2006

INTERN: Michael Anderson, University of Michigan

PROJECT TITLE: X-ray Bright Optically Normal Galaxies (XBONGs) in the XBootes Field
ADVISOR: Dr. Steve Murray
MENTORS: Almus Kenter, Ryan Hickox, Christine Jones, Bill Forman

ABSTRACT:
While X-ray surveys have shown that the X-ray background is due almost entirely to emission from broad line AGN, X-ray observations have also identified a class of galaxies which are X-ray bright (with typical luminosities of 10⁴² ergs/sec and thus generally assumed to be associated with accretion onto a supermassive black home), but whose optical spectra do not show emission lines, as would be expected from an AGN. The nature of these galaxies is presently unknown. One suggestion is that these XBONGS (X-ray Bright Optically Normal Galaxies) may be obscured, so that emission from their nuclei is not seen optically. Another possibility is that the galaxies are so bright, that the galaxy emission dominates the optical spectra. XBONGS also have been suggested to be BL Lac-like systems. A fourth suggestion is that these galaxies do not contain optically thick accretion disks, but instead have an advection donimated (ADAF) or radiatively inefficient accretion flow (RIAF). So far the number of XBONGS that have been identified and studied is relatively small (∼30).
In the XBootes Chandra survey, we have ∼200 XBONG candidates, X-ray luminous galaxies with absorption line optical spectra. With the large Bootes spectroscopic galaxy survey, one can determine the environment for each XBONG and compare their local galaxy density to that of broad line AGN, as well as to normal galaxies with similar optical magnitudes and colors. With this large sample, one also can measure the spatial correlation length and may also be able to measure the luminosity function for XBONGS. A comparison of their environment and X-ray properties (including spectra) to type 1 AGN and to normal galaxies may determine the nature of these unusual galaxies.

INTERN: Sarah Ballard (University of California Berkeley)

PROJECT TITLE:   Star Formation in Bright-Rimmed Clouds
ADVISOR: Dr. Lori Allen

ABSTRACT:
Bright-Rimmed Clouds (BRC) are relatively isolated molecular clouds near hot young O stars. They are recognized in the optical as small dark clouds, often having a cometary morphology, with an ionization front (bright rim) facing the direction of the ionizing stars. Because of their isolated, compact structure, their proximity to young high mass stars, and the presence of an ionization front, bright-rimmed clouds are excellent laboratories for studying triggered star formation. One such sample of BRC are currently being studied in a Spitzer GTO program. The sources were selected from the catalogs of Sugitani & Ogura (Sugitani, Fukui, & Ogura, 1991; Sugitani & Ogura 1994), who scoured optical sky survey plates and compiled a list of small clouds bounded on at least one side by a bright rim, and containing one or more IRAS sources having colors consistent with young stars. To date, no complete census has been obtained of the young stars in BRC, and their status as sites of triggered or sequential star formation remains unproved. With the Spitzer Space Telescope, we now have the ability to detect all of the young stars in these clouds, and to determine whether they contain protostars (evidence of very recent star formation triggered by their neighboring OB associations), or only more evolved T-Tauri stars (coeval with the OB associations). The researcher who takes this project on will perform photometry on the Spitzer data using a local photometry program written in IDL (author of the software, Dr. Rob Gutermuth, is here and will be available for consultation). After a brief period of verifying the photometry results (and tuning the program as needed), the researcher will compile photometry on the entire sample and do statistical studies of the young stellar content of these clouds. These include the multiplicity of sources, evolutionary state of the young stars, the frequency of protoplanetary disks, the spatial distributions, etc. It is anticipated that this work will form the basis for a paper suitable for publication in the Astrophysical or Astronomical Journal.

INTERN: Amy Colon (Hunter College)

PROJECT TITLE: Fabrication of Future X-ray Telescopes by Selective Deposition
ADVISOR: Dr. Suzanne Romaine 
MENTOR: Ricardo Bruni

ABSTRACT:
Mirror figuring using selective coating deposition 
We are currently involved in building a prototype optic for the Constellation-X Mission, the followup Mission to Chandra. Looking to the future of high spatial resolution X-ray optics, improving, or even meeting, the resolution of the Chandra telescope, especially under tight budget constraints of future missions, presents us with serious technical challenges and will strain our imagination and creativity.
Along these lines, we have a program to investigate the figuring of x-ray optics using fine control of the deposition of thin films to correct the figure of the optic. The proposed project will involve the student in a study of grazing incidence X-ray optics and will carry out a program of test coatings to understand and define the limits to which we can take advantage of this technology.
The proposed project will involve the student in the fabrication of materials and coatings which is necessarily an interdisciplinary experience. Several areas including: physics, astronomy, optics, materials science and engineering are applicable in this project.

INTERN: Adrienne Hunacek (Massachusetts Institute of Technology)

PROJECT TITLE: High Resolution Ultraviolet Spectroscopy of the X-ray Binary Cyg X-1
ADVISOR: Dr. Saeqa Vrtilek 
MENTOR: Joey Neilsen

ABSTRACT:
Doppler Tomography of X-ray Binaries
This project is to construct "images" of x-ray binaries using the method of modulation tomography. The student will use existing data from the ESO archives to study the geometry of accretion flow in systems that contain neutron stars of black holes. The process is similar to that used in medical tomography. The images reconstructed via Doppler tomography provide unique and detailed insights into the structure of the accretion flow around compact objects. This should result in a short but interesting paper.

INTERN: Lauren Hund (Furman University)

PROJECT TITLE: Detecting AGN Through Variability in IRAC's Calibration Field
ADVISOR: Dr. Joseph Hora 
MENTOR: Matthew Ashby

ABSTRACT:
The Spitzer Space Telescope is the fourth and final great observatory and has created entirely new opportunities to study and better understand objects in the distant, early universe. This is due to a combination of Spitzer's unprecedented sensitivity in the mid-infrared (3-10 microns) and its privileged position in a novel earth-trailing orbit, where the celestial backgrounds are very low and even thermal emission from the earth is minimized.
We are seeking a motivated student to work with existing Spitzer imaging data of a unique field, the IRAC Calibration Field (IRAC-CF). This particularly infrared-dark region offers an extremely deep view of extragalactic space, even by Spitzer standards. It has been observed for 1-5 hours every 1-4 weeks with Spitzer's Infrared Array Camera (IRAC) since December of 2003. This accumulation of data is expected to continue steadily for the remainder of the Spitzer mission, meaning that the infrared sensitivity will eventually be the deepest in existence, exceeding even the ultra-deep GOODS fields with four times the area.
One special attribute of this dataset is its temporal coverage -- since the field is observed roughly once every month, it is possible to find and characterize distant active nuclei (AGN, or supermassive black holes) in the infrared as they dim and brighten from month to month, and indeed several already have been found. These objects are also being observed monthly from the ground via coordinated R-band imaging at the Palomar 60", so as to correlate the infrared and visible-wavelength behavior of these objects. Other supporting observations with the other Spitzer instruments, HST/ACS, and Akari are either approved or already completed.
This project is well-advanced, but needs some careful attention before it can be brought to completion. The student would be responsible for verifying the existing detections of variable nuclei and for refining the images to isolate even more variable objects. The student will be taught how to use MOPEX (the Spitzer data reduction software) to improve upon the existing mosaics, and how to perform precise source photometry with SExtractor. The student would then manipulate the galaxy catalogs he/she created to examine the trending behavior of these active nuclei.

INTERN: Christopher Klein (California Institute of Technology)

PROJECT TITLE: The Spitzer Interacting Galaxies Survey: IRAC Evaluations of Star Formation
ADVISOR: Dr. Matthew Ashby 
MENTORS: Drs. Andreas Zezas, Howard Smith

ABSTRACT:
The Spitzer Space Telescope is the fourth and final great observatory and has created entirely new opportunities to study and better understand fundamental aspects of star formation in galaxies. This is due to a combination of Spitzer's unprecedented sensitivity in the mid-infrared (3-10 microns) and its privileged position in a novel earth-trailing orbit, where the celestial backgrounds are very low and even thermal emission from the earth is minimized. New Spitzer results are being published every day, and are having a significant impact in many different fields.
We are midway through an approved Spitzer program to study whether and how star formation and nuclear activity within galaxies are influenced by major mergers, i.e., mergers between galaxies of comparable mass. Star formation has long been thought to result from triggering processes of various kinds, including supernovae shock waves and galaxy collisions. The student will have the opportunity to measure the basic set of observable quantities (luminosities, star-formation rates, morphologies) from newly-acquired Spitzer observations of numerous galaxy-galaxy pairs in various stages of merging. Specifically, we are seeking a motivated student to accomplish the following:

1. Process the galaxy images to create optimal mosaics in all four mid-infrared IRAC bands, using existing software with which our team is very familiar.
2. Quantify the amount and spatial extent of star forming activity in the sample galaxies, and search for trends with respect to merger stage and galaxy type. It is hoped that these data will allow us to assess a newly-developed understanding of how galaxies evolve in the infrared.
3. Apply simple criteria to detect active nuclei in cores of the merging objects.

The work outlined is substantial, but it ought to be feasible within the 10-week term of the REU appointment. We have decided to form a three-person team to advise the student. Ashby will serve as team leader and be responsible for the outcome of the REU project; Zezas will serve as backup when Ashby is (briefly) on travel and will help set the analysis strategies; Smith will help relate the results to the nascent galaxy evolution theory. If the student makes rapid progress, he/she may have an opportunity to analyze complementary MIPS 24 micron imaging observations as well, which will aid in the interpretation of the IRAC mosaics.

INTERN: Robert Penna (University of Rochester)

PROJECT TITLE: A Two-Fluid Plasma Shock Wave Model for the Strong Shock in Centaurus A
ADVISOR: Dr. Paul Nulsen

ABSTRACT:
Centaurus A (Cen A) is the nearest radio galaxy to us. Its active nucleus (black hole) pumps out energy in twin radio jets that interact with the surrounding interstellar medium creating radio emitting lobes of relativistic plasma. Energy is being pumped into the southwestern radio lobe fast enough to create a region of high pressure, that expands explosively and drives a strong, Mach 8, shock into the surrounding interstellar gas. In X-ray observations with the Chandra Satellite, the lobe appears as a cavity, surrounded by a region of bright X-ray emission that comes from the heated and compressed, shocked gas.
This is an example of a "collisionless" shock. Shocks are regions of rapid dissipation, where the kinetic energy of supersonic gas gets converted rapidly into thermal energy. Normally, this happens over distances that are similar to the mean-free-path of gas particles. In the plasma around Cen A, the kinetic energy of the protons gets converted into thermal energy much more quickly. However, the electrons still rely on the collisions to get their share of the energy from the protons, and this takes much longer. As a result, the electrons heat up relatively slowly, over distances that are resolved in the X-ray observations.
In a strong shock, like the one in Cen A, the final temperature of the gas depends only on the density of the gas before the shock and its pressure after the shock. The gas inside the lobe is expected to have the same pressure, but the density of the gas outside the lobe varies, so we would expect the shocked gas to have different temperatures around the lobe. It is a puzzle that all the shocked gas seems to have the same temperature. One possible project is to make a model for the collisionless shock around Cen A, to see if we can explain this puzzle, along with other features of the shock.

INTERN: Julia Sandell (Columbia University)

PROJECT TITLE: Recognizing Loops in the Solar Corona: A Diagnostic Tool for Magnetic Field Extrapolation Models
ADVISOR: Dr. Vinay Kashyap
MENTORS: Drs. Ed DeLuca, Mark Weber

ABSTRACT:
The corona on the Sun is made up of very hot plasma (greater than a million degrees) that is threaded and maintained by a pervasive magnetic field. It is believed that the corona is heated to such high temperatures because of the energy released when highly stressed magnetic fields reconnect and relax to a lower potential configuration. The three dimensional structure of the magnetic fields is therefore of much interest. There exist methods that extrapolate the 3D fields from surface flux measurements, and the extrapolated field lines are then validated by comparing with high-resolution EUV images of the solar corona from TRACE. We are now developing a process by which this validation can be done automatically, by comparing the field lines to morphologically identifiable coronal loops. The intern will take an active part in the development of the morphological loop finding method using TRACE data, and in adapting the magnetic field extrapolator to work for future solar missions.

INTERN: Sarah Scoles (Agnes Scott College)

PROJECT TITLE: Optical Counterparts to Supersoft X-ray Sources in the Nucleus of M31
ADVISOR: Dr. Rosanne diStefano

ABSTRACT:
Soft X-ray sources have been studied for only about 15 years. Some may be progenitors of Type Ia supernovae. Some may be black holes. Others may be soft states of X-ray sources that can also exhibit hard states. We are conducting research along several fronts to study soft X-ray sources in other galaxies. Three projects are ideal for a summer intern. (The intern would choose the project.) One of these would be to conduct research to follow up on clues that soft X-ray sources are more common in the vicinity of supermassive black holes. Chandra data from the central regions of a set of nearby galaxies will be studied to determine if there is a genuine excess of soft sources and to quantify and understand the effect, if it is verified. It has been postulated some of these stripped soft sources could be the stripped cores of giant stars that have been tidally disrupted by the supermassive black hole. The second project would be to work with a rich archive of HST observations of the center of M31. This work will explore the connections between X-ray sources and optical emission in the vicinity of the black hole. Finally, we have a suite of ongoing theoretical projects designed to understand the fundamental natures of soft X-ray sources, particularly near galaxy centers.

INTERN: Michael Shaw (Massachusetts Institute of Technology)

PROJECT TITLE: Recovering Long-Term Lightcurves from the Harvard Plates: A Search for Eclipsing Binaries in M44
ADVISOR: Dr. Josh Grindlay 
MENTORS: Bob Simcoe, Silas Laycock

ABSTRACT:
The world's fastest (by 2006) astronomical plate scanner has been just completed and commissioning runs will begin with this project to digitize a century of Harvard plates on the galactic cluster M44. This inauguration of the Digital Access to a Sky Century from Harvard (DASCH) project will digitize (at only 20sec each) at least ∼100 plates (typically 8 x 10in) containing historical (c. 1890 - 1990) images of the open cluster M44 (the Beehive Cluster). Using the well-calibrated stars in this cluster, this will further develop astronomical photometry analysis routines for the digitized plate images and allow a search for eclipsing binaries, and other variables, within or beyond the cluster. New binaries may be discovered within the cluster (since at least one was found from test scans of the cluster with a pre-DASCH commercial scanner) and can be follow up with archival ROSAT and other data to derive system properties. Since M44 is nearly on the ecliptic, a search will be conducted for asteroids or other high proper motion objects. The high galactic latitude (33deg) of the field and large number of mag. 14-15 galaxies included on each plate will permit a search for historical supernovae.