Low-frequency (42, 57, 84 MHz) excited-carbon lines toward Cassiopeia A

Observations of C-recombination absorption lines at 42.1, 57.1, and 84.2 MHz toward Cas A, obtained using the north-south double array (432 x 40 m each) of the wide-band DKR-1000 cross-type radiotelescope at Pushchino Radio Astronomy Station during August-September 1983, are reported. The data are presented in tables and graphs and compared with the predictions of LTE, hydrogenic, and thermal-dielectronic population-level models. The best fit is obtained with a hydrogenic model in which the C lines are associated with molecular clouds at N(H) = 1000-10,000/cu cm, where a C II region of radius 0.76 + or - 0.09 pc, electron temperature 18 + or - 4 K, and electron density 0.28 + or - 0.05 /cu cm is formed by the action of internal or external 91.2-110.1-nm UV sources. The Doppler halfwidth of the lines is given as 17.5 + or - 2.7 km/s.