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List of talks given during the summer of 2008 by SAO scientists
Links to:
Program of the SAO Summer Intern Symposium, August 13, 2008
Abstracts for posters presented at the January, 2009 AAS meeting
INTERN: India Anderson
ADVISOR: Dr. Leonard Strachan
PROJECT TITLE: Testing Solar Wind Models with data from the SOHO Ultraviolet Coronagraph Spectrometer
Abstract:
INTERN: Dan D'Orazio
ADVISORS: Dr. Greg Dobler and Dr. Beth Willman
PROJECT TITLE: Finding Invisible Galaxies with Gravitational Lensing
Abstract:
My research on the gravitational lensing approach to this missing
satellites problem has relied heavily on the available data.
Basically I have built models which describe the gravitational
potential of the lens galaxy plus satellite galaxies and used the
data to constrain the parameters of the model (e.g. how massive are
the satellites, where are they located relative to the lensing galaxy,
etc.) Presently there are very few multiply imaged quasars that can be
used for this purpose, but with upcoming surveys (such as PanSTARRS,
in which Harvard-CfA is a partner) this will change dramatically.
In the anticipation of the influx of new data, I would like to extend
the simple modeling that has been done in the past to include more
realistic satellite populations - as determined by the most recent
simulations of the Milky Way - and apply these models to the presently
available data. The work is theoretical/computational in nature and
encompasses a broad range of astrophysics, from the dark matter halos
of distant galaxies, to the satellite population derived from
simulations, to the physical size of the background "source" quasar.
INTERN: Christene Lynch
ADVISORS: Dr. Gerardo Juan Manuel Luna and Dr. Scott Kenyon
PROJECT TITLE: Time resolved optical spectroscopy of RS Oph after 2006 outburst
Abstract:
The recurrent nova RS Oph went into outburst in
2-12-2006. During this event ~10^{-7} Msun were ejected from the white
dwarf surface with velocities ~5000 km/s. Since then, this material is
expanding and its density and temperature dropping. A few days after
the 2006 outburst, extensive observational campaigns were performed
in various wavelengths ranges, from X-rays to radio. We obtained approximately 200
low-spectral resolution optical observations during ~4 months after the
outburst using the TILLINGHAST telescope together with the FAST spectrograph.
Optical spectroscopy of nova shell is used to
investigate the chemical composition of the nebula, its ionization state,
source of radiation and expansion rate
(see e.g. Augusto & Diaz, 2003, AJ, 125,3349). With the available
data, the student will be able to measure the evolution of
these parameters as the shell is expanding, mapping its different stages and
provide answers to questions as: is the accretion disk reconstructed?
when?, are the nebular abundances compatible with a normal
red giant wind or there was some chemical enrichment during the thermonuclear
outburst?, what is the temperature evolution of the accreting white
dwarf?
INTERN: Greg Mosby
ADVISORS: Dr. Lori Allen and Dr. Kevin Covey
PROJECT TITLE: Properties and Evolution of young stellar clusters in Orion
Abstract:
The interested student will first perform the task of merging the
spectroscopic and photometric data into a single database, then will
use this information to construct Hertzsprung-Russell diagrams, and,
by comparing to pre-main sequence evolutionary models, estimate the ages,
masses, and disk properties of the young stars. In the course of this
work, the student will learn about star formation, the evolution of
protoplanetary disks and the timescales for planet formation. S/he will
also gain experience using standard astronomical software such as IRAF,
and more general software like IDL.
INTERN: Katherine (Kaylea) Nelson
ADVISOR: Dr. Ewan O'Sullivan
PROJECT TITLE: A combined Chandra/XMM-Newton study of nearby elliptical galaxies
Abstract:
The aim of the project is to characterize the X-ray properties of
ellipticals in the local Universe, which host three main classes of X-ray
source; diffuse gas with temperatures of a few million Kelvin, the active
nucleus, and X-ray binaries. With this sample, we hope to be able to
address issues such as:
1) What fraction of nearby ellipticals have stable, gravitationally
bound gas halos? What is the temperature and metal abundance structure of
these halos, and is it correlated with factors such as stellar population
age and nuclear activity?
2) How large is the variation in the luminosity of the X-ray binary
population, and how is it related to properties such as galaxy mass and
globular cluster population?
To address these issues we will measure the relative contributions of the
AGN, X-ray binaries and diffuse emission, determine the spectral
properties and structure of the hot gas halo, and examine the X-ray binary
luminosity function. Comparison with HST imaging data (where available)
and with radio and optical data from the literature will provide further
information on galaxy structure, the stellar population and AGN activity.
A student working on this project will learn how to analyze X-ray and
optical data using existing, well-tested software (CIAO, SAS, HEASOFT,
IRAF), and carry out comparisons between Chandra, XMM-Newton and HST data.
We have ready-made scripts and tasks to carry out parts of this analysis,
which will be used by the student. Since the overall sample is too large
to be analyzed in the short period available, the student will focus on a
subset of 6 galaxies with good quality Chandra and XMM data, covering the
more poorly-know faint end of the optical luminosity range, and including
examples of both gas-rich and binary-dominated systems. The sample size
can be adjusted depending on the progress of the student and data from a
further 10 systems whose XMM observations have already been analyzed can
be included in the final comparisons. As well as experiencing the process
of analysis and interpretation of scientific data, the student will learn
about the relative diagnostic capabilities of different wavebands and
instruments, the structure and properties of elliptical galaxies, the
different classes of X-ray source they host, and the physical mechanisms
behind their emission.
INTERN: Arpita Roy
ADVISOR: Dr. Elizabeth Humphreys
PROJECT TITLE: What does High-Mass Star Formation "Look" like? Accretion and Outflow Close to a Forming High-Mass Star
Abstract:
I have two projects relating to the formation of the closest forming
high-mass star, Source I in Orion. With collaborators in the Radio and
Geoastronomy Division at CfA, we have been working to characterize the
nature of the accretion and outflow process of Source I using very
high resolution (milliarcsecond) radio interferometry observations of
molecular maser emission. The first project within our group is
performing modeling to work out the geometry of the forming star
(e.g., disk plus outflow) and its 3D orientation. We have programs
developed for this use already. The second project is to perform
radiative transfer modeling of emission from the source to work out
the temperature and density of the gas. Again we already have
programs that perform the calculations. The results will be reported
in a publication and/or at the AAS.
INTERN: Greg Salvesen
ADVISORS: Dr. John Raymond and Dr. Dick Edgar
PROJECT TITLE: Cosmic Ray Pressure in the Cygnus Loop
Abstract:
INTERN: David Stark
ADVISORS: Dr. Paul Nulsen and Dr. Ralph Kraft
PROJECT TITLE: Jets in Cen A
Abstract:
We do not yet know what radio jets are composed of. They emit
synchrotron radiation, showing that they contain relativistic
electrons and magnetic fields, but there is good reason to believe
that these only represent a small component of jets. Positively
charged particles are needed to keep jets neutral (otherwise
electrostatic forces would prevent them escaping the nucleus). These
could be ions (mostly protons) or positrons. The ions may be
relativistic or non-relativistic and there may also be other
non-relativistic matter swept up in jets.
One step to determining the composition of a jet is to know its
equation of state. In contrast to more distant radio galaxies, Cen A
is close enough that its eastern radio jet is well resolved in X-ray
observations with Chandra. This enables us to measure the size of the
jet and its pressure distribution. The aim of this project will be to
use the equations for relativistic fluid flow to relate these
properties and determine the equation of state of the jet plasma.
That information will be used to constrain the composition of the jet.
INTERN: Caleb Wheeler
ADVISOR: Dr. Guillermo Torres
PROJECT TITLE: Binarity in the Pleiades Cluster
Abstract:
We are seeking a motivated student who is interested in learning about
stars and the techniques used to study them. The work will involve the
determination of spectroscopic parameters of cluster members (mainly
the effective temperatures and projected rotational velocities) on the
basis of more than 3000 optical spectra accumulated over more than 20
years with the same instrument. For the binary stars, the student
will derive radial velocities using existing software, and will
incorporate also historical radial velocities available from the
literature, to supplement our own measurements. Spectroscopic orbits
based on these velocities will be derived both for single-lined
binaries and double-lined binaries. We hope to significantly increase
the number of spectroscopic binary systems in the Pleiades. This
information will be used to construct the eccentricity versus Log
period diagram, one of the most useful diagnostics of the efficiency
of orbital circularization. This will be used to infer the
circularization timescale for the Pleiades, which can be compared with
theoretical predictions.
The spectroscopic parameters for single stars will be used to study
the rotational properties of members as a function of spectral type.
Their radial velocities, along with the center-of-mass velocities of
the binaries, will be used to determine the internal velocity
dispersion in the Pleiades. If time permits, we will also use the
radial-velocity information to study the kinematics of the cluster.
INTERN: Angie Wolfgang
ADVISORS: Dr. Paul Green and Dr. Kevin Covey
PROJECT TITLE: Characterizing X-ray Active Objects in the ChaMP Survey
Abstract:
One of the major discoveries from the SOHO Ultraviolet Coronagraph
Spectrometer is that ions in the solar corona are heated to much
higher temperatures than the electrons. This result has had a major
impact on what solar physicists think about coronal heating and solar
wind acceleration. Now with more than a solar cycle's worth of UVCS
data we are in a position to test theoretical solar wind
models over a wide range of coronal conditions. This project will test the
latest MHD solar wind models for their accuracy and self-consistency in
predicting plasma parameters in the corona.
If an asteroid were traveling through space in a straight line and
happened to pass near a massive object like the Earth, it would feel
the gravitational pull of the Earth and its trajectory would be
bent. A similar phenomenon occurs for light rays (photons), and the
bending of a photon path by the gravitational pull of a massive body
is called Gravitational Lensing. Gravitational lensing offered the
first proof of Einstein's theory of general relativity
in 1919 when, during a solar eclipse, the light from stars behind the
sun was found to be bent by the gravitational pull of the sun.
Gravitational lensing is observed when the light from a very distant
object, such as a galaxy or a quasar is bent by the gravity of an
(also very distant) object such as a galaxy or cluster of galaxies.
For cases of near perfect alignment, i.e. when the background quasar
is almost directly behind the foreground galaxy, gravitational lensing
can cause the quasar to be split into multiple images. This type of
lensing, where the background object is severely distorted by the lens
galaxy is called strong lensing. Not only does strong lensing provide
striking and spectacular astronomical images, the properties of the
images, namely their positions and brightnesses, contain detailed
information about the gravitational potential of the lens galaxy. With
the gravitational potential, we can infer the distribution of matter
in lens galaxies which are otherwise too far away to study with other
techniques. In fact, lensing has already been proposed as a tool for
studying the missing satellites problem. The Milky Way galaxy is
surrounded by many smaller satellite galaxies. However, the problem is
that detailed computer simulations of the Milky Way indicate that
there should be more than ten times as many satellite galaxies than
are actually observed. A possible solution is that the satellites are
there but that they do not contain stars or gas and are invisible or
dark. At present, gravitational lensing is the only way to detect the
presence of dark matter in distant galaxies, and it has been suggested
that the brightnesses and positions of images in multiply imaged
quasars provide evidence for the existence of the missing satellites
in distant galaxies.
Symbiotic stars are binary systems in which a white dwarf accretes
from a red giant wind which forms a dense nebula surrounding the
system. Observationally, their optical spectra consist of
various absorption bands from the red giant's photosphere, a blue
continuum from the white dwarf photosphere and various emission lines
from the ionized nebula. Some symbiotic system (e.g. RS Oph, T CrB) have
massive white dwarf (M~1.35 Msun) as accretors. These systems, known
as recurrent novae (Sokoloski et al. 2006, Nature, 442, 276),
experience quasi-periodic outburst triggered by the accumulation of
material onto the white dwarf surface.
We recently used the Spitzer Space Telescope, NASA's premier infrared
platform, to completely survey the giant molecular clouds in Orion, the
nearest massive star-forming region to the Sun. Our Spitzer data reveal
thousands of newly discovered young stars in these clouds. To better
characterize these objects, we are using the state-of-the art,
multi-fiber (Hectospec) on the 6.5-meter MMT telescope of Mt. Hopkins
Arizona to acquire classification spectra. So far we have collected spectra
for several hundred stars. These spectra, along with the mid-infrared data
from Spitzer and near-infrared photometry from the Two Micron All Sky
Survey (2MASS), wil allow us to examine fundamental questions related to the
timescales for evolution and dissipation of protoplanetary disks, the
characteristic lifetimes of molecular clouds, the predominance of triggered
star formation, and the dynamical evolution of clusters.
The Chandra and XMM-Newton X-ray observatories have vastly increased our
knowledge of nearby galaxies, providing both exceptionally sharp images
and the sensitivity needed to probe for faint X-ray emission. However,
most studies of ellipticals have focused on the brightest, best known
systems, particularly those which reside at the centers of galaxy
clusters, whose properties are primarily a product of their surrounding
environment rather than their formation history. We have embarked on a
project to develop a more representative view of the X-ray properties of
elliptical galaxies, using a statistically complete sample of ellipticals
observed by Chandra and/or XMM.
High-mass star formation is difficult to study relative to the low
mass case partly because high-mass stars evolve more rapidly and are
rare. Because there are not many examples of high-mass star formation
close by, it is important to study the few that there are in detail so
that we can determine the key processes involved.
Models of cosmic ray acceleration in shock waves predict either very
efficient or very inefficient acceleration, with a ratio of cosmic ray
to gas pressure (P_cr=P_g) near 80% or below 10%. Intermediate values
are unstable. P_cr is hard to measure, but it can be inferred because
the ram pressure, rho*V^2, nearly equals P_cr + P_g. Halpha filaments
of a non-radiative shock delineate the northern 1/3 of the outer edge
of the Cygnus Loop supernova remnant. Their proper motion is about 5
arcseconds between the first and second epoch Palomar surveys. An
upper limit to the distance to the Cygnus Loop is given by the
distance D to a star whose spectrum shows high velocity, high
temperature absorption lines from the shocked gas. The combination of
distance and proper motion gives V. The temperature can be determined
from the X-ray spectrum, and high quality ROSAT PSPC spectra exist
for the entire region (Levenson et al. ApJ 526, 874). From the upper
limit to V and the lower limit to Tx one can derive an upper limit on
P_cr=P_g. We propose that an REU student measure the proper motions
for about 50 segments along the northern Cygnus Loop and fit the ROSAT
spectra for the corresponding post-shock regions. We have tried this
for one segment where we and our collaborators have obtained optical
line profiles and UV spectra (Ghavamian et al. ApJ 547, 995; Raymond
et al. ApJ 584, 770), and P_cr=P_g < 0.60 for the upper limits on
proper motion and D and lower limit on Tx, and P_cr=P_g < 0.06 for the
nominal values of proper motion, D and Tx. Measuring 50 independent
regions will reduce the uncertainty and probably provide a limit
somewhere between these values. To our knowledge, this sort of
analysis has never been published for any SNR shock.
When matter falls into the black hole at the center of a radio galaxy,
some of the energy released is funneled into powerful opposed jets.
These flow out and interact with gas surrounding the galaxy, driving
it out of the way, creating shocks and inflating lobes of radio
emitting plasma. Such effects can be seen in radio and X-ray images
of many radio galaxies. A particularly good example is provided by
the nearest radio galaxy, Centaurus A (Cen A).
The open star cluster known as the "Seven Sisters" (Pleiades) is one
of the most prominent in the northern sky. It has been studied by
astronomers for at least a century. We are currently engaged in a
long-term radial-velocity survey of more than 200 of its members, and
one of the goals of this project is to study the binary population in
the cluster. In particular, we are interested in investigating the
effects of tidal forces in binaries, which tend to synchronize the
rotation of the components to the mean orbital motion, and tend make
the orbits circular with time. These processes are not yet fully
understood theoretically.
The Chandra Multiwavelength project (ChaMP) is a wide-area
X-ray sky survey encompassing nearly 19,000 newly-discovered X-ray sources.
New spectroscopy has been obtained for hundreds of optically bright objects.
These spectra will help us to measure for the first time the true fraction of
nearby galaxies that harbor actively-fed supermassive black holes, and
will also allow us to understand the strange excess blue emission from
X-ray active stars in our own galaxy. We seek a student to assist in the
analysis of spectroscopy from the FAST spectrograph at the FLWO1.5m on Mt
Hopkins of optically bright, X-ray active stars, galaxies and active galactic
nuclei obtained as part of the ChaMP. This includes analysis and
verification of spectra for radial velocities using IRAF,
characterization of the object types by comparison to templates,
compilation of results in a Sybase database for uniform tabulation and
easy retrieval. Final products will be incorporated
into the existing ChaMP database, which will become public after journal
publication of results.