@article{LopezReimersGreggetal.2005,
  author    = {Lopez, S. and Reimers, Dieter and Gregg, M. D. and Wisotzki, Lutz and Wucknitz, Olaf and Guzman, A.},
  title     = {Metal abundances in a damped Ly alpha system along two lines of sight at z=0.93},
  issn      = {0004-637X},
  year      = {2005},
  abstract  = {We study metal abundances in the z = 0.9313 damped Ly alpha system observed along the two lines of sight, A and B, toward the gravitationally lensed double QSO HE 0512-3329. Spatially resolved Space Telescope Imaging Spectrograph spectra constrain the neutral-gas column density to be N(H I) = 1020.5 cm(-2) in both A and B. UV-visual Echelle Spectrograph spectra ( spectral resolution FWHM = 9.8 km s(-1)) show, in contrast, significant line-of-sight differences in the column densities of Mn II and Fe II; these are not due to observational systematics. We find that [Mn/H] = -1.44 and [Fe/H] = -1.52 in damped Ly alpha system A, while [Mn/H] = -0.98 and [Fe/H] > -1.32, and possibly as high as [Fe/H] approximate to -1, in damped Ly alpha system B. A careful assessment of possible systematic errors leads us to conclude that these transverse differences are significant at a 5 sigma level or greater. Although nucleosynthesis effects may also be at play, we favor differential dust depletion as the main mechanism producing the observed abundance gradient. The transverse separation is 5 h(70)(-1) kpc at the redshift of the absorber, which is also likely to be the lensing galaxy. The derived abundances therefore probe two opposite sides of a single galaxy hosting both damped Ly alpha systems. This is the first time firm abundance constraints have been obtained for a single damped system probed by two lines of sight. The significance of this finding for the cosmic evolution of metals is discussed},
  language  = {en}
}
@article{WisotzkiSchechterChenetal.2004,
  author    = {Wisotzki, Lutz and Schechter, P. L. and Chen, H. W. and Richstone, D. and Jahnke, Knud and Sanchez, Sebastian F. and Reimers, Dieter},
  title     = {HE 0047-1756 : a new gravitationally lensed double QSO},
  issn      = {0004-6361},
  year      = {2004},
  abstract  = {The quasar HE 0047-1756, at z = 1.67, is found to be split into two images 1."144 apart by an intervening galaxy acting as a gravitational lens. The flux ratio for the two components is roughly 3.5:1, depending slightly upon wavelength. The lensing galaxy is seen on images obtained in the i (800 nm) and K-s bands (2.1 mum); there is also a nearby faint object which may be responsible for some shear. The spectra of the two quasar images are nearly identical, but the emission line ratio between the two components scale differently from the continuum. Moreover, the fainter component has a bluer continuum slope than the brighter one. We argue that these small differences are probably due to microlensing. There is evidence for a partial Einstein ring emanating from the brighter image toward the fainter one},
  language  = {en}
}
@misc{RuscheBielawskiRiemannetal.2010,
  author    = {Rusche, Tim Maxian and Bielawski, Martina and Riemann, Silke and Reimers, Lutz and Duplouy, Florent and Kuhn, Florian and von Oettingen, Anna},
  title     = {Deutsche Interessen offen diskutieren!},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-41636},
  year      = {2010},
  abstract  = {Außenpolitik ist von den Werten, dem Selbstverst{\"a}ndnis einer Gesellschaft und den {\"o}konomischen Interessen ihrer Volkswirtschaft gepr{\"a}gt. In den ersten beiden Teilen dieses Essays zeigen wir auf, wie Deutschland seine Werte behutsam erneuern sollte und welche Bereiche zur Wahrung seines {\"o}konomischen Wohlstands zentral sind. Auf dieses Fundament setzen wir ein Pl{\"a}doyer f{\"u}r eine neue außenpolitische Kultur, die Interessen offen debattiert und klar definiert, um sie erfolgreich durchzusetzen.},
  language  = {de}
}
@article{SchorckChristliebCohenetal.2009,
  author    = {Schorck, Torben and Christlieb, Norbert and Cohen, Judy G. and Beers, Timothy C. and Shectman, Steve and Thompson, Ian and McWilliam, Andrew and Bessell, Michael S. and Norris, John E. and Mel{\´e}ndez, Jorge and Ram{\"i}rez, Solange and Haynes, D. and Cass, Paul and Hartley, Malcolm and Russell, Ken and Watson, Fred and Zickgraf, Franz-Josef and Behnke, Berit and Fechner, Cora and Fuhrmeister, Birgit and Barklem, Paul S. and Edvardsson, Bengt and Frebel, Anna and Wisotzki, Lutz and Reimers, Dieter},
  title     = {The stellar content of the Hamburg/ESO survey : V. the metallicity distribution function of the Galactic halo},
  issn      = {0004-6361},
  doi       = {10.1051/0004-6361/200810925},
  year      = {2009},
  abstract  = {We determine the metallicity distribution function (MDF) of the Galactic halo by means of a sample of 1638 metal-poor stars selected from the Hamburg/ESO objective-prism survey (HES). The sample was corrected for minor biases introduced by the strategy for spectroscopic follow-up observations of the metal-poor candidates, namely "best and brightest stars first". Comparison of the metallicities [Fe/H] of the stars determined from moderate-resolution (i.e., R similar to 2000) follow-up spectra with results derived from abundance analyses based on high-resolution spectra (i.e., R > 20 000) shows that the [Fe/H] estimates used for the determination of the halo MDF are accurate to within 0.3 dex, once highly C-rich stars are eliminated. We determined the selection function of the HES, which must be taken into account for a proper comparison between the HES MDF with MDFs of other stellar populations or those predicted by models of Galactic chemical evolution. The latter show a reasonable agreement with the overall shape of the HES MDF for [Fe/H] > -3.6, but only a model of Salvadori et al. (2007) with a critical metallicity for low-mass star formation of Z(cr) = 10(-3.4) Z(circle dot) reproduces the sharp drop at [Fe/H] similar to -3.6 present in the HES MDF. Although currently about ten stars at [Fe/H] < -3.6 are known, the evidence for the existence of a tail of the halo MDF extending to [Fe/H] similar to -5.5 is weak from the sample considered in this paper, because it only includes two stars [Fe/H] < -3.6. Therefore, a comparison with theoretical models has to await larger statistically complete and unbiased samples. A comparison of the MDF of Galactic globular clusters and of dSph satellites to the Galaxy shows qualitative agreement with the halo MDF, derived from the HES, once the selection function of the latter is included. However, statistical tests show that the differences between these are still highly significant.},
  language  = {en}
}
@article{WorseckProchaskaMcQuinnetal.2011,
  author    = {Worseck, Gabor and Prochaska, J. Xavier and McQuinn, Matthew and Dall'Aglio, Aldo and Fechner, Cora and Hennawi, Joseph F. and Reimers, Dieter and Richter, Philipp and Wisotzki, Lutz},
  title     = {The end of Helium Reionization at z similar or equal to 2.7 Inferred from cosmic variance in HST/COS He II Ly alpha Absorption spectra},
  series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters},
  volume    = {733},
  journal   = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters},
  number    = {2},
  publisher = {IOP Publ. Ltd.},
  address   = {Bristol},
  issn      = {2041-8205},
  doi       = {10.1088/2041-8205/733/2/L24},
  pages     = {6},
  year      = {2011},
  abstract  = {We report on the detection of strongly varying intergalactic He II absorption in HST/COS spectra of two z(em) similar or equal to 3 quasars. From our homogeneous analysis of the He II absorption in these and three archival sightlines, we find a marked increase in the mean He II effective optical depth from <tau(eff, He II)> similar or equal to 1 at z similar or equal to 2.3 to <tau(eff, He II)> greater than or similar to 5 at z similar or equal to 3.2, but with a large scatter of 2 less than or similar to tau(eff, He II) less than or similar to 5 at 2.7 < z < 3 on scales of similar to 10 proper Mpc. This scatter is primarily due to fluctuations in the He II fraction and the He II-ionizing background, rather than density variations that are probed by the coeval Hi forest. Semianalytic models of He II absorption require a strong decrease in the He II-ionizing background to explain the strong increase of the absorption at z greater than or similar to 2.7, probably indicating He II reionization was incomplete at z(reion) greater than or similar to 2.7. Likewise, recent three-dimensional numerical simulations of He II reionization qualitatively agree with the observed trend only if He II reionization completes at z(reion) similar or equal to 2.7 or even below, as suggested by a large tau(eff, He II) greater than or similar to 3 in two of our five sightlines at z < 2.8. By doubling the sample size at 2.7 less than or similar to z less than or similar to 3, our newly discovered He II sightlines for the first time probe the diversity of the second epoch of reionization when helium became fully ionized.},
  language  = {en}
}
@article{WisotzkiSchechterBradtetal.2002,
  author    = {Wisotzki, Lutz and Schechter, P. L. and Bradt, H. V. and Heinm{\"u}ller, Janine and Reimers, Dieter},
  title     = {HE 0435-1223 : a wide separation quadruple QSO and gravitational lens},
  year      = {2002},
  abstract  = {We report the discovery of a new gravitationally lensed QSO, at a redshift z = 1.689, with four QSO components in a cross-shaped arrangement around a bright galaxy. The maximum separation between images is 2farcs 6, enabling a reliable decomposition of the system. Three of the QSO components have g =~ 19.6, while component A is about 0.6 mag brighter. The four components have nearly identical colours, suggesting little if any dust extinction in the foreground galaxy. The lensing galaxy is prominent in the i band, weaker in r and not detected in g. Its spatial profile is that of an elliptical galaxy with a scale length of ~ 12 kpc. Combining the measured colours and a mass model for the lens, we estimate a most likely redshift range of 0.3 < z < 0.4. Predicted time delays between the components are la 10 days. The QSO shows evidence for variability, with total g band magnitudes of 17.89 and 17.71 for two epochs separated by ~ 2 months. However, the relative fluxes of the components did not change, indicating that the variations are intrinsic to the QSO rather than induced by microlensing. Based in part on observations obtained with the Baade 6.5-m telescope of the Magellan Consortium. Also based in part on observations collected at the European Southern Observatory, La Silla, Chile.},
  language  = {en}
}
@article{ChristliebGreenWisotzkietal.2001,
  author    = {Christlieb, N. and Green, P. J. and Wisotzki, Lutz and Reimers, Dieter},
  title     = {The stellar content of the Hamburg/ESO survey : II. a large, homogeneously-selected sample of high latitude carbon stars},
  year      = {2001},
  language  = {en}
}
@article{ChristliebWisotzkiReimers2001,
  author    = {Christlieb, N. and Wisotzki, Lutz and Reimers, Dieter},
  title     = {Mining the digital Hamburg / ESO objective prism survey},
  isbn      = {3-540-42468-7},
  year      = {2001},
  language  = {en}
}
@article{ReimersWisotzki2001,
  author    = {Reimers, Dieter and Wisotzki, Lutz},
  title     = {The Hamburg all sky bright QSO surveys},
  isbn      = {1-5838-1127-3},
  year      = {2001},
  language  = {en}
}
@article{RuscheBielawskiRiemannetal.2011,
  author    = {Rusche, Tim Maxian and Bielawski, Martina and Riemann, Silke and Reimers, Lutz and Duplouy, Florent and Kuhn, Florian and von Oettingen, Anna},
  title     = {Deutsche Interessen offen diskutieren!},
  series = {WeltTrends-Papiere},
  journal   = {WeltTrends-Papiere},
  number    = {20},
  publisher = {Universit{\"a}tsverlag Potsdam},
  address   = {Potsdam},
  issn      = {1864-0656},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-62734},
  pages     = {9 -- 17},
  year      = {2011},
  abstract  = {Inhalt: 1. Werte und Selbstverst{\"a}ndnis behutsam erneuern Globalisierung Demografischer Wandel Klimawandel 2. Langfristig {\"o}konomischen Wohlstand sichern Bildung Forschung und Entwicklung Außenwirtschaft 3. Pl{\"a}doyer f{\"u}r eine neue außenpolitische Kultur : Deutsche Interessen - Ein Anachronismus? Status quo: Interessendefinition im Hinterzimmer Interessen klar definieren und erfolgreich durchsetzen Entscheidungsmatrix f{\"u}r Auslandseins{\"a}tze Evaluierung des Nutzens Evaluierung der Kosten Ableiten der Entscheidung Und die Moral? - Aber sicher! Der T{\"o}nissteiner Kreis},
  language  = {de}
}
@article{ChristliebWisotzkiReimersetal.2001,
  author    = {Christlieb, N. and Wisotzki, Lutz and Reimers, Dieter and Homeier, D. and Koester, D. and Heber, Ulrich},
  title     = {The stellar content of the Hamburg/ESO survey : I. Automated selection of DA white dwarfs},
  year      = {2001},
  abstract  = {We describe automatic procedures for the selection of DA white dwarfs in the Hamburg/ESO objective-prism survey (HES). For this purpose, and the selection of other stellar objects (e.g., metal-poor stars and carbon stars), a flexible, robust algorithm for detection of stellar absorption and emission lines in the digital spectra of the HES was developed. Broad band (U-B, B-V) and intermediate band (Str{\"o}mgren c_1) colours can be derived directly from HES spectra, with precisions of sigma U-B=0.092 mag; sigma B-V=0.095 mag; sigma c_1=0.15 mag. We describe simulation techniques that allow one to convert model or slit spectra to HES spectra. These simulated objective-prism spectra are used to determine quantitative selection criteria, and for the study of selection functions. We present an atlas of simulated HES spectra of DA and DB white dwarfs. Our current selection algorithm is tuned to yield maximum efficiency of the candidate sample (minimum contamination with non-DAs). DA candidates are selected in the B-V versus U-B and c_1 versus W_lambda (Hbeta +Hgamma +Hdelta ) parameter spaces. The contamination of the resulting sample with hot subdwarfs is expected to be as low as ~ 8\%, while there is essentially no contamination with main sequence or horizontal branch stars. We estimate that with the present set of criteria, ~ 80\% of DAs present in the HES database are recovered. A yet higher degree of internal completeness could be reached at the expense of higher contamination. However, the external completeness is limited by additional losses caused by proper motion effects and the epoch differences between direct and spectral plates used in the HES. Based on observations collected at the European Southern Observatory, La Silla and Paranal, Chile.},
  language  = {en}
}