2013

Links to:

    List of colloquium talks given during the summer of 2013 
    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) 
CO-ADVISOR/MENTOR: Dr. Reinout Van Weeren (HEA Division)

PROJECT TITLE: The Gas Environment of AGNs in a Sample of 3CRR Radio Galaxies

Abstract: 
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.

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) 
CO-ADVISOR: Professor Edo Berger (OIR Division)

PROJECT TITLE: Understanding Magnetic Supersaturation in the Coolest Stars

Abstract: 
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.

ADVISOR: Dr Katja Poppenhaeger (HEA Division) 
CO-ADVISOR/MENTOR: Dr. G. Esra Bulbul (HEA Division) 
CO-ADVISOR/MENTOR: Dr. Andy Goulding (HEA Division)

PROJECT TITLE: Small Stars, Big Blasts: X-ray flares of Low Mass Stars

Abstract: 
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. 

ADVISOR: Dr. Matthew Bayliss (TA/ITC Division) 
CO-ADVISOR: Dr. G. Esra Bulbul (HEA Division)

PROJECT TITLE: A Joint Optical + X-ray analysis of the Triple Merging Cluster, MACSJ1226.8+2153

Abstract: 
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.

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)

PROJECT TITLE: Gas Hydrodynamics in the Cores of Massive Galaxy Clusters

Abstract: 
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.

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)

PROJECT TITLE: Identification and Investigation of Martian Dust Storm Source Regions from Orbital Observations

Abstract: 
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.

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: 
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?

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) 
CO-ADVISOR: Dr. Matthew Walker (TA Division)

PROJECT TITLE: Origins of Stellar Streams in the Outskirts of the Milky Way

Abstract: 
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.

ADVISOR: Dr. Aneta Siemiginowska (HEA Division) 
CO-ADVISOR: Dr. Vinay Kasyap (HEA Division)

PROJECT TITLE: Looking for the Signatures of Interactions between the Radio and the Intercluster Medium in Deep Chandra X-ray Observations

Abstract: 
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.

ADVISOR: Dr. John Raymond (SSP Division) 
CO-ADVISOR: Dr. Richard Edgar (HEA Division)

PROJECT TITLE: Shock Waves in the Cygnus Loop

Abstract: 
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.

ADVISOR: Dr. Randall Smith (HEA Division) 
CO-ADVISOR: Dr. Adam Foster (HEA Division)

PROJECT TITLE: Testing the Sensitivity of the Collisional Cooling Function to the Underlying Ion Population

Abstract: 
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.

ADVISOR: Professor Alicia Soderberg (OIR Division)

PROJECT TITLE: Supernova Forensics

Abstract: 
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.