Past Interns and Projects: Summer 2004
 SAO Summer Intern Program Projects, 2004

INTERN: Ryan Anderson (University of Michigan)

PROJECT TITLE: Spitzer Imaging of Young Stellar Clusters: Surveying Star Forming Regions for Disks and Protostars
ADVISOR: Dr. Tom Megeath
MENTORS: Drs. Lori Allen, Phil Myers

How do stars form? In the last thirty years we have learned that 1.) stars form in cold molecular clouds, 2.) that stars form not in isolation, but in clusters, and 3.) that most stars form with circumstellar disks - these disks are the progenitors of solars systems like are own. However, there is still much to learn. The fact that stars form in dense clusters raises the possibility that interactions between stars may govern the process of star and planet formation. For example, disks may be destroyed in dense clusters by radiation and dynamical stripping, thus preventing the formation of planets.

Studying the formation of stars and early evolution of protoplanetary disks requires sensitive infrared observations. The recently launched Spitzer Space Telescope is already providing such data on star formation. One of the three instruments on board Spitzer, IRAC - Infrared Array Camera, was built at the CfA. In return, we now have over 800 hours guaranteed time observations. Almost 100 hours of this time is being dedicated to surveys of star forming regions, including a survey of young stellar clusters and the Orion Molecular clouds. Spitzer has been taking science observations since the beginning of December, and we are now collecting a growing gallery of star forming regions. Each one of these star forming regions is a snapshot of the cluster forming process, by obtaining many snapshots covering a range of ages and environments, we hope to disentangle the complex feedback mechanisms which may occur in these regions.

As a project, the student will be assigned a star forming region in the Orion molecular cloud containing a cluster of young stars. Using Spitzer data, the student will identify stars with disks and protostars in this cluster, and compare their region with other star forming regions in our database.

INTERN: Debarati Chattopadhyay (Lehigh University)

PROJECT TITLE: Imaging the Solar Corona with the Solar Dynamics Observatory (launch 2008)
ADVISOR: Dr. Mark Weber
MENTORS: Alana Sette

The Atmospheric Imaging Assembly (AIA) for the Solar Dynamics Observatory (launch 2008) will provide images of the whole solar corona in 8 passbands (8 different temperatures) every 10 seconds, 24 hours a day for five years. This project will involve the development of tools to analyze the AIA data stream efficiently. One of the computationally intensive jobs is to compute the "differential emission measure" (DEM) of the corona from the AIA data sets. The DEM defines the amount of plasma at each temperature along the line of sight in the image. We will create simulated images of the corona (from a set of 3-D computations) and process those images to reconstruct the DEM at each point in the image. Parallel processing techniques will be applied with the goal of estimating the computation time required for a full set of 16-Megapixel AIA images.

In addition, the student will help us evaluate the effectiveness of different DEM image display options, including single temperature emission maps and time-progression DEM movies.

INTERN: David (Clay) Hambrick (Harvey Mudd College)

PROJECT TITLE: Shock Heating of Cooling Flow Clusters
ADVISOR: Dr. Paul Nulsen

X-ray emission that reveals the hot intergalactic gas in clusters of galaxies also carries away its heat. Near to the center of many rich clusters, the rate of heat loss is sufficient to cool the gas to low temperatures many times over since the cluster was formed. These are known as cooling flow clusters. Despite the heat loss, observations with Chandra and XMM-Newton show that little of the gas does cool significantly, so that some heat source must make up for the radiative losses.

Chandra observations have also shown that radio sources at the centers of many cooling flow clusters have inflated large cavities in the X-ray emitting gas. When these "bubbles" rise buoyantly through the gas, their energy (enthalpy) is converted to heat in their wakes. This form of heating is substantial, but insufficient to replace radiative losses in most cases. Recently, weak shocks, driven by the expanding radio lobes, have also been detected surrounding the radio lobes in several systems. In each of the three cases analyzed so far, the energy of the shocks is more than adequate to make up for the radiative losses from the cooling flow. In two of them the energy is significant for heating the whole cluster, showing that shock heating by active galactic nuclei could play a significant role in the overall energetics of clusters of galaxies.

Depending on interests, a student will do some of the following: search the Chandra archives for more examples of shocks generated by expanding radio lobes; analyze Chandra data for a system of shocks to determine their basic physical properties, particularly age and total energy; investigate the histories of energy input to the shocks, subject to the observed constraints, especially preservation of abundance gradient.

INTERN: Cecelia Hedrick (University of Nebraska)

PROJECT TITLE: Outbursts in Symbiotic Binary Stars
ADVISOR: Dr. Jennifer (Jeno) Sokoloski

Symbiotic stars are binary star systems in which a red-giant star and a white-dwarf star orbit one another. Since the red giant is very large and puffy, the material at the stellar surface is only gravitationally bound to the rest of the star very loosely. The strong radiation field from the red giant can therefore push the material away in a wind. The companion white dwarf has a very strong surface gravitational field, and it captures a portion of the red-giant wind as it passes by. In some cases, the accreted material forms a disk around th white dwarf.

Observationally, symbiotic binary stars can suddenly brighten in the optical, and then slowly fade. But the cause of these 'outbursts' is not well understood. They could be due to an instability in the accretion disk around the white dwarf, a change in the rate of nuclear burning on the surface of the white dwarf, expansion of the white-dwarf photosphere, or some combination of all of these effects.

We have been collecting weekly optical brightness measurements of five interesting X-ray-bright southern symbiotic stars. The goal the intern's project will be to examine these data and 1) see if we have found any new outbursts, 2) analyze any new outbursts in an attempt to constrain physical mechanisms, and 3) generally characterize the optical variability properties (including searching for periodic variations which could be associated with the orbital motion) of these five systems.

INTERN: Tyrel Johnson (University of Idaho)

PROJECT TITLE: Development and Fabrication of Magnetic Microcalorimeter Detectors for Future Space Missions
ADVISOR: Dr. Susanne Romaine
MENTORS: Dr. Ricardo Bruni

We are currently collaborating with GSFC, Brown University and NIST (CO) to develop magnetic microcalorimeter detectors for use in future X-ray astromony space missions.

The proposed project will involve the student in the fabrication and characterization of materials and devices which is necessarily an interdisciplinary experience. Several areas including: physics, astronomy, materials science and engineering are applicable in this project.

INTERN: David Myer (University of California San Diego)

PROJECT TITLE: X-ray Emission from E/S0 Galaxies
ADVISOR: Dr. Eric Schlegel

E/S0 galaxies essentially have 2 components to their X-ray emission: point sources (read: X-ray binaries) and diffuse emission from hot gas. The point source emission scales with the blue optical luminosity; the diffuse emission appears to follow a different relation. The low-luminosity E/S0s (L_B < 10.5) are expected to be devoid of diffuse emission, yet several show considerable quantities of hot gas.

Archival Chandra observations of a few low-luminosity E/S0 will be analyzed to extract the diffuse emission. The spatial distribution will be extracted and fit with an appropriate profile function. Fit values will be correlated with E/S0 galaxy parameters to examine the role of the expected dominant contributors (mass, age, etc.). One model, for example, implies that the X-ray surface brightness profile should depend on the wind state of the galaxy.

INTERN: Joseph Neilsen (Kenyon College)

PROJECT TITLE: Pulse Profiles and Phased Spectroscopy of SMC X-1
ADVISOR: Dr. Saeqa Vrtilek
MENTORS: Dr. Bram Boroson

Data: 8 roughly 8ksec observations with Chandra Acis-S in CC mode. 4 obs. during X-ray High State and 4 obs during X-ray low state of the roughly 60 day superorbital period.

SMC X-1 is part of a massive X-ray binary system with 0.7 second pulses. It is one of only two known sources to show both pulses and bursts. It is also the only X-ray pulsar for which no spin-down episodes have been observed. This suggests that SMC X-1 has a magnetic moment that is an order of magnitude lower than those of typical X-ray pulsars. Observations with less sensitive instruments suggest that the pulse profile changes dramatically between high and low X-ray states. ACIS-S in CC mode is ideal for determining pulse profiles and conducting pulse phased spectroscopy. We have determined the pulse period with great accuracy from this data. However, it is important to conduct a systematic study of pulse profile as a function of orbital phase, superorbital phase, and energy.

INTERN: Megan Roscioli (Haverford College)

PROJECT TITLE: Morphologies of mid-infrared galaxies
ADVISOR: Dr. Pauline Barmby
MENTORS: Dr. Matthew Ashby

Galaxies detected at mid-infrared wavelengths are believed to be important contributors to the total star formation in the universe, and thus to the cosmic infrared background. Yet the nature of these galaxies -- dusty elliptical galaxies, star-forming spirals, or `train-wreck' mergers -- has remained elusive because of the small areas and limited spatial resolution of previous mid-IR surveys. We how have a huge sample of mid-infrared galaxies from a survey done with the IRAC instrument on the Spitzer Space Telescope. Combining this with a published catalog of morphological parameters measured from Hubble Space Telescope observations of the region will help in the understanding of the nature of this population of galaxies.

INTERN: Krystal Tyler (Purdue University)

PROJECT TITLE: AGN Activity in Nearby Galaxies Detected at Infrared Wavelengths With the Spitzer Space Telescope
ADVISOR: Dr. Michael Pahre
MENTORS: Dr. Giovanni G. Fazio

The new Spitzer Space Telescope provides unprecedented spatial resolution and sensitivity for studying the properties of nearby galaxies in the mid- to far-IR. The goal of this project is to try to detect AGN activity in several dozen nearby galaxies -- of a wide range of morphological types and luminositie s - -- imaged at 3 < lambda < 160 um with Spitzer. The AGN will be identified in two different ways: (1) spatially, by fitting 1-D/2-D models to the light distributions, thereby looking for a point source in the nucleus; and (2) by looking for nuclear regions significantly redder than the inner bulges, via 1-D surface brightness profiles. The sensitivity to AGN activity measured by these methods will be estimated using simple, 2-D model galaxy simulations. The AGN detections/fluxes will be compared to Chandra X-ray Observatory data, either through literature searches or by analysis of archival data (where appropriate) . They will also be compared to the nuclear activity measured for the sample via optical spectroscopy, as documented in the literature (e.g., Ho, Filippenko, & Sargent 1995, 1997, ...).

INTERN: Iris Monica Vargas (University of Puerto Rico)

PROJECT TITLE: Exploring the Playground of the Nucleus: Characterizing the Nuclear Extended Emission in Chandra's Early-Type Galaxy Sample
ADVISOR: Dr. Christine Jones

A sample of 19 galaxies from the O'Sullivan catalogue was selected and further categorized according to velocity dispersion values and the extent of their X-ray emission using data from the radial emission distribution profiles made with funtools/DS9 applications. Galaxies were grouped into eight sets, with velocity dispersion values ranging from low velocity dispersion values 54-74 km/s) to high velocity dispersion values (190-300 km/s) and observed extended emissions in the range of 7-340 arcseconds. Data from the observations were processed and spectra were fitted by XSPEC. Fluxes were obtained for all objects as well as other figures of merit such as temperatures and luminosities. It was determined that the obesrved X-ray extended emission in the low-luminosity early-type galaxies of our sample, is in the scale of a few kiloparsecs and appears to be dominated, in general, by a gas component rather than by unresolved point sources.

INTERN: Linda Watson (University of Florida)

PROJECT TITLE: Study of Stellar Atmospheric Structure and Distance Estimation using a UV-optical Interferometer in Space
ADVISOR: Dr. Margarita Korovska
MENTORS: Drs. Dimitar Sasselov, Massimo Marengo

Direct imaging of stars other then the Sun is crucial for understanding the structure of stellar atmospheres, their activity and magnetic fields, and the variability driven by processes such as periodic pulsation. Surface details cannot be resolved using current ground- and space-based telescopes and interferometers even for nearby giant and supergiant stars. We are currently exploring the possibility of imaging atmospheric structures and studying the pulsation processes in a set of variable stars including Cepheids and evolved giants and supergiants using a long-baseline UV-optical interferometer such as the Stellar Imager (SI). The Stellar Imager is expected to have a ~500m baseline and will produce images with ~0.1 milliarcseconds angular resolution. SI represents an advance in resolution of at least two orders of magnitude when compared to the HST and will thus be an invaluable resource for many areas of astrophysics, including understanding stellar activity, stellar magnetic fields, and for estimating cosmological distances.

This project will concentrate on studies of the potential for interferometric imaging of pulsating atmospheres and stellar surface structures at UV-optical wavelengths. The work will involve simulations of a Cepheid atmospheres and of surface brightness distribution, taking into account the hydrodynamic effects associated with the pulsation processes and will use results from numerical simulations of red giant convection structures to carry out interferometric imaging simulations.

Work Description: The student will run existing software to produce models of surface brightness distributions for a set of cases, and will run a simulator to produce images as seen by the SI interferometer. A summer intern will also carry out diagnostics studies of the stellar activity and variability using the results from these simulations.


Clay Fellow Warren Brown