2008
List of colloquium talks given during the summer of 2008
INTERN: India Anderson (Southern University) ADVISOR: Dr. Leonard Strachan PROJECT TITLE: Testing Solar Wind Models with data from the SOHO Ultraviolet Coronagraph Spectrometer Abstract:
INTERN: Dan D'Orazio (Juniata College) 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 (Gettysburg College) 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 (Yale University) 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 (Colby College) 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 (Franklin & Marshall College) 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 (University of Michigan) ADVISORS: Dr. John Raymond and Dr. Dick Edgar PROJECT TITLE: Cosmic Ray Pressure in the Cygnus Loop Abstract:
INTERN: David Stark (University of Minnesota) 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 (University of Missouri Columbia) 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 (Cornell College) ADVISORS: Dr. Paul Green and Dr. Kevin Covey PROJECT TITLE: Characterizing X-ray Active Objects in the ChaMP Survey Abstract: |