Документ взят из кэша поисковой машины. Адрес
оригинального документа
: http://hea-www.harvard.edu/REU/projects10.html
Дата изменения: Unknown Дата индексирования: Mon Oct 1 20:57:38 2012 Кодировка: Поисковые слова: comet tail |
List of talks given during the summer of 2010 by SAO scientists
Links to:
Program of the SAO Summer Intern Symposium, August 11, 2010
Abstracts for posters presented at the January, 2011 AAS Meeting
INTERN: Justin Brown (Franklin and Marshall College)
ADVISOR: Dr. Mukremin Kilic (SSP Division CfA)
PROJECT TITLE: Testing Stellar Evolution Theory with Low-mass White Dwarfs
Abstract:
Our goal is to measure the binary fraction of white dwarfs as a
function of mass, and test for the signature of He-core white dwarfs
evolved from metal rich single stars. We already obtained optical
spectroscopy of two dozen white dwarfs using the FAST instrument
for the past two years. The intern will reduce these data using simple
IRAF routines and derive radial velocities. Based on these radial
velocity measurements, and optical and near-infrared photometry, we
will evaluate the fraction of single low-mass white dwarfs
as a function of mass. Finding a He-core white dwarf without a binary
companion is a strong test of stellar evolution, with implications for
mass loss on the red giant branch and the production of Type Ia
supernovae.
CO-ADVISOR: Dr. Warren R. Brown (OIR Division CfA)
The Galaxy is not old enough to produce low mass (M < 0.45 solar masses)
white dwarfs through single-star evolution. Thus known low mass
white dwarfs are thought to be helium-core white dwarfs formed in binary
systems in which a companion strips the outer envelope of the evolving star
before it ignites helium in its core. An alternative, however, is
that metal rich stars may lose too much mass on the red giant branch
(due to larger opacity in their atmospheres) and do not ignite helium
burning, thereby forming helium-core white dwarfs. Thus the binary
fraction of low mass white dwarfs provides a sensitive
test of stellar evolution and mass loss on the red giant branch.
INTERN: Jared Coughlin (Villanova University)
ADVISOR: Dr. Darin Ragozzine (TA Division CfA)
PROJECT TITLE: Transneptunian objects
Abstract:
How probable is it that exoplanetary systems have the appropriate
alignment (with respect to Earth) to see mutual events?
This observationally-motivated theoretical study will bring exoplanet
mutual events to the fore as a potential tool for studying planetary
systems beyond on own.
CO-ADVISOR: Dr. Matthew J. Holman (TA Division CfA)
Exoplanet mutual events are when two extra-solar planets cross in
front of one another as seen from Earth. Similar events occasionally
occur in other contexts, such as solar system mutual events.
Transiting exoplanets themselves are a type of mutual event between a
planet and its host star. Throughout astrophysics, mutual events
encode significant amounts of unique information that often cannot be
determined in any other way. Even though mutual events between two
exoplanets have not been previously considered in any detail, they
potentially offer an exciting amount of interesting science that would
otherwise not be possible. This project will expand preliminary
investigations already underway and will look at larger ensembles of
simulated planetary systems to examine in more detail the type and
frequency of exoplanet mutual events that could be observed by the
Kepler Space Telescope and/or the James Webb Space Telescope. The main
goal of the project is to determine the basic properties of these
events:
When mutual events do occur, how frequent are they?
What is the typical duration and expected light curve amplitude of
various events, especially the most frequent ones?
What information is needed to accurately predict mutual events
in advance?
What orbital and physical properties can be determined from
realistic observations of these events?
ADVISOR: Dr. Paul E. J. Nulsen (HEA Division CfA)
PROJECT TITLE: Composition of Radio Lobes
Abstract:
Energy released in these outbursts can heat surrounding gas enough to
affect the supply of gas to the black hole, which creates a feedback
loop that links the rate of gas cooling to the rate and size of
outbursts. By limiting gas cooling, this "AGN feedback" can also
regulate the rate of star formation and there is mounting evidence
that this is what holds the rate of star formation in massive
galaxies to a trickle, in effect setting the brightness of the most
luminous galaxies. As a result, there is great interest in
understanding how radio sources work in detail.
In addition to the relativistic electrons and magnetic field, radio
lobes probably contain other relativistic particles (cosmic rays) and
thermal material that are largely undetectable. We need to be be able
to relate the composition of radio lobes to their observable properties
in order to study AGN feedback. The aim of this project is to
investigate the composition of the radio lobes of one of the nearest
extragalactic radio sources, Fornax A.
The radio spectrum constrains the strength of the magnetic field and
the number of relativistic electrons, but additional information is
required to determine these separately. Relativistic electrons
scatter microwave background photons into the X-ray band. Detecting
this "inverse Compton" emission provides an independent constraint.
However, non-uniformities in the radio and X-ray emission raise
theoretical challenges for the simple models that have been employed
to interpret such data. X-ray and radio data will be used to study
the radio source Fornax A. The project will involve both data
analysis and theory, depending on the interests of the student.
CO-ADVISOR: Dr. Ralph P. Kraft (HEA Division CfA)
An extragalactic radio source is formed when a "supermassive" black
hole at the center of a galaxy spews enormous amounts of energy into
its surroundings through a pair of narrow, opposed jets. The jets
inflate lobes with relativistic electrons and magnetic field. We see
the radio source because relativistic electrons in a magnetic field
emit synchrotron radiation.
INTERN: Sam McCandlish (Brandeis University)
ADVISOR: Dr. Rosanne DiStefano (TA Division CfA)
PROJECT TITLE: The Prediction of Gravitational Lensing Events
Abstract:
INTERN: Elisabeth Otto (Ohio State University)
ADVISOR: Dr. Paul J. Green (HEA Division CfA)
CO-ADVISOR: Dr. Anna Luise Frebel (OIR Division CfA)
PROJECT TITLE: Stalking the Elusive Dwarf S Star
Abstract:
INTERN: Dominiqe Segura-Cox (University of Michigan)
ADVISOR: Dr. Joseph L. Hora (OIR Division CfA)
PROJECT TITLE: Star Formation in the Massive Cygnus-X Complex
Abstract:
We are conducting a Spitzer Legacy survey of the Cygnus-X complex, with the
following goals: 1) to analyze the evolution of high mass protostars with a
large and statistically robust sample at a single, known distance, 2) study
the role of clustering and triggering in high mass star formation, 3) study
low mass star formation in a massive molecular cloud complex dominated by
the energetics of ~100 O-stars, and 4) determine what fraction of all
young low mass stars in the nearest 2 kpc are forming in this one massive
complex. The data have been obtained during the past couple years,
preliminary catalogs and mosaics have been completed, and candidate
young stellar objects (YSOs) have been identified.
Before the cryogen was exhausted on Spitzer, we obtained IRS spectra of a
sample of ~20 massive YSOs. The spectra of the objects provide key data,
along with the rest of the objects Spectral Enery Distribution (SED), to
determine the characteristics of the object, including the physical
parameters and evolutionary state. An initial characterization can be done
by fitting the spectra and SEDs with the grid of precomputed models by
Robitaille et al. (2007). More detailed modeling of the individual sources
can be done depending on the spectral information in the IRS data. For
example, if [Ne II] and [S IV] are detected, these lines can be used to
estimate the exciting stars temperature. The continuum emission and
silicate absorption depth can provide constraints to fit models that will
allow us to estimate the masses of the gas and dust, the column densities
of the absorbing material, and the luminosities of the objects. The
project would consist of completing the reduction of the spectra and
performing an analysis of the massive YSOs.
INTERN: Brian Svoboda (Western Washington University)
ADVISOR: Dr. Karin Oberg (RG Division CfA)
PROJECT TITLE: Origins of chemical complexity during (exo-)planet formation
Abstract:
INTERN: Kimberly Ward-Duong (Northern Arizona University)
ADVISOR: Dr. Scott W. Randall (HEA Division CfA)
PROJECT TITLE: Mergers, Feedback, and the IntraCluster Medium
Abstract:
AS0851: The mass of a galaxy's central black
hole is known to be strongly correlated with the properties of the
host galaxy's central stellar velocity dispersion (sigma) and with the
host galaxy's stellar bulge mass (or K-band luminosity).
NGC6861 in AS0851 has one of the highest central stellar
velocity dispersions measured for any elliptical galaxy, similar to
that of M87 the dominant galaxy in the massive Virgo galaxy cluster,
yet NGC6861 is only the second brightest galaxy in only a moderately
massive galaxy group. The mass of the central black hole inferred
from the black hole mass - sigma relation is ~2 billion solar masses,
almost an order of magnitude greater than the black hole mass
inferred from the mass of NGC6861's stellar bulge. The question
is why, and which, if either, correlation correctly
predicts NGC6861's black hole mass? The answer must lie in the
interaction and AGN feedback history of the two dominant galaxies,
NGC6868 and NGC6861. We have identified preliminary
features of interest in a previous study of this system (Machacek
et al. 2010, ApJ, 711, 1316), but the data were too sparse for a complete
analysis. We have recently obtained a total of >100 ks of Chandra data on
each dominant galaxy, NGC6868 and NGC6861. In this project the student will
learn to use standard X-ray imaging and analyis tools (ds9, CIAO,
FTOOLS, XSPEC) as well as specialized scripts to construct images
and temperature maps from combined Chandra data on these galaxies
to identify X-ray bridges, hot spots, edges, tails and other
features of interest. The student will use these analyses to
determine the thermodynamic properties of the diffuse gas and
origin of observed wakes and tails, measure galaxy and gas velocities,
model galaxy orbits and interaction history of NGC6861 and
NGC6868, and constrain the mass of NGC6861's black hole.
INTERN: Sarah Wellons (Princeton University)
ADVISOR: Dr. Alicia M. Soderberg (TA Division CfA)
PROJECT TITLE: A Detailed Study of the Host Galaxies of Type Ib Supernovae
Abstract:
INTERN: Schuyler Wolff (Western Kentucky University)
ADVISOR: Dr. Ruth Murray-Clay (TA Division CfA)
PROJECT TITLE: Resonance capture in planetary systems
Abstract:
Standard theories of resonance capture assume that the planet starts on a
roughly circular orbit. In the outer solar system, it has been suggested
that Neptune may have had a substantial eccentricity at the beginning of
its migration, which was damped as migration proceeded. Studies of
extrasolar systems in resonance suggest that for observed systems to
form, substantial eccentricity damping must have occurred during
migration. In this summer project, the student will use N-body
simulations to investigate the differences in resonance capture resulting
from eccentricity damping. He or she will apply the results either to
resonance structure in the Kuiper belt in anticipation of an unbiased
census of orbits from Pan-STARRS, or to exoplanet systems in anticipation
of direct imaging surveys which may yield many resonant systems. The
student will learn how to use a standard N-body integrator and how to
plot with IDL.
A course covering Hamiltonian dynamics would be useful background. I
will attend a conference in Philadelphia on the Trans-Neptunian region of
our solar system during the week of June 28. I have money available to
bring the REU student with me if he or she is interested. Dynamics of
the small objects in the solar system informs much of our understanding
of dynamics as applied to extrasolar systems, so this would be
appropriate regardless of which project the student wishes to do.
CO-ADVISOR: Dr. Hagai Perets (TA Division CfA)
When monitoring programs designed to discover gravitational lensing
events began, it was assumed that the lenses would be located
several kpc from Earth. Theoretical work shows, however, that nearby
lenses (within roughly a kpc) contribute significantly to the rate.
Observations are now beginning to confirm this. The project we plan
for this summer is designed to take the study of nearby lenses an
important step farther, by developing methods to predict future
events. We will use theory and archived data to work out the optimal
methods with which to carry out this new enterprise. We will follow up
on specific nearby systems that may be first for which lensing events
are predicted and then detected.
Stars with C/O close to or above unity (S and C stars, respectively)
are normally thought to all be giants, since only thermal pulses on
the asymptotic giant branch can dredge up carbon. But mass transfer
in a binary system can chemically imprint a (lower mass) companion's
atmosphere even after the (higher mass) AGB star has faded to a white
dwarf. Dwarf Carbon (dC) stars, created through the same process,
are now known to be more common by far than giants. So where are the
S dwarfs? Constraints on the S dwarf fraction would place useful
limits on the intensity and duration of binary mass transfer episodes.
Yet none have ever been found. We have obtained FAST spectra of a
sample of 56 known S giants. We will prepare and publish the
the first digital spectral atlas of S giants. We will then use synthetic
SDSS colors and proper motions to find S dwarfs from the SDSS.
CO-ADVISOR: None.
The Cygnus-X region is one of the brightest regions of the sky
at all wavelengths and one of the richest known regions of star formation
of the Galaxy. It contains as many as 800 distinct HII regions, a number of
Wolf-Rayet and OIII stars and several OB associations. Cygnus-X also
contains one of the most massive molecular complexes of the nearby Galaxy,
significantly larger than other nearby molecular clouds with OB
associations such as Orion A, M17, or Carina.
CO-ADVISOR: None.
Chemistry plays an important role in the structure and evolution of
the disks around young stars where planets form, with implications for
the composition of comets and planets both in our Solar System and in
the increasing number of extrasolar systems. Especially interesting
are detections of small organic molecules in disks around Sun-like
stars, which bear on the origins of life. The aim of this project is
to constrain how and where in the disk these small organic molecules
form, using recently acquired observations of gas-phase formaldehyde
(H2CO) in such disks from the Submillimeter Array (SMA). The first
part of the project will be to use the SMA data directly to constrain
the spatial extent of H2CO in disks and to compare its distribution
and average temperature with observations of other, better understood,
molecules. This part will involve analysis of interferometry
spectral data using Miriad and IDL. The second part of the project will be
to address the origins. Current models of the chemistry in disks
underestimate the H2CO abundances by orders of magnitude. These models
only include gas phase chemistry, however, and laboratory experiments
suggest that H2CO can also form on icy dust grains -- the
building blocks of comets and planets. This process will be
investigated by modifying an existing modeling code to include this
surface formation pathway as well as different pathways
to evaporate the H2CO into the gas phase. The model results will be
compared with the SMA observations using a radiative transfer code.
We expect this project will advance the overall understanding of the
chemical evolution in disks, in particular the role of grain
surfaces for the formation of organic species.
CO-ADVISOR: Dr. Marie Machacek (HEA Division CfA)
One of the most important questions facing models of galaxy evolution
today is how central supermassive black holes, found in
most galaxies, co-evolve with their host galaxies. A key element to
this puzzle is understanding the dynamical connections between
galaxy interactions in galaxy groups and clusters, the feedback cycle from
active galactic nuclei (AGNs), and black hole fueling and growth.
Signatures of these interactions are imprinted on the hot X-ray
emitting gas in the form of edges (cold fronts or shocks),
stripped tails, outflows, cavities and buoyant bubbles,
or other asymmetric features. Measurements of temperatures and
densities in these features allow us to constrain 3-dimensional
velocities, orbits, and the interaction history of the galaxies, as
well as the flow of matter and energy from the AGN and the host
galaxy into the surrounding gas.
CO-ADVISOR: None.
We will test whether metallicity is the key parameter that enables
some Type Ibc supernova progenitors to produce gamma-ray bursts while
most cannot. Unfortunately we can't measure the metallicity of the
dying star after the explosion. However, low metallicity stars are
likely to be found in low metallicity galaxies. Therefore, by
studying the properties of the host galaxies of Type Ibc supernovae we
can learn about the properties of the progenitors. The student will
analyze a sample of spectra for two dozen Type Ibc supernovae and
extract the metallicity and star-formation rates. Through comparison
with models, we will extract information about the stellar population
in each host galaxy. These diagostics will be compared with the
properties of gamma-ray burst host galaxies as compiled from the
literature. Through this effort we will shed light on whether
gamma-ray burst progenitor stars are lower metallicity than those of
ordinary supernovae.
CO-ADVISOR: None.
As planets migrate through the disks from which they were born, they can
capture other bodies into mean motion resonances. In these special
dynamical configurations, the two bodies orbit their host stars with
periods dynamical configurations, the two bodies orbit their host stars with
periods that form an integer ratio. This phenomenon occurs
in the solar system, where Pluto and more than 100 other Kuiper belt
objects are known to be in resonance with Neptune. For example, Pluto
orbits twice for every three orbits of Neptune, and this configuration
protects Pluto from close encounters with Neptune that would otherwise
eject it from the solar system. Extrasolar planetary systems in which
two planets are in resonance have also been observed, presumably also
resulting from capture during migration.