A Mass and Density Estimate for the Unshocked Ejecta in Cas A based on Low Frequency Radio Data

Details A Mass and Density Estimate for the Unshocked Ejecta in Cas A based on Low Frequency Radio Data A Mass and Density Estimate for the Unshocked Ejecta in Cas A based on Low Frequency Radio Data

Jan 2012

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21910303d&link_type=abstract

American Astronomical Society, AAS Meeting #219, #103.03

Astronomy and Astrophysics

Astronomy

Scientific paper

One of the key discoveries from the spectral mapping of Cassiopeia A with the Spitzer Space Telescope was the discovery of infrared emission from cold silicon- and oxygen-rich ejecta interior to the reverse shock. When mapped into three dimensions, the ejecta distribution, including both hot and cold ejecta, appears quite flattened. On the front and back sides of Cas A, the Si- and O-rich ejecta have yet to reach the reverse shock while around the edge these layers are currently encountering the reverse shock giving rise to the Bright Ring structure that dominates Cas A's X-ray, optical, and radio morphology. In addition to morphology, the density and total mass remaining in the cold, unshocked ejecta are important parameters for modeling Cas A's explosion and subsequent evolution. The density estimated from the Spitzer data is not particularly useful (upper limit of 100/cm^3), however the cold ejecta are also observed via free-free absorption at low radio frequencies. Using Very Large Array observations at 330 and 74 MHz, we have a new density estimate of 2.3/cm^3 and a total mass estimate of 0.44 M_solar for the cold, unshocked ejecta. Our estimates are sensitive to a number of factors including temperature and geometry but we are quite pleased that our unshocked mass estimate is within a factor of two of estimates based on dynamical models. We will also ponder the presence, or absence, of cold iron- and carbon-rich ejecta and how these affect our calculations.

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