Cooling of Cosmic Gas - Jim Babb

We will investigate collisions between helium atoms and hydrogen
molecules using quantum scattering methods.  The resultant rotational and
vibrational excitation of molecules is a major cooling mechanism in
interstellar clouds and in objects formed in the early universe. Rate
coefficients for the cooling collisions which play an important role
in determining the thermal balance of primordial molecular clouds will
be calculated.


When is a Dwarf Star No Longer a Dwarf Star? - Bob Donahue, Sallie Balliunas 
 
For lower main sequence stars (i.e., dwarf stars with convection zones
and chromospheric activity), several relationships have been 
empirically derived over the years between the observable quantities 
of chromospheric Ca II H and K flux, B-V color index, and (when
detectable) rotation, to estimate values for other properties such 
as age, rotation (when it's not observed), and the existence of 
longer-term activity variations, etc.

These measurements are very important to understanding the Sun in
terms of its relationship to other stars (the ``solar stellar 
connection''), the ubiquity of planetary systems like our own,
and the role solar variations play in terrestrial climate change.

However, these relationships are not as well defined for evolved 
(giant) stars.  One difference is that for giants, stellar mass 
can no longer be presumed to be simply a function of B-V, and mass 
now plays a crucial role in a star's position on the H-R diagram and 
its subsequent evolution.

In between, there is a population of stars that either have just
begun to evolve off of the main sequence, or are about to do so.
They seem to share more in common with younger main sequence stars
than with red giants, but it is not clear which of the aforementioned 
relationships frequently used for lower main sequence stars
are still valid, or how far a star can evolve off of the main sequence
before these relationships can no longer be effectively used.

With the release of quality parallax measurements from the Hipparcos 
satellite, and highly-precise photometric data from robotic telescopes
on the ground, the existing measurements of chromospheric activity can
be analyzed for those stars presumed to be older than the Sun in greater
detail.

The project we would like to consider this summer (and work can be
extended into the next year as a senior project if desired) is
to use these data to examine slightly-evolved/older stars in detail 
in order to shed some light on the nature of sub-giant stars.
Or put another way, ``When is a dwarf star no longer a dwarf star?''

We'll be happy to supply lots of reprints that give the necessary
background.


Galaxy Clusters and Cosmology - John Huchra

Interest in the use of galaxy clusters to constrain cosmological
models is at an all time high.  One of the most important limits
on the value of Omega, the ratio of the actual mean mass density
of the Universe to the density needed to close it, can be estimated
by comparing the  abundances of clusters at high redshift (and thus
a long time ago) with the nearby density of clusters (e.g. see
Bahcall, Astroph 9711062).  This project is aimed at improving
the local cluster density function by creating as large  a sample
of uniformly measured clusters (redshifts, velocity dispersions,
temperatures) as possible from the literature plus extensive
redshift databases at CfA.  The goal will be to take a volume limited
sample of rich galaxy clusters and develop software and databases
to produce estimates of cluster properties.  The project may involve 
some observing at Mt. Hopkins, AZ, or the analysis of data already
obtained.

Depending on the intern's interest and abilities, additional 
work might be done on a detailed dynamical analysis of the Virgo 
cluster or measuring the Hubble Constant with relative distance 
estimates for a much smaller set of nearby clusters (see Jergen and 
Tammann 1993, A\&Ap 276, 1. for the first such attempt or J. Huchra's
article at http://msowww.anu.edu.au/~heron).


Cluster Formations and Large Scale Structures - Christine Jones-Forman 

One of the major changes in our understanding of the Universe has been
realization of the complexity and richness of the structure on large
scales.  Galaxy voids as well as supercluster filaments are found
through large redshift surveys.  On smaller scales, studies show that
clusters retain information about the larger scale structures from
which they form.  Recent observation evidence supports the growth of
clusters of galaxies by the infall of matter (galaxies and gas) along
filaments.  Recently, for the first time, X-ray emission has been
found from a filament. This filament leads to the rich cluster,
A85, and has an extent of at least 4 Mpc in length.  In this study, we
will use deep ROSAT PSPC images for a sample of clusters, which show
evidence of subcluster mergers, to search for X-ray emission from filaments.


Studies of HRC XRCF Calibration Data -  Steve Murray 

This project is to analyze calibration measurments for the AXAF High 
Resolution Camera (HRC) that was obtained during the tesing done last
year at the X-Ray Calibration Facility (XRCF). The HRC is one of two focal
plane instruments on the AXAF Observatory, scheduled for launch in December
1998. Specifically, there are data pertaining to the count rate linearity of
the HRC response. This information is needed to determine how to use the
HRC when observing bright X-ray objects where the source count rate may exceed
the detector limits. Another set of calibration data pertaining to the HRC
shutters has not been analyzed. These data are needed to help in properly 
locating the shutter blades with respect to the detector center. Since the
shutters will be used to determine the focus of the instrument, we
need to have a very good understanding to their location and how to use the
data to deduce the focus position. In this part of the project, we need to
develop the data algorithms for focus location, test them against
calibration data, and evaluate their accuracy.

The project involves learning about the HRC detector, the HRC data analysis
system, and the XRCF. The intern will work directly with the Principal 
Investigator for the HRC and other HRC Instrument Team members. Images
from calibration will be produced, studied, and analyzed. There will also be
a laboratory component to the work to help familiarize the intern with
the instrument.


A Catalog of Infrared Images of Young Star Clusters - Phil Myers 

Most stars appear to form in groups and clusters, rather than in
isolation, but the process of fragmentation of a parent gas cloud into
stars is still poorly understood. Important clues to the cluster formation
process come from the spatial structure and relative separations of stars
in young clusters. Because of the absorption and scattering properties of
interstellar dust grains, the youngest and most obscured clusters are
visible at near-infrared wavelengths but invisible at optical wavelengths.
In the last decade, technical improvements in infrared imaging arrays have
provided us with an avalanche of new data on the very youngest
clusters.

These images are published in many separate articles, and some are
not published in journals but are nonetheless available from their authors
or from data archives.  We propose to compile a catalog of all available
infrared images of star clusters within a radius of about 1 kiloparsec from
the Sun.  This will contain several hundred images.  We then propose to
analyze the data to answer key questions about young clusters, including:

1.  What is the dominant "mode" of star formation?  Are more young
stars within 1 kpc known in big clusters, in small clusters, or in
isolation?

2.  What is the geometry of cluster formation?  Is the projected
spatial distribution of stars in a cluster more nearly uniform, with
regular spacing between stars and a single characteristic size scale, or
more nearly "fractal,"  with each group having a progression of smaller
subgroups, and thus a wide range of size scales?

The catalog resulting from this project will be a valuable resource
to  astronomers interested in observations of clusters and in theories of
their formation.


Developing Multilayer Coatings for the Next Generation X-ray
Telescope - Suzanne Romaine 

Recent innovations in multilayer coatings allows us to extend the
energy range of grazing incidence optics to 100 keV. We are investigating
the response of multilayer coatings and will be constructing a
prototype telescope for the next generation X-ray mission. The summer
intern would be exposed to the fabrication and characterization of 
multilayer optics, data taking techniques and general laboratory practices.
Characterization techniques include: X-ray reflectivity,
transmission electron microscopy, optical microscopy, Rutherford 
backscattering and Auger Electron Spectroscopy.

The knowledge gained from each of these projects is applicable in a
variety of disciplines, including: physics, astronomy, materials science
and engineering.


Flare Heating in the Active Evolved Star II Peg - Steven Saar 

The coronae of the sun and many cool stars are superheated
to millions of degrees.  It is thought that two processes are involved; 
steady magnetic wave heating, and random flare heating, caused
by the explosive reconnection of magnetic fluxtubes.
The relative importance of these effects is debated, though it is thought
that flares may be more important in more active stars.

We have obtained high time resolution ultraviolet spectra with the Hubble Space
Telescope of the active subgiant II Peg.  We will study the variations in
emission lines (formed at about 100,000 K, just below the corona) 
to see how much of the emission is formed by explosive flare events.
By comparing with similar data from other kinds of stars, we can begin to 
explore how flare heating varies with stellar properties. 


The X-ray Spin/Orbit Light Curve Behavior of
Intermediate Polars - Eric M. Schlegel

Intermediate Polars are interacting binary stars
in which one of the stars is a red dwarf and the other star is a
compact object, a white dwarf.  The white dwarf spins at a rate not
locked to the orbital period of the system.  In addition, a magnetic
field influences, but does not dominate, the flow of matter between
the stars.  X-rays are emitted by the accreting material and show both
orbital and spin modulations.  These modulations have also been shown
to be a function of energy.  The Rossi X-ray Timing Explorer has
collected data on two IPs that should cover the spin-orbit plane with
improved time resolution and signal-to-noise compared to previous
missions.  The spectra can also pin down the temperature of the
radiation.  The data on one or both IPs will be analyzed.

The 4.2 Day Precessing Period of the Intermediate Polar TV Col - Eric M. Schlegel

Intermediate Polars are interacting binary stars
in which one of the stars is a red dwarf and the other star is a
compact object, a white dwarf.  The white dwarf spins at a rate not
locked to the orbital period of the system.  In addition, a magnetic
field influences, but does not dominate, the flow of matter between
the stars.  X-rays are emitted by the accreting material and show both
orbital and spin modulations.  In addition, one IP, TV Col, shows a
precession period of 4.2 days.  The Rossi X-ray Timing Explorer
collected 1 orbital period of data at the quadrature phases of TV Col.
Our goal is to describe the behavior of the orbital modulation as a
function of the precession period.  The spin period is sufficiently
short that we can also search for changes in the spin modulation as a
function of the orbital and precession periods.

The Eclipsing Cataclysmic Variable WZ Sge - Eric M. Schlegel

Cataclysmic variables are interacting binary
stars in which one of the stars is a red dwarf losing mass to the
other star which is a compact object, a white dwarf.  The accretion
material forms a disk around the white dwarf and matter accretes onto
the white dwarf from the disk.  Time-resolved optical spectroscopy has
recently been obtained on the eclipsing CV WZ Sge which contains an
accretion disk.  The data will be analyzed to study the total light
curve, emission line light curves, and the radial velocity behavior of
the emitting material.  In addition, data have been obtained
aperiodically over the past 15 years.  These data will be resurrected
to provide a long-term picture of the behavior of this system.

The Eclipsing Cataclysmic Variable VZ Scl - Eric M. Schlegel

Cataclysmic variables are interacting binary
stars in which one of the stars is a red dwarf losing mass to the
other star which is a compact object, a white dwarf.  The accretion
material forms a disk around the white dwarf and matter accretes onto
the white dwarf from the disk.  Time-resolved optical spectroscopy has
recently been obtained on the eclipsing CV VZ Scl which contains an
accretion disk.  The data will be analyzed to study the total light
curve, emission line light curves, and the radial velocity behavior of
the emitting material.

A Summary of the Optical Observations of Type IIn
Supernovae - Eric M. Schlegel (HEA Division), Peter Garnavich (OIR Division)

Type IIn supernovae were first recognized as a
subclass about 8-9 years ago.  They are Type II supernovae because
they show hydrogen in their optical spectra, but the subclass
designation 'n' indicates that the lines are considerably more narrow
than usual.  From the time of recognition, optical observations
(photometry, spectroscopy) have been accumulating, but no overall
summary that compares the light curves and spectroscopy has been
produced.  We will collect all of the optical data that exists on IIn
supernovae to investigate common properties.


The Energy Sources of Southern Herbig-Haro Objects - Dave Wilner

The study of the youngest stars provides valuable information about the
star formation process.  ``Herbig-Haro objects'' are optical manifestations
of the bipolar winds driven by stars in formation. The young stars
themselves are usually deeply embedded in their natal gas clouds and
cannot be seen at all at optical wavelengths.  But they often emit
radio continuum emission, and the radio emission can escape the dusty 
protostellar environment. We have observed the vicinity of several
Herbig-Haro objects in southern dark clouds using the Australia
Telescope Compact Array. The goals of this study are (1) to detect
radio continuum emission from the young stars that 
power the Herbig-Haro objects, (2) to search for extended radio emission 
connecting the Herbig-Haro objects with their energy sources, (3) to
search for radio emission associated with other sources in these regions, and 
(4) to measure the spectral indices of detected sources to better
understand the physical process responsible for the radio emission.

The project involves the calibration and imaging of radio interferometer
data. The student will learn the basics of interferometry, a technique
where many  telescopes are used to synthesize the angular resolution of
a single, much  larger telescope.  Then the student will prepare and
analyze the data in hand  using a software package (MIRIAD) developed
for this purpose. For each  detected radio source, the brightness can be
visualized and measured, and  physical conditions can be determined. The
list of sources obtained from these observations will be a result worthy
of publication.