Photoelectric photometry of asteroids 33 Polyhymnia and 386 Siegena

Abstract

Photometric parameters of the asteroids 33 Polyhymnia and 386 Siegena were obtained during an international campaign performed at three observatoroes: Table Mountain Observatory (A. W. Harris), European Southern Observatory (ESO; C.-I. Lagerkvist), and Catania Astrophysical Observatory (V. Zappalá and F. Scaltriti). The photoelectric observations were carried out in the period August 15–September 14, 1980. The rotational periods and amplitudes observed are: P syn = 9 h dot 763 ± 0 h dot , Ampl. = 0 m dot 11 ± 0 m dot 01 for Siegena and P syn = 18 h dot 601 ± 0 h dot 004, Ampl. = 0 m dot 14 (near opposotion) and Ampl. = 0 m dot 17 ± 0 m dot 01 (at ∼10° phase angle) for 33 Polyhymnia. The multiple-scattering factor Q [as defined by K. Lumme and E. Bowell, Astron. J. 86, 1694–1704, 1705–1721 (1981a,b)] is found to be 0.15 ± 0.06 for 386 and 0.26 ± 0.03 for 33, implying higher albedos in each case than expected according to their taxonomic classes, C and S, respectively [ E. Bowell, T. Gehrels, and B. Zellner, in Asteroids, pp. 1108–1129, Univ. of Arizona Press, Tucson (1979) ]. The color indices B - V and U - B, were measured and found to differ significantly from those given by Bowell et al.. Our values are, for 386, B - V = 0.71 and U - B = 0.36; and for 33, B - V = 0.81 and U - B = 0.39.