2010
Links to:
List of colloquium talks given during the summer of 2010
Program of the SAO Summer Intern Symposium, August 11, 2010
2010 Summer Program Calendars for June , July , and August
Abstracts for posters presented at the January, 2011 AAS Meeting
INTERN: Justin Brown (Franklin and Marshall College)
ADVISOR: Dr. Mukremin Kilic (SSP Division)
CO-ADVISOR: Dr. Warren R. Brown (OIR Division)
PROJECT TITLE: Testing Stellar Evolution Theory with Low-mass White Dwarfs
Abstract:
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.
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.
INTERN: Jared Coughlin (Villanova University)
ADVISOR: Dr. Darin Ragozzine (TA Division)
CO-ADVISOR: Dr. Matthew J. Holman (TA Division)
PROJECT TITLE: Transneptunian objects
Abstract:
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:
How probable is it that exoplanetary systems have the appropriate alignment (with respect to Earth) to see mutual 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?
This observationally-motivated theoretical study will bring exoplanet mutual events to the fore as a potential tool for studying planetary systems beyond on own.
INTERN: Jason Kong (University of California at Berkeley)
ADVISOR: Dr. Paul E. J. Nulsen (HEA Division)
CO-ADVISOR: Dr. Ralph P. Kraft (HEA Division)
PROJECT TITLE: Composition of Radio Lobes
Abstract:
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.
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.
INTERN: Sam McCandlish (Brandeis University)
ADVISOR: Dr. Rosanne DiStefano (TA Division)
CO-ADVISOR: Dr. Hagai Perets (TA Division)
PROJECT TITLE: The Prediction of Gravitational Lensing Events
Abstract:
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.
INTERN: Elisabeth Otto (Ohio State University)
ADVISOR: Dr. Paul J. Green (HEA Division)
CO-ADVISOR: Dr. Anna Luise Frebel (OIR Division)
PROJECT TITLE: Stalking the Elusive Dwarf S Star
Abstract:
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.
INTERN: Dominiqe Segura-Cox (University of Michigan)
ADVISOR: Dr. Joseph L. Hora (OIR Division)
CO-ADVISOR: None.
PROJECT TITLE: Star Formation in the Massive Cygnus-X Complex
Abstract:
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.
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)
CO-ADVISOR: None.
PROJECT TITLE: Origins of chemical complexity during (exo-)planet formation
Abstract:
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.
INTERN: Kimberly Ward-Duong (Northern Arizona University)
ADVISOR: Dr. Scott W. Randall (HEA Division)
CO-ADVISOR: Dr. Marie Machacek (HEA Division)
PROJECT TITLE: Mergers, Feedback, and the IntraCluster Medium
Abstract:
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.
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)
CO-ADVISOR: None.
PROJECT TITLE: A Detailed Study of the Host Galaxies of Type Ib Supernovae
Abstract:
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.
INTERN: Schuyler Wolff (Western Kentucky University)
ADVISOR: Dr. Ruth Murray-Clay (TA Division)
CO-ADVISOR: None.
PROJECT TITLE: Resonance capture in planetary systems
Abstract:
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.
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.