Now showing items 1-20 of 22

    • 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 ...
    • The chromospheric activity and ages of M dwarf stars in wide binary systems 

      Silvestri, Nicole M.; Hawley, Suzanne L.; Oswalt, T. D. (2005-05)
      We investigate the relationship between age and chromospheric activity for 139 M dwarf stars in wide binary systems with white dwarf companions. The age of each system is determined from the cooling age of its white dwarf ...
    • Emission lines properties of the radio-loud quasar LAMOST J1131+3114 

      Shi, Zhixin; Comte, Georges; Luo, Ali; Zhao, Yuehong; Zhao, Jingkun; Oswalt, T. D.; Wu, Fuchao (2014-04)
      The radio-loud quasar LAMOST J1131+3114 (Ton 580, B2 1128+315), showing asymmetrical profile in Hβ and [O III] lines, has been selected from the LAMOST Pilot Survey for further study. We present an analysis of its emission ...
    • Fragile binary candidates in the SDSS DR8 spectroscopic archive 

      Zhao, Jingkun; Oswalt, T. D.; Zhao, Gang (2011-12-15)
      We present a catalog of 80 very wide fragile binary candidates (projected separations >10,000 AU) from the Sloan Digital Sky Survey Data Release Eight spectral archive. The pairs were selected based on proper motion, radial ...
    • Hubble space telescope observations of cool white dwarf stars: Detection of new species of heavy elements 

      Shipman, Harry L.; Barnhill, Maurice; Provençal, Judith L.; Roby, Scott W.; Bues, Irmela; Córdova, France A.; Hammond, Gordon L.; Hintzen, Paul M N; Koester, Detlev; Oswalt, T. D. (1995-03)
      Observations of cool white dwarf stars with the Hubble Space Telescope has uncovered a number of spectral features from previously unobserved species. In this paper we present the data on four cool white dwarfs. We present ...
    • The initial-final mass relation among white dwarfs in wide binaries 

      Zhao, Jingkun; Oswalt, T. D.; Willson, Lee Anne; Wang, Qian; Zhao, Gang (2012-02-20)
      We present the initial–final mass relation derived from 10 white dwarfs in wide binaries that consist of a main-sequence star and a white dwarf. The temperature and gravity of each white dwarf were measured by fitting ...
    • LP 133-373: A new chromospherically active eclipsing dMe binary with a distant, cool white dwarf companion 

      Vaccaro, Todd R.; Rudkin, Mark J.; Kawka, Adéla; Vennes, Stéphane; Oswalt, T. D.; Silver, Isaac M.; Wood, Matt A.; Smith, Jonathan Allyn (2007-06-01)
      We report the discovery of the partially eclipsing binary LP 133-373. Nearly identical eclipses along with observed photometric colors and spectroscopy indicate that it is a pair of chromospherically active dM4 stars in a ...
    • Multisite observations of the PMS δ Scuti star V351 Ori 

      Ripepi, Vincenzo; Marconi, Marcella; Bernabei, Stefano; Palla, Francesco; Pinheiro, F. J G; Folha, Daniel F M; Oswalt, T. D.; Terranegra, L.; Rudkin, Mark J.; Johnston, Kyle B. (2003-09)
      We present the results of multisite observations spanning two years on the pre-main-sequence (PMS) star V351 Ori. A total of around 180 hours of observations over 29 nights have been collected, allowing us to measure five ...
    • A multisite photometric campaign on the pre-main-sequence δ Scuti pulsator IP Persei 

      Ripepi, Vincenzo; Bernabei, Stefano; Marconi, Marcella; Palla, Francesco; Ferro, Armando Arellano; Bonanno, Alfio M.; Ferrara, P.; Frasca, Antonio; Jiang, Xiaojun; Oswalt, T. D. (2006-04)
      We present the results of a photometric multisite campaign on the δ Scuti Pre-Main-Sequence star IP Per. Nine telescopes have been involved in the observations, with a total of about 190 h of observations over 38 nights. ...
    • A new look at the local white dwarf population 

      Holberg, Jay B.; Sión, Edward M.; Oswalt, T. D.; McCook, George P.; Foran, S.; Subasavage, John P. (2008-04)
      We have conducted a detailed new survey of the local population of white dwarfs lying within 20 pc of the Sun. A new revised catalog of local white dwarfs containing 122 entries (126 individual degenerate stars) is presented. ...
    • Orbital Characteristics of the Subdwarf-B and F V Star Binary EC 20117-4014 (=V4640 Sgr) 

      Otani, Tomomi; Oswalt, T. D.; Lynas-Gray, Anthony Eugene; Kilkenny, David; Koen, Chris; Amaral, Marc; Jordan, Riley (2018-06-01)
      Among the competing evolution theories for subdwarf-B (sdB) stars is the binary evolution scenario. EC 20117-4014 (=V4640 Sgr) is a spectroscopic binary system consisting of a pulsating sdB star and a late F main-sequence ...
    • The physical properties of double degenerate common proper motion binaries 

      Sión, Edward M.; Oswalt, T. D.; Liebert, James W.; Hintzen, Paul M N (1991-04)
      We present spectral types and spectrophotometry for 21 double degenerate (DD) common proper motion binaries and provide estimates of their colors, absolute visual and bolometric magnitudes, and cooling ages. The most typical ...
    • The rapidly pulsating subdwarf B star PG 1325+101 I. Oscillation modes from multisite observations 

      Silvotti, R.; Bonanno, Alfio M.; Bernabei, Stefano; Fontaine, G.; Charpinet, Stéphane; Leccia, Silvio; Kjeldsen, Hans; Oswalt, T. D.; Rudkin, Mark J.; Johnston, Kyle B. (2006-11)
      In this article we present the results of 215 h of time-series photometry on the rapidly pulsating subdwarf B star PG 1325+101 (Teff - 35 000 K, log g = 5.8, log N(Hs)/N(H) = -1.7), obtained during 25 days of observation ...
    • The rapidly pulsating subdwarf B star PG 1325+101 II. Structural parameters from asteroseismology 

      Charpinet, Stéphane; Silvotti, R.; Bonanno, Alfio M.; Fontaine, G.; Brassard, Pierre; Chayer, Pierre; Green, Elizabeth M.; Oswalt, T. D.; Rudkin, Mark J.; Johnston, Kyle B. (2006-11)
      We present a detailed analysis of the rapidly pulsating subdwarf B star (or EC14026 star) PG 1325+101. This analysis exploits the outcome of dedicated multisite observations using time-series photometry that revealed the ...
    • Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. XII. Ground-based monitoring of 3C 390.3 

      Dietrich, Matthias; Peterson, Bradley M.; Albrecht, P.; Altmann, Martin; Barth, Aaron J.; Bennie, P. J.; Bertram, Ray; Bochkarev, Nikolai G.; Oswalt, T. D.; Tao, Jun (1998-04)
      Results of a ground-based optical monitoring campaign on 3C 390.3 in 1994-1995 are presented. The broadband fluxes (B, V, R, and I), the spectrophotometric optical continuum flux Fλ(5177 Å), and the integrated emission-line ...
    • The temporal spectrum of the sdB pulsating star HS 2201+2610 at 2 ms resolution 

      Silvotti, R.; Janulis, Rimvydas; Schüh, Sonja L.; Charpinet, Stéphane; Oswalt, T. D.; Silvestri, Nicole M.; González-Pérez, J. M.; Kalytis, Romualdas; Meištas, E. G.; Carlson, Glenn (2002-07)
      In this article we present the results of more than 180 hours of time-series photometry on the low gravity (log g = 5.4, Teff = 29 300 K, log He/H = -3.0 by number) sdB pulsating star HS 2201+2610, obtained between September ...
    • UV observations of the cool DBQA5 white dwarf LDS 678A: Limits on the atmospheric composition, pressure shift, and gravitational redshift derived from C I 2479 

      Oswalt, T. D.; Sión, Edward M.; Hammond, Gordon L.; Vauclair, Gérard P.; Liebert, James W.; Wegner, Gary A.; Koester, Detlev; Marcum, Pamela M. (1991-02)
      We present a high-resolution ultraviolet spectrum of the helium-rich degenerate LDS 678A, obtained with the International Ultraviolet Explorer (IUE) satellite. LDS 678A is the coolest metallic line degenerate (DQ or DZ) ...
    • Where Are the Magnetic White Dwarfs with Detached, Nondegenerate Companions? 

      Liebert, James W.; Wickramsinghe, Dayal T.; Schmidt, Gary D.; Silvestri, Nicole M.; Hawley, Suzanne L.; Szkody, Paula; Ferrario, Lilia; Webbink, Ronald F.; Oswalt, T. D.; Smith, Jonathan Allyn (2005-05)
      The Sloan Digital Sky Survey has already more than doubled the sample of white dwarfs with spectral classi- fications, the subset with detached M dwarf companions, and the subset of magnetic white dwarfs. In the course ...
    • 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 ...
    • 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 ...