Tuesday, May 24, 2011, 8:00 AM - 7:00 PM 224

Tuesday, May 24, 2011, 8:00 AM - 7:00 PM
224

The Sun and The Solar System

Poster Session

Essex Ballroom

224.01

8:00 AM - 7:00 PM

Tens of thousands of small bodies comprise the Kuiper Belt, the remnant planetesimals beyond Neptune. Their orbits are thought to have been sculpted during a period of upheaval in the early Solar System, when the giant planets underwent scattering and/or migration. Therefore they are a rich collection of artifacts for Solar System archaeology. In the “classical” region from 40-50 AU, a population of “hot” objects with inclinations up to 30° overlies a flat “cold” population, with distinct physical properties (i.e. size, color, binary fraction); a third population is in orbital resonance with Neptune. Migration of Neptune, the standard explanation for capturing objects into resonance, preserves cold objects formed in situ but does not produce a hot population. Alternatively, Neptune may have undergone a period of high eccentricity during which it scattered hot objects from the inner disk into the classical region, but this scenario does not produce or preserve a cold population. To investigate which histories produce both hot and cold objects, we fully explore the parameter space of Neptune's initial semi-major axis (a) and eccentricity (e) as well as migration, eccentricity damping, and precession timescales. We determine which dynamical processes affect the orbital evolution of Kuiper Belt Objects (KBOs) and model them analytically. We find that to produce an eccentricity distribution of KBOs consistent with major qualitative observed features, Neptune must be scattered to one of two particular regions of parameter space, both located within e > 0.15 and 25 < a < 29 AU, and then migrate to its current location at 30 AU. Its eccentricity must either damp on a timescale < 0.3 Myr or precess* on a timescale < 0.5 Myr. Thus scattering and migration both play roles in the dynamical history of the Solar System.

224.02

8:00 AM - 7:00 PM

The Near-Earth Object (NEO) 2002 VE68 was discovered by the LONEOS Survey on November 11, 2002 (MPEC 2002-V52). With a semi-major axis of 0.723 AU, 2002 VE68 is in a 1:1 mean motion resonance with Venus and can be considered a quasi-satellite of the planet. Orbital integrations by Mikkola et al. (2004) suggest that 2002 VE68 was likely an NEO injected into its current orbit by a close Earth encounter approximately 7000 years ago and will remain a Venusian quasi-satellite for another 500 years. This object has been designated a Potentially Hazardous Asteroid by the Minor Planet Center. We took advantage of the object's 2010 apparition to collect rotationally resolved Bessel BVRI photometry over the course of three nights (November 10/12/13 2010) using the JPL Table Mountain 0.6-m telescope near Wrightwood, California. The object's mean colors (B-R=1.106+/-0.019 mag; V-R=0.419+/-0.021 mag; R-I=0.348+/-0.014 mag) are most compatible with an X-type spectral classification (Bus Taxonomy). A slight reflectance dip at 0.55 micron is consistent with the deep 0.50 micron feature observed in the spectrum of the E-type asteroid 2867 Steins (Weissman et al. 2008). The spectral resolution that our BVRI photometry affords is often insufficient to resolve the E-M-P sub-classes within the X-spectral complex (Tholen Taxonomy; Zelner et al. 1985). After converting the photometry from magnitude to flux units, we found a best-fit synodic period P_syn = 13.50+/-0.01 hr. Our photometry yields an absolute magnitude H_v=20.59+/-0.02 mag, implying an effective diameter D~200m (rho=0.25). The lightcurve amplitude of 2002 VE68 (~0.9 mag) suggests that it may be a contact binary.

224.03

Rotationally Resolved Photometry of the V-type Near-Earth Asteroid 4055 Magellan (1985 DO2)

Karen Garcia¹, T. Truong¹, M. D. Hicks², T. Barajas¹, J. Foster^1
1California State University Los Angeles, ²Jet Propulsion Laboratory.

8:00 AM - 7:00 PM

The Near-Earth Asteroid (NEA) 4055 Magellan was discovered by Glo Helin at Palomar Mountain (IAUC 4638) and was one of the first known minor planets with surface reflectance properties comparable to that of 4 Vesta (Tholen, 1988). Broad-band photometry and near-IR spectroscopy revealed strong 0.9 and 1.9 micron proxene bands, suggesting a compositional similarity of 4055 Magellan with that of 4 Vesta and the basaltic achondrite meteorites (Cruikshank et al. 1991). In anticipation of the Dawn mission to 4 Vesta we obtained 5 partial nights, 2010 August 9/10/12/13/14, of Bessel R photometry of 4055 Magellan at the Jet Propulsion Laboratory Table Mountain 0.6-m telescope (TMO). We measured a synodic period of 7.488+/-0.001 hr, similar to the 7.475+-0.001 hr period obtained by Pravec et al. (http://www.asu.cas.cz/~ppravec/newres.txt). Our object exhibited a large lightcurve amplitude (delta_M~0.8 mag) implying a highly elongated shape. We used our TMO photometry and the absolute magnitude as tabulated by the Minor Planet Center to construct a rudimentary solar phase curve. We derived a phase parameter g=0.30, similar to the phase behavior as measured by Pravec and colleagues (http://www.asu.cas.cz/~ppravec/neo.html). Our high g implies a shallow solar phase slope, consistent with the object's high albeldo (rho=0.31) obtained from thermal measurements (Delbo et al. 2003). The photometric properties of the V-type 4055 Magellan , such as shallow phase slope and high albedo, are consistent with 4 Vesta, giving us confidence in using NEA vestoids as photometric analogs for 4 Vesta.

224.04

Searching For Hazardous Asteroids

Brian Elwood¹, A. W. Puckett², K. Coble¹, S. Cortes^3
1Chicago State University, ²University of Alaska at Anchorage, ³University of Arizona.

8:00 AM - 7:00 PM

We are searching for asteroids that are possible threats to our planet using astronomical images. The images were taken with the WIYN 0.9-meter telescope at the Kitt Peak National Observatory outside Tucson, Arizona. A variety of measurements of a selected asteroid’s orbit is collected and added to an astrometry file. This increases the accuracy percentage of predicting the asteroid’s position in the future. The types of software used in this research are Astrometrica, Image J, Find_Orb, and Guide. Astrometrica is an interactive software tool for astrometric data reduction of CCD images. Image J is used to measure the positions of celestial objects. The Find_Orb software is used to generate orbits for the asteroid and the Guide software displays the multiple orbits generated from Find_Orb. This work was supported in part by funding from the IL Space Grant Consortium.

224.05

8:00 AM - 7:00 PM

In this presentation we show new RAGE hydrocode simulations of the effective disruption and mitigation of Earth bound asteroids and other Potentially Hazardous Objects (PHOs) by a strong explosion. This is just one possible method of impact-hazard mitigation. We present RAGE hydrocode models of the shock-generated disruption of PHOs by surface/subsurface nuclear bursts using scenario-specific models from realistic RADAR shape models. The RAGE code has been extensively verified and validated (V&V) We will show 2D models for the disruption by a large energy source at various depths-of-burial on such PHO models (~100 kton - 10 Mton), specifically for the shape of the asteroid 25143 Itokawa. We study the effects of non-uniform composition (rubble pile), porosity, effective source energy, and the optimal depth of burial from the surface explosion to the central explosion. The results of our actual hydrocode modeling shows that the resultant asteroid fragments are given sufficient velocity to escape gravitational recombination and results in effective mitigation of the hazard for ~300 m size objects.

224.06

The Monitoring of Transient Lunar Phenomena

Jarrel Doorn¹, M. Eaton¹, G. Ahrendts¹, T. Barker^1
1Wheaton College.

8:00 AM - 7:00 PM

Transient Lunar Phenomena (TLP’s) are described as short-lived changes in the brightness of areas on the face of the Moon. TLP activity has a higher number of reports, though unsubstantiated, in specific areas of the Moon such as the Aristarchus plateau. Our current research includes the division of lunar images taken through multiple filters using a Santa-Barbara Instrument Group (SBIG) ST8-E CCD camera mounted on a 0.45m Centurion telescope. We are also taking spectra of regions such as Aristarchus and the crater Ina, which shows evidence of recent activity (Schultz, P., Staid, M., Pieters, C. Nature, Volume 444, Issue 7116, pp. 184-186, 2006) using an SBIG DSS-7 spectrometer mounted on a 0.30m Schmidt-Cassegrain optical tube assembly on a Software Bisque Paramount drive system. Future research will include infrared imaging of the lunar surface. We are grateful for the support provided by the NASA Rhode Island Space Grant Consortium and the National Geographic Society.

224.07

8:00 AM - 7:00 PM

We have begun a program of assessing outer Solar system formation theories. In that endeavor, we have investigated the formation scenarios of Thommes ejection (Thommes et al. 2001) and the Nice Model (Tsiganis et al. 2006). Our results indicate that Thommes ejection is able to reproduce the satellite systems of Saturn in ~88% of simulations, while the regular moons of Jupiter are formed in ~50% of the simulations. Given the known resonances exerted by the giant planets and the evidence that the outer planets likely experienced significant re-configuration, it is necessary to evaluate the possibility of satellite formation during planetary migration.

224.08

8:00 AM - 7:00 PM

The unique orbital configurations and mass distributions observed in the satellite systems of Jupiter and Saturn provide a means to assess outer Solar system evolution theories. Thommes ejection theory (Thommes et al. 2001), where Uranus and Neptune form near Jupiter and are perturbed into their current locations, has been successfully and extensively tested. An in-depth analysis of the effects planetary ejection has on a system of forming moons is needed to assess the validity of the Thommes model.

224.09

8:00 AM - 7:00 PM

The vertical structure of the Martian ionosphere consists of two main layers. Maximum electron densities are produced in the M2 layer, which occurs at approximately 140 km, and is created by extreme-ultraviolet solar photons. The weaker M1 layer occurs at approximately 120 km and is produced by solar soft X-rays and associated electron impact ionization. Interpreting the vertical shape of the Martian ionosphere is a key tool for understanding ionosphere behavior and the physical processes involved. The vertical structure of the dayside M2 layer usually consists of a shape similar to idealized Chapman layer theory. However, deviations from this theory are expected as a result of the over-simplified assumptions made by idealized Chapman layer theory. We have investigated 485 vertical electron density profiles from the MaRS radio occultation instrument aboard Mars Express from 2002 to 2010. We will report observations of the vertical structure of the ionosphere of Mars that deviate substantially from the predictions of idealized Chapman layer theory. The examples of unusual M2 layer shapes that we will show include a flat-topped layer, a sharply pointed layer, and a wavy layer. These shapes have not been reproduced by current models of the ionosphere of Mars, which implies significant gaps in our present understanding of the ionosphere of Mars.

224.10

An External Source for Charon’s Atmosphere: Accretion of Pluto’s Atmosphere

Prabal Saxena¹, M. Summers^1
1George Mason University.

8:00 AM - 7:00 PM

Pluto’s moon Charon may have a significant atmosphere as a consequence of the gravitational capture of Pluto’s extended, escaping atmosphere.  Estimates of this capture based process by Charon suggest that it may have a collisionally dominated atmosphere.  However, the surface pressure on Charon depends sensitively upon the capture rate and upon Charon’s atmospheric temperature.  For the lowest estimate of capture rate, ~ 1.9 x 10²⁴ molecules s^-1, based upon Strobel’s Pluto escape rate calculation (Strobel, 2008), Charon will have a collisionally thick atmosphere if its atmospheric temperature is < 50K.  For the higher Pluto escape rates of Tian and Toon (2005) of 2.4 x 10²⁵ s^-1, Charon will have a collisionally thick atmosphere for atmospheric temperatures < 60K.    As we show, observations of Charon’s atmosphere can be used to provide an indirect measure of Pluto’s atmospheric escape rate.

224.11

8:00 AM - 7:00 PM

We attempted to observe the 10 February 2011 occultation of a star of UCAC2 magnitude 15.5 by the Kuiper-belt object (20000) Varuna (visual magnitude 20.2), to determine its size, albedo, and other basic properties. Our original predictions showed the path going between Hawaii and Alaska, but SMARTS astrometry a month before the event moved the prediction 1,646 km north, so we added sites in the northwestern continental US and Alaska. We had clear weather at several sites in the predicted path (Alaska, Pacific Northwest), another site in the 1-sigma path (California), and several sites near the 3-sigma path (Hawaii, China, Taiwan, Japan), though no occultation was detected. Clouds or other problems prevented observations at several other sites. The appulse observations will be used to improve the ephemeris for future Varuna observations. See http://occult.mit.edu/research/occultations/kbo/Varuna/Varuna.20110210/index.html and stellaroccultations.info.

224.12

8:00 AM - 7:00 PM

Observations of the stellar occultation of the magnitude 16.2 star 26029635 UCAC2 (2MASS ID 1275509401) by (50000) Quaoar were made at MIT’s George R. Wallace, Jr., Astrophysical Observatory on the night of 11 February 2011 UT (Sallum, this meeting). A single occultation chord dataset was obtained and will be analyzed to place a lower limit on the size of Quaoar based on this chord. The resulting value will be compared to Quaoar size estimates from other techniques including direct imaging with the Hubble Space Telescope (Brown 2004), and Spitzer Infrared imaging (Stansberry 2007), which give significantly differing results given their error bars (1260 ± 190 km and 844.4 +206.7/-189.6 km, respectively).

224.13

8:00 AM - 7:00 PM

Here we report the first recorded observations of a stellar occultation by Kuiper Belt Object (KBO) (50000) Quaoar. We detected a single-chord stellar occultation by Quaoar of a magnitude 16.2 star designated 26029635 UCAC2 (2MASS ID 1275509401), which occurred on 11 February 2011 UT.

224.14

8:00 AM - 7:00 PM

We describe the development of an automated system which can respond to new detections of Near Earth Objects (NEOs) from Pan-STARRS (PS1). The system can automatically download observations of candidate NEOs from Pan-STARRS, compute orbits and observability, find free observation times and schedule observations on the robotic telescopes of the LCOGT network. We present results from the first few months of development and operation and plans for the future with the 6 site, 40 telescope global LCOGT network.

224.15

Monitoring Active Centaurs by Pan-STARRS 1

Hsing-Wen Lin¹, Y. Chen¹, W. Ip¹, M. Holman², W. Chen¹, P. Protopapas^2
1Institute of Astronomy, Taiwan, ²Harvard-Smithsonian Center for Astrophysics.

8:00 AM - 7:00 PM

Centaurs are Solar system small bodies orbiting around the sun between the orbit of Jupiter and Neptune. They are believed to be resupplying the current population of short period comets. About 13% Centaurs show cometary-like activities. However, those active Centaurs never cross the ice-line of solar system; the volatility of water ice hence should not be the triggering source of cometary activity. CO ice is an alternative and has been reported in two Centaurs, but it is too volatile to explain the distribution of measured perihelion. Some other materials had been suggested to be the triggering source of active Centaurs, for example, amorphous ice.

224.16

8:00 AM - 7:00 PM

Several recent observational results suggest that coronal mass ejection (CME) plasma is heated even after leaving the flare site. The source of the heating is probably the magnetic field of the erupting flux rope, but the mechanisms that convert magnetic to thermal energy during these events are not well understood. By performing a time-dependent ionization analysis on CMEs observed by SOHO/UVCS, we assess the efficacy of several candidate heating mechanisms, including heating by the CME current sheet, kink/tearing instabilities of the flux rope, turbulence, thermal conduction, energetic particles, and wave heating.

224.17

8:00 AM - 7:00 PM

We searched the Atmospheric Imaging Assembly (AIA) database for observations of active region coronal loops seen in the 171-A images, which have a peak response temperature of Log T = 5.8. The twelve resulting loops were then analyzed to determine whether the cross-field temperature was isothermal or multithermal. A few of the twelve loops could be recognized as isothermal based on the narrowness of the resulting Differential Emission Measure (DEM) curves. These loops could then be modeled as a single magnetic flux tube. Most of the loops, however, were classified as multithermal as they have relatively broad DEM curves. These loops were more likely composed of several or even many magnetic strands, which might be tangled but are still able to confine plasma of different temperatures.

224.18

Observing Isothermal and Multithermal Coronal Loops using SDO-AIA

Sankaet Pathak¹, J. Schmelz^1
1University of Memphis.

8:00 AM - 7:00 PM

The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) is designed to provide an unprecedented view of the solar corona. The six coronal filters peak at different temperatures and cover the entire active region temperature range, making AIA ideal for multi-thermal analysis. Here, we chose several loops in different active regions using images in the 211-A filter, which has a peak response temperature of Log T = 6.3 K. The purpose of this analysis was to determine if the loops were isothermal or multithermal. A few of our 12 loops have narrow temperature distributions, which appear consistent with isothermal plasma. Other loops have intermediate-width temperature distributions and must, therefore, be multi-stranded. The remaining loops have unrealistically broad temperature distributions. However, after a series of tests we found that this problem was the result of missing low-temperature lines in the AIA 131-A channel. We, therefore, repeated the analysis without the 131-A data; these loops then appeared well constrained and multi-stranded.

224.19

Analysis of Full Coronal Loops Observed with the Atmospheric Imaging Assembly

Ben Jenkins¹, J. Schmelz^1
1University of Memphis.

8:00 AM - 7:00 PM

Using EUV image data from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory, we have done multi-thermal analysis along the entire length of a collection of coronal loops. The six coronal filters of AIA peak at different temperatures to produce data that span the entire range of temperatures found in these loops. We have selected cooler loops for this analysis that were chosen from images taken with the 171-A filter, which has a peak response temperature around 0.63 MK. The object of this investigation is to determine if the plasma is isothermal or multi-thermal either (a) along the line of sight or (b) along the length of the loop. We have used both an automatic and a manual method to determine the Differential Emission Measure (DEM) distribution at the loop apex and the foopoints. We find that the temperature distribution is narrow, but not consistent with isothermal plasma. In addition, the DEM-weighted temperature changes much less along the loop length than predicted by standard RTV models.

224.20

Differential Emission Measure Analysis of Coronal Loop Data From AIA, EIS, and XRT

Jennifer W. Garst^1
1Univ. Of Memphis.

8:00 AM - 7:00 PM

Last year’s launch of the Solar Dynamics Observatory (SDO) has provided additional data to constrain the temperature of coronal loops, allowing for a more detailed analysis of the nature of the heating. Specifically, the high temperature constraints that have been missing from prior analyses are now available to be considered. Images from a coronal loop on the solar disk on December 10, 2010 from both the Atmospheric Imaging Assembly (AIA) and the X-Ray Telescope (XRT) instruments onboard SDO are analyzed along with data from the same date taken by the Extreme Ultraviolet Imaging Spectrometer (EIS) instrument onboard Hinode. Differential emission measure techniques are used to consider whether the loops are isothermal or multithermal in nature. Conclusions regarding the comparison of this data will be presented.

224.21

8:00 AM - 7:00 PM

The Extreme Ultraviolet Imaging Spectrometer and the X-Ray Telescope aboard Hinode are designed to complement one another. This study uses X-Ray Bright Points, simple emission features in the Solar Corona, as sources of emission data for the purpose of obtaining a cross-calibration factor for the two instruments. After calibrating and co-aligning the data from each instrument individually, pixels are selected within several coronal Bright Points. By analyzing this equivalent data from both instruments, separate Differential Emission Measures and Emission Measure Loci Plots are produced. These results are then used to produce the desired instrument cross calibrations. The use of Bright Points eliminates the need for prolonged and uncertain background subtraction. Due to the simple thermal characteristics of the Bright Points, this method could be used to calibrate other instruments as well.

224.22

The Solar Rotation and its Evolution During Cycle 23

Sylvain G. Korzennik¹, A. Eff-Darwich^2
1Harvard-Smithsonian Center for Astrophysics, ²IAC, Spain.

8:00 AM - 7:00 PM

We present the most exhaustive and accurate inferences of the internal solar rotation rate and its evolution during solar cycle 23. A full solar cycle of MDI observations have been analyzed using our state of the art fitting methodology. Time series of various lengths have been fitted, from a single 4608-day long epoch (64 times 72 day or 12.6 yr) down to 64 separate segments for the "traditional" 72-day long epochs. We used time series of spherical harmonic coefficients computed by the MDI group but using an

224.23

8:00 AM - 7:00 PM

Reconstructions of total solar irradiance (TSI) rely mainly on linear relations between TSI variation and indices of facular area. When these are extrapolated to the prolonged 15^th - 17^th century Spörer and Maunder solar activity minima, the estimated solar dimming is insufficient to explain the mid- millennial climate cooling of the Little Ice Age. We draw attention here to evidence that the relation departs from linearity at the lowest activity levels. Imaging photometry and radiometry indicate an increased TSI contribution per unit area from small network faculae by a factor of 2-4 compared to larger faculae in and around active regions. Even partial removal of this more TSI - effective network at prolonged minima could enable climatically significant solar dimming, yet be consistent with the weakened but persistent 11- yr cycle observed in Be 10 during the Maunder Minimum. The mechanism we suggest would not alter previous findings that increased solar radiative forcing is insufficient to account for 20^th century global warming.