| dc.description.abstract | Since the identi cation of proto-planetary nebulae (PPNe) as transition objects between
the asymptotic giant branch stars and planetary nebulae more than two decades
ago, astronomers have attempted to characterise these exciting objects. Today many
questions still elude a conclusive answer, partly due to the sheer diversity observed
within this small subset of stellar objects, and partly due to the low numbers detected.
Fortunately, many of these objects display a rich spectrum of emission/absorption lines
that can be used as diagnostics for these nebulae.
This dissertation presents a study of six PPNe using the relatively new (at NIR
wavelengths) integral eld spectroscopy technique. This method has allowed the investigation
of distinct regions of these nebulae, and in certain cases the application of
magneto-hydrodynamic shock models to the data.
The goal of this research has been to investigate the evolution of PPNe by detailed
examination of a small sample of objects consisting of a full range of evolutionary types.
Near-IR ro-vibrational lines were employed as the primary tool to tackle this problem.
In all six sources the 1!0S(1) line is used to map the spatial extent of the H2. In
three of these objects the maps represent the rst images of their H2 emission nebulae.
In the case of the earliest-type object (IRAS 14331-6435) in this sample, the line
map gives the rst image of its nebula at any wavelength. In the only M-type object
(OH 231.8+4.2) in the sample, high-velocity H2 is detected in discrete clumps along
the edges of the bipolar out
ow, while a possible ring of slower moving H2 is found
around the equatorial region. This is the rst detection of H2 in such a late-type object
but due its peculiarities, it is possibly not representative of what is expected of M-type
objects. In IRAS 19500-1709, an intermediate-type object, the line map shows the H2
emission to originate in clumpy structures along the edges of a bipolar shell/out
ow.
The remaining three objects have all been the subject of previous studies but in each
case new H2 lines are detected in this work along with other emission lines (Mg ii,
Na i & CO). In the case of IRAS 16594-4656, MHD shock models have been used to
determine the gas density and shock velocity.
Two new python modules/classes have been written. The rst one to deal with
the data cubes, extract
ux measurements, rebin regions of interest, and produce line
maps. The second class allows the easy calculation of many important parameters, for
example, excitation temperatures, column density ratio values, extinction estimates
from several line-pairs, column density values, and total mass of the H2. The class
also allows the production of input les for the shock tting procedure, and simulated
shocks for testing this tting process.
A new framework to t NIR shock models to data has been developed, employing
Monte Carlo techniques and the extensive computing cluster at the University of Hertfordshire
(UH). This method builds on the approach used by many other authors, with
the added advantages that this framework provides a method of correctly sampling the
shock model parameter space, and providing error estimates on the model t. Using
this approach, data from IRAS 16594-4656 have been successfully modelled using the
shock models.
A full description of this class of stellar objects from such a small sample is not
possible due to their diverse nature. Although H2 was detected across the full spectral
vi
range of post-AGB objects, the phase at which H2 emission begins is still not clear.
The only M-type object in this work is a peculiar object and may not be representative
of a typical post-AGB star.
The H2 PPNe appear to be located at lower Galactic latitudes (b 20 ) than the
total PPNe population, possibly pointing to an above average mass and hence younger
age of these objects. | en_US |
