2004 REU/PIA Projects

From Binaries to Triples
Rebecca Barlow - Mt. Holyoke College

Extracted from Midterm Report: Searching fro Companion Stars

Binary stars are simply a pair of stars orbiting around a common center of mass.  However, binary systems are not created orbiting one another.  During the first stage of stellar evolution, a giant interstellar gas cloud collapses and fractionalizes into smaller individual gas clouds with their own center of mass.  The smaller gas clouds vary in mass and size but their  gravitational interactions cause eventually formation of individual stars of the same age.  These clusters of stars interact between themselves.  It has been hypothesize that closed binary systems were create from interactions with multiple stars.

To further explorer this theory, I searched through 2MASS (2 Micron All Sky Survey) Database.  A list of target stars that based on previous spectroscopic reports was composed.  I examined the basic imagery of each target star, using IRAF and ds9.  If it appeared to have deformities such as an arm, a blog, or a bump.Next step in photometry is identifying possible companion stars.  This basically requires searching through VizieR for all nearby stars under 2 acr-minutes.  VizieR would list the apparent brightness in the J, Hs, and K filters for each possible companion stars.  Knowing the parallax for the target star,  the absolute brightness at 10 parsecs can be calculated for each possible companion star in the J, Hs, and K filters.  To establish visual relationships between the target star and the possible companions, a color ( J_mag - K_mag) vs absolute brightness graph was plotted.   Then I overlaid the main sequence at the 10 parsecs on the graph.  Basically using the plot, the stars closest to the main sequence were most likely the companion stars from the star cluster at 2 acr-minutes from the target.  Predictions about evolution stage of the target star and the companion star were estimated from the graph.  However, absolute magnitude is dependent on knowledge of distance and apparent brightness.  Distance can be distorted for example from interstellar dust, and apparent brightness is dependent on stellar mass and temperature.  This plot formed gives us a rough idea which stars may indeed be companions to the target, but the stars in question will have to be further explored through spectra.

To apply the process of examining the absolute brightness vs color to the 88 stars on the target list. A program was written in Supermongo. Next step is to examine those possible companion stars and reexamining the *.fits files.  If there are old images of the target star, then they should be compared to the recent 2MASS images to see whether that companion star has the same proper motion as the target star.  If both stars has similar proper motions, then there is a good indication that they are physical companion stars.

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Cataclysmic Variable Stars
Luke Galli - Colorado College

What are Cataclysmic Variables?

Most simply stated, a Cataclysmic Variable  is a two star system in which the stars orbit closely enough together that they exchange stellar material. CVs are composed of a white dwarf and a red dwarf. A white dwarf is the burnt out core of a star nearing the end of its life. It is a small, extremely dense, bright star. On the other hand a red dwarf is a smaller version of the sun which is much larger, less massive, and burns less brightly than the white dwarf. The clock-like orbiting and exchange of material between stars cause dramatic changes in brightness which have attracted astronomers attention for years. Four decades ago Robert Craft established the current model of Cataclysmic Variables (CVs) and since then much work has gone into classifying various types of CVs.

Overview

I worked with Dr. Alan Whiting from CTIO and Dr. Linda Schmidtobreik from ESO to find new CVs by taking spectrum of candidate stars and identify period information through high resolution spectrum and optical photometry.  The project was basically divided into three stages: Choosing candidates, taking the data, and reducing and analyzing the data.

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Deep Lensing Survey follow-up
Alice Globus - Wells College

What are Quasars?

QUASi stellAR objectS better know as quasar are categorized within  a class of galaxies named active galactic nuclei (AGN).  A galaxy is classified as an AGN due to that fact that their nucleus produces more radiation then the rest of the galaxy.  It is now widely accept among the astrophysical community that there is a super massive blackhole at the center of an AGN.

When observing quasars it appears as a point source (like a star), however enough energy is radiating that it has to be a galaxy and not a star.  Even more impressively quasars give off more energy then 100 galaxies combined!!!  To put things into perspective, one quasar can give off energy one trillion times the amount of our sun!  Quasars are at relatively high redshift in comparison to other classes of AGN.

Main Goals:

   1. Looking to find quasar candidates within dark matter overdensitities, by using weak gravitational lensing method .
   2. Using the KX method to identify the quasar candidates.
   3. Prepare a power point presentation for CTIO on March 19, 2004 and a poster for American Astronomical Society in January  2005.

While working at the CTIO REU program, the main goal of my research here is to identify quasar candidates within an ten arcminute field.  In order to achieve this goal there are several steps I had to take.  First off I had to gain an understand of how the field was chosen. Secondly, understand how weak gravitational lensing was used to find the mass overdensity.   The mass overdensities were identified by the Deep Lens Survey.  Then learn about the KX method, which the technique that I am using to identify quasar candidates within the mass overdensity.  Finally, learn how to plot the data IDL to produce the graphs so I can easily identify the candidates.

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Photometry of Nearby Supernovae
Ethan Knox - Humboldt State University

No abstract available, sorry for the inconvenient

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3D Ionization Codes for Planetary Nebulae
Melissa Rice - Wellesley College

No abstract available, sorry for the inconvenient

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E+A Galaxies
Kyle Walker - Ohio State University

Extracted from online report

E+A galaxies have been historically thought of as Elliptical galaxies with a large population of A stars.  These ancient galaxies, around 10 billion years old, are characterized by strong Balmer absorption (spectral lines arising from the n=2 transitions of the hydrogen atom) and weak OII (ionized oxygen) emission.  The Balmer absorption is the primary feature of hot, recently formed A-type stars, but with the lack of OII emission, we know these galaxies have stopped star formation within the past 1-2 billion years.

Nowadays, the name E+A is not often used because some galaxies with stong A components have been shown to be spirals.  Instead, the terms K+A (for the old stars plus the young stars) and post-starburst (PSG) are more commonly used.

E+A galaxies have been historically thought of as Elliptical galaxies with a large population of A stars. These ancient galaxies, around 10 billion years old, are characterized by strong Balmer absorption (spectral lines arising from the n=2 transitions of the hydrogen atom) and weak OII (ionized oxygen) emission.  The Balmer absorption is the primary feature of hot, recently formed A-type stars, but with the lack of OII emission, we know these galaxies have stopped star formation within the past 1-2 billion years. After finding good candidates by their spectra, we can use the SDSS SkyServer to obtain images of the galaxies. Next we can do more observations to confirm if these objects are indeed E+A galaxies. By using the CTIO 1.5-Meter Telescope's spectrograph we can obtain moderate resolution spectra of the nearby E+A's and show that there is no emission from beyond the central bulge of the galaxy.
 

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Planetary Nebulae interactions with the ISM
Javier Fuentes - Universidad de La Serena

Abstract

We present a study of five Planetary Nebulae (PNe) that may be interacting with the Inter-Stellar Medium (ISM). Three of these nebulae clearly have their central star displaced from the center of the object, indicating interaction. Images from the CTIO 0.9m telescope and low resolution long slit spectra in the range 358-698nm taken with the RC spectrograph on the CTIO 1.5m telescope during February 2004 were obtained. From the spectra we extracted 37 emission lines which were then used to compute the reddening, electron temperatures and densities, some chemical abundances (O, N, Ne, S & Ar) for each of our PNe. We also made an attempt at calculating their distances using the method of comparing forbidden line fluxes with those of recombination lines taking into account some estimate of the filling factor by analysing the structure in the images, but we are forced to conclude that these distances are very uncertain.
The possible --and even likely in the case of ISM interaction-- presence of shocks would affect the abundance determinations, making their uncertainty larger.

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Ages, Metallicities and Kinematics of Nuclei in Fornax dEs
Bárbara Rojas - Universidad de Chile

No abstract available, sorry for the inconvenient

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