SUBMILLIMETER OBSERVATIONS OF THE SHOCKED MOLECULAR GAS ASSOCIATED WITH THE SUPERNOVA REMNANT IC-443

Submillimeter observations of various simple molecules in the shocked molecular gas associated with the supernova remnant IC 443 are present ed. CO 3-2 line profiles along the shocked ring are used to constrain the global kinematics of the region. It is found that in the S-SE part of the ring (clumps A-C) the shock occurs mostly along the line of si ght, whereas in the NE-NW part, the shock must be mostly perpendicular (clumps D, E, G). High-resolution (20-30'') maps in (CO)-C-12 2- 1 an d/or 3-2 have been obtained for clumps B, E, F and G, and show rapid v ariations in line profiles from position to position, probably reflect ing the inhomogeneous composition of the preshocked gas. At most place s, the gas appears to have undergone more than one shock, but it is ve ry difficult to assess the nature of the shock(s) (J vs. C-type) from the observed profiles. The conditions in the preshocked gas are well c onstrained from the observed self-absorption of CO and other molecules in clump G, and from the narrow CO emission in clump B. The temperatu re is T-o approximate to 10-20 K, and the density n(o) approximate to 10(4) cm(-3). The total preshocked gas column density is N(H-2) approx imate to (2+/-1) x 10(21) Cm-2, corresponding to A(v) approximate to 3 -4 mag. Thus, the preshocked cloud has similar properties to a translu cent cloud, and probably contains substantial amounts of atomic hydrog en and carbon. Searches for other molecules in the shocked gas have be en performed at two positions in clump G and one position in clump B. High-frequency lines of HCO+, HCN, HNC, CS, SO, SiO, H2CO and C2H have been detected, and significant upper limits have been obtained for va rious other, more complex molecules. The physical parameters in the sh ocked gas have been derived from an analysis of the excitation of thes e species. The temperature is well determined by the H2CO observations . It is found that in clump G, the observations cannot be reproduced b y a single-density model, but that at least two components are needed. The lower density (n approximate to 10(5) cm(-3), T approximate to 80 K) gas is responsible for most of the CO, HCO+ 1-0, HCN 1-0 and CS 2- 1 emission, whereas the higher density, warmer gas (n approximate to 3 x 10(6) cm(-3), T approximate to 200 K) provides most of the high fre quency emission. In clump B, the higher velocity components appear to have somewhat lower densities. Within the observational uncertainties, the abundances of HCO+ and HCN in the low-density component are not s ignificantly enhanced compared with the well-determined preshock value s. In the high-density component, the abundance of HCO+ is substantial ly lower. For the other molecules, the preshocked gas abundances are n ot well constrained, but the observed shocked abundances do not differ by more than factors of a few from those observed in cold, dark cloud s, except for SiO in the high-density component. Either the temperatur e in the dense shocked gas was not raised to sufficiently high values to modify the chemical abundances, or some important component of the shock models is missing, or the various chemical processes have conspi red to cancel any enhancements in IC 443. The latter explanation is pl ausible because the shock contained a substantial amount of atomic hyd rogen which can rapidly destroy many of the intermediate molecules in the reaction networks. The observed abundances are substantially lower than those found in one-fluid hydrodynamic shock models with a small H/H-2 ratio, but appear consistent with the li