Digitized Images of the best Palomar 5m (200 inch) photographic plates of Cassiopeia A taken between October 1951 and September 1989.

Palomar Observatory 's 5m (200 inch) telescope images represent the best ground-based photographs taken of the Cassiopeia A supernova remnant (Cas A) during the period from 1951 to 1989. The first Palomar image was taken in September 1951 by Walter Baade less than a month after F. Graham Smith announced the first accurate position of the Cas A remnant based on radio measurements. Most of these plates were obtained by Walter Baade, Rudolph Minkowski and Sidney van den Bergh, with a few addition ones taken by Halton Arp, Joseph Miller and Donald Shane at the request of Baade and/or Minkowski. These Palomar images formed the basis of the first investigations of the Cas A's optical emission structure and expansion properties. The images were obtained at the prime focus of the 5m telescope on photographic plates 5 x 7 inches in size with various Kodak photographic emulsions and optical filters. They were often taken with the prime focus Ross corrector and have a plate scale of $0.1''$ per millimeter. This 12 image collection is those good to fair quality images deemed to be among the best taken. Photographic plates were first cleaned of surface dust and then digitized using the high- speed digitizing scanning machine DASCH (Simcoe 2006, Laycock 2010) at the Harvard–Smithsonian Center for Astrophysics. Only the central $7.7' \times 5.9'$ region of these plates were scanned and then digitized at a pixel scale of 0.42$''$ pixel$^{-1}$. However, three of some of the best images were separately scanned at a higher resolution ($0.141''$ pixel$^{-1}$) using the Yale Astronomy Department's PDS microdensitometer. Most images are in FITS format with WCS coordinates and are typically 3.7 MB in size where as three "HiRes" versions of plates PH3033S, PH563vB, and PH7252vB are 26 MB in size and cover a somewhat larger scanned FOV thus covering the remnant's NE ejecta jet more completely.