'HIPPARCOS AND THE HR DIAGRAM'
Royal Astronomical Society Discussion Meeting - Friday 14th February
Some of the first scientific results from ESA's Hipparcos satellite will be presented at a Royal Astronomical Society Discussion Meeting in London on 14th February. Several of these results have a significant bearing on current debates regarding the size and age of the universe. A press briefing session will be held during the meeting lunch break, when a panel of scientists will briefly describe the results being presented and answer questions.
Press Briefing (media only)Place: The Scientific Societies' Lecture Theatre, 23 Savile Row ('Fortress House'), London W1 (Entrance in Burlington Place, on left side of building)
Time: 1.10 p.m. to 1.55 p.m., Friday 14 February 1997
Panel: Professor Michael Perryman (ESTEC & Leiden Observatory); Dr Floor van Leeuwen (Royal Greenwich Observatory); Professor Michael Feast (University of Cape Town); Dr Jasper Wall (Royal Greenwich Observatory).
The following notes on the mission have been prepared by the meeting organizers, Prof. Michael Perryman and Dr Floor van Leeuwen.
The Hipparcos mission
Hipparcos, the European Space Agency's astrometry satellite, was launched in August 1989. Its aim was the accurate determination of the distances and motions of more than one hundred thousand stars, in order to provide an optical reference frame of unprecedented accuracy, and to furnish fundamental astrophysical data unachievable from ground-based measurements of stellar positions. The mission operated until mid-1993, and all of the mission's scientific objectives were significantly surpassed. Processing of the high quality scientific data has resulted in two major stellar catalogues: the Hipparcos Catalogue (compiled and verified by two independent consortia), and the Tycho Catalogue (containing lower accuracy data on more than one million stars). Scientific exploitation has started over the last few months with the distribution of the final data to Principal Investigators. The mission products will be made available to the astronomical community in June 1997.
The role of the UK
The UK has been involved in the Hipparcos project from its very start around 1976. The principal institute involved was the Royal Greenwich Observatory, which was a major partner in one of the two consortia responsible for the data reductions. Other institutes that have been involved were Mullard Space Science Laboratories (during the software development) and the Institute of Astronomy, University of Cambridge (during preparations for the Hipparcos Input Catalogue).
The HR diagram
The Hertzsprung-Russell or HR Diagram is one of the most basic tools in astrophysics: it shows the relations that exist between temperature and luminosity for different types of stars. Its properties are used to understand stellar structure and stellar evolutionary processes. While the colours of stars can be directly observed, their luminosities depend on a measurement of the distance of the object, needed to convert the observed light intensities into emitted intensities. HR diagrams were first constructed around 1910 for star clusters. There, stars are all at almost the same distance from our Sun, and the corrections from observed to actual luminosities are the same for all those stars. The calibrations of specific features of the HR diagram, and the positions of groups of stars used for calibration of distances of extra galactic objects, have direct implications for our understanding of the cosmos.
Today's meeting has two aims:
1) A presentation of the mission products, their quality as well as their limitations, further enhanced by examples of how to use these data;
2) Presentations of some of the first results obtained from the mission. In many cases results will be preliminary only, and are presented in order to give a first impression of the impact we expect the mission results to have. These can be divided into three groups: a) general statistical results on luminosities and dynamics for nearby stars; b) studies of the two nearest open clusters; c) detailed astrophysical interpretations. The last group includes the first discussion of the calibration of the Cepheid and Mira period-luminosity relations as well as calibrations of white dwarf parameters.
[Scientific abstracts available to media under embargo. Contact Jacqueline Mitton.]
The names given below are those of the speakers: generally these individuals are representatives of (sometimes large) scientific collaborations.
1. Prof. Michael A. C. Perryman (ESTEC/Leiden Observatory) Review of the mission products, their release and access
2. Dr D. W. Evans (RGO, Cambridge) Nearby stars, solar neighbourhood
3. Prof. James Binney, University of Oxford Spectral classifications and Hipparcos distances for star within 80 pc from the Sun
4. C. S. Hansen Ruiz, Tenerife, Spain Definition of the Pleiades Main Sequence
5. Dr Floor van Leeuwen, RGO The Pleiades distance, combining ground-based and Hipparcos astrometry
6. Prof. Michael A. C. Perryman, ESTEC/Leiden Observatory The Hyades as seen by Hipparcos
7. Dr J. Lub, Leiden Observatory Walraven photometry and Hipparcos parallaxes
8. Prof. Michael Feast, University of Cape Town Miras and Cepheid distance scale9. Dr M. Barstow, University of Leicester The white dwarf temperature scale and mass-radius relation
Dr Jacqueline Mitton, RAS Public Relations Officer
Phone: Cambridge ((0)1223) 564914 FAX: Cambridge ((0)1223) 572892