Past Interns and Projects: Summer 2005
 
 SAO Summer Intern Program Projects, 2005


INTERN: Jennifer Blum (Columbia University)

PROJECT TITLE: Stellar Rotation
ADVISOR: Dr. Andrea Dupree
MENTORS: Jeno Sokoloski

ABSTRACT:
The He I 10830{\AA} line in the spectra of cool luminous stars, can reveal the dynamics of the chromosphere because the line-forming process is independent of local conditions. Following photoionization of neutral helium by the star's X-ray and EUV flux, helium recombines into a metastable state. Thus, absorption in the He I line serves as an excellent tracker of the mass outflow leading to mass loss. Using high resolution spectra from the Fourier Transform Spectrograph on the Canada-France-Hawaii telescope (CFHT) and the SOFIN echelle spectrograph on the Nordic Optical Telescope (NOT), we analyze the presence and strength of the He I $\lambda$10830 line to determine the chromospheric expansion velocity in 22 luminous cool stars of spectral types G and K. About half of the stars show absorption at outflowing velocities in excess of 100 km s$^{-1}$ which are comparable to typical stellar escape velocities at 1 R_star. For these targets we also explore the relation between the extent of He I $\lambda$10830 absorption and X-ray flux. This research was supported by the NSF REU Program at SAO.


INTERN: Laura Book (University of Illinois Urbana-Champain)

PROJECT TITLE: FU Orionis outbursts
ADVISOR: Dr. Lee Hartman
MENTORS: Debarati Chattopadhyay

ABSTRACT:
The purpose of this project is to make time dependent calculations of simple accretion disk models with an aim toward explaining FU Orionis outbursts. These events consist of jumps in mass accretion rate by several orders of magnitude in protoplanetary disks. The large, rapid increases of mass provide significant physical constraints on the structure of pre-planetary disks that are otherwise unobtainable. The project will consist of calculating the evolution of disks with a two-zone model that allows for the effects of limited disk ionization on the magnetorotational instability and a parameterized version of angular momentum transport by gravitational instability. The results of these calculations will be used to construct light curves to compare with observations.


INTERN: Krzysztof Findeisen (Cornell University)

PROJECT TITLE: AGN Heating of Galaxies and Groups
ADVISOR: Dr. Paul Nulsen
MENTORS: Ryan Hickox

ABSTRACT:
X-ray observations with the Chandra satellite have shown that large amounts of energy can spew from supermassive black holes, also called active galactic nuclei (AGN), at the centers of large galaxies. The energy emerges from AGN in pairs of opposing jets and gets deposited in the surrouding region. In the massive elliptical galaxies and groups of galaxies that have atmospheres of hot X-ray emitting gas, the energy inflates cavities in the gas. The plasma inside the cavity often emits at radio wavelengths, so we see a 'radio lobe' inside it. In some cases Chandra has also detected shock fronts (like sonic booms) that surround the cavities, created when the cavities are inflated with explosive speed.

The energy injected into the gas by this process has a major effect on the hot gas. Without it, the gas should have cooled long ago to form stars, so it probably has a large effect on the process of galaxy formation. By measuring the energy we can also infer how rapidly the supermassive black holes grow. We would like to know how often this happens, how much energy is injected, and whether it happens in all galaxies. These questions can be answered in part by doing a survey of nearby galaxies and groups of galaxies from the Chandra archive to find cavities. From the size of a cavity and the pressure of the surrounding gas, we can determine the energy required to make it. By seeing how common they are, we can estimate how frequently they occur and how much energy they pump into the gas.


INTERN: Conrad Hutchenson (University of Arizona)

PROJECT TITLE: IR Properties of Galaxies in Clusters and Groups
ADVISOR: Dr. John Huchra
MENTORS: Nathalie Martimbeau

ABSTRACT:
The 2 Micron All-Sky Survey is the source of a major new catalog of galaxies with well measured photometric properties in the near infrared. Distances/redshifts have now been measured for a complete sample of ~24,000 galaxies from this catalog and morphological types have been estimated for almost all the galaxies.

We will complete the visual classification of the remaining 10% of the sample and use this complete survey to study the global properties of the galaxies in the sample, including color versus morpological type, color versus luminosity, the interal extinction in spiral galaxies from color versus inclination.

If time permits, we will also study differences in galaxy properties as a function of their environment. The major scientific question is to understand how the process of galaxy formation depends (or not, as the case might be) on environment by clearly measuring the how global properties change versus such parameters as the local galaxy density and the depth of the potential wells (galaxy clusters) in which they form.


INTERN: Harrison Prentice-Mott (University of Pennsylvania)

PROJECT TITLE: Cryogenic X-ray Detector Laboratory
ADVISOR: Dr. Eric Silver
MENTORS:

ABSTRACT:
The student will learn about broad band , high resolution x-ray and gamma-ray detectors that are being developed for use in space- and ground-based applications. These include fundamental physics measurements of highly charged ions produced in heavy ion accelerators and laboratory plasmas; 2) spectroscopic measurements of cosmic x-ray

and gamma ray sources such as black holes, supernova remnants and clusters of galaxies; 3) industrial and medical applications where high resolution x-ray spectroscopy is important to materials and chemical analysis. The intern will participate in laboratroy experiments associated with improving the performance of these instruments and thereby learn low temperature and solid state physics and how to to do spectroscopic analysis. There are several specific , self-contained projects that the intern will be able to concentrate on and present to the group at the completion of his/her internship.


INTERN: Michael Rutkowski (Hampden-Sydney College)

PROJECT TITLE: The Supernova Remnant E0102-72
ADVISOR: Dr. Eric Schlegel
MENTORS:

ABSTRACT:
E0102-72, a remnant in the Small Magellanic Cloud, has a circular shape with 'spokes' connecting back to the center. It shows strong emission lines of oxygen and because of this emission, it has been used to monitor the increasing absorption layer on the ACIS detector on Chandra. That means there is a large quantity of data on this object available in the data archive. This project will extract the best of the data, those pointings closest to the optical axis of the telescope, and sum them to (1) search for a point source of emission; (2) search for time-dependent motion in the rim. The second is particularly interesting: over approximately 6 years of observations, the reverese shock has been moving all that time. It may be detectable in the SE portion of the remnant where a sharp rim exists.


INTERN: Shannon Schmoll (University of Washington)

PROJECT TITLE: A Search for Asteroids in the EXPLORE Project Dataset
ADVISOR: Dr. Gabriela Mallen-Ornelas
MENTORS: Dr. Matt Holman

ABSTRACT:
The currently accepted theory for the formation of planetary systems postulates that terrestrial planets formed by the collisional growth of kilometer-sized rocky bodies known as planetesimals. Asteroids are leftover relics from this phase in the history of the Solar System. It is believed that the asteroid belt contains objects of different origins, ranging from planetesimals to fragments of planet embryos. The size distribution of asteroids is critical for understanding their collisional history.

The goal of this project is to identify and characterize a sample of faint asteroids in images from the EXPLORE search for transiting extrasolar planets. The EXPLORE database consists of thousands of images of 3 fields taken every 2-3 minutes over a period of 1-2 weeks per field. The images were taken with CCD mosaic cameras on the CTIO and KPNO 4m telescopes and the 3.6m CFHT. These observations constitute a unique dataset in terms of depth and time sampling of the observations and will therefore lead to a sample of main belt asteroids fainter than those in most existing studies. Moreover, it will be possible to produce light curves on the discovered asteroids, leading to a period measurement for the fastest rotators.

Asteroids can be found in difference images created as a by-product of the search for transiting planets. Difference images are produced by subtracting a template image from each frame, thus leaving a mostly empty frame, with only time-variable and moving objects remaining. The student will find the asteroids, calculate their orbital elements (by modifying existing computer programs), produce a luminosity function for the sample, create light curves, and interpret the results.


INTERN: Megan Schwamb (University of Pennsylvania)

PROJECT TITLE: Applications of Gravitational Lensing: Light Curve Studies
ADVISOR: Dr. Rosanne Di Stefano
MENTORS:

ABSTRACT:
One way to detect and study masses lying between us and a distant bright source field is to study light curves that may contain evidence of gravitational lensing by these masses. A new generation of observing programs is being planned. We will carry out some theoretical studies that can serve as input to the design of these programs, optimizing their potential to study dark matter, and also to teach us about local stellar remnants.

The focus of the project can be guided by the interests of the student. We could concentrate on simulations of specific source fields, on the search for MACHOs, on the study of binarity through monitoring observations, or on the search for planets.


INTERN: Paul Sell (University of Toledo)

PROJECT TITLE: High-redshift Galaxies Study
ADVISOR: Dr. Matthew Ashby
MENTORS: Dr. Jia-Sheng Huang

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 owing to a combination of its 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 minimi zed.

We are seeking a motivated student to work with Spitzer imaging data to attempt to detect elusive nascent galaxies at redshifts of z=4 using a version of the now well-established dropout technique. The project is organized into three phases.

The first phase involves collecting and reducing optical broadband data at the KPNO 4 m Mayall telescope with the MOSAIC wide-field camera. Drs. Ashby and Huang will be traveling to Kitt Peak to acquire these data (four nights have already been granted for this purpose, June 9-12), and we would hope the student would join us for that observing run so as to gain real hands-on experience with at a world-class astronomical facility (they have funding to pay your expenses if it fits into your schedule). The reduction portion of this work would involve standard processing of the imaging data acquired at KPNO, various quality assessment tasks, and the generation of a catalog of sources in the resulting combined images.

The second phase of the project will entail `value-added' analysis to the catalog. Among other things, the catalog would be combined with an existing catalog of sources detected by IRAC, and searched for objects that are visible to IRAC but only weakly detected or not detected at all by the MOSAIC camera. Such optically-faint infrared-bright objects will form the basis of a sample of candidate high-redshift galaxies.

The third phase will be a check on the validity/feasibility of the selection technique. Existing spectroscopic redshift databases can be examined for overlap with the sample, and photometric redshift techniques c an also be applied as proof-of-concept.

Completion of the first two phases of the work alone would certainly be worthy of a AAS poster presentation, and we expect that the student should be able to accomplish those and possibly most or all of the third portion in the 9 or 10 weeks available. The first two phases constitute the primary objective of the student's work. We would hope, however, that the student would be able to make significant contributions in the third phase, and woule want to be involved in subsequent proposals that we plan in order to follow up on the most promising sources spectroscopically. That portion of the plan would require a large-aperture observatory and would not of course be possible on the short timescales of the summer work period. It would nonetheless give the student further scope for work in this field if he/she were interested in building on the experience.


INTERN: Sarah Sonnett (College of Charleston)

PROJECT TITLE: Spitzer/IRAC Photometry of T Dwarfs
ADVISOR: Dr. Brian Patten
MENTORS: Dr. Massimo Marengo

ABSTRACT:
The Spitzer Space Telescope is one of NASA's Great Observatories. One of the three science instruments on board Spitzer is the Infrared Array Camera (IRAC), a four channel camera that uses two pairs of 256x256 pixel InSb and Si:As IBC detectors to provide simultaneous images at 3.6, 4.5, 5.8, and 8 microns. With the goal to define the IRAC colors for brown dwarfs, we have acquired photometry for some ~80 stellar and sub-stellar mass objects with spectral types of late-M, L and T. Our data shows that the T dwarfs stand out from the other brown dwarfs in IRAC colors, and provide the most insight into the nature of brown dwarf atmospheres. In particular, we find that the T dwarf photometry and colors do not agree entirely with the predictions of theoretical models, suggesting there is a second parameter, other than temperature, that one must consider. The most likely candidate is mass, since sub-stellar mass objects cool continuously after their formation. Among objects with similar spectral type, the range of mass suggested by our sample is from about 15 to 70 Jupiter masses.

Because our original GTO sample was designed to sample as wide a range of spectral types as possible, with a only a few representatives for each spectral type bin, we need to expand our sample size of T dwarfs to better test how observation compares to theoretical modeling for these objects. An additional sample of T dwarf data has been acquired under the Nearby Stars GTO program for this purpose.

The student will reduce and analyze IRAC images for about a dozen relatively nearby brown dwarfs. The student will become familiar with the IRAC camera and how the data were taken with this space-based instrument. Software developed locally will be used to produce cosmic-ray-cleaned, co-added data from multiple exposures of the same object. Routines in IRAF will be used to extract the photometry for the objects of interest from each field. These new data will be combined with existing data for late-M, L, and T dwarfs, to better investigate the preliminary conclusions we have drawn from the data analyzed thus far about T dwarfs in the solar neighborhood.

 
 

Clay Fellow Warren Brown