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List of
colloquium talks given during the summer of 2013
Links to:
Program of the SAO Summer Intern Symposium, August 14, 2013
2013 Summer Program Calendars for June
, July
, and August
Abstracts for posters presented at the January 2014 AAS Meeting
INTERN: Michael Calzadilla (Southern Florida University)
ADVISOR: Dr. Christine Jones (HEA Division CfA)
PROJECT TITLE: The Gas Environment of AGNs in a Sample of 3CRR Radio Galaxies
Abstract:
We will use Chandra observations to investigate the gas environments
for a sample of 3CRR radio sources. Our specific goals are to measure
the extent, luminosity, gas mass, and for brighter sources the gas
temperature of the extended X-ray emission associated with 3CRR
sources. We also will estimate gas cooling times
and inflow rates and correlate these with radio morphologies and with the
X-ray and radio luminosities of the nucleus.
INTERN: Benjamin Cook (Princeton University)
ADVISOR: Dr. Peter Williams (OIR Division CfA)
PROJECT TITLE: Understanding Magnetic Supersaturation in the Coolest Stars
Abstract:
ADVISOR: Dr Katja Poppenhaeger (HEA Division CfA)
PROJECT TITLE: Small Stars, Big Blasts: X-ray flares of Low Mass Stars
Abstract:
ADVISOR: Dr. Matthew Bayliss (TA/ITC Division CfA)
PROJECT TITLE: A Joint Optical + X-ray analysis of the Triple
Merging Cluster, MACSJ1226.8+2153
Abstract:
The proposed project will be a joint analysis using publically available
archival data from Chandra, HST/ACS (imaging of all three cores/X-ray
peaks), along with proprietary weak lensing data (including published
lensing maps from Subaru; Oguri, Bayliss et al 2012) and cluster member
dynamics (>> 100 total members out to several virial radii from
GMOS+Magellan,+Hectospec) that are available through Advisor Bayliss.
The student will be working with the X-ray data in combination
with the cluster member dynamics to look for physical evidence of the
merger physics, including hints of X-ray emission from filaments between
the merging clumps, sharp gas density edges and the unambiguous
temperature jumps, and evidence for substructure and differential bulk
motions in the cluster member galaxies across the merging
superstructure. Depending on the background/skill of the student, the
weak and strong lensing information will also be combined with the
X-ray analysis to de-project the three dimensional shape of the
individual merging clumps.
ADVISOR: Dr. Marie E. Machacek (HEA Division CfA)
PROJECT TITLE: Gas Hydrodynamics in the Cores of Massive Galaxy Clusters
Abstract:
In this project the student will use high spatial resolution data from
the Chandra X-ray Observatory to perform standard X-ray imaging and
spectral analysis on two massive galaxy clusters (ZW3146 and RXJ1347)
in two different stages of merger, to understand how the mergers affect
the hydrodynamic state (temperatures and densities) and bulk motions
of the cluster gas. These observational results will be compared to
existing simulations to determine merger parameters and constrain the
microphysical properties of the inter-cluster medium.
ADVISOR: Dr. Huiqun Wang (AMP Division CfA)
PROJECT TITLE: Identification and Investigation of Martian
Dust Storm Source Regions from Orbital Observations
Abstract:
The closure of the martian dust cycle refers to the spatial and
temporal scale over which the net flux (deflation vs. deposition)
of dust is balanced. The length of time over which the Martian dust
cycle is closed remains unknown. Understanding the variability of
active dust lifting sources will observationally corroborate the
predictions made by general circulation models (GCMs), and constrain
the proportional role dust storms play in closing the dust cycle.
We will focus on the surface sources of dust storms on Mars by
analyzing observations from the Mars Global Surveyor (MGS) and Mars
Reconnaissance Orbiter (MRO), and (if time permits), utilizing
specific directed numerical experiments with the MarsWRF GCM to
address the following science questions:
These questions will be addressed in four steps. First, we will
examine Mars Daily Global Maps (MDGMs), produced with wide-angle
images from the MGS/Mars Orbital Camera (MOC) and from the MRO/Mars
Color Imager (MARCI), for locations of active dust lifting and
construct a database of dust lifting locations over $5$ Mars years
(MYs). Next, we will correlate these dust lifting locations to surface
properties such as thermal inertia, mineralogy, topography and albedo
using publically-available data. Thirdly, we will study the
three-dimensional spatial structure of the dust mixing ratio within dust storms
associated with the previously constructed database identified by
MRO/MARCI with the MRO/Mars Climate Sounder (MCS). Finally, if time
permits, using the MarsWRF GCM, we will simulate local and regional
scale dust storms like those observed with MARCI at high horizontal
resolution and examine the impact such a storm has on the
meteorological parameters (e.g., surface wind stress) that may
influence future dust storms at various scales.
This project will help constrain the martian dust cycle using currently
available datasets, and aid significantly in characterizing the dynamics
of atmospheric regions over daily, seasonal, and inter-annual time
scales. The student will have the opportunity to gain experience in Mars
data analysis and numerical modeling and knowledge of the martian
surface-atmosphere system in general.
ADVISOR: Dr. Nelson Caldwell (OIR Division CfA)
PROJECT TITLE: Origins of Stellar Streams in the Outskirts of the Milky Way
Abstract:
ADVISOR: Dr. Aneta Siemiginowska (HEA Division CfA)
PROJECT TITLE: Looking for the Signatures of Interactions between the
Radio and the Intercluster Medium in Deep Chandra X-ray Observations
Abstract:
ADVISOR: Dr. John Raymond (SSP Division CfA)
PROJECT TITLE: Shock Waves in the Cygnus Loop
Abstract:
ADVISOR: Dr. Randall Smith (HEA Division CfA)
PROJECT TITLE: Testing the Sensitivity of the Collisional Cooling
Function to the Underlying Ion Population
Abstract:
ADVISOR: ( Division CfA)
PROJECT TITLE: Supernova Forensics
Abstract:
CO-ADVISOR/MENTOR: Dr. Reinout Van Weeren (HEA Division CfA)
Understanding the influences of local galaxy environment and the roles
of supermassive black holes in galaxy evolution are critical. Through
observations as well as numerical simulations, significant progress
has been made in both of these areas. We now better understand the
role of galaxy mergers and the rapid growth of black holes through
radiatively efficient accretion at high redshifts, as well as the
radiatively inefficient accretion modes that dominate at low
redshifts. We also know the importance of AGN feedback in reheating
cooling gas in galaxy centers and thus keeping elliptical-type
galaxies red and dead. However, many questions about AGN accretion
and outbursts remain. In particular, what triggers an outburst? What
governs the power of the outburst? To address these questions,
we must understand the environment near the AGN as well as the large scale
environment outside the host galaxy. These environments affect the
processes of how black holes are fed and grow as well as how AGN
outbursts are triggered.
CO-ADVISOR: Professor Edo Berger (OIR Division CfA)
Sun-like stars obey a saturated rotation/activity relationship: the
faster they spin, the more magnetically active they are (as traced by
observables such as radio, X-ray, and H-alpha emission) up until a point
at which magnetic activity tops out. Recent data collected by our group
and others, however, indicate that in the very smallest stars - M dwarfs
and brown dwarfs - there is a new "supersaturation" region, in which
extremely fast-spinning stars show a decrease in their magnetism. We'll
work with the REU student to investigate this phenomenon using our
recent data and measurements of many stars from the literature. The key
goals will be to use high-quality data and analysis to rigorously
establish (or reject) the existence of supersaturation and to learn
about the physical basis for this effect, with the aim of presenting
these results in a refereed publication. The student will learn about
topics including "NoSQL" database techniques, coding, modern statistical
analysis, the astrophysics of small stars, and writing up results for
publication.
INTERN: Ying Feng (Penn State University)
CO-ADVISOR/MENTOR: Dr. G. Esra Bulbul (HEA Division CfA)
CO-ADVISOR/MENTOR: Dr. Andy Goulding (HEA Division CfA)
Low mass stars are prime candidates for finding exoplanets in the
habitable zone. An important factor to assess the actual habitability of a
planet is the frequency and intensity of magnetic flares of the host star,
i.e. energetic outbursts in the stellar atmosphere which emit all over the
electromagnetic spectrum. Low mass stars (M dwarfs) often produce powerful
flares, and X-ray observations are very sensitive tracers for this. In
this project, the summer student will reduce data from the X-ray telescope
XMM-Newton to analyze flare occurrence and energetics in low mass stars.
The aim is to test if there are changes in the flare-energy distribution
between very low-mass, fully convective M dwarfs and more massive
stars which possess a radiative core.
INTERN: Jocelyn Ferrara (Barnard College - Columbia)
CO-ADVISOR: Dr. G. Esra Bulbul (HEA Division CfA)
Galaxy clusters form via mergers of smaller sub-clusters. During such
mergers, most of the kinetic energy of the hot baryonic gas gas
belonging to the colliding sub-clusters is dissipated by shocks into
thermal energy of the intra-cluster medium. A particularly striking
example of a cluster merger is MACSJ1226.8+2153. MACS1226, featuring a
complex X-ray morphology in the cluster core, has been observed with
the Chandra X-ray Telescope for 20 ks in 2003 and 130 ks in
2011. Optical observations show three distinct cluster cores, each
with strong lensing features, centered roughly on the locations of
three peaks in the Chandra X-ray emission. This cluster appears to be
a rare triple-merger in progress.
INTERN: Christina Kreisch (Washington University - St. Louis)
One of the key challenges facing cosmological models today is the
nature of dark energy, the constituent of our universe responsible for
its accelerated expansion. One powerful tool to probe its equation of
state is the evolution of the distribution of masses for
large scale structure, specifically galaxy groups and clusters, across
cosmic time. Most of the ordinary matter in galaxy clusters is in the
form of diffuse, hot X-ray emitting gas that, if hydrodynamically
relaxed, traces the total gravitational potential of the cluster, and allows
the measurement of the cluster's total mass. However, in current
cosmological models, galaxy clusters grow by interaction and merger,
and so are often not relaxed. It is vital to understand the effects of
these mergers on the hydrodynamical state of the cluster gas, both to
advance our models of galaxy cluster evolution and to assess how galaxy cluster
properties, derived observationally, can best be used to test
cosmological models.
INTERN: Laura Kulowski (Brown University)
Global dust storms are a uniquely Martian atmospheric phenomenon.
Their seemingly random occurrences in southern spring and summer
have thus far eluded prediction and theoretical understanding. In
addition to global dust storms, dust storms at successively smaller
scales occur at increasing frequencies with regional dust storms
preferentially developing in certain seasons and locations and local
dust storms occurring nearly daily over the planet.
Where and what are the sources of dust storms on Mars?
What is the correlation of dust sources to surface properties?
What is the three-dimensional structure of dust in and around dust storms?
What is the impact of dust storms on future storm generation?
INTERN: Shengkai Alwin Mao (University of California - Berkeley)
CO-ADVISOR: Dr. Matthew Walker (TA Division CfA)
According to the standard cosmological model, galaxies like the Milky
Way are built 'hierarchically' by mergers and accretion of vast
numbers of smaller dark matter halos, many of which should have
hosted 'dwarf' galaxies. Several tens of dwarf galaxies are known to have
survived, intact, to the present day and are observed as satellites of
the Milky Way. Others were not so lucky and were destroyed by tidal
forces, and are today visible as 'streams' of stars in the
outskirts of the Milky Way. In order to understand how many of these
dwarf galaxies served as Galactic building blocks -- and ultimately to
study the nature of their host dark matter halos -- we
have obtained high dispersion optical spectra from the MMT and
Magellan telescopes for several known stellar streams. The prospective
student would use a mix of standard analysis programs and newly
written programs, to measure velocities and atmospheric compositions
of these stars in order to determine their origins. This project gives
students the opportunity to work with existing data to study the
formation of the Milky Way and its relation to the properties of dark
matter. As the project is ongoing, some opportunity exists for helping
to obtain new data as part of a remote observing run.
INTERN: Kathryn McKeough (Carnegie Mellon University)
CO-ADVISOR: Dr. Vinay Kasyap (HEA Division CfA)
We will investigate the deep Chandra observations of a galaxy cluster
with a powerful radio source in the center. The main goal is to look
for signatures of interactions between the radio source and cluster
environment and investigate statistical issues related to detection of
such structures in X-rays. We plan to apply the advanced image
analysis technique developed by the CHASC to the data to assess the
significance of any detected structures. These studies are important
for our understanding the feedback and the impact of the quasar on the
cluster environment at high redshift.
INTERN: Amber Medina (New Mexico State University)
CO-ADVISOR: Dr. Richard Edgar (HEA Division CfA)
Several years ago, we worked with REU student Greg Salvesen to measure the
proper motions of shock waves in the Cygnus Loop supernova remnant and
compare the resulting shock velocities with electron temperatures derived
from fitting X-ray spectra (Salvesen et al, 2009, ApJ, 702, 327;
http://arxiv.org/abs/0812.2515). We have now obtained high resolution
profiles of the hydrogen H alpha line for about 30 positions along
these shocks using the HECTOCHELLE instrument on the MMT telescope.
The profiles are made up of two components: The broad component is
around 250 km/s wide, corresponding to a post-shock proton temperature
around 2 million K, and the narrow component is about 35 km/s wide,
corresponding to a pre-shock proton temperature around
30,000 K. The intensity ratio of the two components is
sensitive to electron temperature.
Preliminary fits to some of the line profiles show a range of broad component
widths and a strong photoionization precursor ahead of the shock. The
project for this summer would be a systematic study of the line profiles,
including combining spectra from sets of fibers to improve signal-to-noise
ratios and the study of variations in the sky background. The result should be
a paper on the photoionization precursor and the relationship between the
proton temperatures and shock speeds. In particular, we will compare with
the surprising result of Salvesen et al. that the electron temperatures
exceed those expected from the shock speeds at many positions. The student
will learn about fitting procedures and uncertainty estimates, the relevant
atomic processes, the physics of collisionless shock waves and supernova
remnants.
INTERN: Robert T. Sutherland (Auburn University)
CO-ADVISOR: Dr. Adam Foster (HEA Division CfA)
The cooling function [L(T)] of a hot (0.1-10 keV) optically-thin collisional
plasma determines how fast the plasma will cool by radiation, and is a key
aspect in hydrodynamic models of supernova remnants, starburst galaxies, and
galaxy clusters. Although the details of the cooling curve depend upon
millions of individual atomic rates, in practice it is dominated at each
temperature by emission lines from a few specific ions. The total radiative
losses, therefore, depend upon the abundance of these ions and therefore their
ionization and recombination rates at particular temperatures. We have a
computer code (apec, written in C) that uses an atomic database (AtomDB) to
calculate the cooling function. The code contains hooks that vary the input
atomic rates in order to test the sensitivity of the final results to the input
rates. This project would involve using apec and AtomDB to determine, as a
function of temperature, which ionization and recombination rates most
significantly impact the cooling curve. The final result will be the
first-ever error estimate for the cooling function. More importantly, the
project will determine the most important ionization and recombination rates at
different energies \& temperatures, enabling targeted experimental measurements
to reduce these errors.
INTERN: V. Ashley Villar (Massachusetts Institute of Technology)
CO-ADVISOR/MENTOR: Professor Alicia Soderberg ( OIR Division CfA)
For decades astronomers have studied supernovae almost exclusively in the
optical bands where the bolometric luminosity peaks. However, some of
the most important discoveries about stellar death have been made at
other wavelengths, from radio to GeV. We will study several supernovae
and their environments across the electro-magnetic spectrum to shed
light on the final days, months, years in the life of a dying star.