TY  - JOUR
A1  - Wisotzki, Lutz
A1  - Christlieb, N.
A1  - Liu, M. C.
A1  - Maza, J.
A1  - Morgan, N. D.
A1  - Schechter, P. L.
T1  - Discovery of a New Multiple Gravitationally Lensed QSO
Y1  - 2001
SN  - 1-583-81074-9
ER  - 
TY  - JOUR
A1  - Christlieb, N.
A1  - Wisotzki, Lutz
A1  - Reimers, Dieter
T1  - Mining the digital Hamburg / ESO objective prism survey
Y1  - 2001
SN  - 3-540-42468-7
ER  - 
TY  - JOUR
A1  - Christlieb, N.
A1  - Wisotzki, Lutz
A1  - Reimers, Dieter
A1  - Homeier, D.
A1  - Koester, D.
A1  - Heber, Ulrich
T1  - The stellar content of the Hamburg/ESO survey : I. Automated selection of DA white dwarfs
N2  - 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 (Strömgren 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.
Y1  - 2001
ER  - 
TY  - JOUR
A1  - Christlieb, N.
A1  - Green, P. J.
A1  - Wisotzki, Lutz
A1  - Reimers, Dieter
T1  - The stellar content of the Hamburg/ESO survey : II. a large, homogeneously-selected sample of high latitude carbon stars
Y1  - 2001
ER  - 
TY  - JOUR
A1  - Christlieb, N.
A1  - Wisotzki, Lutz
A1  - Graßhoff, G.
T1  - Statistical methods of automatic spectral classification and their application to the Hamburg/ESO Survey
N2  - We employ classical statistical methods of multivariate classification for the exploitation of the stellar content of the Hamburg/ESO objective prism survey (HES). In a simulation study we investigate the precision of a three- dimensional classification (Teff, log g, [Fe/H]) achievable in the HES for stars in the effective temperature range 5200 K<Teff<6800 K, using Bayes classification. The accuracy in temperature determination is better than 400 K for HES spectra with S/N>10 (typically corresponding to BJ<16.5). The accuracies in log g and [Fe/H] are better than 0.68 dex in the same S/N range. These precisions allow for a very efficient selection of metal-poor stars in the HES. We present a minimum cost rule for compilation of complete samples of objects of a given class, and a rejection rule for identification of corrupted or peculiar spectra. The algorithms we present are being used for the identification of other interesting objects in the HES data base as well, and they are applicable to other existing and future large data sets, such as those to be compiled by the DIVA and GAIA missions.
Y1  - 2002
ER  -