Thesis Abstracts
A Photometric Investigation of the Fields
of Two Short-Period Cepheids in Cygnus
Georgi I. Mandushev
M.Sc. Thesis, Saint Mary's University
1994 August
Thesis Supervisor: David G. Turner
Photoelectric, photographic and CCD
photometry, as well as spectroscopic
observations and proper motion data for stars in
the fields of the short-period galactic Cepheids
V1726 Cygni and SU Cygni are presented and
analyzed. The existence of a sparsely populated
cluster associated with V1726 Cyg has been
confirmed, and a new, loose stellar group has
been found in the vicinity of SU Cyg.
The newly obtained distance modulus for
C2128+488 (Anon. Platais), the cluster
associated with V1726 Cyg, is Vo-Mv = 10.98 +/-
0.02 , corresponding to a distance of 1568 +/- 13
pc. The spatial coincidence and the close match
of the radial velocity, proper motion and age of
V1726 Cyg with those of the cluster indicate a
high probability of cluster membership for the
Cepheid. The space reddening of V1726 Cyg,
found from two neighbouring stars, is E(B-V) =
0.43 +/- 0.02 and its luminosity as a cluster
member is Mv = -3.42 +/- 0.07. This value is
close to that predicted from the PL relation under
the assumption that V1726 Cyg is an overtone
pulsator, an assumption which is strongly
supported by the Fourier parameters of the
Cepheid's light curve. It implies, however, an
unrealistically small value for the colour term in
the PLC relation; a more acceptable value for
the colour term is obtained if V1726 Cyg is
assumed to pulsate in the fundamental mode.
The newly found group of stars in the
vicinity of SU Cyg has a distance modulus of Vo-
Mv = 10.08 +/- 0.02 (d = 1040 pc). It contains
mostly early A to late F-type stars, with a few
early B-type stars whose membership is more
uncertain. The nature of this group is not
entirely clear; it might be associated with the
nearby association Vul OB4, which is at the
same distance (Turner, unpublished), or
represent a very sparse cluster, probably in its
final stages of dissolution.
A reddening of E(B-V) = 0.16 has been
determined for SU Cyg from a nearby (20
arcseconds) star having an accurate MK spectral
type. While the Cepheid is spatially coincident
with the stellar group, its absolute magnitude
implied from possible membership is brighter
than that predicted from the PLC relation. This
fact, together with the discrepancy between the
observed colour of the cluster turnoff and the one
expected for a Cepheid with the period of SU
Cyg, indicates that the latter is merely projected
by chance against the slightly more distant stellar
group. The probable discovery of a new
planetary nebula, located about 3 arcminutes
south of SU Cyg, and a possible new cluster 17
arcminutes west of SU Cyg, are also reported.
A Study of Molecular Gas Associated
With the HH24 Optical Jets
Lifang Ma
M.Sc. Thesis, Saint Mary's University
1994 September
Thesis Supervisor: George F. Mitchell
The HH24 complex has been mapped in
12CO J=3-2 emission at 14" resolution using the
15-m James Clerk Maxwell Telescope (JCMT) on
Mauna Kea, Hawaii. The map in 12CO J=3-2
emission exhibits complicated morphology with at
least two outflows emanating from the region of
the field centre. A blue-shifted molecular lobe
found in the northeastern part of the field aligns
well with the optically-detected flow HH24G,
while near the field centre the 12CO red-shifted
flow is coincident with the shocked H2 region
and the optically-detected moving gas designated
HH24A. The spatial coincidence of the
molecular outflows with the optical outflows
suggests that the two phenomena may be
physically associated. Analysis of the data
shows that the molecular outflow is asymmetric,
with the blue-shifted flow having five times more
mass and momentum than the red-shifted flow.
The momentum flux of the blue-shifted outflow
coincident with HH24G is found to be one order
of magnitude larger than the momentum of the
optical jet. The result implies that the optical jet
is incapable of driving the molecular outflow.
However, the conclusion is strongly affected by
uncertainties in estimates of the momentum flux
for both the optical jet and the molecular outflow.
Infrared and Submillimeter Emission
from Dust Surrounding Ultracompact H
II Regions
Jeffrey T. Daines
M.Sc. Thesis, The University of Calgary.
1994 April
Thesis Supervisor: Sun Kwok
Ultracompact HII regions are thought to
be ionized regions around newly formed massive
stars embedded in dense molecular clouds. The
ionized region is seen at only at radio
wavelengths as it is surrounded by a dust cloud
which intercepts most of the other radiation and
reradiates it at far infrared and submillimeter
wavelengths. The massive stars powering the
HII region are thought to have collapsed out of
the cores of the surrounding molecular cloud.
Models predict that a significant portion of the
energy distribution of UC HII regions is emitted in
submillimeter wavelengths. This thesis
investigates the composition and density
structure of the dust surrounding UC HII regions
by examining their low resolution infrared spectra
and far infrared and submillimeter photometry.
Special emphasis is placed on distinctive
features in the low resolution spectra believed to
be due to polycyclic aromatic hydrocarbon
molecules.
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