@article{UBHD-67796553,
  author={R{\"o}ser, Siegfried and Schilbach, Elena and Schwan, Heiner},
  title={PPM-Extended (PPMX)},
  subtitle={a catalogue of positions and proper motions},
  year={2008},
  pages={401-408},
  language={eng},
  issn={1432-0746},
  volume={488},
  number={1},
  note={Gesehen am 30.03.2015},
  journal={Astronomy and astrophysics},
  doi={10.1051/0004-6361:200809775},
}
@article{UBHD-67490137,
  author={Schwan, Heiner and Wielen, Roland},
  title={Maintenance of the ICRF},
  subtitle={statistical treatment},
  year={1998},
  pages={326-328},
  language={ger},
  volume={11},
  journal={Highlights of astronomy},
}
@article{UBHD-67489569,
  author={Wielen, Roland and Lenhardt, Helmut and Schwan, Heiner and Dettbarn, Christian},
  title={The combination of ground-based astrometric compilation catalogues with the HIPPARCOS catalogue},
  subtitle={I. Single-star mode},
  year={1999},
  pages={1046-1054},
  language={eng},
  issn={1432-0746},
  volume={347},
  number={?},
  note={Gesehen am 29.10.2013},
  journal={Astronomy and astrophysics},
}
@incollection{UBHD-67489571,
  author={Wielen, Roland and Schwan, Heiner and Dettbarn, Christian and Jahreiß, Hartmut and Lenhardt, Helmut},
  title={The combination of HIPPARCOS data with ground-based astrometric measurements},
  year={1999},
  pages={161-170},
  language={eng},
  isbn={3-7001-2774-X and 978-3-7001-2774-1},
  booktitle={Modern astrometry and astrodynamics},
  editor={Dvorak, Rudolf},
}
@article{UBHD-67489567,
  author={Wielen, Roland and Dettbarn, Christian and Jahreiß, Hartmut and Lenhardt, Helmut and Schwan, Heiner},
  title={Indications on the binary nature of individual stars derived from a comparison of their HIPPARCOS proper motions with ground-based data},
  subtitle={I. Basic principles},
  year={1999},
  pages={675-685},
  language={eng},
  issn={1432-0746},
  volume={346},
  number={?},
  note={Gesehen am 29.10.2013},
  journal={Astronomy and astrophysics},
}
@conference{UBHD-67489570,
  author={Wielen, Roland and Schwan, Heiner and Dettbarn, Christian and Jahreiß, Hartmut and Lenhardt, Helmut},
  title={The sixth catalogue of fundamental stars (FK6) and the problem of double stars},
  year={1998},
  pages={123-132},
  language={eng},
  isbn={3-8171-1588-1 and 978-3-8171-1588-4},
}
@conference{UBHD-67495789,
  author={Wielen, Roland and Schwan, Heiner and Dettbarn, Christian and Jahreiß, Hartmut and Lenhardt, Helmut},
  title={Statistical astrometry based on a comparison of individual proper motions and positions of stars in the FK5 and the HIPPARCOS catalogue},
  year={1997},
  pages={727-732},
  language={eng},
  isbn={92-9092-291-5 and 978-92-9092-291-9},
}