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Wideband photometry of Saturn in 2006-2007.

Article Excerpt
ABSTRACT

The writer carried out brightness measurements of Saturn and its rings with four different color filters. The selected normalized magnitudes of Saturn + rings for a ring tilt angle of 14[degrees] are B(1,0) = -8.25[+ or -]0.03, V(1,0) = -9.36[+ or -]0.03, R(1,0) = -10.01[+ or -]0.04 and 1(1,0) = -10.16[+ or -]0.04. The opposition surge values for Saturn + rings on Feb. 11, 2007 (solar phase angle = 0.15[degrees]) were 0.19 and 0.06 magnitudes for the B and V filters respectively. The writer concludes that the B-V and V-R color indexes of Saturn + rings do not change much when the solar phase angle drops from 6[degrees] to 1[degrees]. The rings become a little bluer though as the solar phase angle drops from 1[degrees] to 0[degrees] due to the larger opposition surge in blue light.

Key Words: Saturn, photoelectric photometry, opposition surge

INTRODUCTION

Several recent studies show that Saturn undergoes seasonal and other changes, which may affect its brightness and color. Two groups of astronomers Perez-Hoyos et al. (1) and Karkoschka and Tomasko (2) report that Saturn's haze layers undergo seasonal changes. Karkoschka and Tomasko report that Saturn's aerosol particles grew larger between 1995 and 2003. Perez-Hoyos and co-workers report that HST images show that the tropospheric haze at 10[degrees] S, 40[degrees] S and 73[degrees] S grew darker in blue (439 nm) light between 1996 and 2003. This change is probably due to seasonal changes. McGhee and co-workers (3) report that Saturn's B ring has spokes that are probably made up of ~1 micron particles that lie either above or within the ring. They point out that the spokes are most obvious at low ring tilt angles.

Brightness measurements of Saturn and its rings covering at least one cycle of Saturn seasons (29.5 years) will reveal information on seasonal brightness and color changes. These measurements will also yield information on how the rings change in brightness and color with changing ring tilt and solar phase angles. In this report, I will summarize my brightness measurements made of Saturn between Oct. 30, 2006 and April 13, 2007. The purpose of this work is fourfold:

1) Gain...

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