A high-resolution long-slit spectroscopic study of the various bipolar outflow components in M 2-9 ("Butterfly Nebula") *
Received 9 September 1999 / Accepted 12 November 1999
High-resolution long-slit spectrograms of the line emission from the bipolar nebula M 2-9 obtained at various slit positions are presented. The data are used to study in detail both the kinematic and morphological properties of the various components of the bipolar outflow in M 2-9. Three main regions of outflow have been distinguished: a compact inner region represented by the central core, an extended intermediate region represented by the bright bipolar lobes, and an outer region represented by the faint outer loops. All three regions show a remarkably high bipolar symmetry with a uniform inclination of the bipolar axes (73o), whereas the deduced outflow velocities and kinematical ages are largely different from each other.
In the central core region, two physically distinct gas components, a high-velocity component and a low-velocity component, have been identified. The fast gas is of relatively high excitation and represents a highly collimated bipolar outflow system (micro-jets) with velocities of up to 195 km s-1. The kinematical age of the micro-jets is extremely small (10 years). The observations suggest that the outflow source is surrounded by a dense equatorial disk obscuring the inner portions of the receding jet. The slow gas is of lower excitation and is suggested to represent a wind either from the equatorial disk or from the evolved stellar component of the presumed central binary.
In each of the bipolar lobes, a (co-axial) double-shell structure has been identified, consisting of an inner shell of fast hot gas and an outer shell of slow cool gas/dust. The hot gas, traced by the narrow line component representing in situ emission, shows outflow velocities of 46 km s-1 indicating a kinematical age of 1300 years. The highest velocities are found near the bipolar axis. The cool gas/dust, traced by the broad line component representing dust-scattered emission, exhibits outflow velocities of 17 km s-1. The kinematical age of the cool-gas shell is about three times as large as that of the hot-gas shell.
The faint outer loops, traced by dust-scattered H line emission, present large redshifts in both loops indicating outflow velocities of 141 km s-1. The deduced kinematical age is 1300 years, comparable to that of the bipolar lobes, suggesting that both the outer loops and the bipolar lobes were formed at the same time.
Our results confirm that M 2-9 exhibits many properties which have little in common with those of planetary nebulae. In particular, the detection of fast bipolar jets and of a dense disk in the core region strengthen the hypothesis that M 2-9 probably belongs to a class of close mass-exchanging binary systems, like symbiotic novae, which are sources of collimated fast bipolar outflows.
Key words: ISM: planetary nebulae: individual: M 2-9 ISM: jets and outflows ISM: kinematics and dynamics stars: circumstellar matter ISM: dust, extinction
© European Southern Observatory (ESO) 2000
Online publication: February 9, 2000