EARLY RESULTS FROM HIPPARCOS DATA
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:
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)
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