Accession Number : ADA464488


Title :   Low-Frequency Observations of Galactic Supernova Remnants and the Distribution of Low-Density Ionized Gas in the Interstellar Medium


Descriptive Note : Journal article


Corporate Author : NAVAL RESEARCH LAB WASHINGTON DC E O HULBURT CENTER FOR SPACE RESEARCH


Personal Author(s) : Kassim, Namir E.


Full Text : http://www.dtic.mil/get-tr-doc/pdf?AD=ADA464488


Report Date : 15 DEC 1989


Pagination or Media Count : 11


Abstract : New long-wavelength observations of Galactic supernova remnants (SNRs) at 30.9 and 57.5 MHz are used to derive detailed low-frequency radio spectra for 32 SNRs. Of these, approximately two-thirds show turnovers at low frequencies, implying the presence of a widespread, but inhomogeneous, ionized absorbing medium along the lines of sight. These observations are combined with other low-frequency data to derive free-free optical depths toward 47 SNRs and to constrain the physical properties of the ionized gas responsible for the absorption. Three generally accepted ionized components of the interstellar medium (ISM) which absorb low-frequency radio emission are (1) H II regions; (2) extended H II region envelopes (EHEs); and (3) the warm ionized medium (WIM).


Descriptors :   *OBSERVATION , *LOW FREQUENCY , *IONIZED GASES , *SUPERNOVAE , *INTERSTELLAR SPACE , REPRINTS , SPECTRA , NEBULAE , RADIO SOURCES(ASTRONOMY) , GALAXIES , LOW DENSITY , LONG WAVELENGTHS


Subject Categories : ASTRONOMY


Distribution Statement : APPROVED FOR PUBLIC RELEASE