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Abstract In the absence of a parallax distance to a pulsar or a surviving binary in a supernova remnant (SNR), distances to Galactic SNRs are generally very uncertain. However, by combining Gaia data with wide-field, multifiber echelle spectroscopy, it is now possible to obtain accurate distances to many SNRs with limited extinction by searching for the appearance of high-velocity Caiior Naiabsorption lines in hot stars as a function of distance. We demonstrate this for the SNR S147 using the spectra of 259 luminous blue stars. We obtain a median distance of 1.37 kpc (1.30–1.47 kpc at 90% confidence), which is consistent with the median parallax distance to the pulsar of 1.46 kpc (1.12–2.10 kpc at 90% confidence) but with significantly smaller uncertainties. Our distance is also consistent with the distance to the candidate unbound binary companion in this SNR, HD 37424 at a photogeometric distance of 1.45 kpc (1.40–1.50 kpc at 1σ). The presence of high-velocity absorption lines is correlated with the Hα/O [iii] emission-line flux of the SNR but not with the radio flux. 

Abstract We present initial results from a James Webb Space Telescope (JWST) survey of the youngest Galactic core-collapse supernova remnant, Cassiopeia A (Cas A), made up of NIRCam and MIRI imaging mosaics that map emission from the main shell, interior, and surrounding circumstellar/interstellar material (CSM/ISM). We also present four exploratory positions of MIRI Medium Resolution Spectrograph integral field unit spectroscopy that sample ejecta, CSM, and associated dust from representative shocked and unshocked regions. Surprising discoveries include (1) a weblike network of unshocked ejecta filaments resolved to ∼0.01 pc scales exhibiting an overall morphology consistent with turbulent mixing of cool, low-entropy matter from the progenitor’s oxygen layer with hot, high-entropy matter heated by neutrino interactions and radioactivity; (2) a thick sheet of dust-dominated emission from shocked CSM seen in projection toward the remnant’s interior pockmarked with small (∼1″) round holes formed by ≲0.″1 knots of high-velocity ejecta that have pierced through the CSM and driven expanding tangential shocks; and (3) dozens of light echoes with angular sizes between ∼0.″1 and 1′ reflecting previously unseen fine-scale structure in the ISM. NIRCam observations place new upper limits on infrared emission (≲20 nJy at 3μm) from the neutron star in Cas A’s center and tightly constrain scenarios involving a possible fallback disk. These JWST survey data and initial findings help address unresolved questions about massive star explosions that have broad implications for the formation and evolution of stellar populations, the metal and dust enrichment of galaxies, and the origin of compact remnant objects.