm images also reveal a counterjet to the well-known northeast jet feature imaged previously at X-ray, optical, and radio wavelengths. This IR counterjet corresponds well with (optical) fast-moving knots confirming its outflow nature. The opposing jetlike features define a symmetry axis that bisects the SNR and suggest that the supernova explosion was axisymmetric. The IR images also show a region in which the SNR forward shock appears to be propagating into a ~650 M⊙ molecular cloud. The new images also show other details of the surrounding ISM structure, including two groups of knots extending ~6'-12' on either side of the SNR.

Using the Multiband Imaging Photometer for Spitzer (MIPS) and Infrared Array Camera (IRAC) instruments on the Spitzer Space Telescope, we have investigated an aggregate of at least nine candidate bright young stellar objects in the southern region of the Lynds 1228 cloud in Cepheus. The spectral energy distributions (SEDs) encompass both infrared Class II and Class III types, and at least one object has no excess at wavelengths shorter than 24 μm. There are five known IRAS sources in the region. We find that the fluxes of these sources are generally overestimated by IRAS because of confusion, and one appears in both the IRAS Point Source and Faint Source Catalogs. This small group of young stellar objects provides a good example of the power of Spitzer to resolve star-forming regions confused in the IRAS catalogs. The SEDs of these sources illustrate that there can be a diversity of disk evolutionary states within a coeval stellar aggregate.

We present observations of the spiral galaxy M33 with Spitzer at 24, 70, and 160 μm. The excellent resolution and mapping capabilities of Spitzer combined with the proximity of M33 result in observations that enable a detailed study of the distribution of star formation (SF) and dust in the galaxy. We compare the morphology of M33 at far-infrared wavelengths with other standard SF indicators such as Hα and radio continuum using a Fourier filtering technique to separate the diffuse emission components from compact sources. We find that the infrared emission at 24 and 70 μm follows closely the structure of the ionized gas, indicating that it is heated largely by hot, ionizing stars. At 160 μm a diffuse cold dust component matches only approximately the structure of the old red stellar population or the distribution of blue light. It is, however, very similar to the structure of the diffuse nonthermal radio emission.

High energy observations of Cas A suggested the presence of synchrotron radiation, implying acceleration of cosmic rays by young supernova remnants. We detect synchrotron emission from Cas A in the near-infrared using Two Micron All Sky Survey (2MASS) and Palomar 200 inch PFIRCAM observations. The remnant is detected in J, H, and Ks bands, with Ks band brightest and J faint. In the J and H bands, bright [Fe II] lines (1.24um and 1.64um) are detected spectroscopically. The Palomar observations include Ks continuum, narrow-band 1.64um (centered on [Fe II]) and 2.12um (centered on H2(1-0)) images. While the narrow-band 1.64um image shows filamentary and knotty structures, similar to the optical image, the Ks image shows a relatively smooth, diffuse shell, remarkably similar to the radio image. The broad-band near-infrared fluxes of Cas A are generally consistent with, but a few tens of percent higher than, an extrapolation of the radio fluxes. The hardening to higher frequencies is possibly due to nonlinear shock acceleration and/or spectral index variation across the remnant. We show evidence of spectral index variation. The presence of near-infrared synchrotron radiation requires the roll-off frequency to be higher than 1.5e14 Hz, implying that electrons are accelerated to energies of at least 0.2 TeV. The morphological similarity in diffuse emission between the radio and Ks band images implies that synchrotron losses are not dominant. Our observations show unambiguous evidence that the near-infrared Ks band emission of Cas A is from synchrotron emission by accelerated cosmic-ray electrons.

Supernova remnants may exhibit both thermal and nonthermal X-ray emission. We present Chandra observations of RCW 86. Striking differences in the morphology of X-rays below 1 keV and above 2 keV point to a different physical origin. Hard X-ray emission is correlated fairly well with the edges of regions of radio emission, suggesting that these are the locations of shock waves at which both short-lived X-ray emitting electrons, and longer-lived radio-emitting electrons, are accelerated. Soft X-rays are spatially well-correlated with optical emission from nonradiative shocks, which are almost certainly portions of the outer blast wave. These soft X-rays are well fit with simple thermal plane-shock models. Harder X-rays show Fe K alpha emission and are well described with a similar soft thermal component, but a much stronger synchrotron continuum dominating above 2 keV, and a strong Fe K alpha line. Quantitative analysis of this line and the surrounding continuum shows that it cannot be produced by thermal emission from a cosmic-abundance plasma; the ionization time is too short, as shown both by the low centroid energy (6.4 keV) and the absence of oxygen lines below 1 keV. Instead, a model of a plane shock into Fe-rich ejecta, with a synchrotron continuum, provides a natural explanation. This requires that reverse shocks into ejecta be accelerating electrons to energies of order 50 TeV. We show that maximum energies of this order can be produced by radiation-limited diffusive shock acceleration at the reverse shocks.

Supernova remnants may exhibit both thermal and nonthermal X-ray emission. Such remnants can be distinguished by the weakness of their X-ray lines because of the presence of a strong nonthermal X-ray continuum. RCW 86 is a remnant with weak lines, resulting in low and peculiar abundances when thermal models alone are used to interpret its X-ray spectrum. This indicates the presence of a strong nonthermal synchrotron continuum. We analyze ASCA X-ray spectra of RCW 86 with the help of both nonequilibrium ionization thermal models and nonthermal synchrotron models. A two-temperature thermal model and a simple nonthermal model with an exponential cutoff (plus interstellar absorption) give reasonable results. We obtain a blast-wave velocity of 800 km s-1, a shock ionization age of 1 × 1011-3 × 1011 cm-3 s, and the break in nonthermal spectra at 2 × 1016-4 × 1016 Hz. The strength of the nonthermal continuum correlates well with the radio brightness in the bright southwest section of the remnant. This is convincing evidence for X-ray synchrotron emission in RCW 86.

While shell-like, Crab-like, and composite supernova remnants (SNRs) represent well-defined classes, there is another group of SNRs with different X-ray and radio morphologies: shell-like in the radio and centrally filled in the X-ray (with little or no limb brightening). We present the results of a systematic X-ray study of 19 such remnants, using ROSAT and ASCA data. We show that they have physical and environmental properties distinct from the other categories, and we propose that they form a unique class that we term "mixed-morphology" supernova remnants. We found two prominent distinctions of this new class: their dominant X-ray emission mechanism is thermal despite their X-ray morphological similarity to Crab-like SNRs, and their emission arises primarily from swept-up interstellar material, not ejecta. The temperature across each remnant is nearly uniform, and the density and pressure are constant or increase toward the remnant center, contrary to the standard Sedov model. Most of these remnants are interacting with molecular or H I clouds, as indicated in some cases by strong infrared line emission or OH masers. The population represents at least 8% of all Galactic SNRs and as much as 25% of all X-ray-detected Galactic SNRs. This suggests that supernovae often explode in an environment that is conducive to the formation of a mixed-morphology remnant. The two most likely mechanisms for forming these remnants—evaporation of many small interior clouds and interior "fossil radiation" evolved in a denser than normal medium—require a reservoir of material with density higher than the typical intercloud ISM.

Whether supernovae are major sources of dust in galaxies is a long-standing debate. We present infrared and submillimeter photometry and spectroscopy from the Herschel Space Observatory of the Crab Nebula between 51 and 670 micron as part of the Mass Loss from Evolved StarS program. We compare the emission detected with Herschel with multiwavelength data including millimeter, radio, mid-infrared and archive optical images. We carefully remove the synchrotron component using the Herschel and Planck fluxes measured in the same epoch. The contribution from line emission is removed using Herschel spectroscopy combined with Infrared Space Observatory archive data. Several forbidden lines of carbon, oxygen and nitrogen are detected where multiple velocity components are resolved, deduced to be from the nitrogen-depleted, carbon-rich ejecta. No spectral lines are detected in the SPIRE wavebands; in the PACS bands, the line contribution is 5% and 10% at 70 and 100 micron and negligible at 160 micron. After subtracting the synchrotron and line emission, the remaining far-infrared continuum can be fit with two dust components. Assuming standard interstellar silicates, the mass of the cooler component is 0.24(+0.32)(-0.08) Msolar for T = 28.1(+5.5)(-3.2)K. Amorphous carbon grains require 0.11 +/- 0.01 Msolar of dust with T = 33.8(+2.3)(-1.8) K. A single temperature modified-blackbody with 0.14Msolar and 0.08Msolar for silicate and carbon dust respectively, provides an adequate fit to the far- infrared region of the spectral energy distribution but is a poor fit at 24-500 micron. The Crab Nebula has condensed most of the relevant refractory elements into dust, suggesting the formation of dust in core-collapse supernova ejecta is efficient., 12 pages, 6 figures, ApJ in press, final version after proofs corrected

We have used the Caltech Submillimeter Observatory (CSO) to follow-up a sample of WISE-selected, hyperluminous galaxies, so called W1W2-dropout galaxies. This is a rare (~ 1000 all-sky) population of galaxies at high redshift (peaks at z=2-3), that are faint or undetected by WISE at 3.4 and 4.6 um, yet are clearly detected at 12 and 22 um. The optical spectra of most of these galaxies show significant AGN activity. We observed 14 high-redshift (z > 1.7) W1W2-dropout galaxies with SHARC-II at 350 to 850 um, with 9 detections; and observed 18 with Bolocam at 1.1 mm, with five detections. Warm Spitzer follow-up of 25 targets at 3.6 and 4.5 um, as well as optical spectra of 12 targets are also presented in the paper. Combining WISE data with observations from warm Spitzer and CSO, we constructed their mid-IR to millimeter spectral energy distributions (SEDs). These SEDs have a consistent shape, showing significantly higher mid-IR to submm ratios than other galaxy templates, suggesting a hotter dust temperature. We estimate their dust temperatures to be 60-120 K using a single-temperature model. Their infrared luminosities are well over 10^{13} Lsun. These SEDs are not well fitted with existing galaxy templates, suggesting they are a new population with very high luminosity and hot dust. They are likely among the most luminous galaxies in the Universe. We argue that they are extreme cases of luminous, hot dust-obscured galaxies (DOGs), possibly representing a short evolutionary phase during galaxy merging and evolution. A better understanding of their long-wavelength properties needs ALMA as well as Herschel data., Will be Published on Sep 1, 2012 by ApJ

We present a 3-dimensional analysis of the supernova remnant Cassiopeia A using high resolution spectra from the Spitzer Space Telescope. We observe supernova ejecta both immediately before and during the shock-ejecta interaction. We determine that the reverse shock of the remnant is spherical to within 7%, although the center of this sphere is offset from the geometric center of the remnant by 810 km/s. We determine that the velocity width of the nucleosynthetic layers is approximately 1000 km/s over 4000 square arcsecond regions, although the velocity width of a layer along any individual line of sight is, 31 pages, 14 figures, ApJ, in press

We present mid-infrared continuum and emission line images of the Galactic oxygen-rich supernova remnant (SNR) G292.0+1.8, acquired using the MIPS and IRS instruments on the Spitzer Space Telescope. The MIPS 24 micron and 70 micron images of G292.0+1.8 are dominated by continuum emission from a network of filaments encircling the SNR. The morphology of the SNR, as seen in the mid-infrared, resembles that seen in X-rays with the Chandra X-ray Observatory. Most of the mid-infrared emission in the MIPS images is produced by circumstellar dust heated in the non-radiative shocks around G292.0+1.8, confirming the results of earlier mid-IR observations with AKARI. In addition to emission from hot dust, we have also mapped atomic line emission between 14 micron and 36 micron using IRS spectral maps. The line emission is primarily associated with the bright oxygen-rich optical knots, but is also detected from fast-moving knots of ejecta. We confirm our earlier detection of 15-25 micron emission characteristic of magnesium silicate dust in spectra of the radiatively shocked ejecta. We do not detect silicon line emission from any of the radiatively shocked ejecta in the southeast of the SNR, possibly because that the reverse shock has not yet penetrated most of the Si-rich ejecta in that region. This may indicate that G292.0+1.8 is less evolved in the southeast than the rest of the SNR, and may be further evidence in favor of an asymmetric SN explosion as proposed in recent X-ray studies of G292.0+1.8., 16 pages, 1 table, 7 figures, accepted for publication in ApJ

We present Spitzer MIPS SED and IRS observations of 14 Galactic Supernova Remnants previously identified in the GLIMPSE survey. We find evidence for SNR/molecular cloud interaction through detection of [OI] emission, ionic lines, and emission from molecular hydrogen. Through black-body fitting of the MIPS SEDs we find the large grains to be warm, 29-66 K. The dust emission is modeled using the DUSTEM code and a three component dust model composed of populations of big grains, very small grains, and polycyclic aromatic hydrocarbons. We find the dust to be moderately heated, typically by 30-100 times the interstellar radiation field. The source of the radiation is likely hydrogen recombination, where the excitation of hydrogen occurred in the shock front. The ratio of very small grains to big grains is found for most of the molecular interacting SNRs to be higher than that found in the plane of the Milky Way, typically by a factor of 2--3. We suggest that dust shattering is responsible for the relative over-abundance of small grains, in agreement with prediction from dust destruction models. However, two of the SNRs are best fit with a very low abundance of carbon grains to silicate grains and with a very high radiation field. A likely reason for the low abundance of small carbon grains is sputtering. We find evidence for silicate emission at 20 $\mu$m in their SEDs, indicating that they are young SNRs based on the strong radiation field necessary to reproduce the observed SEDs.

We report results from a multi-wavelength analysis of the Galactic SNR RCW 86, the proposed remnant of the supernova of 185 A.D. We report new infrared observations from {\it Spitzer} and {\it WISE}, where the entire shell is detected at 24 and 22 $��$m. We fit the infrared flux ratios with models of collisionally heated ambient dust, finding post-shock gas densities in the non-radiative shocks of 2.4 and 2.0 cm$^{-3}$ in the SW and NW portions of the remnant, respectively. The Balmer-dominated shocks around the periphery of the shell, large amount of iron in the X-ray emitting ejecta, and lack of a compact remnant support a Type Ia origin for this remnant. From hydrodynamic simulations, the observed characteristics of RCW 86 are successfully reproduced by an off-center explosion in a low-density cavity carved by the progenitor system. This would make RCW 86 the first known case of a Type Ia supernova in a wind-blown bubble. The fast shocks ($> 3000$ km s$^{-1}$) observed in the NE are propagating in the low-density bubble, where the shock is just beginning to encounter the shell, while the slower shocks elsewhere have already encountered the bubble wall. The diffuse nature of the synchrotron emission in the SW and NW is due to electrons that were accelerated early in the lifetime of the remnant, when the shock was still in the bubble. Electrons in a bubble could produce gamma-rays by inverse-Compton scattering. The wind-blown bubble scenario requires a single-degenerate progenitor, which should leave behind a companion star., Accepted for publication in ApJ. 50 pages, 9 figures

In the past few years, the extinction law has been measured in the infrared wavelengths for various molecular clouds and different laws have been obtained. In this paper we seek variations of the extinction law within the Trifid nebula region. Such variations would demonstrate a local dust evolution linked to variation of the environment parameters such as the density or the interstellar radiation field. The extinction values, A_lambda/A_V, are obtained using the 2MASS, UKIDSS and Spitzer/GLIMPSE surveys. The technique is to inter-calibrate color-excess maps from different wavelengths to derive the extinction law and to map the extinction in the Trifid region. We measured the extinction law at 3.6, 4.5, and 5.8 um and we found a transition at A_V ~ 20 mag. Below this threshold the extinction law is as expected from models for R_V=5.5 whereas above 20 mag of visual extinction, it is flatter. Using these results the color-excess maps are converted into a composite extinction map of the Trifid nebula at a spatial resolution of 1 arcmin. A tridimensional analysis along the line-of-sight allowed us to estimate a distance of 2.7 kpc for the Trifid. The comparison of the extinction with the 1.25 mm emission suggests the millimeter emissivity is enhanced in the dense condensations of the cloud. Our results suggest a dust transition at large extinction which has not been reported so far and dust emissivity variations., Accepted for publication in A&A. 10 pages, 8 figures

We used the Spitzer Space Telescope's Infrared Spectrograph to create a high resolution spectral map of the central region of the Cassiopeia A supernova remnant, allowing us to make a Doppler reconstruction of its 3D structure. The ejecta responsible for this emission have not yet encountered the remnant's reverse shock or the circumstellar medium, making it an ideal laboratory for exploring the dynamics of the supernova explosion itself. We observe that the O, Si, and S ejecta can form both sheet-like structures as well as filaments. Si and O, which come from different nucleosynthetic layers of the star, are observed to be coincident in velocity space in some regions, and separated by 500 km/s or more in others. Ejecta traveling toward us are, on average, ~900 km/s slower than the material traveling away from us. We compare our observations to recent supernova explosion models and find that no single model can simultaneously reproduce all the observed features. However, models of different supernova explosions can collectively produce the observed geometries and structures of the interior emission. We use the results from the models to address the conditions during the supernova explosion, concentrating on asymmetries in the shock structure. We also predict that the back surface of Cassiopeia A will begin brightening in ~30 years, and the front surface in ~100 years., Comment: 35 pages, 16 figures, accepted to ApJ

(Abridged) We present an analysis of X-ray observations made of the Galactic supernova remnants (SNRs) HB21 (G89.0+4.7) and CTB 1 (G116.9+0.2), two well-known mixed-morphology (MM) SNRs. We find a marked contrast between the X-ray properties of these SNRs: for HB21, the extracted ASCA spectra of the northwest and southeast regions of the X-ray emitting plasma can be fit with a single thermal model with marginally enhanced silicon and sulfur abundances. For both of these regions, the derived column density and temperature are N_H~0.3x10^22 cm^-2 and kT~0.7 keV, respectively. No significant spatial differences in temperature or elemental abundances between the two regions are detected and the X-ray-emitting plasma in both regions is close to ionization equilibrium. Our Chandra spectral analysis of CTB 1 reveals that this source is likely an oxygen-rich SNR with enhanced abundances of oxygen and neon. The extracted ASCA spectra for the southwestern and northeastern regions of CTB 1 cannot be fit with a single thermal component. Based on our fits to these spectra, we derive a column density N_H~0.6x10^22 cm^-2 and a temperature for the soft thermal component of kT_soft~0.28 keV. The hard emission from the southwest may be modeled with either a thermal component (kT_hard~3 keV) or by a power law component (Gamma~2-3) while the hard emission from the northeast may be modeled with a power law component (Gamma~1.4). We have also extracted ASCA GIS spectra of the discrete X-ray source 1WGA J0001.4+6229 which is seen in projection toward CTB 1. These spectra are best fit using a power-law model with a photon index Gamma=2.2^{+0.5}_{-1.2} which is typical for featureless power-law continua produced by rotation-powered pulsars. This source may be a neutron star associated with CTB 1., Comment: 46 pages, 16 figures, accepted for publication in the Astronomical Journal

We present the global distribution of fine structure infrared line emission in the Cassiopeia A supernova remnant using data from the Spitzer Space Telescope's Infrared Spectrograph. We identify emission from ejecta materials in the interior, prior to their encounter with the reverse shock, as well as from the post-shock bright ring. The global electron density increases by >~100 at the shock to ~10^4 cm^-3, providing evidence for strong radiative cooling. There is also a dramatic change in ionization state at the shock, with the fading of emission from low ionization interior species like [SiII], giving way to [SIV] and, at even further distances, high-energy X-rays from hydrogenic silicon. Two compact, crescent-shaped clumps with highly enhanced neon abundance are arranged symmetrically around the central neutron star. These neon crescents are very closely aligned with the "kick" direction of the compact object from the remnant's expansion center, tracing a new axis of explosion asymmetry. They indicate that much of the apparent macroscopic elemental mixing may arise from different compositional layers of ejecta now passing through the reverse shock along different directions., 9 pages, 8 figures, accepted by ApJ

The Spectral Energy Distribution (SED) mode of the Multiband Imaging Photometer for Spitzer (MIPS) Space Telescope provides low-spectral resolution (R ~ 15-25) spectroscopy in the far infrared using the MIPS 70 um detector. A reflective grating provides a dispersion of 1.7 um per pixel, and an effective wavelength coverage of 52.8--98.7 um over detector rows 1-27. The final 5 detector rows are contaminated by second-order diffracted light and are left uncalibrated. The flux calibration is based on observations of MIPS calibration stars with 70 um flux densities of 0.5--15 Jy. The point-source flux calibration accuracy is estimated to be 10% or better down to about 0.5 Jy at the blue end of the spectrum and to 2 Jy near the red end. With additional uncertainties from the illumination and aperture corrections included, the surface brightness calibration of extended sources is accurate to ~15%. Repeatability of better than 5% is found for the SED mode through multiple measurements of several calibration stars., To Appear in PASP

We performed Spitzer Infrared Spectrograph mapping observations covering nearly the entire extent of the Cassiopeia A supernova remnant (SNR), producing mid-infrared (5.5-35 micron) spectra every 5-10". Gas lines of Ar, Ne, O, Si, S and Fe, and dust continua were strong for most positions. We identify three distinct ejecta dust populations based on their continuum shapes. The dominant dust continuum shape exhibits a strong peak at 21 micron. A line-free map of 21 micron-peak dust made from the 19-23 micron range closely resembles the [Ar II], [O IV], and [Ne II] ejecta-line maps implying that dust is freshly formed in the ejecta. Spectral fitting implies the presence of SiO2, Mg protosilicates, and FeO grains in these regions. The second dust type exhibits a rising continuum up to 21 micron and then flattens thereafter. This ``weak 21 micron'' dust is likely composed of Al2O3 and C grains. The third dust continuum shape is featureless with a gently rising spectrum and is likely composed of MgSiO3 and either Al2O3 or Fe grains. Using the least massive composition for each of the three dust classes yields a total mass of 0.02 Msun. Using the most-massive composition yields a total mass of 0.054 Msun. The primary uncertainty in the total dust mass stems from the selection of the dust composition necessary for fitting the featureless dust as well as 70 micron flux. The freshly formed dust mass derived from Cas A is sufficient from SNe to explain the lower limit on the dust masses in high redshift galaxies., Comment: 8 figures: Accepted for the publication in ApJ

We observed the oxygen-rich Large Magellanic Cloud (LMC) supernova remnant N132D (SNR 0525-69.6), using all instruments onboard the Spitzer Space Telescope, IRS, IRAC, and MIPS (Infrared Spectrograph, Infrared Array Camera, Multiband Imaging Photometer for Spitzer). The 5-40 micron IRS spectra toward the southeastern shell of the remnant show a steeply rising continuum with [NeIII] and [OIV] as well as PAH emission. We also present the spectrum of a fast moving ejecta knot, previously detected at optical wavelengths, which is dominated by strong [NeIII] and [OIV] emission lines. We interpret the continuum as thermal emission from swept-up, shock-heated dust grains in the expanding shell of N132D, which is clearly visible in the MIPS 24 micron image. A 15-20 micron emission hump appears superposed on the dust continuum, and we attribute this to PAH C-C-C bending modes. We also detect the well-known 11.3 micron PAH C-H bending feature, and find the integrated strength of the 15-20 micron hump about a factor of seven stronger than the 11.3 micron band in the shell of the remnant. IRAC 3-9 micron images do not show clear evidence of large-scale, shell-like emission from the remnant, partly due to confusion with the ambient ISM material. However, we identified several knots of shocked interstellar gas based on their distinct infrared colors. We discuss the bright infrared continuum and the polycyclic aromatic hydrocarbon features with respect to dust processing in young supernova remnants., Accepted by ApJ

Spitzer IRAC and MIPS images of the Trifid Nebula (M20) reveal its spectacular appearance in infrared light, highlighting the nebula's special evolutionary stage. The images feature recently-formed massive protostars and numerous young stellar objects, and a single O star that illuminates the surrounding molecular cloud from which it formed, and unveil large-scale, filamentary dark clouds. The hot dust grains show contrasting infrared colors in shells, arcs, bow-shocks and dark cores. Multiple protostars are detected in the infrared, within the cold dust cores of TC3 and TC4, which were previously defined as Class 0. The cold dust continuum cores of TC1 and TC2 contain only one protostar each. The Spitzer color-color diagram allowed us to identify ~160 young stellar objects and classify them into different evolutionary stages. The diagram also revealed a unique group of YSOs which are bright at 24 micron but have the spectral energy distribution peaking at 5-8 micron. Despite expectation that Class 0 sources would be "starless" cores, the Spitzer images, with unprecedented sensitivity, uncover mid-infrared emission from these Class 0 protostars. The mid-infrared detections of Class 0 protostars show that the emission escapes the dense, cold envelope of young protostars. The mid-infrared emission of the protostars can be fit by two temperatures of 150 and 400 K; the hot core region is probably optically thin in the mid-infrared regime, and the size of hot core is much smaller than that of the cold envelope. The presence of multiple protostars within the cold cores of Class 0 objects implies that clustering occurs at this early stage of star formation. The TC3 cluster shows that the most massive star is located at the center of the cluster and at the bottom of the gravitational-potential well., Accepted for publication in ApJ. Full resolution images are available at http://spider.ipac.caltech.edu/staff/rho/

The remnant of the supernova of 1006 AD, the remnant first showing evidence for the presence of X-ray synchrotron emission from shock-accelerated electrons, was observed for ~1000 ksec with INTEGRAL for the study of electron acceleration to very high energies. The aim of the observation was to characterize the synchrotron emission, and attempt to detect non-thermal bremsstrahlung, using the combination of IBIS and JEM-X spatial and spectral coverage. The source was detected with JEM-X between 2.4 and 8.4 keV bands, and not detected with either ISGRI or SPI above 20 keV. The ISGRI upper limit is about a factor of four above current model predictions, but confirms the presence of steepening in the power-law extrapolated from lower energies (< 4 keV)., 5 pages, 3 figures, 1 table, accepted for publication in the Astrophysical Journal

The Multiband Imaging Photometer for Spitzer (MIPS) provides long wavelength capability for the mission, in imaging bands at 24, 70, and 160 microns and measurements of spectral energy distributions between 52 and 100 microns at a spectral resolution of about 7%. By using true detector arrays in each band, it provides both critical sampling of the Spitzer point spread function and relatively large imaging fields of view, allowing for substantial advances in sensitivity, angular resolution, and efficiency of areal coverage compared with previous space far-infrared capabilities. The Si:As BIB 24 micron array has excellent photometric properties, and measurements with rms relative errors of 1% or better can be obtained. The two longer wavelength arrays use Ge:Ga detectors with poor photometric stability. However, the use of 1.) a scan mirror to modulate the signals rapidly on these arrays, 2.) a system of on-board stimulators used for a relative calibration approximately every two minutes, and 3.) specialized reduction software result in good photometry with these arrays also, with rms relative errors of less than 10%.

The Trifid Nebula, a young star-forming HII region, was observed for 16 hours by the Chandra X-ray Observatory. We detected 304 X-ray sources, thirty percent of which are hard sources and seventy percent of of which have near-infrared counterparts. Chandra resolved the HD164492 multiple system into a number of discrete X-ray sources. X-ray emission is detected from components HD164492A (an O7.5III star which ionizes the nebula), B and C (a B6V star), and possibly D (a Be star). HD164492A has a soft spectrum (kT ~ 0.5 keV) while the component C blend shows much harder emission (kT ~ 6 keV). The soft spectrum of the O star is similar to emission seen from other single O stars and is probably produced by shocks within its massive stellar wind. Lack of hard emission suggests that neither a magnetically confined wind shock nor colliding wind emission is important in HD164492A. A dozen stars are found to have flares in the field and most of them are pre-main sequence stars (PMS). Six sources with flares have both optical and 2MASS counterparts. These counterparts are not embedded and thus it is likely that these sources are in a later stage of PMS evolution, possibly Class II or III. Two flare sources did not have any near-IR, optical, or radio counterparts. We suggest these X-ray flare stars are in an early pre-main sequence stage (Class I or earlier). We also detected X-ray sources apparently associated with two massive star forming cores, TC1 and TC4. The spectra of these sources show high extinction and X-ray luminosities of 2 - 5 x 10^{31} erg/s. If these sources are Class 0 objects, it is unclear if their X-ray emission is due to solar-type magnetic activities as in Class I objects, or some other mechanism., 28 pages, 6 figures: Accepted by ApJ

We investigate the density structure of the interstellar medium using new high-resolution maps of the 8 micron, 24 micron, and 70 micron surface brightness towards a molecular cloud in the Gum Nebula, made as part of the Spitzer Space Telescope Galactic First Look Survey. The maps are correlated with 100 micron images measured with IRAS. At 24 and 70 micron, the spatial power spectrum of surface brightness follows a power law with spectral index -3.5. At 24 micron, the power law behavior is remarkably consistent from the 0.2 degree size of our maps down to the 5 arcsecond spatial resolution. Thus, the structure of the 24 micron emission is self-similar even at milliparsec scales. The combined power spectrum produced from Spitzer 24 micron and IRAS 25 micron images is consistent with a change in the power law exponent from -2.6 to -3.5. The decrease may be due to the transition from a two-dimensional to three-dimensional structure. Under this hypothesis, we estimate the thickness of the emitting medium to be 0.3 pc., Comment: 13 Pages, 3 Figures, to be published in Astrophysical Journal Supplement Series (Spitzer Special Issue), volume 154. Uses aastex v5.2

We present images of the galaxy NGC 55 at 24, 70, and 160 micron obtained with the Multiband Imaging Photometer for Spitzer (MIPS) instrument aboard the Spitzer Space Telescope. The new images display the far infrared emission in unprecedented detail and demonstrate that the infrared morphology differs dramatically from that at shorter wavelengths. The most luminous emission region in the galaxy is marginally resolved at 24 micron and has a projected separation of nearly 520 pc from the peak emission in the optical and near infrared. This region is responsible for ~9% of the total emission at 24 micron and is likely a young star formation region. We show that this and other compact sources account for more than 1/3 of the total 24 micron emission. We compute a total infrared luminosity for NGC 55 of 1.2*10^9 L_sun. The star formation rate implied by our measurements is 0.22 M_sun/yr. We demonstrate that the cold dust is more extended than the warm dust in NGC 55--the minor-axis scale heights are 0.32, 0.43, and 0.49 kpc at 24, 70 and 160 micron, respectively. The dust temperature map shows a range of temperatures that are well-correlated with the 24 micron surface brightness, from 20 K in low-surface-brightness regions to 26 K in high-surface-brightness regions., Comment: 5 pages, 6 figures, accepted to ApJS

International audience; The Infrared Spectrograph on the Spitzer Space Telescope has observed several A dwarfs as potential standards and cross-calibrators, and one of these stars, HD 46190, shows the spectroscopic signature of a debris disk. The disk produces a spectral excess that can be fitted with a cool blackbody of ~81 K. If the emitting particles are spherical blackbodies, they would lie at a distance of ~82 AU from the central star. The spectrum from the disk can also be fitted with a spectrum rising proportionally with wavelength, and this spectral behavior is consistent with material falling into the inner disk as a result of Poynting-Robertson drag.

We present ROSAT PSPC and ASCA observations of the supernova remnant (SNR) W28. The overall shape of X-ray emission in W28 is elliptical, dominated by a centrally-concentrated interior emission, sharply peaked at the center. The ASCA spectra reveal emission lines of Ne, Mg, Si, and Fe K$��$ and continuum extending at least up to 7 keV, showing thermal origin with a hot thermal component. We found that spectral variations are present in W28. The southwestern shell can be fit well by a plane-shock model with a temperature of 1.5 keV, and the northeastern shell, with a lower temperature of 0.56 keV. Unlike for the southwestern and northeastern shells, the central emission requires a two-temperature components with 0.6 keV and 1.8 keV. The low temperature component is similar to those seen in other Mixed-morphology SNRs. The X-ray luminosity of W28 is 6x 10^34 ergs/s, and the estimated X-ray mass is only ~20 - 25 solar mass. A comparison of W28 with other typical Mixed-morphology SNRs reveals significant differences in its X-ray properties; W28 has a significantly higher temperature and noticeable spectral variations. W28 belongs to a class of SNRs considered by Chevalier (1999), with a radiative shell interacting with clumpy molecular clouds. X-ray emission at its center is a ``fossil'' radiation from gas which was shocked early in the evolution of the remnant, and its centrally-peaked morphology could have been caused by processes such as evaporation, electron thermal conduction, and mixing induced by various hydrodynamical instabilities. But W28 poses a challenge for existing models of X-ray emission, because the evaporation model of White & Long (1991) is in conflict with observations, while the presence of temperature variations seems inconsistent with SNR models with efficient thermal conduction., total 44 pages including 17 figures. Accepted by ApJ

Radio surveys of supernova remnants (SNRs) in the Galaxy have uncovered 19 SNRs accompanied by OH maser emission at 1720 MHz. This unusual class of maser sources is suggested to be produced behind a shock front from the expansion of a supernova remnant running into a molecular cloud. An important ingredient of this model is that X-ray emission from the remnant enhances the production of OH molecule. The role of X-ray emission from maser emitting (ME) SNRs is investigated by comparing the X-ray induced ionization rate with theory. One aspect of this model is verified: there is a strong association between maser emitting and mixed-morphology (MM) or thermal composite SNRs --center-filled thermal X-ray emission surrounded by shell-like radio morphology. We also present ROSAT and ASCA observations of two maser emitting SNRs: G21.8--0.6 (Kes 69) and G357.7--0.1 (Tornado)., Comment: 13 pages, 2 tables, 1 figure, ApJ (in press)

Infrared continuum observations provide a means of investigating the physical composition of the dust in the ejecta and swept up medium of the Cas A supernova remnant. Using low resolution Spitzer IRS spectra (5-35 $\mu$m), and broad-band Herschel PACS imaging (70, 100, and 160 $\mu$m), we identify characteristic dust spectra, associated with ejecta layers that underwent distinct nuclear burning histories. The most luminous spectrum exhibits strong emission features at $\sim9$ and 21 $\mu$m and is closely associated with ejecta knots with strong Ar emission lines. The dust features can be reproduced by magnesium silicate grains with relatively low Mg to Si ratios. Another dust spectrum is associated with ejecta having strong Ne emission lines. It has no indication of any silicate features, and is best fit by Al$_2$O$_3$ dust. A third characteristic dust spectrum shows features that are best matched by magnesium silicates with a relatively high Mg to Si ratio. This dust is primarily associated with the X-ray emitting shocked ejecta, but it is also evident in regions where shocked interstellar or circumstellar material is expected. However, the identification of dust composition is not unique, and each spectrum includes an additional featureless dust component of unknown composition. Colder dust of indeterminate composition is associated with emission from the interior of the SNR, where the reverse shock has not yet swept up and heated the ejecta. Most of the dust mass in Cas A is associated with this unidentified cold component, which is $\lesssim0.1$ $M_{\odot}$. The mass of warmer dust is only $\sim 0.04$ $M_{\odot}$., Comment: 45 pages. 21 Figures. Accepted for publication in ApJ

New observations of the supernova remnant 3C391 are in the H2 2.12 micron and [Fe II] 1.64 micron narrow-band filters at the Palomar 200-inch telescope, and in the 5-15 micron CVF on ISOCAM. Shocked H2 emission was detected from the region 3C391:BML, where broad millimeter CO and CS lines had previously been detected. A new H2 clump was confirmed to have broad CO emission, demonstrating that the near-infrared H2 images can trace previously undetected molecular shocks. The [Fe II] emission has a significantly different distribution, being brightest in the bright radio bar, at the interface between the supernova remnant and the giant molecular cloud, and following filaments in the radio shell. The near-infrared [Fe II] and the mid-infrared 12-18 micron filter images are the first images to reveal the radiative shell of 3C391. The mid-infrared spectrum is dominated by bright ionic lines and H2 S(2) through S(7). There are no aromatic hydrocarbons associated with the shocks, nor is their any mid-infrared continuum, suggesting that macromolecules and very small grains are destroyed. Comparing 3C391 to the better-studied IC443, both remnants have molecular- and ionic-dominated regions; for 3C391, the ionic-dominated region is the interface into the giant molecular cloud, showing that the main bodies of giant molecular clouds contain significant regions with densities 100 to 1000/cm^3 and a small filling factor with higher-density. The molecular shocked region resolves into 16 clumps of H2 emission, with some fainter diffuse emission but with no associated near-infrared continuum sources. One of the clumps is coincident with a previously-detected OH 1720 MHz maser. These clumps are interpreted as a cluster of pre-stellar, dense molecular cores that are presently being shocked by the supernova blast wave.

The Trifid Nebula is a young HII region recently rediscovered as a "pre-Orion" star forming region, containing protostars undergoing violent mass ejections visible in optical jets as seen in images from the Infrared Space Observatory and the Hubble Space Telescope. We report the first X-ray observations of the Trifid nebula using ROSAT and ASCA. The ROSAT image shows a dozen X-ray sources, with the brightest X-ray source being the O7 star, HD 164492, which provides most of the ionization in the nebula. We also identify 85 T Tauri star and young, massive star candidates from near-infrared colors using the JHKs color-color diagram from the Two Micron All Sky Survey (2MASS). Ten X-ray sources have counterpart near-infrared sources. The 2MASS stars and X-ray sources suggest there are potentially numerous protostars in the young HII region of the Trifid. ASCA moderate resolution spectroscopy of the brightest source shows hard emission up to 10 keV with a clearly detected Fe K line. The best model fit is a two-temperature (T = 1.2x10^6 K and 39x10^6 K) thermal model with additional warm absorbing media. The hotter component has an unusually high temperature for either an O star or an HII region; a typical Galactic HII region could not be the primary source for such hot temperature plasma and the Fe XXV line emission. We suggest that the hotter component originates in either the interaction of the wind with another object (a companion star or a dense region of the nebula) or from flares from deeply embedded young stars., Comment: Accepted in ApJ (Oct, 20 issue, 2001)

We present near-infrared images of the supernova remnant RCW 103 (G332.4-0.4) from the Two Micron All Sky Survey (2MASS). In all three 2MASS bands—J, H, Ks—emission is detected, revealing a barrel-shaped, shell-like morphology. However, the J and H band shells are displaced with Ks band shell. The J and H band emission are mostly from [Fe II] lines while the Ks band emission is mostly from molecular hydrogen, as inferred from previous near-infrared spectroscopy. The 2MASS images show that the displacement between the [Fe II] and H2 is not just due to a projection effect; instead, it appears that the layers emitting [Fe II] and H2 lines are intrinsically double shells. We compared the 2MASS images with radio and X-ray images at comparable resolutions. The X-ray and radio shells coincide with the J and H band shells, while the Ks band shell is located outside of the shock front. We discuss the origin of the molecular hydrogen shell in terms of a magnetic precursor or excitation by a radiative precursor. We ...

We report the discovery of the shocked molecular gas in the supernova remnant HB 21. We derive the physical parameters of the shocked gas from CO J=1-0 and J=2-1 line observations. We discuss the correlation of the shocked molecular gas with the previously detected, shocked atomic gas and the associated infrared emission., 24 pages, 10 figures, To appear in the ApJ, scheduled for the April 10, 2001 issue (v551)

We present Infrared Space Observatory spectroscopy of sites in the supernova remnants W28, W44, and 3C391, where blast waves are impacting molecular clouds. Atomic fine-structure lines were detected from C, N, O, Si, P, and Fe. The S(3) and S(9) lines of H2 were detected for all three remnants. The observations require both shocks into gas with moderate (~ 100 /cm3) and high (~10,000 /cm3) pre-shock densities, with the moderate density shocks producing the ionic lines and the high density shock producing the molecular lines. No single shock model can account for all of the observed lines, even at the order of magnitude level. We find that the principal coolants of radiative supernova shocks in moderate-density gas are the far-infrared continuum from dust grains surviving the shock, followed by collisionally-excited [O I] 63.2 and [Si II] 34.8 micron lines. The principal coolant of the high-density shocks is collisionally-excited H2 rotational and ro-vibrational line emission. We systematically examine the ground-state fine structure of all cosmically abundant elements, to explain the presence or lack of all atomic fine lines in our spectra in terms of the atomic structure, interstellar abundances, and a moderate-density, partially-ionized plasma. The [P II] line at 60.6 microns is the first known astronomical detection. There is one bright unidentified line in our spectra, at 74.26 microns. The presence of bright [Si II] and [Fe II] lines requires partial destruction of the dust. The required gas-phase abundance of Fe suggests 15-30% of the Fe-bearing grains were destroyed. The infrared continuum brightness requires ~1 Msun of dust survives the shock, suggesting about 1/3 of the dust mass was destroyed, in agreement with the depletion estimate and with theoretical models for dust destruction., Comment: 40 pages; 10 figures; accepted by ApJ July 11, 2000

We present Spitzer Infrared Spectrograph 14-36 ?m mapping observations of the supernova remnant N132D in the Large Magellanic Cloud. This study focuses on the processing of polycyclic aromatic hydrocarbons (PAHs) that we previously identified in the southern blast wave. The mid-infrared spectra show strong continuum emission from shock-heated dust and a unique, nearly featureless plateau in the 15-20 ?m region, which we attribute to PAH molecules. The typical PAH emission bands observed in the surrounding interstellar medium ahead of the blast wave disappear, which indicates shock processing of PAH molecules. The PAH plateau appears most strongly at the outer edge of the blast wave and coincides with diffuse X-ray emission that precedes the brightest X-ray and optical filaments. This suggests that PAH molecules in the surrounding medium are swept up and processed in the hot gas of the blast wave shock, where they survive the harsh conditions long enough to be detected. We also observe a broad emission feature at 20 ?m appearing with the PAH plateau. We speculate that this feature is either due to FeO dust grains or connected to the processing of PAHs in the supernova blast wave shock.