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2007 REU Students' AAS Abstracts

AAS Winter 2008, Austin
Implementation of the Pan-STARRS Image Processing Pipeline
Julia Fang (Northwestern University & IfA) and C. Aspin (IfA)

Pan-STARRS, or the Panoramic Survey Telescope and Rapid Response System, is a wide-field imaging facility that combines small mirrors with gigapixel cameras. It surveys the entire available sky several times a month, which ultimately requires large amounts of data to be processed and stored right away. Accordingly, the Image Processing Pipeline--the IPP--is a collection of software tools that is responsible for the primary image analysis for Pan-STARRS. It includes data registration, basic image analysis such as obtaining master images and detrending the exposures, mosaic calibration when applicable, and lastly, image sum and difference. In this paper I present my work of the installation of IPP 2.1 and 2.2 on a Linux machine, running the Simtest, which is simulated data to test your installation, and finally applying the IPP to two different sets of UH 2.2m Tek data. This work was conducted by a Research Experience for Undergraduates (REU) position at the University of Hawaii's Institute for Astronomy and funded by the NSF.


DPS October 2007 Orlando
Dynamical Stability of Terrestrial and Giant Planets in the HD 155358 Planetary System
James Haynes (IfA)

We present the results of a study of the dynamical evolution and the habitability of the system HD 155358. This system is unique in that it is one of the two low metallicity stars discovered to host a multiple planet system. HD 155358 is host to two Jupiter-sized planets, with minimum masses of 0.86 and 0.50 Jupiter-masses. The orbit of the lower mass planet of this system is located at the inner edge of the system's habitable zone. To determine whether this system can harbor terrestrial-type planets, we numerically integrated the orbits of its planets and an Earth-like object for different values of their masses and orbital eccentricities. Results indicate that this system could potentially host stable orbits for terrestrial-sized planets in its habitable zone, but the stability of these orbits is very sensitive to the precise characteristics of the giant planets of the system. We also studied the long term stability of larger bodies (Neptune- and Saturn-mass) in the system. Our results show that a Neptune- or Saturn-mass body could exist in stable orbits in this system fairly close in, potentially within the range of present detection techniques, again depending on the precise configurations of the giant planets.


AAS Winter 2008, Austin
Beryllium Abundances in Solar Mass Stars

Julie A. Krugler (Michigan State Univ) and A. M. Boesgaard  (IfA)

Light element abundance analysis allows for a deeper understanding of the chemical composition of a star beneath its surface. Beryllium provides a probe down to 3.5x10^6 K, where it fuses with protons. In this study, Be abundances were determined for 52 F and G dwarfs selected from a sample of local thin disc stars. These stars were selected by their mass to be in a mass range of 0.9 to 1.1 solar masses as determined by Lambert & Reddy (2004). They have effective temperatures from 5600 to 6400 K, and their metallicities [Fe/H] -0.65 to +0.11. The data were taken over several nights, with forty-six spectra taken with the Keck HIRES instrument and six spectra on the Canada France Hawaii Telescope (CFHT) using the Gecko spectrograph. The abundances were calculated via spectral synthesis, fitting a 4Å region around the resonance lines of Be II. The data were then analyzed to investigate the Be abundance as a function of age, temperature, and metallicity and its relation to the lithium abundance for this narrow mass range. Be is found to increase with metallicity and the linear relationship evident when extended to metallicities down to -4.0 dex with slope 0.86 ± 0.02. The relation of the Be abundance to effective temperature is dependent upon metallicity, but when metallicity effects are taken into account, there is a spread 1.2 dex. We find a 1.5 dex spread in A(Be) when plotted against age, with the largest spread occurring from 6-8 Gyr. The relation with Li is found to be linear with slope 0.36 ± 0.06 for the temperature regime of 5900-6300 K. This research was conducted through the Research Experiences for Undergraduate (REU) program at the University of Hawaii's Institute for Astronomy and was funded by the NSF.


AAS Winter 2008, Austin
Theoretical Mid-Infrared Modeling of Starburst Galaxies
Kirsten Larson (The College of Wooster) and L. Kewley (IfA)

We investigated the ability of the stellar models Starburst99 and MappingsIII to model starburst galaxies using infrared diagnostics and Spitzer data. The infrared diagnostics were useful for distinguishing between starforming galaxies and AGN. The theoretical starburst models indicate that the infrared emission-line ratios are largely degenerate and are extremely sensitive to the age of the stellar population and the star formation history prescription (instantaneous versus continuous). Additional information from the near-infrared or optical spectra are required to resolve the degeneracies encountered in the infrared emission-line ratios. This work was conducted by a Research Experience for Undergraduates (REU) position at the University of Hawaii's Institute for Astronomy and funded by the NSF.


AAS Winter 2008, Austin
Cloud Structure and the Origins of the Stellar Initial Mass Function in ρ Ophiuchus
Dylan R. Nelson (UC Berkeley & IfA), J. J. Swift (IfA), J. P. Williams (IfA)

We explore the relationship between dense molecular cores and young, pre-main sequence stars in rho-Ophiuchus, an active star-forming region. Our analyses synthesize multi-wavelength data, including dust extinction maps, dust emission at 1.2mm, mid-infrared images, and molecular line emission from several species. Following the investigation of several core identification algorithms - including a new technique based on Bayesian statistics - we select a final sample of dense cores from a hybrid of techniques applied to the 1.2mm dust emission. The spatial distribution of these cores appears scale free over two orders of magnitude, following the spatial distribution of young stars over a wide dynamic range. However, measured velocity dispersions of the dense gas in cores imply that a vast majority are stable against gravitational collapse. The average column density of cores systematically decreases with core size suggesting that some of the larger cores may be transient or fragment into multiple star systems. Several cores harbor multiple embedded sources, while other cores previously thought to be "starless" are found to contain newly identified sources. In light of these results, we find it unlikely that cores identified through dust emission or extinction have a one-to-one mapping with the subsequent generation of stars arising from them. Furthermore, simple modeling suggests that the similarity between the observed core mass function and the stellar IMF does not necessitate a one-to-one mapping between members of the two distributions. Understanding the similarities between ensembles of dense cores and the stellar initial mass function will require in depth studies that consider the distribution of dust, molecular line emission, and deep near and mid-infrared imaging from nearby regions of active star formation. This work received funding from the NSF as part of the REU program at the Institute for Astronomy, University of Hawaii.


DPS October 2007 Orlando
Olivine-Pyroxene Distribution of S-type Asteroids in the Main Belt
Shaye Storm, S. J Bus, and R. P. Binzel

The mineralogical composition of asteroids can be constrained using visible and near-IR (VNIR) spectroscopy. The most prominent spectral features observed over this wavelength range are due to olivine and pyroxene, the two most abundant minerals in both chondritic and achondritic meteorites. The observed ratio of these two minerals is highly dependent on the amount of heating that an asteroid has undergone. The 1-micron band minimum and the band area ratio between the 2- and 1-micron bands (BAR) reveal relative abundances of olivine and/or pyroxene on an asteroid surface (Gaffey et al. 1993, Icarus 106:573). A large sample of S-, A-, V-, and R-type asteroid spectra was collected over the visible and near-IR wavelengths during the second phase of the Small Main-belt Asteroid Spectroscopic Survey (Bus and Binzel 2002, Icarus 158:106) and using the low-resolution SpeX spectrograph (Rayner et al. 2003, PASP 115:362) at NASA's Infrared Telescope Facility (IRTF). Here we present a methodology for calculating the location of the 1-micron band minimum and BAR with appropriate 1- sigma uncertainties. This method was used to characterize approximately 200 S-type asteroids throughout the main belt. We will also present the distribution of olivine / pyroxene throughout the main belt by measuring how the S-type mineralogy varies with heliocentric distance. This will provide a better understanding of both the thermal processing across the main belt and subsequent mixing of asteroids through collisional and dynamical processes. This work was conducted through a Research Experience for Undergraduates (REU) position at the University of Hawaii's Institute for Astronomy and funded by the NSF.


AAS Winter 2008, Austin
Mass Determinations of Population II Binary Stars
Kathryn Williamson (University of Georgia and IfA) and J. N. Heasley (IfA)

Accurate mass determinations of Population II stars are essential to understanding the metallicity effects in stellar evolutionary models of the old stars in the Galactic halo. This research contributes accurate mass estimates for the three dwarf Population II binary systems HD 157948, HD 195987, and HD 200580. Results were obtained via a simultaneous least-squares adjustment of double-line spectroscopic and astrometric data to find the best fit orbital parameters and masses with error estimates. Monte Carlo simulations of theoretical data sets were used to test the consistency and accuracy of the optimization techniques in order to gauge the reliability of results. These theoretical data were designed to match orbital parameters that likely describe the three binary systems of this study. The results of the Monte Carlo analysis imply that reported mass estimates and error bars are indeed reliable for each particular orbit and given set of observation times. These reported masses can, therefore, effectively contribute to a Population II Mass-Luminosity Relationship. This work was conducted during a Research Experience for Undergraduates (REU) at the University of Hawaii's Institute for Astronomy and funded by the NSF.


 
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