We performed Spitzer Infrared Spectrograph mapping observations covering nearly the entire extent of the Cassiopeia A supernova remnant (SNR), producing mid-infrared (5.5Y35 m) spectra every 5 00 Y10 00 . 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 m. A line-free map of 21 m peak dust made from the 19Y23 m 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 SiO 2 , Mg protosilicates, and FeO grains in these regions. The second dust type exhibits a rising continuum up to 21 m and then flattens thereafter. This ''weak 21 m'' dust is likely composed of Al 2 O 3 and C grains. The third dust continuum shape is featureless with a gently rising spectrum and is likely composed of MgSiO 3 and either Al 2 O 3 or Fe grains. Using the least massive composition for each of the three dust classes yields a total mass of 0.020 M . Using the most massive composition yields a total mass of 0.054 M . 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 m 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.

We present Spitzer IRAC images and representative 5.27Y38.5 m IRS spectra of the Cas A SNR. We find that various IRAC channels are each most sensitive to a different spectral and physical component. Channel 1 (3.6 m) provides an excellent match to the radio synchrotron images. Where channel 1 is strong with respect to the other IRAC channels, the longer wavelength spectra show a broad continuum gently peaking around 26 m, with weak or no lines. We suggest that this is due to unenriched progenitor circumstellar dust behind the outer shock. Where channel 4 (8 m) is relatively brightest, the long-wavelength spectra show a strong, 2Y3 m wide peak at 21 m, likely due to silicates and protosilicates. Strong ionic lines of [Ar ii], [Ar iii], [S iv], and [Ne ii] also appear in these regions. We suggest that in these locations, the dust and ionic emission originate from the explosion's O-burning layers. The regions where channels 2 (4.5 m) and 3 (5.6 m) are strongest relative to channel 4 show a spectrum that rises gradually to 38 m, becoming flatter longward of 21 m, along with higher ratios of [Ne ii] to [Ar ii]. We suggest that the dust and ionic emission in these locations arise primarily from the C-and Ne-burning layers. All of these findings are consistent with asymmetries deep in the explosion, producing variations in the velocity structure in different directions, but generally preserving the nucleosynthetic layering. At each location, the dust and ionic lines in the mid-infrared and the hotter and more highly ionized optical and X-ray emission are then dominated by the layer currently encountering the reverse shock in that direction.

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Symmetrical peripheral gangrene (SPG) is a rare complication of septicaemia and disseminated intravascular coagulation (DIC) characterised by distal ischaemia in two or more extremities without large vessel obstruction. SPG has high mortality and morbidity rates, though consensus guidelines for management have yet to be produced. We herein present the case of a 28-year-old woman with meningococcal septicaemia complicated with extensive bilateral upper and lower limb SPG. We discuss the various management options of SPG. While reported cases are scarce in the literature, early recognition of sepsis and prompt withdrawal of vasoconstrictors in an intensive care setting, combined with timely heparinisation, appear to be the most common management strategy thus far.