Diffuse Atomic and Molecular Gas near IC443

arXiv:0903.0638v1 [astro-ph.GA] 3 Mar 2009 Diffuse Atomic and Molecular Gas near IC 443 A. Hirschauer1, S. R. Federman2, George Wallerstein3, and T. Means3 ABSTRACT We present an analysis of results on absorption from Ca II, Ca I, K I, and the molecules CH+, CH, C2, and CN that probes gas interacting with the supernova remnant IC 443. The eleven directions sample material across the visible nebula and beyond its eastern edge. Most of the neutral material, including the diatomic molecules, is associated with the ambient cloud detected via H I and CO emission. Analysis of excitation and chemistry yields gas densities that are typical of diffuse molecular gas. The low density gas probed by Ca II extends over a large range in velocities, from −120 to +80 km s−1 in the most extreme cases. This gas is distributed among several velocity components, unlike the situation for the shocked molecular clumps, whose emission occurs over much the same range but as very broad features. The extent of the high-velocity absorption suggests a shock velocity of 100 km s−1 for the expanding nebula. Subject headings: ISM: abundances — ISM: kinematics and dynamics — ISM: molecules — ISM: supernova remnants (IC 443) 1. Introduction IC 443 seems to be an example of the interaction of a supernova remnant (SNR) with an interstellar cloud or complex of clouds. As such it provides the opportunity to observe the effects of the SN shock penetrating the high density gas of the clouds. This involves heating the cloud to x-ray temperatures, followed by rapid cooling leading to a significant increase in the cloud’s density. IC 443 has been a very popular target and comparison object primarily for x-ray observations and as an object with emission by excited molecules. According to 1Department of Physics, University of Notre Dame, Notre Dame, IN 46556. 2Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606; steven.federman@utoledo.edu 3Department of Astronomy, University of Washington, Seattle, WA 98195; wall@astro.washington.edu – 2 – SIMBAD there have been 619 published studies or references to published studies between 1850 and 2007. IC 443 has provided an opportunity to compare observations and theory of the hydro- dynamics and radiative transfer associated with the penetration of clouds by a SN shock. Specific calculations were first made by McKee & Cowie (1975) and reviewed by Chevalier (1977). Early detailed spectroscopic observations of absorption from the SN shocked clouds associated with the Vela Remnant were described by Jenkins, Silk, & Wallerstein (1976). Here we describe measurements on atomic and molecular absorption seen in the spectra of stars behind IC 443 and attempt to link them to the wealth of results already available. Observations of SNRs may be made by a wide variety of instruments each of which defines the spectral resolution, spectral coverage, and spatial resolution. We present new data on interstellar (IS) absorption from atoms and molecules at visible wavelengths. Such observations provide the finest spatial resolution and high spectral resolution, but are limited by the availabilty of background stars. The stars must be of sufficient brightness and have a relatively simple absorption spectrum to permit a clear definition of the IS features. Members of the Gem OB1 association afford us the opportunity to probe significant portions of the sky in the vicinity of IC 443. Early molecular observations with good spatial resolution of phenomena associated with IC 443 were obtained by Cornett, Chen, & Knapp (1977) and Scoville et al. (1977) using the CO line at 2.6 mm. The former achieved a resolution of 24′′ × 27′′ while the latter had a half-power beamwidth of 2′. Both studies compared their contours with the red image of the Palomar Sky Survey where the emission is dominated by H-alpha. The strongest emission was observed to come from the region between the two most prominent H-alpha emitting clouds, hinting that the CO was associated with a molecular cloud rather than with the nearby H II regions. In fact most papers since then have referred to IC 443 as the interaction of a SNR with a molecular cloud. As such it is probably the most readily observable example of an SNR associated with a molecular cloud because both the Vela Remnant and the Cygnus Loop seem to involve atomic gas with only a small amount of associated molecules. Two papers within the past few years have attracted attenion to IC 443 once again. Snell et al. (2005) used the Submillimeter Wave Astronomy Satellite to observe previously inaccessable lines of H2O, O2, C I, and 13CO along with ground-based observations of CO and HCO+. The authors invoke a combination of a fast J-type shock with velocity of about 100 km s−1 and a slow shock (10 to 20 km s−1) that could be either J-type of C-type. Using the Very Large Array and Arecibo telescopes Lee et al. (2008) observed 21 cm H I emission with a resolution of 40 arcseconds, comparable to that of the

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