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 In Focus

Exoplanets Detection and Physical Properties

Published 2000-01-28

In 2004 Dr Claes-Ingvar Lagerkvist, Department of Astronomy and Space Physics, Uppsala University obtained STINT support on the Project Based Personnel Exchange Programme, PPP, for two years for cooperation with the Institute of Planetary Research, DLR in Berlin (Deutsches Zentrum für Luft- und Raumfahrt). In late 2005 he was granted continued support for a third year.

The detection and study of extrasolar planets is a key active research area in planetary and astronomical sciences. Almost 200 planetary systems around solar-type stars are known up to now. These include several systems of two or more planets. The existence of massive gas planets in orbits close to their central star and the lack of planets around 10 Jupiter masses (the so-called "brown dwarf desert") have raised fundamental questions concerning the validity of existing theories of planet formation. Following the recent detection of an Earth-sized planet one of the most exiting open questions for the future is the possible existence of Earth-like planets.

Key questions are:

  • Do terrestrial planets exist?
  • What is the frequency of planets (terrestrial and gas planets) and planetary systems?
  • What are the sizes and orbital parameters of extrasolar planets?
  • What is the physical and chemical nature of these planets?
  • How do planetary systems form?
  • How do planets and planetary systems evolve?

In order to better understand the general formation mechanisms for other planetary systems, a larger sample of known extrasolar planets is needed. This can be achieved by different observational techniques. An efficient method is photometric measurements of a large number of stars to detect transit events (the dimming of the light of the central star during transit of the planet through the line-of-sight) from which general characteristics of an exoplanet can be determined. The dimming of the stellar light is proportional to the ratio of the planetary to the stellar diameter. For Jupiter sized planets the intensity variation (~1%) can be detected with a small ground based telescope.

German collaborator:

A group on the investigation of extrasolar planets exists at DLR, Institute of Planetary Research (DLR-PF), Berlin, Germany ( The Berlin Exoplanet Search Telescope (BEST), commissioned and operated by DLR-PF, is a ground based system designed to search for transit events in several thousands of stars simultaneously. The system is operated as a ground-based support facility in the framework of the DLR-PF scientific participation in the COROT satellite mission. During 2004 an upgraded version of BEST was relocated to Observatoire de Haute-Provence (OHP), France. Regular observations of selected target fields have been ongoing since the spring of 2005. In parallel with the observations a gradual improvement of the system to allow remote controlled operations is taken place. This includes an improved data reduction pipeline, able to detect possible transits in thousands of stellar systems in near real time.

Many variable stars are detected during the search for exoplanets.

Swedish collaborator:

The Institute of Astronomy and Space Physics at the University of Uppsala, Sweden, has a research group with extensive experience in planetary research ( Since 2004 a new 90-cm telescope is operational at the Institute of Astronomy and Space Physics. The telescope is equipped with a CCD camera, including a filter wheel for color characterization of stars. The telescope is highly suitable for observations of potential planetary systems by the method of photometric transits. It can be used to search for planets in long-duration observing runs, but is most valuable for follow-up observations of planetary candidates found with telescope dedicated only to transit search, such as BEST.


During 2004-2005 the following has been achieved:

  • a close collaboration between the partners has been developed.
  • the Uppsala partner has performed follow-up observations of several transit candidates discovered during the BEST survey and thereby fully characterized their physical properties.
  • in the above period the Westerlund telescope has been commissioned and is fully operational. As a part of that process the German partner has provided know-how based on their experience from the BEST project. The BEST data pipeline has been implemented and adopted to the Uppsala telescope.
  • six students have been active in the collaboration with observations and data reduction as part of their Master Thesis.


  • further strengthen the already established collaboration between the two institutes.
  • follow-up observations performed with the Westerlund telescope are expected to continue for transit targets discovered by the regular operations of BEST.
  • the technical design for remote control implemented on BEST will be transferred and adopted on the Westerlund telescope. This improvement will allow the Uppsala telescope to be operated in a more automatic mode compared to the present situation.
  • student exchange will continue. Due to the already established collaboration, observation and data processing on both BEST and the Westerlund telescope will be an integrated part of their education.
  • The ongoing survey to detect new exoplanets will continue on a regular basis. The results are to be presented in a joint scientific publication during the later part of 2006.

Claes-Ingvar Lagerkvist
Department of Astronomy and Space Physics
Uppsala University

Senast uppdaterad: 07-06-28 14:18

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