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2006 REU Program
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Maintained by LG
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2006 REU Students' AAS Abstracts

AAS Summer 2007, Honolulu
Earth-like Planets around GJ 876
Joseph Castro and N. Haghighipour (IfA, University of Hawaii)

GJ 876 is a 0.32 solar-mass M4 dwarf currently hosting three known planets. The inner planet of this star is a 7.5 Earth-masses body at 0.02 AU with an unknown orbital eccentricity. The two outer planets of this system are Jovian-type and located at 0.130 AU and 0.208 AU from the central star. We have studied the possibility of the existence of other Earth-like objects between the two inner planets of this system. We carried out numerical simulations of the dynamical stability of test particles in the region between 0.03 AU and 0.12 AU, for different values of the orbital eccentricity of the currently known Earth-sized object. We also studied the orbital dynamics of additional Earth-like planets in this region. Results indicate that additional terrestrial bodies may only exist in a small region between 0.04 AU and 0.05 AU from the central star. The inner region of the planetary system of GJ 876 seems to be dynamically full.


AAS Winter 2007, Seattle
Earth-like Planets around GJ 876
Joseph Castro and N. Haghighipour (IfA, University of Hawaii)

Gamma Cephei is a spectroscopic binary consisting of a 1.59 solar-mass K1 IV subgiant primary star and a 0.34-0.92 solar-mass red giant secondary star. The primary of this system is host to a 1.7 Jupiter-mass planet at approximately 2.1 AU and with an eccentricity of 0.12. Numerical simulations were carried out on the dynamical stability of additional hypothetical planets located 3 to 5 AU from the primary star. To ensure a comprehensive search, various values for the mass, eccentricity, and inclination of the additional Jupiter-like planets were used. Similar simulations were also carried out for possible Saturn and Neptune-like planets within the same range. Results indicate that Gamma Cephei appears to be dynamically full and no stable orbits of any additional planets were found.


AAS Winter 2007, Seattle
Conditional Density Analysis of the Hubble Deep Field
Brittany L. Dames and P. H. Coleman (IfA, University of Hawaii)

The Hubble Deep Field galaxy data set is reanalyzed using conditional density methods which are more suitable for distributions of unknown correlation structure than n-point correlation statistics or the related power spectrum analyses. The large-scale distribution of galaxies is known to exhibit power-law correlation on small scales (perhaps up to tens of megaparsecs) and is thought to become uncorrelated (homogeneous) on large enough scales. This sample is used to probe much larger scales, and the initial angular analysis presented here shows no evidence for a change in correlation structure. This implies that the large-scale distribution of luminous matter may in fact be power-law correlated on all scales. This has strong implications for current cosmological models based on the Robertson-Walker metric which describes a homogeneous space of constant curvature.


AAS Winter 2007, Seattle
New and Improved Ephemerides of Nix and Hydra during the 1985 to 1990 Mutual Events between Pluto and Charon
Garrett Elliott (Ohio State University) and D. J. Tholen (IfA, Hawaii)

Acknowledging the non-Keplerian orbits for the Plutonian moons Nix and Hydra due to significant perturbations by Charon, new ephemeris positions were calculated to assist with their detection in previous observations of the Pluto system. To compensate for unknown albedo and density, we varied their masses from 1.0 x 1016 kg to 2.5 x 1018 kg to allow for extremes of Pluto-like albedo and a water-ice density to comet-like albedo and Pluto-like density, respectively. New ephemeris positions of Nix and Hydra should allow us to identify them in stacked images from archival Hubble Space Telescope data. Also, the coplanar orbits of Nix, Hydra, and Charon result in a shared season of mutual events. In Pluto and Charon mutual event observations made between 1985 and 1990, Nix or Hydra mutual events with Pluto may have been unknowingly observed. Although mutual events between Nix or Hydra and Charon did occur, the focus of the observations during this time was on the events between Charon and Pluto. This situation makes the possibility that there were observations of one of these Nix or Hydra and Charon events very remote.


AAS Winter 2007, Seattle
The Composition of the Old, Metal-Rich Open Cluster, NGC 6791
Elizabeth Jensen (Smith College), A. M. Boesgaard (IfA, Hawaii), and C. P. Deliyannis (Indiana University)

The populous open cluster, NGC 6791, has presented an anomaly as it appears to be very old (8-10 Gyr), yet metal-rich. We have made high resolution (45,000) spectroscopic observations of two turn-off stars (V = 17.4) with HIRES on the Keck I telescope on Mauna Kea. We have determined the stellar parameters for these two stars spectroscopically. The high metallicity of NGC 6791 is confirmed by our results, [Fe/H] = +0.40. In addition we have found elemental abundances for Na, Si, Ca, Ti, Ni, Cr, and Y. We compare our results with those of field star samples that are both old and metal-rich: a) six dwarf stars with [Fe/H] > +0.01 and age > 8.5 Gyr from Edvardsson et al. (1993), b) nine old dwarf stars with [Fe/H] from +0.05 to +0.39 from Chen et al. (2003), and c) four old dwarf stars with [Fe/H] from +0.15 to +0.47 from Feltzing & Gonzalez (2001). The abundances of these elements are in agreement in the field and in the cluster with the possible exception of Ti which appears higher in the cluster stars; it is not clear why Ti would be enhanced when Si and Ca are not. We discuss the possible interpretations of the cluster peculiarities.


AAS Winter 2007, Seattle
Planetary Nebulae and Stellar Kinematics in Interacting Spiral Galaxy M82
Lent C. Johnson (Colby College), R. H. Mendez, and A. M. Teodorescu (IfA, Hawaii)

Using an on-band/off-band filter technique, we identify 114 planetary nebulae (PNs) in the edge-on spiral galaxy M82 using the FOCAS instrument at the 8.2m Subaru Telescope. Radial velocities were determined for 100 of these PNs using a method of slitless spectroscopy, from which we obtain a clear picture of the galaxy's rotation. We find evidence for a Keplerian decline in M82s rotation curve, in agreement with results derived by CO(2-1) and HI measurements (Sofue 1998). These results affirm the use of PN as effective, accurate kinematic probes of galaxies.


AAS Summer 2007, Honolulu
Coronal Mass Ejections: A Study of Structural Evolution and Classification
Chris Lowder (Georgia Tech), S. R. Habbal, and H. Morgan (IfA, Hawaii)

Coronal mass ejections (or CMEs) are known for their majestic, yet explosive, outflow from the Sun. Although different criteria are often used for their classification, this paper seeks to classify them based on the following factors: (1) The velocity of the CME; (2) the structure of the CME itself, and (3) the angular separation of the "legs" of the CME as it expands. Given that the outer edge and the inner core of the CME move at different velocities, this difference can track the structural evolution of the outburst. Using data from solar minimum and maximum, CMEs will be analyzed and a new classification scheme will be developed based on the characteristics outlined above.


AAS Winter 2007, Seattle
A Correlative Study between Coronal Mass Ejections, Prominences and Flares
Anthony Rasca (Carroll College), S. R. Habbal, and H. Morgan (IfA, Hawaii)

The exact cause of coronal mass ejections (CMEs) remains unsettled despite three decades of observations since their discovery in the early 1970s. Their association with events at the Sun, such as prominence eruptions and solar flares, is often established from a near-time and -position angle coincidence on the solar disk and limb. Using a list from randomly chosen CMEs in the LASCO/C2 catalog, a comparison is made of the number of associated events from observations at solar maximum (1999-2000) and during the declining phase of the solar cycle (2004-05). Images of the Fe XII and He II lines from SOHO/EIT are used to locate events associated with the CMEs. The results show solar maximum CMEs having four times more associated prominence eruptions, without an associated flare, than at solar minimum (12% vs. 3%). CMEs at solar minimum have five times the number of flare-associated prominences (11% vs. 2%), and twice the number of flare-associated active regions (29% vs. 14%). A histogram of the CMEs speed distribution shows a trend with a skewed peak in the range of 200-399 km/s at both phases of the solar cycle. When separated into event-associated cases, a similar distribution with speed is found with the flare-associated events, whereas a peak in the percent of CME-associated prominence eruptions appears in the range of 600-799 km/s. Using this information and the fact that prominence eruptions were most commonly observed at the solar limb, we estimate that the mean prominence-associated CME speed lies within the range of 600-799 km/s and the mean flare-only associated speed lies in the 200-399 km/s range. Such results point to the importance of prominence eruptions in fast-propagating CMEs.


AAS Summer 2007, Honolulu
Habitable Planets in the Planetary System of HD 69830
Sarah Rugheimer (Calgary) and N. Haghighipour (IfA, Hawaii)

We present the results of a study of the dynamical evolution and habitability of HD 69830 planetary system. Being the first multiplanet extrasolar planetary system with three Neptune-sized objects, HD 69830 provides new grounds for testing the possibility of the existence of smaller objects, such as terrestrial planets, particularly in its habitable zone. We numerically integrated the orbits of the planets of this system for different values of their masses, and also studied the long-term stability of many Earth-like objects in its habitable zone. Results indicate that the planetary system of HD 69830 is dynamically stable and its habitable zone can harbor terrestrial planet for long times. The only exception is at 0.735 AU inside this region where an island of stability appears.


AAS Winter 2007, Seattle
Using Fe and Mg in Olivine as an Indicator of Asteroidal Hydrothermal Alteration
Anne Sweet (Macalaster College) and L. Chizmadia (IfA, Hawaii)

Amoeboid olivine aggregates (AOAs) found in CO3 meteorites are sensitive indicators of parent body alteration. Because chondritic meteorites are considered to be some of the most primordial material of the early solar system, studying these features reveals information about the hydrothermal alteration undergone after the time of their formation. As water encounters the AOAs, the Mg-rich olivine, forsterite (Mg2SiO4), is replaced with Fe-rich olivine, creating fayalite (Fe2SiO4). The calculation of the Fe/Mg ratio of the AOAs, along with a visual examination of the ferroan veins and diffusive halos in these features, allows for a classification of the petrologic subtype (3.0-3.8) of the meteorite. By using a scanning electron microscope for meteorite mapping, feature identification, and element mapping, as well as an electron microprobe for accurate elemental abundance calculation, we were able to accomplish this classification. In this work we present the subtype classification of six previously unclassified meteorites (ALH83108, A-882094, MET00694, MET00711, MET00747, QUE97416, and Y-82094) along with the analysis of two previously studied meteorites as standards (Lance and ALH77003). We found that on the basis of the distribution of the mol% Fe/(Mg+Fe) that Y-82094 is a CO3.3, QUE97416 is a CO3.5, ALH83108, MET00694, MET00711 and MET00747 are CO3.8, and that A-882094 is probably a breccia since the AOAs show different levels of alteration ranging from CO3.4 to CO3.6.


 
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