Browsing Research publications by Author "Koester, D."

Now showing items 1-20 of 29

    • Binaries discovered by the SPY project. II. HE 1414-0848: A double degenerate with a mass close to the Chandrasekhar limit 

      Napiwotzki, R.; Koester, D.; Nelemans, G.; Yungelson, L.; Christlieb, N.; Renzini, A.; Reimers, D.; Drechsel, H.; Leibundgut, B. (2002-05)
      In the course of our search for double degenerate (DD) binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (ESO SNIa Progenitor surveY { SPY) we discovered that the white dwarf ...

    • Binaries discovered by the SPY project. III. HE 2209-1444: A massive, short period double degenerate 

      Karl, C.; Napiwotzki, R.; Nelemans, G.; Christlieb, N.; Koester, D.; Heber, U.; Reimers, D. (2003-11)
      In the course of our search for double degenerate (DD) binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY – SPY) we discovered HE2209−1444 to be ...

    • Binary White Dwarfs in the Supernova Ia Progenitor Survey 

      Napiwotzki, R.; Karl, C.; Nelemans, G.; Yungelson, L.; Christlieb, N.; Drechsel, H.; Heber, U.; Homeier, D.; Koester, D.; Leibundgut, B.; Marsh, T.R.; Moehler, S.; Renzini, A.; Reimers, D. (Astronomical Society of the Pacific, 2007)
      We report results of a systematic radial velocity survey for double degenerate (DD) binaries as potential progenitors of type Ia supernovae: SPY (ESO Supernovae Ia Progenitor surveY). More than 1000 white dwarfs (WDs) and ...

    • DAZ White Dwarfs in the SPY Sample 

      Koester, D.; Rollenhagen, K.; Napiwotzki, R.; Voss, B.; Christlieb, N.; Homeier, D.; Reimers, D. (Astronomical Society of the Pacific, 2005)
      We search for faint Ca II lines in the spectra of about 800 apparently single white dwarfs observed at high resolution for the SPY (ESO Supernova Progenitor Survey) survey. Photospheric Ca is detected in 24 DAZ; in 25 ...

    • Discovery of eleven new ZZ Ceti stars 

      Castanheira, B.G.; Kepler, S.O.; Mullally, F.; Winget, D.E.; Koester, D.; Voss, B.; Kleinman, S.J.; Nitta, A.; Eisenstein, D.J.; Napiwotzki, R.; Reimers, D. (2006)

    • Discovery of seven ZZ Ceti stars using a new photometric selection method 

      Voss, B.; Koester, D.; Ostensen, R.; Kepler, S.O.; Napiwotzki, R.; Homeier, D.; Reimers, D. (2006)

    • Double Degenerate and Progenitors of Supernovae Type Ia 

      Napiwotzki, R.; Yungelson, L.; Nelemans, G.; Marsh, T.R.; Leibundgut, B.; Renzini, A.; Homeier, D.; Koester, D.; Moehler, S.; Christlieb, N.; Reimers, D.; Drechsel, H.; Heber, U.; Karl, C.; Pauli, E.M. (Astronomical Society of the Pacific, 2004)
      We report on systematic radial velocity surveys for white dwarf { white dwarf binaries (double degenerates { DDs) including SPY (ESO Supernovae Ia progenitor survey) recently carried out at the VLT. A large sample of DD ...

    • The ESO supernovae type Ia progenitor survey (SPY) : The radial velocities of 644 DA white dwarfs 

      Napiwotzki, R.; Karl, C. A.; Lisker, T.; Catalan, S.; Drechsel, H.; Heber, U.; Homeier, D.; Koester, D.; Leibundgut, B.; Marsh, T. R.; Moehler, S.; Nelemans, G.; Reimers, D.; Renzini, A.; Stroer, A.; Yungelson, L. (2019-07-27)
      Close double degenerate binaries are one of the favoured progenitor channels for type Ia supernovae, but it is unclear how many suitable systems there are in the Galaxy. We report results of a large radial velocity survey ...

    • First VLT spectra of white dwarfs in a globular cluster 

      Moehler, S.; Heber, U.; Napiwotzki, R.; Koester, D.; Renzini, A. (2000)
      We present the first spectra obtained with the Very Large Telescope for white dwarfs in a globular cluster. Estimates of atmospheric parameters are obtained and compared to evolutionary tracks. We discuss possible implications ...

    • High resolution UVES/VLT spectra of white dwarfs observed for the ESO SN Ia Progenitor Survey III. DA white dwarfs 

      Koester, D.; Voss, B.; Napiwotzki, R.; Christlieb, N.; Homeier, D.; Lisker, T.; Reimers, D.; Heber, U. (2009-10)
      Context. The ESO Supernova Ia Progenitor Survey (SPY) took high-resolution spectra of more than 1000 white dwarfs and pre-white dwarfs. About two thirds of the stars observed are hydrogen-dominated DA white dwarfs. Here ...

    • High-resolution UVES/VLT spectra of white dwarfs observed for the ESO SN Ia progenitor survey (SPY). I 

      Koester, D.; Napiwotzki, R.; Christlieb, N.; Drechsel, H.; Hagen, H.J.; Heber, U.; Homeier, D.; Karl, C.; Leibundgut, B.; Moehler, S.; Nelemans, G.; Reimers, D.; Pauli, E.M.; Renzini, A.; Yungelson, L. (2001-11)

    • HS 0146 1847 - a DAZB white dwarf of very unusual composition 

      Koester, D.; Napiwotzki, R.; Voss, B.; Homeier, D.; Reimers, D. (2005-08)

    • HS 2333 + 3927: a new sdB binary with a large reflection effect 

      Karl, C.; Heber, U.; Drechsel, H.; Napiwotzki, R.; Altmann, M.; Ostensen, R.; Folkes, S.; Solheim, J.E.; Cordes, O.; Voss, B.; Koester, D. (2004)
      We report the discovery of a binary, HS 2233 + 3927, consisting of an sdB star with a faint companion. From its lightcurve the orbital period of 14,844 s, the mass ratio, the inclination, and other system parameters are ...

    • HS 2333 3927: A new sdB dM binary with a large reflection effect 

      Heber, U.; Drechsel, H.; Ostensen, R.; Karl, C.; Napiwotzki, R.; Altmann, M.; Cordes, O.; Solheim, J.E.; Voss, B.; Koester, D.; Folkes, S. (2004-06)

    • The magnetic and metallic degenerate G77-50 

      Farihi, J.; Dufour, P.; Napiwotzki, R.; Koester, D. (2011-06)
      An accumulation of multi-epoch, high-resolution optical spectra reveal that the nearby star G77-50 is a very cool DAZ white dwarf externally polluted by Mg, Fe, Al, Ca and possibly Na, Cr, Mn. The metallic and hydrogen ...

    • The Mass of the sdB Primary of the Binary HS 2333+3927 

      Heber, U.; Drechsel, H.; Karl, C.; Ostensen, R.; Folkes, S.; Napiwotzki, R.; Altmann, M.; Cordes, O.; Solheim, J.E.; Voss, B.; Koester, D. (Astronomical Society of the Pacific, 2005)
      Short period sdB binaries with cool companions are crucial to understand pre-CV evolution, because they will evolve into cataclysmic variables, when the sdB will have left the extended horizontal branch. Recently we ...

    • Metal traces in white dwarfs of the SPY (ESO Supernova Ia Progenitor Survey) sample 

      Koester, D.; Rollenhagen, K.; Napiwotzki, R.; Voss, B.; Christlieb, N.; Homeier, D.; Reimers, D. (2005-03)

    • New Results from the Supernova Ia Progenitor Survey 

      Napiwotzki, R.; Karl, C.; Nelemans, G.; Yungelson, L.; Christlieb, N.; Drechsel, H.; Heber, U.; Homeier, D.; Koester, D.; Kruk, J.; Leibundgut, B.; Marsh, T.R.; Moehler, S.; Renzini, A.; Reimers, D. (Astronomical Society of the Pacific, 2005)
      We report on a systematic radial velocity survey for double degenerate (DD) binaries as potential progenitors of type Ia supernovae: SPY (ESO Supernovae Ia Progenitor surveY). More than 1000 white dwarfs and pre-white ...

    • Rotation Velocities of DA White Dwarfs with Convective Atmospheres 

      Karl, C.; Heber, U.; Napiwotzki, R.; Dreizler, S.; Koester, D.; Reid, I.N. (Astronomical Society of the Pacific, 2005)
      The sharp H® NLTE line cores of hydrogen rich (DA) white dwarfs allow their projected rotational velocities to be determined. High resolution optical spectra of 22 stars obtained with the Keck I telescope are matched by ...

    • Rotation velocities of white dwarfs determined from the Ca II K line 

      Berger, L.; Koester, D.; Napiwotzki, R.; Reid, I.N.; Zuckerman, B. (2005)