MULTIPLE OUTFLOWS IN THE BIPOLAR PLANETARY-NEBULA M1-16 - A MOLECULARLINE STUDY

Extensive observations of the molecular gas in the young, compact plan etary nebula M1-16 have been made, using the Swedish-ESO-Submillimeter Telescope. A map of the CO J = 2-1 emission shows that the molecular envelope contains both a slow and a fast outflow with expansion veloci ties of 19 km s-1 and > 34 km s-1, respectively. The slow outflow is m ildly elliptical, while the fast molecular outflow is bipolar. This fa st outflow is roughly aligned with the very fast outflows recently fou nd in the optical, while the long axis of the slow elliptical outflow is roughly orthogonal to the optical outflow axis. The kinematic times cales for the CO fast outflow and the optical very fast outflow agree closely, supporting the view that the former represents material in th e slow outflow accelerated by the very fast outflow. The kinematic sig nature of a disk expanding with about 15.5 km s-1 can also be seen in the CO J = 2-1 data. The mass-loss rate (a) for the slow outflow is gr eater-than-or-equal-to 2.8 x 10(-5) M. yr-1 and possibly as large as 9 x 10(-5) M. yr-1, (b) for the fast outflow is greater-than-or-equal-t o 5 x 10(-6) M. yr-1, and (c) for the very fast optically visible outf low is almost-equal-to 5 x 10(-7) M. yr-1. The disk mass is almost-equ al-to 6 x 10(-3) M.. Grain photoelectric heating results in temperatur es of 20-70 K in molecular gas of the slow outflow. The C-13/C-12 abun dance ratio in M1-16 is found to be 0.33, quite possibly the highest f ound for any evolved object. Upper limits for the O-18/O-16 and O-17/O -16 ratios were found to be consistent with the values found in AGB st ars. A search for other molecular species in M1-16 resulted in the det ection of the high-excitation species HCN, CN, (CN)-C-13, HCO+, and (H CO)-C-13+ and possibly N2H+. Both the HCO+/HCN and CN/HCN line-intensi ty ratios are enhanced, the former by a very large factor, over the va lues found in the envelopes of AGB stars, probably as a result of enha ncement of the CN and HCO+ abundances due to photochemistry induced by the stellar UV. The CS J = 2-1, SiO J = 2-1 (v = 0), and SiS J = 6-5 lines were not detected to low levels. For the high-excitation molecul es, adequate collisional excitation of rotational levels and survival against photodissociation by the UV radiation requires significant clu mping of the molecular gas into clumps with H-2 densities approximatel y 10(5) cm-3. The IRAS fluxes of M1-16, assuming negligible contributi on from line emission, imply the presence of about (1.7-0.4) x 10(-3) M. of cool dust (temperature around 50 K) and a smaller quantity, (2.7 -3.1) x 10(-6) M., of warmer dust (temperature around 125 K) for a pow er-law emissivity index p = 1-2. The evolutionary nature of M1-16 cann ot be explained by existing single-star models of post-AGB evolution. The very high C-13/C-12 abundance ratio in M1-16 suggests a possible e volutionary connection between M1-16 and the rare class of J-type sili cate-carbon stars which also have high C-13/C-12 ratios and are though t to be binary systems with accretion disks.