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2005 REU Students' AAS Abstracts

Maintained by LG

AAS 207th Meeting, 8-12 January 2006
[4.16] Using AOAs to Document Aqueous Alteration in the CO3 Parent Asteroid
C. Bendersky (Mount Holyoke College), L. Chizmadia (Institute for Astronomy, University of Hawaii)

Chondritic meteorites are considered to be among the most primitive materials remaining from the early solar system. Chondritic meteorites have experienced few changes since their formation; only subtle changes are observed, due to aqueous and thermal alteration. CO3 carbonaceous chondrites are of particular interest for studying incipient alteration because they show a clear metamorphic sequence, designated 3.0 (least altered) to 3.8 (most altered). Amoeboid olivine aggregates (AOAs) are fine grained, irregularly shaped objects composed dominantly of olivine with minor amounts of anorthite, diopside and spinel. The fine grained and porous nature of AOAs make them very sensitive to hydrothermal alteration.

We used established procedures of measuring the size, shape and distribution of relict Mg-rich olivine patches, and the Fe content and distribution of the olivine to assign petrologic subtypes to seven CO3 chondrites which had not previously been assigned a petrologic subtype (metamorphic stage).

ALH85003 and ALH82101 are 3.5. There is an even volume of Mg-rich olivine and Fe-rich olivine. Their Fe-rich olivine veins have widened into 10-15 micron channels. ~0.8 micron halos around relic Mg-rich olivine cores separate the cores from the Fe-rich veins.

A-881632 is a 3.6. The inclusions are dominated by Fe-rich olivine. Veins are no longer apparent; instead Mg-rich olivine cores remain. These Mg-rich cores have 2-3 micron halos.

DaG 055 is a 3.7. There is no remnant Mg-rich olivine. The Fe contents of the AOAs and matrix have not equilibrated.

Finally, Y-790992, EET92126 and Y-791717 are 3.8. Only Fe-rich olivine remains in the AOAs. The Fe content of the matrix and the AOAs have fully equilibrated.

AAS 207th Meeting, 8-12 January 2006
[74.02] Habitable Extrasolar Planetary Systems: The Case of rho Cancri
D. Cotto-Figueroa (University of P.R. at Humacao), N. Haghighipour (Institute for Astronomy, University of Hawaii)

Having the largest number of extrasolar planets, a Neptune-mass object on a 2.8 days orbit, and an outer planet that orbits at 5.3 AU which is comparable to Jupiter's distance from the Sun, rho Cancri has become an interesting system for study of habitability. In this paper, we present the results of a study of the orbital evolution and dynamical stability of Earth-like planets in this system. Numerical integrations of the system, using the orbital parameters reported by McArthur et al. (2004), indicate that the system may not be stable. In search of stable planetary orbits, an extensive search of the parameter-space of the system was carried out, and a stable region was identified. Within this region, dynamical stability of an Earth-like planet in the habitable zone of the system was studied and two regions of stability were recognized.

This research took place at the University of Hawaii's Institute for Astronomy during a Research Experience for Undergraduates (REU) internship funded by the National Science Foundation (NSF).

AAS 207th Meeting, 8-12 January 2006
[74.01] Habitability in the Upsilon Andromedae System
A. Dove (University of Missouri - Columbia), N. Haghighipour (Institute for Astronomy, University of Hawaii)

Upsilon Andromedae is an F8 V star with a stellar companion orbiting at about 750 AU. Doppler velocity measurements have revealed the presence of three planets orbiting the star, with periods of about 4.6 days, 241 days, and 1267 days (Butler et al., 1999). Like many extrasolar planets orbiting at radii greater than 0.2 AU, the outer two planets of Ups And exhibit high eccentricities (greater than 0.1). Planet-planet scattering is one mechanism that has been suggested to cause perturbations that excite the eccentricities of these planets (Ford et al., 2005). We investigate the habitability of the Ups And planetary system as it undergoes planet-planet scattering and evolves from a hypothetical four-planet system into its observed state. We present the results of the numerical integrations of the system with a fourth planet at a distance of 4.76 AU from the central star. Our results demonstrate that an Earth-like planet could not remain stable in the HZ of this system. We also show, through an extensive survey of the parameter-space of this system, that it is important to include the inner planet of this system in the simulations of its dynamical evolution, and in the study of its habitability.

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 207th Meeting, 8-12 January 2006
[177.04] Chandra Analysis of a Possible Cooling Core Cluster at z = 1.03
K. Dolan (Lawrence University), H. Ebeling (Institute for Astronomy, University of Hawaii at Manoa)

We present an analysis of Chandra observations of a massive cluster of galaxies at high redshift, Cl J1415+3612 at z = 1.03, investigating whether the cluster possesses a cooling core. If the cluster does possess a cooling core, it will be the earliest known example of a massive cooling core cluster. We find Cl J1415+3612 to be of a relaxed morphology through the use of a two-dimensional X-ray surface brightness model, and we use spectral fitting to find that the temperature of the cluster is kT = 5.7 ± 0.49 keV. Spectral fitting gives a temperature of 7.03 ± 0.01 keV for the core and 4.45 ± 0.58 keV for the outer cluster, which suggests that the core is warmer than the rest of the cluster, but too few counts are available for the spectral fits to be definitive. We find through one-dimensional spatial modeling that the radial surface brightness profile of the cluster cannot be satisfactorily modeled without some strong central peak in addition to the standard beta model, which is suggestive of the presence of a cooling core.

The use of spectrally normalized exposure maps is also discussed, and we mention the importance of correcting for the degradation of the Chandra ACIS low-energy quantum efficiency when performing spectral fits to energies below 1 keV.

AAS 207th Meeting, 8-12 January 2006
[68.03] A Wide-Field Optical and Near-Infrared Search for Brown Dwarf Candidates
J. S. Katz (Columbia University), E. Magnier (Institute for Astronomy, University of Hawaii)

The Two Micron All Sky Survey (2MASS) has been a great resource for astronomers in search of low-mass objects. J, H, and K photometry from 2MASS has been used to pinpoint brown dwarf candidates by their distinctive near-infrared colors. We present a study which utilizes this resource in conjunction with overlapping I-band photometry from the Canada-France-Hawaii Telescope's 12,288 by 8,192 pixel mosaic CCD to isolate previously unidentified brown dwarf candidates based on their optical and near-infrared colors. Our selection criteria included a high signal to noise ratio in detections from both sources and a color range of 4 < I - J < 10 and J - K <= 1.5. This range corresponds to published estimates of the colors of late-type dwarfs and also excludes reddened background giants. This analysis produces 217 candidates that meet these criteria; their attributes and credibility are discussed. The group, representing spectral types from M9 to L6 or later, could contribute greatly to the current understanding of brown dwarfs if spectroscopically confirmed. Additionally, this study provides insight into the expectations of brown dwarf discoveries from the upcoming 3π steradian Pan-STARRS survey.

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 207th Meeting, 8-12 January 2006
[69.15] Beryllium: A Cosmic Chronometer?
C. Peruta (University of Arizona), A.M. Boesgaard (Institute for Astronomy, University of Hawaii)

The process spallation, by which beryllium is formed, is the key to understanding many topics in astronomy today. It is still not certain whether spallation occurs within the local vicinity of supernovae where C N O is excited into interstellar gas or conversely on a global scale by high energy protons bombarding C N O in the interstellar gas. If global, the instantaneous abundance can be characterized by a scatter around the mean value significantly smaller than for Fe or O. Beryllium would therefore be a more reliable chronometer than [Fe/H] or [O/H]. I present Be abundances from 20 metal poor stars ([Fe/H] < -1.5). The stars were observed with high resolution/high S/N spectroscopy and abundances were determined by fitting synthesized spectra. These abundances are plotted against [Fe/H] and combined with results from previous Be studies to confirm whether or not there is an intrinsic spread in Be at low metallicities. If there is a spread, we can infer the most likely mechanism for Be formation is spallation in the vicinity of supernovae and therefore A(Be) is not a good chronometer. This study shows that there is a spread around [Fe/H] = -1.5 and -2.5 with a typical error of 0.10 dex for all Be abundances.

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 207th Meeting, 8-12 January 2006
[21.02] Metallicity and Star Formation in High EW(H-alpha) Galaxies
J. E. Pollack (New College of Florida), L. J. Kewley, D. Sanders (Institute for Astronomy, University of Hawaii), M. J. Geller (Smithsonian Astrophysical Observatory)

We present an investigation into the chemical abundances and star formation properties of the central regions in ~330 Updated Zwicky Catalog (UZC) galaxies at cz > 5000 km/s. These galaxies were selected to have strong bursts of recent star formation by constraining the sample to galaxies with high EW(H-alpha) and detectable 60-micron IRAS fluxes. Spectra were obtained for the 330 galaxies with the CfA FAST spectrograph. We calculate metallicities using Kewley and Dopita's (2000) metallicity and ionization parameter diagnostics using the [NII], [OII], [OIII], [SII], and the Balmer emission lines. We use stellar population synthesis models to derive the age of the recent bursts of star formation. Finally, we investigate the metallicity and burst age in terms of morphology and the presence of companions.

Funding for this research was provided by the National Science Foundation Research Experience for Undergraduates program hosted by the Institute for Astronomy at University of Hawaii-Manoa.

AAS 207th Meeting, 8-12 January 2006
[10.07] New Debris Disks Around Low-Mass Stars
J. J. Wray (Princeton University), M. C. Liu (Institute for Astronomy, University of Hawaii), I. N. Reid (STScI)

Debris disks provide an opportunity to learn about the planet formation process in other solar systems as well as our own. To date, most studies have focused on disks around early or mid-type stars, excluding the much more common low-mass dwarfs either by choice or simply because any disks they may have are too low luminosity to be detected. We have conducted the largest and most thorough search for K and M dwarf debris disks to date, and have found several new candidate disks. The candidates include both warm, asteroid belt-type rings and cold disks more nearly analogous to the Kuiper belt. The candidates were identified from a sample of 1,400 dwarf stars within a 25 pc radius, cross-matched with IRAS flux densities compiled from a number of sources. The completeness and reliability of the matches have been tested rigorously and found to be high.

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.