Now showing items 21-40 of 889

    • BPM 24754: A new southern ZZ Ceti star 

      Giovannini, Odilon; Kepler, Souza Oliveira; Kanaan, Antonio; Costa, Andrea F Murillo; Koester, Detlev (1998-01)
      We report the discovery of a new long-period ZZ Ceti star through the analysis of photometric time series gathere on 7 nights between 1995 and 1996. The light curve displays a periodic variation with a period of ∼ 18 min ...
    • Understanding the cool DA white DWARF pulsator, G29-38 

      Kleinman, Scot J.; Nather, R. Edward; Winget, Don Earl; Clemens, J. Christopher; Bradley, Paul A.; Kanaan, Antonio; Provençal, Judith L.; Claver, Charles F.; Watson, Todd K.; Wood, Matt A. (1998-03-01)
      The white dwarfs are promising laboratories for the study of cosmochronology and stellar evolution. Through observations of the pulsating white dwarfs, we can measure their internal structures and compositions, critical ...
    • Asteroseismology of a star cooled by neutrino emission: The pulsating pre-white dwarf PG 0122 + 200 

      O'Brien, Marlea Sean; Vauclair, Gérard P.; Kawaler, Steven D.; Watson, Todd K.; Winget, Don Earl; Nather, R. Edward; Montgomery, Michael H.; Nitta, Atsuko; Kleinman, S.J.; Wood, Matt A. (1998-03-01)
      Observation of g-rnode pulsations in the variable pre-white dwarf (GW Virginis) stars provides a unique means to probe their interiors and to study the late stages of stellar evolution. Multisite campaigns have in several ...
    • White dwarf cosmochronometry. I. Monte Carlo simulations of proper-motion and magnitude-limited samples using Schmidt's 1/Vmax estimator 

      Wood, Matt A.; Oswalt, T. D. (1998-04-20)
      Observationally, white dwarf stars are a remarkably homogeneous class with a minimum observed Teff ∼ 4000 K. Theoretically, the physics that determines their cooling timescales is relatively more straightforward than that ...
    • Broadband optical observations of BL lacertae during the 1997 outburst 

      Webb, James R.; Freedman, Ian; Howard, Emily S.; Ma, Feng; Belfort, Michelle; Rave, Heather A.; Rumstay, Ken S.; Oswalt, T. D.; Marshall, Daniel; Robishaw, Timothy (1998-06)
      We present BVRI observations of BL Lacertae during its recent outburst. These observations, made during a 3 month period, cover a significant portion of the optical flare. The reduced data are displayed as light curves and ...
    • Time series energy production in smoothed particle hydrodynamics accretion disks: Superhumps in the AM Canum venaticorum stars 

      Simpson, James C.; Wood, Matt A. (1998-10-10)
      The energy production time series of our purely hydrodynamic accretion disk simulations display remarkable similarities with the observed light curves of dwarf novae superhumps in general and the AM CVn stars in particular. ...
    • Small-scale magnetic flux ropes in the solar wind 

      Moldwin, M. B.; Ford, S.; Lepping, Ronald P.; Slavin, James A.; Szabo, Adam (2000-01-01)
      Small-scale magnetic flux ropes have been discovered in the solar wind at 1 AU in observations from the IMP 8 and WIND spacecraft. These small magnetic structures (diameter of 270 R(E), on average) have some similar ...
    • How big is our sun? 

      Moldwin, M. B. (2000-04)
      Putting large numbers into human perspective by using ratios of a known quantity to an unknown quantity is an important scientific skill. An astronomy activity that encourages the use of estimation and helps students get ...
    • Multiband microvariability observations of BL lacertae during the outburst of 1997 

      Clements, Sandra D.; Carini, Michael T. (2001-01)
      BL Lac was observed in the V and R bands on 11 nights in 1997 July during a major optical outburst. It varied continuously, exhibiting nightly variations ranging from 0.1 to 0.6 mag. Over the course of the 11 nights, BL ...
    • White dwarfs in common proper motion binary systems: Mass distribution and kinematics 

      Silvestri, Nicole M.; Oswalt, T. D.; Wood, Matt A.; Smith, Jonathan Allyn; Reid, Iain Neill; Sión, Edward M. (2001-01)
      We present the mass distribution, gravitational redshifts, radial velocities, and space motions of white dwarf stars in common proper motion binary systems. The mass distribution we derive for the 41 DA white dwarfs in ...
    • Automated alignment by hybrid video and 3-D video moiré with both conventional and parallel processing 

      Garita, Barbara; Gutiérrez, Hector Martin; László, Ildikó; Blatt, Joel H. (2001-02-12)
      A problem common to automated assembly in manufacturing or in automated docking of spacecraft is angular and lateral alignment of components. A hybrid video system utilizing both conventional imaging and 3-D video moiré ...
    • On the origin of reverse polarity TCRs 

      Moldwin, M. B.; Collier, Michael R.; Slavin, James A.; Szabo, Adam (2001-05-15)
      Reverse polarity, or South-then-North (SN) bipolar, traveling compression regions (SN TCRs) are often observed in the Earth's magnetotail lobes. These events have been interpreted as either slowly earthward propagating ...
    • Acceleration of ³He nuclei at interplanetary shocks 

      Desai, Mihir I.; Mason, Glenn M.; Dwyer, Joseph R.; Mazur, Joseph E.; Smith, Charles W.; Skoug, Ruth M. (2001-05-20)
      e have surveyed the 0.5-2.0 MeV nucleonˉ¹ ion composition of 56 interplanetary (IP) shocks observed with the Ultra - Low-Energy Isotope Spectrometer on board the Advanced Composition Explorer from 1997 October 1 through ...
    • Seawater temperature trends at USA tide gauge sites 

      Maul, George A.; Davis, Andria M.; Simmons, Jeffrey W. (2001-10-15)
      Seawater temperatures have been measured at United States tide gauges throughout most of the 20th century. All available records have been digitized, and the longest 14 have been analyzed by linear least-square regression. ...
    • A generalized framework for reasoning with angular directions 

      Mitra, Debasis (2001-11-03)
      This extended abstract presents a new scheme for qualitative reasoning with directions between points in 2D-space, called Star-ontology(6). The current results of our study on the complexity issues for reasoning with ...
    • Evidence of different magnetotail responses to small solar wind pressure pulses depending on IMF Bz polarity 

      Moldwin, M. B.; Mayerberger, S. S.; Rassoul, Hamid K.; Collier, Michael R.; Lepping, Ronald P.; Slavin, James A.; Szabo, Adam (2001-11-15)
      The response of the magnetotail to small flux rope associated pressure pulses depends on the IMF Bz polarity. Clear and large amplitude magnetotail reverse polarity South-then-North traveling compression regions (SN TCRs) ...
    • Isotopic composition of solar energetic particle events measured by Advanced Composition Explorer/ULEIS 

      Dwyer, Joseph R.; Mason, Glenn M.; Mazur, Joseph E.; Gold, Robert E.; Krimigis, Stamatios M.; Möbius, Eberhard S.; Popecki, Mark A. (2001-12-10)
      Since its 1997 August launch, the Ultra Low Energy Isotope Spectrometer (ULEIS) on board the Advanced Composition Explorer (ACE) has observed a large number of solar energetic particle (SEP) events in the 0.4-3 MeV nucleonˉ¹ ...
    • A determination of the local density of white dwarf stars 

      Holberg, Jay B.; Oswalt, Terry D.; Sión, Edward M. (2002)
      The most recent version of the Catalog of Spectroscopically Identified White Dwarfs lists 2249 white dwarf stars. Among these stars are 109 white dwarfs that have either reliable trigonometric parallaxes or color-based ...
    • Asteroseismology of RXJ 2117+3412, the hottest pulsating PG 1159 star 

      Vauclair, G.; Moskalik, Paweł A.; Pfeiffer, Burkhard R K; Chevreton, M.; Dolez, Noël; Serre, B.; Kleinman, Scot J.; Barstow, Martin A.; Sansom, Anne E.; Wood, Matt A. (2002-01)
      The pulsating PG 1159 planetary nebula central star RXJ 2117+3412 has been observed over three successive seasons of a multisite photometric campaign. The asteroseismological analysis of the data, based on the 37 identified ...
    • A new heavy ion abundance enrichment pattern in ³He-rich solar particle events 

      Mason, Glenn M.; Mazur, Joseph E.; Dwyer, Joseph R. (2002-01-20)
      We report the first examples of ³He-rich solar energetic particle (SEP) events with heavy ion enrichments that are not ordered generally by mass. A second new feature is the large enrichment of ¹⁴N, the first time large ...