High-velocity NaI and CaII absorption components observed towards the IC 443 SNR

¹ Experimental Astrophysics Group, Space Sciences Laboratory, UC Berkeley, Berkeley, CA 94720, USA
² Department of Physics, Univ. of Wisconsin - La Crosse, La Crosse, WI 54601, USA

Corresponding author: B. Y. Welsh, bwelsh@ssl.berkeley.edu

Received: 7 May 2003
Accepted: 16 June 2003

Abstract

We present high-resolution spectra ( km s^-1) of the interstellar NaI and CaII interstellar absorption lines observed towards 4 early-type stars with distances of 900–1500 pc in the line-of-sight towards the IC 443 Supernova Remant (SNR). The spectra of two of these stars (HD 43582 and HD 254577) exhibit a very complex pattern of absorption with cloud components covering a total velocity range of -100 km s^-1 to +50 km s^-1. The relative absorption strength of many of the higher velocity components is highly variable between these two stars, suggesting that the disturbed interstellar gas in this region possesses significant density gradients and/or large differences in ionization and element depletion. In addition, we have detected three additional high-velocity components at , -84.0 and -67.6 km s^-1 solely in their CaII lines, suggesting that the very highest velocity gas is more ionized and/or warmer than the lower velocity components or it has a highly variable level of gas phase element abundances. 
The column density ratios of NaI/CaII for the higher velocity cloud components are all <0.2, which is consistent with appreciable levels of dust grain destruction due to interstellar shocks caused by interaction of the expanding SNR blast-wave with the ambient interstellar medium. The distance to IC 443 is confirmed at ~1500 pc, which places the remnant at a similar distance to the Gem OB1 stellar association. Finally we note that the model of Chevalier (1999), in which the SNR is expanding into a clumpy interstellar medium, can best reproduce the observed patterns of both emission and absorption.