Bibcode
DOI
Cuesta, L.; Phillips, J. P.
Bibliographical reference
Astronomical Journal v.111, p.1227
Advertised on:
3
1996
Citations
12
Refereed citations
9
Description
We have acquired low- and intermediate-resolution spectroscopy at 11
positions across the nucleus of NGC 6210. As a consequence, we are able
to map the variation of velocity, temperature, line excitation, and
density over the projected core and halo of this source. Temperatures
reach a peak value Te≌1.1×104K close
to the nucleus, and thereafter decline by ˜24% towards the
periphery of the core, some 7.5 arcsec from the central star. By
contrast, density peaks towards the north, achieving maximal values
ne≌6.1×103, and subsequently falls by
˜72% towards the southern limits of the region; a distribution
which is reminiscent of (and presumably causally related to) the
observed radio structure. Line excitation is highly variable, with
low-excitation lines particularly enhanced to the NW, along arms
extending NW and (to a lesser degree) SE into the halo, and close to a
bright condensation located some ˜17 arcsec outside of the primary
shell. These low-excitation extensions, and the associated NW
condensation, appear also to be the location of a significant kinematic
disturbance; a feature which is narrowly focused, and possesses
characteristics reminiscent of a highly collimated jet. it is apparent,
in brief, that the nucleus of NGC 6210 is ejecting material along two,
and possibly four opposing directions, with curvature of this outflow
indicating possible rotation of the collimating source. The kinematics
of the halo appear to be similarly disturbed, with evidence for at least
three circularly symmetric, low-amplitude ripples extending through the
exterior velocity field. Halo linewidths appear also to be appreciable,
of order 50 km s-1, although the precise origin of this
broadening remains far from clear. Finally, and in keeping with the maps
of density and line excitation, it is clear that the velocity structure
of the core is by no means straightforward. Detailed consideration of
our results suggests, however, that we may be observing a partially
disrupted shell, of type recently proposed in the cases of NGC 6905 and
NGC 7026. In particular, the kinematic trends for locations close to
P.A.=335° are reminiscent of spheroidal expanding shells-although
with notable disparities which may suggest some elongation or
fragmentation of the outflow. Alternatively, orthogonal axes reveal
strongly variable, and more-or-less parallel velocity trends between
front and rear shells, resulting in positive velocities to the west, and
corresponding negative velocities to the east. Such a tendency can be
reasonably modeled in terms of a pseudocylindrical outflow structure,
provided we assume appreciable ionization stratification, substantial
radial velocity gradients, and that the exterior has appreciable
nonradial asymmetries arising from localized fragmentation.