EVIDENCE FOR INFALL TOWARD Z-CANIS-MAJORIS FROM RADIO AND NEAR-INFRARED SPECTROSCOPY

We report radio line observations of CO(1-0), (CO)-C-13(1-0), CS(5-4), CS(2-1), (CS)-S-34(2-1), (HCO+)-C-13(1-0), HCS+(2-1), and N2H+(1-0) a nd near-infrared spectroscopy (in the K, L, and M bands) of Z CMa and its surroundings. Our results show that the CS(2-1) cloud around Z CMa is in approximate virial equilibrium and has a mass of some 42 Mo.. T he CS(5-4), (CS)-S-34(2-1), and (HCO+)-C-13(1-0) data reveal a central ly condensed and flattened inner cloud core structure perpendicular to the CO(1-0) outflow, which has a dynamical timescale of some (2 x 10( 3))-(1 x 10(4)) yr. The mass of the CS(5-4) core is 8.0-15 Mo., which is close to the magnetic critical mass. Along the major axis of the CS (5-4) core there is a velocity gradient, which can be interpreted as a superposition of initial cloud rotation and infall. Evidence for an i nfalling inner cloud core with a temperature gradient, an r(-1.5) dens ity law, and an r(-0.5) velocity law is provided by the redshifted sel f-absorption feature in the (HCO+)-C-13 profile, present in a very com pact region oriented perpendicularly to the CO(1-0) outflow of Z CMa. Motivated by these signs of infall in the inner cloud core, we probe w ith our observational data the inside-out collapse model of Shu and th e predictions of Galli & Shu for the collapse of a magnetized cloud co re. Our medium-resolution K-band spectrum shows besides the redshifted , very marginal Bry line four vibrationally excited first-overtone CO band heads in absorption. The slopes seen in the K-band spectrum are i ntrinsic to the FU Orionis-type disk of Z CMa and suggest the presence of the vibration-rotation bands of water vapor, implying a temperatur e around 2000 K and a hydrogen nuclei density on the order of 10(12) c m(-3) at 2.2 mu m. The likely cause of these water-band wings is the s trong heating produced by the mass accretion through the inner disk on to the star. Our L band does not show the 3.08 mu m water ice feature. Instead, our spectrum suggests the presence of a 2.9 mu m feature, pr obably due to stretching vibrations of OH, or a shift of the water-ice band to 2.9 mu m, caused by large grains when scattering dominates.