%R 1997PASP..109.1073H
%J-1076
%T Time-Series Ensemble Photometry of SX Phoenicis Stars. II. ae Ursae Majoris
%A HINTZ E., HINTZ M.L., JONER M.D.
%F contents_97_10
%K Stars
%B \begin{tex}We have examined the short period, double-mode variable star AE Ursae Majoris. Using time series ensemble photometry
we have determined six new times of maximum light. We also applied a Fourier decomposition to the data to determine the
component frequencies of the light curve. Using our data, along with archival data, we find that the period of AE UMa is
continually decreasing at a rate of $-1.14\times 10^{-10}$ d ${\rm d}^{-1}$. However, from the Fourier decomposition we
find that the period ratio ${\rm P}_{1}/{\rm P}_{0}$ has remained constant at 0.773. We also find that AE UMa is
incorrectly classified as a SX Phoenicis star.
\end{tex}

%R 1997PASP..109.1077G
%J-1084
%T Elemental Abundances and Atmospheric Parameters of Seven F-G Supergiants
%A GIRIDHAR S., FERRO A., PARRAO L.
%F contents_97_10
%K Stars
%B Spectroscopic abundance determinations for a sample of seven F-G stars have been carried out. The majority of them
have large galactic latitudes. One objective in deriving spectroscopic abundances is to differentiate evolved objects
seen at high galactic latitudes from the young population I supergiant stars that happened to have large galactic
latitudes but actually belong to the galactic disk. Secondly, it is important to get good calibrators for photometric
metallicity indices. It has been suggested in the past that many high galactic latitude F-G stars that are classified as
supergiants are in reality subgiants or dwarfs. Our spectroscopically derived gravities show that two of the stars
studied in this paper, HR 5165 and HD 114520, are not supergiants as classified in Bright Star Catalogue but are
subgiants belonging to the solar neighbourhood. In our sample, HR 3229 and HR 8470 display solar abundances and the
derived gravities support the bright giant luminosity class ascribed to them. HR 4114, HR 4912 and HR 7671 have
abundances significantly different from those of young supergiants of galactic disk. The evolutionary status of these
objects is discussed.

%R 1997PASP..109.1085S
%J-1088
%T Hipparcos Astrometry of Infrared-Selected Sources and the Connection Between Optical and Infrared Reference Frames
%A SUTTON E.
%F contents_97_10
%K Stars
%B Astrometric data from the Hipparcos satellite are reported for the optical counterparts of 87 bright infrared
sources. These sources may be useful in defining a reference frame for infrared observations. The data are also useful
in studying the locations of circumstellar SiO masers.

%R 1997PASP..109.1089T
%J-1092
%T Parallaxes and Proper Motions of Prototypes of Astrophysically Interesting Classes of Stars. I. R Coronae Borealis
Variables
%A TRIMBLE V., KUNDU A.
%F contents_97_10
%K Stars
%B Hipparcos data were obtained under the 1982 announcement of opportunity for the seven brightest R CrB stars then
known. None of the parallax measurements is different from zero in a statistically significant way, though most of the
proper motions are. The body of the data nevertheless suggest that the stars belong to two rather different populations
in either luminosity, kinematics, or both. The best-known stars (R. CrB itself, RY Sgr, and perhaps others) probably are
the very luminous, M subscript v = -4 to -5, objects they are generally accused of being, but others may belong to a
fainter class for which there is some independent evidence among stars in the Large Magellanic Cloud. Alternatively, or
in addition, the apparently fainter stars may belong to a higher-velocity population that we have had rather bad luck in
sampling. Of two rash assumptions, the one that all seven stars are at the same distance of 1200 pc leads to a velocity
ellipsoid U superscript 2 superscript 1/2, V superscript 2 superscript 1/2, W superscript 2> superscript 1/2 = 41, 30,
35 km sec superscript -1, which is "not inconsistent" with values typical of (other) old disk populations, like carbon
stars, long period variables, and planetary nebulae. The seemingly less rash assumption that all stars have M subscript
v = -4.5 leads to U superscript 2 superscript 1/2, V superscript 2 superscript 1/2, W superscript 2 superscript 1/2, =
52, 60, and 104 km sec supercript -1, resembles no known stellar population, at least not in our galaxy.

%R 1997PASP..109.1093R
%J-1099
%T Stroemgren u Photometry of CH Cygni in 1995 and 1996
%A RODGERS B., HOARD D.W., BURDULLIS T., MACHADO-PELAEZ L., O'TOOLE M., REED S.
%F contents_97_10
%K Stars
%B \begin{tex}Rapid time-resolution, Str\"{o}mgren $u$-band photometry of CH~cygni shows a marked decrease in quasi-periodic, short
time scale ($\sim2000$--$3000$ s) variability between 1995 August and 1996 June. In 1995, we detected variability of
$\sim0.3$--$0.4$ mag with periods of $\approx2200$ s and $\approx2700$ s, which are remarkably similar to periods
reported by Hoard (1993) from similar $u$-band measurements of CH~Cyg in 1992. In contrast, during a number of nights in
1996 the $u$ magnitude was roughly constant within 0.1 mag, and the light curves showed no evidence of rapid
variability. The average $u$ magnitude of CH~Cyg decreased by $\sim0.9$ mag between 1995 and 1996, suggesting a common
source for the quasi-periodic variability and the $u$-band luminosity, namely the hot component in the interacting
binary. We discuss several possible explanations for this variability, including the spin of an accreting, magnetic
white dwarf (as in the intermediate polar class of cataclysmic variables) and the reprocessing of accretion-induced
radiation from the white dwarf in circumstellar material.
\end{tex}

%R 1997PASP..109.1100P
%J-1113
%T Superhumps in Cataclysmic Binaries. XII. CR Bootis, a Helium Dwarf Nova
%A PATTERSON J., KEMP J., SHAMBROOK A., THOMAS E., HALPERN J.P., SKILLMAN D.R., HARVEY D.A., VANMUNSTER T., RETTER A.,
FRIED R., NOGAMI D., BUCKLEY.D., KATO T., BABA H.
%F contents_97_10
%K Stars
%B \begin{tex}CR Bootis is an enigmatic blue variable star with rapid photmetric variations and a spectrum dominated by helium. It
sonsists of two white dwarfs in close orbit, with a probable underlying binary period of 1471 s. For years we have
marveled at the star's large nightly variations - ramping up or down at a rate of \sim0.1/hr. An intensive photometry
campaign in 1996 showed that this variability is cyclic with a quasiperiod of about 19 hr, and demonstrated association
of 14990 s photometric variations ("superhumps") with extended bright states ("superoutbursts"). During superoutburst,
the 1490 s signal initially decreased with $\dot P = -2\times 10^{-5}$, but then stabilized at 1487.29\pm0.02 s after
\sim 300-600 binary orbits. Spectroscopy reveals variably asymmetric absorption lines, with the asymmetry migrating on a
probable period of 36 hr; this may be the period of accretion disk precession. Neither the helium composition, nor the
degeneracy of the mass-losing component, nor the shortness of the period (all of the periods) seem to present any
barrier to the star in being fully certificable as a bona fide dwarft nova. Stabilization of the superhump period at
such a low value (1487.29 s) favors a model in which period changes arise from eccentricity changes rather than mean
radius changes in the disk. This naturally explains why decreasing period and decreasing amplitude are strongly linked
in the superhumps of dwarf novae.
\end{tex}

%R 1997PASP..109.1114N
%J-1121
%T The 1994 Superoutburst of the New SU UMa-type Dwarf Nova, SX Leonis Minoris
%A NOGAMI D., MASUDA S., KATO T.
%F contents_97_10
%K Stars
%B We present observations of SX LMi obtained during the 1994 long outburst at Ouda Station. Superhumps, with a period
of 0.06950 (\pm 0.00002) d, are detected. This confirms SX LMi as a new member of the SU UMa-type dwarf novae. We
measured the recurrence cycle of normal outbursts and superoutbursts to be about 35 d and 250 d, repsectively, from
outburst records by RoboScope (Indiana University) and amateur observers. These recurrence cycles are typical values for
normal SU UMa stars. However, the outburst amplitude (\sim3.8 mag) of SX LMi is small for an SU UMa star and close to
those of ER UMa stars. This small outburst amplitude might be understood if the viscosity at quiescence and the
mass-transfer rate are slightly high in SX LMi.

%R 1997PASP..109.1122J
%J-1127
%T The Consistency of Stroemgren-Beta Photometry for Northern Galactic Clusters. III. M67
%A JONER M., TAYLOR B.
%F contents_97_10
%K Stellar Clusters and Associations
%B \begin{tex}We have measured M67 stars in a Str{\" o}mgren-$\beta$ system based ultimately on data for the Hyades and Coma
clusters. By comparing our results to previously published data, we have derived formal corrections required to put the
other data on our system. Corrections which are statistically significant by our criteria are found for Str{\" o}mgren
measurements made by Strom et al.\ (1971, PASP, 83, 768). Those corrections range between 36 and 61 mmag. In addition,
corrections of 17 and 8 mmag, respectively, are found for $\beta$ measurements made by Eggen (1981, ApJ, 247, 503) and
Nissen et al.\ (1987, AJ, 93, 634). In addition to considering M67, we have updated earlier work of ours which was done
on Praesepe and NGC 752. After revising our criterion for statistical significance, we have changed our judgment about
two corrections which we had derived for published data for those clusters. Further work will be required to verify the
reality of those corrections. We have also compared our results to closely similar work which was done by Nissen (1988,
A{\&}A, 199, 146) and which had previously escaped our notice. Differences between our results and those of Nissen
appear to exist for $\beta$ in Praesepe and for $c_1$ in NGC 752. Independent measurements support our Praesepe result,
but the problem for NGC 752 remains unresolved. 
\end{tex}

%R 1997PASP..109.1128R
%J-1144
%T Period Changes of RR Lyrae Stars in Globular Clusters
%A RATHBUN P.G., SMITH H.A.
%F contents_97_10
%K Stellar Clusters and Associations
%B We have used data from the literature to reexamine the period changes of RR Lyrae variables in seven globular
clusters. There is a tendency for the ore extreme rates of period change to be found in RRab rather than RRcd stars.
Particularly absent from the RRcd star sample are stars showing large rates of period decrease, a result which may in
part reflect the small proportion of RRcd variables in Oosterhoff type I clusters. The apparent coupling of period
change to pulsation mode is not easily interpreted as an evolutionary effect, and appears to be without adequate
explanation.

%R 1997PASP..109.1145R
%J-1148
%T The Sun's Displacement from the Galactic Plane: Limits from the Distribution of OB-Star Latitudes
%A REED B.C.
%F contents_97_10
%K The Galaxy
%B Galactic latitudes and photographic magnitudes for large sample (N \sim 3600 - 12000) of OB stars within 10 degress
of the galactic plane and 4 kpc of the Sun have been used to estimate the Sun's displacement Zo from the galactic plane.
Reasonable choices of average absolute magnitudes and extinction parameters limit Zo to not less than about 6 nor more
than about 13 pc, with Zo = 10 - 12 pc mostly likely.

%R 1997PASP..109.1149H
%J-1153
%T US 3215: An Active gE2 Galaxy
%A HOWELL S.B., PESCE J.E., CONDON J.J., CIARDULLO R., USHER P.D.
%F contents_97_10
%K Quasars and Active Galactic Nuclei
%B The object US 3215 is an optically variable galaxy with very broad Balmer lines, relatively strong forbidden lines
and a weak UV-excess continuum. It has been classed as a Seyfert 1 galaxy. We report that optical CCD images taken in
excellent seeing reveal a central mini-quasar in an elliptical galaxy with a de Vaucouleurs profile extending across an
angular diameter of \sim arcsec. This corresponds to a linear size of almost 50 kpc (Ho = 50 km /sec/Mpc). Our data
indicate that the host galaxy is of type gE2 and is the gravitational center of a cluster of galaxies. A companion
galaxy is observed at a projected distance of 24 kpc. H and K magnitudes were obtained and the index H - K is consistent
with quasar colors. A VLA snapshot at 1425 MHz gives an upper limit to radio emission at a flux level of 0.2 mJy beam -1
that is consistent with the Sy 1 designation. Thus US 3215 appears to be an active broad-line cluster gE2 galaxy.

%R 1997PASP..109.1154T
%J-1164
%T The Orthogonal Transfer CCD
%A TONRY J., BURKE B.E., SCHECHTER P.L.
%F contents_97_10
%K Astronomical Instrumentation
%B We have designed and built a new type of CCD that we call an orthogonal transfer CCD (OTCCD), which permits parallel
clocking horizontally as well as vertically. The device has been used successfully to remove image motion caused by
atmospheric turbulence at rates up to 100~Hz, and promises to be a better, cheaper way to carry out image motion
correction for imaging than by using fast tip/tilt mirrors. We report on the device characteristics, and find that the
large number of transfers needed to track image motion does not significantly degrade the image either because of charge
transfer inefficiency or because of charge traps. For example, after 100~sec of tracking at 100~Hz approximately 3\% of
the charge would diffuse into a skirt around the point spread function. Four nights of data at the
Michigan-Dartmouth-MIT (MDM) 2.4-m telescope also indicate that the atmosphere is surprisingly benign, in terms of both
the speed and coherence angle of image motion. Image motion compensation improved image sharpness by about 0.5\arcsec\
in quadrature with no degradation over a field of at least 3 arcminutes.

%R 1997PASP..109.1165S
%J-1166
%T A High-Sensitivity Quadrant Detector for Image-Stabilization Applications
%A STILLBURN J., FLETCHER M., LECKIE B., BARRICK G., MONNET G.
%F contents_97_10
%K Astronomical Instrumentation
%B No abstract.

%R 1997PASP..109.1167B
%J-1169
%T Multiple Drift Scans: A Method for Radio Contimuum Observations in a Radome
%A BARVAINIS R.
%F contents_97_10
%K Astronomical Instrumentation
%B This paper outlines a new applicaton of the technique of drift scanning, for single-dish radio continuum measurements
within a radome. A radome scatters varying amounts of ground radiation into the receiver feed for different antenna
positions, causing difficult-to-cancel total power fluctuations as astronomical sources are tracked. Parking the
telescope and allowing a source to drift through the beam largely eliminates this problem, and integration time can be
built up by doing multiple drift scans on a given source. This technique has resulted in near-theoretical noise
performance for the Haystack telescope, albeit with the rather low on-source duty cycle inherent in this technique. But
even with the low duty cycle, multiple drift scanning has proven superior to the standard radome-retrace beamswitching
techniques used previously. 

%R 1997PASP..109.1170C
%J-1180
%T A Numerical Method for Calculating Stellar Occultation Light Curves from an Arbitrary Atmospheric Model
%A CHAMBERLAIN D.M., ELLIOT J.L.
%F contents_97_10
%K Computing and Data Analysis
%B \begin{tex}We present a method for speeding up numerical calculations of a light curve for a stellar occultation by a planetary
atmospheric model that has spherical symmetry. This improved speed makes least squares fitting for model parameters
practical. Our method takes as input several sets of values for the first two radial derivatives of the refractivity at
different values of model parameters, and interpolates to obtain the light curve at intermediate values of one or more
model parameters. It was developed for small occulting bodies such as Pluto and Triton, but is applicable to planets of
all sizes. We also present the results of a series of tests showing that our method calculates light curves that are
correct to an accuracy of $10^{-4}$ of the unocculted stellar flux. The test benchmarks are (i) an atmoshphere with a
1/r dependence of temperature, which yields an analytic solution for the light curve, (ii) an atmosphere that produces
an exponential refraction angle, and (iii) a small-planet isothermal mode. With our method, least-squares fits to
noiseless data also converge to values of parameters with fractional errors consistent with the level of synthetic noise
added to the light curve. We conclude: (i) one should interpolate refractivity derivatives and then form light curves
from the interpolated values, rather than interpolating the light curves themselves; (ii) for best accuracy, one must
specify the atmospheric model for radii many scale heights above half light; and (iii) for atmospheres with smoothly
varying refractivity with altitude, light curves can be sampled as coarsely as two points per scale height.
\end{tex}

%R 1997PASP..109.1181K
%J-1188
%T Optical Night-Sky Brightness at Mauna Kea over the Course of a Complete Sunspot Cycle
%A KRISCIUNAS K.
%F contents_97_10
%K Atmospheric Phenomena and Seeing
%B \begin{tex}We have produced a data base of $V$-band and $B$-band night-sky brightness measurements rather evenly spread out over
the course of a whole sunspot cycle from September 1985 to August 1996. Almost all the data were obtained at the 2800-m
level of Mauna Kea using the same telescope, same photomultiplier tube, filters, and diaphragm, thus minimizing various
sources of systematic error and allowing an estimate of the sources of random error. The yearly $V$-band averages of
observed sky brightness ranged from 21.287 to 21.906 magnitudes per square arc second. The color of the sky is $B-V$ =
0.930 and does not change discernibly over the course of the sunspot cycle. After correcting the $V$-band data to the
zenith, we find that the airglow component varied a factor of 4.5 over the course of the solar cycle. Once the 11-year
solar cycle effect is removed from the data, the most significant contribution to the scatter of individual data points
appears to be the short term variations on time scales of tens of minutes like those observed by the Whole Earth
Telescope project.
\end{tex}

%R 1997PASP..109.1189G
%J-1189
%T Dense Molecular Gas in Galaxies and the Evolution of Luminous Infrared Galaxies
%A GAO Y.
%F contents_97_10
%K Dissertation Summaries
%B \begin{tex}This thesis explores the molecular gas (the raw material for star formation), especially the {\it dense} molecular
gas content of luminous infrared galaxies (LIGs) and ``normal'' galaxies using millimeter line observations. Most LIGs
are closely interacting/merging galaxies and ``normal'' spiral galaxies are believed to be the building blocks of LIGs.
We here study and compare the distributions and masses of the total molecular gas and the {\it dense} molecular gas,
traced by CO and HCN emission respectively, in LIGs, starburst galaxies and ``normal'' spiral galaxies. The molecular
gas properties are then compared with the stages of galaxy- galaxy interaction and the far-IR luminosity to understand
the star formation process and evolution of LIGs. We first study the {\it dense} molecular gas extent and distribution
in $\sim $ 10 nearby ``normal'' galaxies by mapping HCN emission (complementary with CO) at least along the major axes.
We present the first detailed observational evidence that HCN emission in galaxies, \ie, the {\it dense} molecular gas,
is not confined to the inner $\sim 1$ kpc nuclear region, although the highest concentrations of {\it dense} molecular
gas are in the center. A significant fraction of {\it dense} molecular gas is distributed in the inner disks of galaxies
outside the nuclear or inner ring starburst regions, and can be detected to radii as large as a few kpc, perhaps to
diameters of $\sim D_{\rm 25}/4$. Then we have further surveyed HCN emission in more than $\sim $ 40 relatively distant
IR/CO bright ``normal'' galaxies and LIGs. Therefore, a statistically significant sample of HCN data in galaxies is
established. We find that LIGs, especially ultraluminous ones, contain tremendous amount of {\it dense} molecular gas
fueling the starbursts. Although LIGs are rich in molecular gas, some ``normal'' galaxies could have as much molecular
gas as LIGs. However, the {\it dense} molecular gas content of even gas-rich ``normal'' galaxies is much less than that
of LIGs of comparable molecular gas content. We show that HCN emission is better correlated with IR emission than that
of CO. The total {\it dense} molecular content, the ratio of HCN/CO luminosity and the distribution of the surface
brightness ratio $I_{\rm HCN}/I_{\rm CO}$ are important high mass star formation indicators. We also confirm that the
star formation efficiency indicated by $L_{\rm IR}/L_{\rm CO}$ depends on the fraction of {\it dense} molecular gas
($L_{\rm HCN}/L_{\rm CO}$) and that the $L_{\rm IR}/L_{\rm HCN}$ ratio is similar in all galaxies, ultraluminous or not,
hot or cold in dust temperature, illustrating the starburst nature of ultraluminous IR galaxies. A second goal of this
thesis is to study LIGs in the intermediate merging process, to determine the relationship between the various IR/CO
properties and galaxy-galaxy interactions. We find a correlation between the CO luminosity and the projected separation
of merger nuclei in a sample of more than $\sim 50$ LIG mergers, which suggests that the molecular content is decreasing
as merging advances. Although the correlation is weak for the truly ultraluminous ($L_{\rm IR}>10^{12} \ls$) IR mergers,
which could simply be due to the incompleteness of the sample since ultraluminous mergers are at great distances, the
correlation is better established with less luminous LIG mergers, more close to a {\it volume-limited} statistically
complete sample. The correlation slope for this nearby almost complete sample is the same as that of the large,
heterogeneous sample of 50 mergers. We conducted new CO observation in $\sim 20$ LIG mergers to provide the CO data for
this statistically complete sample of nearby LIG mergers. This correlation seems to have important constraints on both
the merger- induced star formation models and the evolution scenario of LIGs. We have also conducted high resolution
interferometry CO imaging in two spectacular LIGs, Arp 118 and Arp 119. We detected strong CO emission from rings/tails
more than 10 kpc away from the nuclei, and most molecular gas is extranuclear. Detailed study of the distribution and
kinematics of the molecular gas can provide the dynamical clues to the origin and evolution of these LIGs. Finally, we
study the environment and spatial distribution of LIGs. We found that LIGs have stronger clustering than that of \IRAS
galaxies, yet most of them are not inside the groups of galaxies. Using various previous studies along with our own
present investigations, we suggest that some LIGs are remnants of the merged groups of gas-rich galaxies.
\end{tex}

%R 1997PASP..109.1190G
%J-1190
%T Detection of Extended Red Emission in the Diffuse Interstellar Medium
%A GORDON K.
%F contents_97_10
%K Dissertation Summaries
%B \begin{tex}Extended Red Emission (ERE) has been detected in many dusty astrophysical objects and this raises the question: Is
ERE present only in discrete objects or is it an observational feature of all dust, i.e.\ present in the diffuse
interstellar medium? In order to answer this question, we determined the blue and red intensities of the radiation from
the diffuse interstellar medium (ISM) and examined the red intensity for the presence of an excess above that expected
for scattered light. The diffuse ISM blue and red intensities were obtained by subtracting the integrated star and
galaxy intensities from the blue and red measurements made by the Imaging Photopolarimeter (IPP) aboard the Pioneer 10
and 11 spacecraft. The unique characteristic of the Pioneer measurements is that they were taken outside the zodiacal
dust cloud and, therefore, are free from zodiacal light. The color of the diffuse ISM was found to be {\em redder} than
the Pioneer intensities. If the diffuse ISM intensities were entirely due to scattering from dust (i.e.\ Diffuse
Galactic Light or DGL), the color of the diffuse ISM would be {\em bluer} than the Pioneer intensities. Finding a {\em
redder} color implies the presence of an excess red intensity. Using a model for the DGL, the blue diffuse ISM intensity
was found to be entirely attributable to the DGL. The red DGL was calculated using the blue diffuse ISM intensities and
the approximately invariant color of the DGL calculated with the DGL model. Subtracting the calculated red DGL from the
red diffuse ISM intensities resulted in the detection of an excess red intensity with an average value of $\sim$10~${\rm
S}_{10}({\rm V})_{\rm A0V}$. This represents the detection of ERE in the diffuse ISM since H$\alpha$ emission cannot
account for the strength of this excess and the only other known emission process applicable to the diffuse ISM is ERE.
Thus, ERE appears to be a general characteristic of dust. The correlation between $N_{HI}$ and ERE intensity is $(1.43
\pm 0.31)\times 10^{-29}$~ergs~s$^{-1}$~\AA$^{-1}$~sr$^{-1}$~\mbox{H atom}$^{-1}$ from which the ERE photon conversion
efficiency was estimated at 10\%. 
%K Dissertation Summaries
\end{tex}

%R 1997PASP..109.1191S
%T The Milliarcsecond Structure of A Sample of Southern Blazers
%A SHEN Z.-Q.
%F contents_97_10
%B \begin{tex}This dissertation presents the results wherein a total of 48 southern and equatorial
extragalactic radio sources were investigated with two sessions of a snap-shot VLBI imaging survey at 5~GHz. The survey
was the first of its kind in the southern hemisphere and filled a gap in VLBI observations of southern radio sources.
The fringes were detected for 45 sources, and images were obtained for 43. Of these 43 sources imaged, 21 had not
previously been mapped with VLBI at milliarcsecond scale. Based on these observations and upon other published results,
a thorough description of structures was presented for each source. Superluminal motion was confirmed and/or inferred in
6 sources by comparing with previous maps and the temporal variability of the radio flux density. No significant
differences in the source morphologies were found between the survey and northern hemisphere VLBI surveys (e.g., Pearson
\& Readhead survey). The bending of the jet from milliarcsecond to arcsecond scales seems to be a common feature in
blazars. A statistical comparison with $\gamma$--ray detection suggests the dominance of blazars among the detected
$\gamma$--ray sources; this might imply the importance of the beaming effect in the $\gamma$--ray emission. This
dissertation also describes the study of a southern millimeter bright blazar, OV--236, through multi--frequency,
multi--epoch VLBI observations. An analysis of the observational data reveals, for the first time, that a bent,
superluminal ($\beta_{\normalsize app}$~=~2.08) subparsec--scale jet exists in OV--236, which substantiates other
evidence of an enhanced jet--curvature in the vicinity of the core. There is a large difference (75$^\circ$) in the
position angle between the parsec and subparsec scale jet. The limb brightening, seen at the east end of parsec--scale
jet and also at the west end of the core, may signify an interaction of the source with ambient media, further
suggesting that the bending of the subparsec--scale jet might be caused by such an effect and that a similar bending
might occur within the parsec--scale jet. There is probably a correlation between the flux density outbursts and the
genesis of new components. Finally, some suggestions are made for the future research. In brief, these are: 1) Survey
the remaining sources to form a complete sample for statistical analysis; and 2) Conduct follow--up observations of some
particularly interesting sources, such as superluminal candidates, compact steep spectrum sources and
$\gamma$--ray--loud blazars, to obtain detailed information on structural evolution. A proposal entitled
``Multi--Frequency High--Resolution Imaging Observations of OV--236'' was submitted to the VLBI Space Observatory
Programme (VSOP) and has been selected to be part of the VSOP Key Science Program. The aim is to obtain the spectrum and
to derive the distributions of relativistic electrons and the magnetic field as well as to study the fine structure
within the curved superluminal jet.
%K Dissertation Summaries
\end{tex}