Bibcode
DOI
Guerrero, M. A.; Villaver, E.; Manchado, A.
Bibliographical reference
The Astrophysical Journal, Volume 507, Issue 2, pp. 889-908.
Advertised on:
11
1998
Journal
Citations
47
Refereed citations
45
Description
We present spatially resolved echelle spectroscopy, obtained at high
spectral resolution, for 15 multiple-shell planetary nebulae. Most
exhibit faint detached halos (IC 1295, MA 3, M 2-2, M 2-40, NGC 6804,
NGC 6826, NGC 6884, NGC 6891, NGC 7662, PM 1-295, and Vy 2-3).
Furthermore, we have included some with attached shells (IC 1454, K
1-20, K 3-73, and PM 1-276) to allow comparison of the kinematic
properties of the two subclasses of multiple-shell planetary nebulae. In
addition, some of the nebulae in our sample show a triple-shell
structure, composed of the bright main nebula and a combination of two
attached shells (PB 9), one attached shell and one detached halo (NGC
6826, NGC 6891, NGC 7662, and Vy 2-3), or two detached shells (NGC
6804). A new method for computing the expansion velocities of those
shells that do not show line splitting has been developed. This method
assumes a thick-shell model and uses the observed Hα emission
brightness profile to compute the volume emissivity dependence,
ɛ(r), with the distance from the center of the nebula. The
expansion velocity is then worked out by modeling how much the width of
a the Hα line decreases with the radius of the shell. The radial
velocity, expansion velocities of each shell, and turbulence
contribution to the line width are presented. The expansion velocity of
the detached halos spans from 12 to 30 km s^-1. It is worth noting that
the expansion velocities obtained by this method are greater than if
they were computed with a thin-shell model, as has previously been done.
In relation to the attached shells, their expansion velocities span from
10 to 30 km s^-1. When the expansion velocities of the outer attached
shells are related to the ellipticity of the inner shells, a trend
toward faster expansion of the outer than the inner shells at higher
ellipticities is found. The turbulent contribution to the line width has
also been established. It is smaller for halos (0 km s^-1 <=
sigma_tur <= 6 km s^-1) than for attached shells (0 km s^-1 <=
sigma_tur <= 15 km s^-1). This suggests that large-scale hydrodynamic
processes are more important in attached shells than in detached halos.
We have also studied the kinematics of the detached halos whose
morphology is perturbed from a round shape to a dipole asymmetry,
indicating its interaction with the surrounding interstellar medium. We
found systematic differences between the kinematical behavior of the
enhanced edge of the halo and the opposite side in these cases, thus
revealing the kinematic effect of the interaction of the halos with the
interstellar medium.