Photoelectric photometry and rotation periods of three large and dark asteroids: 49 Pales, 88 Thisbe and 92 Undina.

Photoelectric observations of the asteroids 49 PaTh 88 Thisbe and 92 Undina, all with diameters greater than 150 km, are presented. They were carried out by F. Scaltriti and V. Zappala at the Astronomical Observatorv of Torino and by H.J. Schober at Kitt Peak National Observatory and at the Observatoire de Haute Provence. For 49 Pales a rotation period P = 1() 42 + was found with a maximum amplitude of about 0.18 mag; an analysis of the opposition effect was also performed. 88 Thisbe shows a rough lightcurve with several small scale features; the period results: P = + 0ho()o.6 and the amplitude ranges from 0.19 to 0.16 mag. For 92 Undina the complete lightcurve was observed, not confirming the previous short observations by Porter and Wallentine (1977). The resulting rotation period is P =1 5h94 + and the amplitude is 0.17 mag. Key words: Asteroid - Lightcurve - 49 Pales - 88 Thisbe -92 Undina