2005AJ....130..853S -
Astron. J., 130, 853-861 (2005/August-0)
Kinematic structure of H2and [Fe II] in the bipolar planetary nebula M2-9.
SMITH N., BALICK B. and GEHRZ R.D.
Abstract (from CDS):
We present new high-dispersion, long-slit, infrared (IR) spectra of the double-shell bipolar planetary nebula M2-9 in the emission lines [Fe II] λ16435 and H2v=1-0 S(1) λ21218. H2 spectra reveal for the first time the kinematic structure of the outer shell in M2-9. Kinematics of the inner shell, traced by [Fe II], resemble those of optical forbidden lines like [N II] λ6583, although we note subtle differences. [Fe II] and H2 shells have expansion speeds roughly proportional to distance from the star (``Hubble'' flows) and share the same dynamical age of 1200-2000 yr, depending on the distance to M2-9. Thus, the inner ionized lobes and outer molecular lobes, as well as the molecular torus and ``outer loops'' measured by other observers, were all formed around the same time. Consequently, their nested structure likely arises from an excitation gradient rather than independent ejections. H2 and [Fe II] emission is distributed more uniformly than [N II], and IR lines are not dominated by the moving ionization pattern like visual-wavelength lines. We suggest that this is because IR lines of [Fe II] and H2 are excited by relatively isotropic far-UV radiation (Balmer continuum), whereas optical lines respond to a directed rotating beam of Lyman continuum. Finally, we highlight intriguing similarities between M2-9 and the Homunculus of η Car, despite the different central engines powering the two nebulae.
Abstract Copyright:
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Journal keyword(s):
Stars: Circumstellar Matter - ISM: Planetary Nebulae: General - ISM: Planetary Nebulae: Individual: Alphanumeric: M2-9 - Stars: Evolution - Stars: Mass Loss
Simbad objects:
9
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