Hipparcos: Folded Light Curves
The light curves on this page are taken from Volume 12: Part A of The Hipparcos and Tycho Catalogues. This contains `folded' light curves for periodic stars. The variability period for each star was either known before the Hipparcos mission, or more typically was refined or discovered as part of the data reductions of the Hipparcos data by groups at the Royal Greenwich Observatory (UK) or Geneva Observatory (Switzerland).
Hipparcos acquired an estimate of the magnitude of each star at 100-150 times throughout the four-year mission. If the star varies regularly in its brightness, the period of variability can often be determined (sometimes with great difficulty!). By `folding' the data points at this period, the light curve of the variable star is built up.
In each plot, the vertical axis gives the magnitude of the star at each observation. The horizontal axis gives the `phase' of the light curve, where the phase runs from 0 (start of the period) to 1 (end of the period), with the phase from 1 to 1.5 repeated for clarity. The data points mark the magnitude of the star when it was observed (after lengthy calibration by the Hipparcos scientific teams!) and the vertical ticks indicate the estimated errors on each magnitude estimate. The orange curve marks the variability signature that was fitted to the light curves in the process of determining the periods.
Note the very different types of variability, the different amplitudes, and the different brightnesses of these systems. You will see that the `error bars' are typically smaller when the star is brighter - the error bars are almost invisible for the brightest stars. Some objects are very well `behaved' in their variability signature; others are seen to be a little more erratic!
The 10 examples shown here are representative of 2693 Hipparcos objects whose light curves are given in the Hipparcos Catalogue.