%R 1997PASP..109..937H
%J-950
%T Star Formation in Irregular Galaxies: A Review of Several Key Questions
%A HUNTER D.
%F contents_97_09
%K Invited Review
%B Star formation takes place in a different and simpler environment in irregular galaxies compared to spirals. Because
they lack spiral density waves, non-interacting irregular galaxies are interesting laboratories for all of the internal
processes other than spiral density waves that are involved in normal star formation. Most irregular galaxies are
currently forming stars, and some are forming stars at rates that are comparable to those for spiral galaxies. In
addition, there is a larger range in star formation rates among irregular galaxies than spirals. I discuss the status of
our knowledge about large-scale star formation processes in irregular galaxies in the context of four key questions:
What regulates star formation on global and local scales in irregular galaxies? What feedback processes are operating?
What are the consequences of differences in the interstellar medium on the star formation process? What role does the
extended gas play in the evolution of irregular galaxies? Answers to these questions are important for understanding not
only how star formation works in irregular galaxies, but in understanding the process by which galaxies form stars and
evolve anywhere.

%R 1997PASP..109..951K
%J-957
%T A Photometric Study of V798 Cygni
%A KIM C., JONER M.
%F contents_97_09
%K Stars
%B \begin{tex}New photometric $(uvby\beta)$ observations of the intrinsic variable star V798 Cyg have been secured and used to
derive values of foreground reddening, E($b - y$) = 0\fm117, and metallicity, [Fe/H] = 0.64. Intrinsic ($b - y$) and
$c_{1}$ values indicate a mean effective temperature, $< T_{eff} >$ = 7150 K, and a mean surface gravity, $<\log g>$ =
3.39. Pulsation theory and theoretical evolutionary tracks yield a mass of 2.3$M_{\odot}$ and an age of 0.63 Gyrs.
Although V798 Cyg has been described as being multi-periodic, this conclusion is not confirmed by our observations. V798
Cyg in most respects resembles a typical population I dwarf Cepheid.
\end{tex}

%R 1997PASP..109..958A
%J-968
%T 9 Temperatures for A0-K0 Supergiants from 13-Color Photometry
%A ALFARO H.B., FERRO A.A., SCHUSTER W.J.
%F contents_97_09
%K Stars
%B \begin{tex}Observations on the 13-color photometric system are reported for 71 A0-K0 supergiant stars brighter than V=6.0. Three
independent methods to determine the effective temperatures for A0-K0 supergiants from their 13C photometry are
discussed: 1) Calibrations between T$_{eff}$ and reddening-free indices are developed; temperatures were collected from
the literature for the calibration stars, and most of them were spectroscopically determined. 2) An empirical
correlation between intrinsic colors in the 13C system and T$_{eff}$ has been derived. 3) The unreddened colors are
compared with synthetic colors calculated by Kurucz (1989); this leads to simultaneous estimates for T$_{eff}$ and log
$g$. The estimated uncertainties in T$_{eff}$by the three methods are comparable and are approximately plus or minus
200-300K. 
\end{tex}

%R 1997PASP..109..969K
%J-976
%T The Spectrum Near Maximum Light of the Unusal R Coronae Borealis Variable DY Persei
%A KEENAN P.C., BARNBAUM C.
%F contents_97_09
%K Stars
%B DY Per was confirmed photometrically as an R CrB variable by Alksnis in 1994. Spectra near maximum light show the
high-speed ejection of matter (sodium at -174 km/sec in DY Per) characteristic of many of these variable stars. Moderate
hydrogen deficiency may also be present. DY Per is remarkable in having a temperature many hundreds of degrees lower
than most of the R CrB variables. It is unusual also in not showing clear spectroscopic evidence of high
luminosity.

%R 1997PASP..109..977L
%J-981
%T CG Muscae: A Cataclysmic Mis-Classification
%A LAYDEN A., WACHTER S.
%F contents_97_09
%K Stars
%B We have obtained extensive photometry of the suspected cataclysmic variable CG~Muscae, and find that it is in fact an
RR Lyrae star. We measure its light curve parameters and derive physical parameters including metal abundance, reddening
and distance. We also have discovered three new variables in the nearby field. We suspect that two are contact binary
stars, while the third is too faint to determine its variability type with certainty.
Pacific

%R 1997PASP..109..982F
%J-989
%T A Reassessment of the IUE Emission Line Spectrum of the Planetary Nebula NGC 5189 and Its Central Star
%A FEIBELMAN W.
%F contents_97_09
%K Interstellar Medium and Nebulae
%B Archival high-and low-dispersion IUE spectra of NGC 5189 and its central star were reexamined. It was found that
earlier published results misinterpreted nebular features for stellar emission lines due to incorrect coordinates and/or
incorrect pointing of the spacecraft. NGC 5189 has a UV spectrum rich in emission lines of He II, C II], C III, C III],
C IV, C V, N III], N IV], O I, O III], O IV], O V, O VI, O VII, O VIII, [Ne III], [Ne IV], [Ne V], [Mg V], [Ar IV], Si
III], and Fe II. The data were reextracted and the emission line fluxes were measured. Electron density for C III] and
terminal wind velocities from C IV P Cygni profiles were determined. Comparisons of the IUE spectra of NGC 5189 and NGC
6905 show that these objects have very similar characteristics.

%R 1997PASP..109..990C
%J-997
%T Expansion of the Supernova Remnant RCW 103
%A CARTER L.M., DICKEL J.R., BOMANS D.J.
%F contents_97_09
%K Interstellar Medium and Nebulae
%B \begin{tex}A new CCD image of the supernova remnant RCW\,103 was taken in 1995 to compare with a photographic plate taken in
1970. We calculated the proper-motion expansion of the outer edge and several filaments by comparing radial slices
through each of the data sets. The mean expansion rate of the outer edge is 1\farcs 8~$\pm$~0\farcs 2 per 25 years, or
about 1100 km sec$^{-1}$. At this velocity the remnant is most likely around 2000 years old. In addition, it must have
made the transition from the double-shock phase of evolution to the point-blast phase fairly recently for the initial
energy of the supernova explosion to be within a reasonable range.
\end{tex}

%R 1997PASP..109..998S
%J-1056
%T An Optical Atlas of Extreme Ultraviolet Explorer (EUVE) Sources
%A SHARA M.M., BERGERON L.E., CHRISTIAN C.A., CRAIG N., BOWYER S.
%F contents_97_09
%K Atlases
%B The Extreme Ultraviolet Explorer (EUVE) has been detecting EUV sources since its launch in June 1992. Positions of
540 sources have been made available to the community by the EUVE team. We have extracted 7' X 7' images centered on
these 540 EUVE sources from the Space Telescope Science Institute digitized sky archives. We present these images as
mosaic finder charts to aid observers trying to identify EUVE sources, or to characterize known sources.

%R 1997PASP..109.1057O
%J-1061
%T Holographic Atmospheric Turbulence Simulator for Testing Adaptive Optics Systems
%A OTSUBO M., TAKAMI H., IYE M.
%F contents_97_09
%K Astronomical Instrumentation
%B The basic principles, the manufacturing processes and the performance of a wavefront turbulence generator system that
incorporates a computer generated hologram are described. This system was shown to be useful for evaluating in the
laboratory the performance of the prototype adaptive optics system that was constructed for the 8 m Subaru
telescope.

%R 1997PASP..109.1062G
%J-1067
%T Imaging With STIS on the Hubble Space Telescope: Astronomy at V=30
%A GREGG M., MINNITI D.
%F contents_97_09
%K Astronomical Instrumentation
%B \begin{tex}In February, 1997, the second Space Shuttle servicing mission to the Hubble Observatory installed the Space Telescope
Imaging Spectrograph (STIS). This new instrument will greatly enhance the spectroscopic capabilities of the Hubble Space
Telescope by providing a longslit format and CCD detector technology. STIS can also be used as an imager, providing an
alternative to the Wide Field Planetary Camera 2. The optical filter set of STIS is limited and does not contain
standard bandpasses, but we show here that this does not preclude useful two-color broad band photometry. Because the
STIS bandpasses reach $\sim 1.5$ magnitudes deeper than WFPC2, the STIS photometric system may be preferable for many
applications where a faint limiting magnitude and fine spatial resolution are overriding considerations. The two optical
wide-band choices on STIS are a clear aperture and a longpass ($\lambda > 5500$\AA) filter. We define an effective
shortpass filter from the difference of these, making two-color photometry possible with STIS. We present preliminary
transformations between the STIS system and Cousins BVRI bandpasses, showing that these transformations are very
well-behaved over almost all temperatures, luminosities, and abundances for normal stars. In an 8-orbit cycle, STIS will
be able to reach signal-to-noise of $\sim 5-10$ at V = 30.0 in its clear and longpass imaging modes, a significant
increase in the power of HST to address a number of fundamental issues out of reach of current instrumentation
capabilities on the ground or in space.
\end{tex}

%R 1997PASP..109.1068L
%J-1068
%T Genetic Algorithms, Pulsar Planets, and Ionized InterstellarMicroturbulence
%A LAZIO T.J.
%F contents_97_09
%K Dissertation Summaries
%B \begin{tex}We probe the intense microturbulence in the Galactic center and the radio-wave scattering it generates by analyzing
observations of extragalactic sources, OH and H${}_2$O masers, and free-free emission. The region responsible for the
enhanced, anisotropic angular broadening of Sgr~A${}^*$ and nearby OH masers is within 150~pc of the Galactic center and
has an angular radius $\approx 1\arcdeg$. The enhanced scattering probably occurs in the interface regions between
$10^7$~K gas and molecular clouds and is a manifestation of the energetic processes occurring in the Galactic center.
Radio scattering measurements are also used to probe turbulent gas toward the Galactic anticenter. Ionized gas at
Galactocentric distances $\sim 50$~kpc is suggested by absorption lines in quasar spectra, the appearance of the
\ion{H}{1} disks of nearby galaxies, and models for low-redshift quasar absorption systems and Galactic ``fountains.''
We conducted multifrequency, Very Long Baseline Array (VLBA) observations on twelve extragalactic sources in order to
measure their scattering diameters. Seven sources are at $|b| < 1\arcdeg$ and their lines of sight potentially probe
path lengths $\gtrsim 50$~kpc through the disk. We find that the ionized disk is unwarped, has an extent of $\approx
20$~kpc, and traces the extent of massive star formation in the outer Galaxy. Planetary companions to neutron stars are
challenging to recognize amid the several processes that contribute to pulsar arrival time data. We use a genetic
algorithm to search for planetary companions to pulsars. Genetic algorithms are an optimization method that uses
biological-like concepts such as survival of the fittest, mutation, and chromosome exchange. The algorithm searches
parameter space in the same way that life finds optimal niches in the biological environment---incremental rewarding of
successful variations. Fitting for Keplerian orbits requires a search through four non-linear parameters per planet and
is especially difficult if there is a large range of planetary masses and orbital periods. We find that the GA is more
efficient and more accurate than the downhill simplex and simulated annealing algorithms. We confirm the presence of a
second planetary companion to PSR~B0329$+$54 and identify possible companions to B1911$-$04 and
B1929$+$10.
\end{tex}

%R 1997PASP..109.1069V
%T A Nearby Study of Blue Dwarf Galaxies
%A VANZI L.
%F contents_97_09
%K Dissertation Summaries
%B \begin{tex}Blue Dwarf Galaxies (BDG) are objects of low luminosity ($M_V\ge-18$) and very blue visible colors. Both the colors
and the presence of narrow emission lines in their spectra are usually interpreted to result from intense episodes of
star formation. The metallicity of the BDG is usually low with values in the range $10^{-2}-1~Z_{\odot}$. Wolf-Rayet
(WR) features are detected in many cases in the optical spectra. This is an unexpected characteristic since according to
stellar evolution, the number of WR stars in a star forming region should increase with the metallicity while WR
features are only rarely detected in solar metallicity galaxies. Different morphologies are found among BDG including
compact elliptical, irregular, magellanic, interacting. Due to the low luminosity in most of these objects the starburst
(SB) episode dominates the emitted radiation. Therefore starbursts can be studied in more detail in dwarf galaxies than
in giant spiral galaxies where the presence of a quiescent stellar population is important in defining the observed
characteristics. Moreover BDG are a unique laboratory to study the star formation process in low metallicity
environments. We have used new imaging and spectroscopy in the near infrared to study both the star formation history
and the excitation mechanism of the near infrared lines in BDG. The observations were taken with the Steward Observatory
telescopes. We concentrated on 8 objects selected to be a reppresentative but bright sample of BDG, they are: II Zw 40,
He2-10, NGC 3077, NGC 4214, NGC 4449, NGC 1569, NGC 4861 and NGC 5253. The data were used to constrain a starburst
model. For II Zw 40 we were able to fit the observations using a gaussian star formation rate with FWHM=5 My and a solar
neiborhood IMF. The star formation episode appears to have occured about 4 Myr ago with aproximately one tenth of the
total mass of the galaxy involved. Evidence for an evolved population was found in the outer parts of II Zw 40. We also
studied the possible periodicity of the starbursting process ruling out episodes comparable to the present one for the
last billion years. For all the other galaxies we confirm the tendency of the burst in BDG to be very short, no more
than a few million years. The short duration of the burst deduced from our modelling is consistent with the detection of
WR features, since short bursts also produce a WR/O ratio higher than a long duration or continous burst. The presence
of WR stars is well correlated with the age of the burst. We found a very good correlation between the [FeII] line at
$1.64 \mu m$ and the age of the burst for a sample of SB galaxies, well explained in terms of a model where all the
[FeII] emissin originates from supernova remnants. All the BDG, with the exception of He2-10, show a deficiency in
[FeII], in agreement with the low metal content of these objects. Using observations of M 82 we calibrated the [FeII]
emission for solar metallicity SB, obtaining good agreement with the supernova remnants observed in the Galaxy. The
correlation between molecular hydrogen emission ($H_2$) at $2.12 \mu m$ and age is weaker. In this case there is a
minimum emission level associated with supernovae and an additional contribution from different excitation mechanisms.
No deviation from the general trend is detected for BDG when compared to normal starburst in agreement with an
independency of $H_2$ on metallicity. Indications for fluorescently excitated $H_2$ were found in a few cases. We
briefly analyzed the FIR-radio relatioship finding that BDG follow the trend defined by IR galaxies, despite the low
metallicity of the BDG. Finally we use the HeI line at $1.70 \mu m$ as an indicator for the presence of high mass stars.
Our results show a tendency of commonly used [OIII]/H$\beta$ parameter to overestimate the stellar temperature. The
correlation between the $1.70 \mu m$ line and the age of the burst is very good. We belive this line is a very reliable
indicator of stellar temperature being less affected by the extinction and the electron temperature than the temperature
indicators in the visible.
\end{tex}