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EARLY RESULTS FROM HIPPARCOS DATA

Last Updated on Sunday, 02 May 2010 20:19
Published on Friday, 25 February 2005 00:00

 

Astronomers attending a Royal Astronomical Discussion Meeting in London today will get the first tantalizing glimpse of the kind of significant results being extracted from the Hipparcos satellite's harvest of data. Scientists working on the data emphasise that the discussions today revolve around their earliest and most preliminary findings, but highlights emerging already include: 


  • Cepheid variable stars appear to be more luminous and distant than previously thought. Since these stars are used to gauge the distances to other galaxies, this implies that the universe may be larger than previous estimates by about 10 per cent. The result also implies that the oldest known stars are no more than 11 billion years old, consistent with an age for the universe a whole of perhaps 12 billion years.

     

  • Previous estimates that our own Galaxy is 8 to 10 billion years old, based on the rate at which white dwarf stars gradually cool down, are confirmed as reliable by completely independent Hipparcos observations of white dwarfs.

     

  • The nearby Pleiades star cluster, whose distance is used as a stepping stone for determing the distance to much more remote clusters in our Galaxy and to galaxies beyond our own, appears to be nearer than previously thought - at about 360 light years rather than 400, implying, curiously, that the Pleiades stars are intrinsically fainter than typical stars with comparable colours in the solar neighbourhood.

     

  • A picture of stellar movements in our local part of the Galaxy allows a clear recognition of the very old stars, dating from the time when the Galaxy had not collapsed to its present disk-like shape, which are travelling through space in a completely different way from the Sun and its cohort.

     

  • With the real intrinsic brightness of 40,000 stars measured by Hipparcos, far more giant and supergiant stars are being identified for certain on the basis of their luminosity where previously their detection relied on interpreting their spectra correctly. These identifications will help astrophysicists understand these stars and their spectra better.

     

  • Work is well under way that will give important new insights into the nearest star cluster to the Sun, the Hyades. Careful analysis of which stars belong to the cluster, where they are positioned in relation to each other, and how they are moving, is going to result in a re-evaluation of the cluster's distance. This distance is of crucial importance because it calibrates most other methods used for finding the distances to more remote objects.

     

The flood of new data available to astronomers from ESA's Hipparcos stems from its ability to detect any apparent change in the position of a star with an accuracy equivalent to measuring from Earth the height of a child standing on the Moon. This made it possible to determine the positions, distances and real movements of large numbers of stars with unprecedented precision. The full data will be published in June 1997, when it will be available to any astronomers who wish to use it. Until then, early access to the data is being restricted to the research groups involved in carrying out the Hipparcos mission.

The organizers of the RAS Discussion Meeting are Prof. Michael A. C. Perryman (ESTEC/Leiden Observatory) and Dr Floor van Leeuwen (Royal Greenwich Observatory, Cambridge)

 


Contacts for contributions referred to above

Prof. Michael A. C. Perryman (ESTEC/Leiden Observatory) phone +31 71 565 3615; e-mail This email address is being protected from spambots. You need JavaScript enabled to view it. presents Review of the mission and The Hyades as seen by Hipparcos

 

Dr Floor van Leeuwen, (RGO, Cambridge) phone 01223 374765; e-mail This email address is being protected from spambots. You need JavaScript enabled to view it. The distance to the Pleiades

 

Dr Dafydd Wyn Evans (RGO, Cambridge) phone 01223 374000; e-mail This email address is being protected from spambots. You need JavaScript enabled to view it. Stars in the solar neighbourhood

 

Prof. Michael Feast, University of Cape Town phone +27 21 650 2396; e-mail This email address is being protected from spambots. You need JavaScript enabled to view it. Cepheid and Mira variable stars and the distance scale

 

Prof. James Binney, University of Oxford phone 01865 727650; This email address is being protected from spambots. You need JavaScript enabled to view it. Spectral classifications and distances for stars within 80 pc of the Sun

 

Dr Martin Barstow (University of Leicester) phone 0116-252-3492; e-mail This email address is being protected from spambots. You need JavaScript enabled to view it. The white dwarf temperature scale and mass-radius relation

 


Note on the Hertzsprung-Russell Diagram

The astronomers convening at the RAS have called their meeting 'The Hertzsprung-Russell (HR) Diagram and Hipparcos'. The HR diagram is a simply a plot of intrinsic luminosity against temperature for a sample of stars. Each star is represented by a point on the diagram, determined by observation. Plotting data in this way has proved to be an immensely valuable tool for astronomers, providing insight into the physical nature of stars and the way they evolve. Hipparcos is helping improve the accuracy with which HR diagrams can be drawn up since determining a star's intrinisic luminosity depends on knowing its distance.

On the HR diagram, temperature runs from hot on the left to cool on the right. Luminosity increases up the vertical axis. Points representing ordinary stars, such as the Sun, fall on a diagonal band from the upper left to lower right, known to astronomers as 'the main sequence'. The position of a star on the main sequence is primarily determined by its mass, the most massive stars being the hottest and brightest, and vice versa. White dwarf stars, which are hot but very small, fall at the lower left, while red giants and supergiants, which are cool but very large, plot at the upper right.

The diagram is named after the Danish astronomer Ejnar Hertzsprung, who first drew up such a diagram in 1911, and the American Henry Norris Rusell, who independently realized its significance in 1913.

 

Issued by: Dr Jacqueline Mitton
RAS Public Relations Officer
Phone: Cambridge ((0)1223) 564914
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