Guy Perrin, winner in 2005 of the HP-SF2A award

1er mai 2005

The angular resolution of observational instruments, i.e. their capacity to distinguish two close point sources, grows in a linear way with the diameter of the collector. Our eye, sensitive in the visible, has an angular resolution of approximately an arc minute (1/60th of degree), that is to say 1/30th of the angular diameter of the Sun or the Moon seen from the Earth. The resolution of the space telescope Hubble at the same wavelengths, thanks to its pupil of 2,40 m, reaches 50 milli arcseconds. That is equivalent to the apparent diameter of the photosphere of the largest stars seen from the solar system. To resolve these stars, and other compact objects such as for example galaxy nuclei, it is thus necessary to increase the dimensions of the collectors to reach a few tens or even a few hundreds of meters. If a few tens of meters seem accessible today, it is necessary to go to interferometry to exceed this limit. It consists in making interfere the beams resulting from at least two telescopes, obtaining then an angular resolution given not by the size of the individual collectors but by the distance separating them. This technique is the speciality of Guy Perrin, winner in 2005 of the HP-SF2A award.

Figure 1 Observations par VINCI de la pulsation de L Car, de période de 35,5 jours. Les points sont les mesures interférométriques, et la courbe est l’ajustement déduit de l’intégration de la vitesse radiale, le long du cycle.

Figure 2 La taille moyenne des étoiles Mira et de leur enveloppe moléculaire est comparée à la taille du système solaire interne. Les orbites de la Terre, Mars et Jupiter sont représentées, ainsi que la position du Soleil. Quand le Soleil deviendra une étoile de type Mira dans environ 5 milliards d’années, il atteindra presque l’orbite de Mars, et son enveloppe moléculaire ira bien au delà de Mars. Cliquer sur l’image pour l’agrandir [en]Figure 2 Field of view of the instrument MIDI projected on the sky. The image in the background has been obtained by adaptive optics at 2,2 microns. The width of the slit of MIDI is 1 arc second. Click on the image to enlarge it

References

VLTI watches the pulsation of four southern Cepheids
Foreseeing the Sun’s fate : Astronomical interferometry reveals the close environment of Mira stars
First observation of an active galactic nucleus with the VLTI : resolution of the torus at the heart of NGC 1068

Contact

Guy Perrin
(Observatoire de Paris, LESIA)