1 Introduction

This paper is the second of a series on the chemically peculiar (CP) stars, especially the magnetic types. We are systematically comparing their elemental abundances with those theories which try to explain their substantially non-solar elemental abundances, such as the various radiative diffusion scenarios of Michaud (1970) and his collaborators. Paper I (Lopez-Garcia & Adelman 1993) concerned the silicon star HD 43819 and the CP star HD 147550, which we discovered was a very cool HgMn star. For this paper we selected two silicon stars.

Bonsack (1977) studied the magnetic field and radial velocity of HD 133029 (= HR 5597 = ADS 9477A) and found radial velocity variations with a period of 2.88706 days which were consistent with the photometric variations documented by Winzer (1974) and by Wolff & Morrison (1975). Rather than periodic magnetic field strength variations, Bonsack found that significant and sometimes rapid ($\geq$500 G hour^-1) variations occur. His effective magnetic field strength measurements using Zeeman spectroscopy range from 850 to 3300 G. Borra & Landstreet (1980) found + 2905 to 4065 G using H$\beta$ and argued that Bonsack's observations are not necessarily incompatible with their observed smooth variability of $H_{\rm e}$. Bonsack (1977) found definite evidence that certain lines vary in strength and derived v sin i=21 km s^-1, similar to Preston's (1971) upper limit. Spectrophotometry by Adelman & White (1980) revealed quite broad continuum features at both $\lambda$4200 and $\lambda$5200 with some evidence for the $\lambda$6300 feature. Recently Adelman (1998) reported that differential uvby photometry obtained with the Four College Automated Photometric Telescope (FCAPT) indicated a period of 2.88756 $\pm$ 0.00004 days and amplitudes of variability of 0.020 to 0.025 mag. Each magnitude has a single wave low amplitude light curve. These are crudely in phase, yet show details which suggest a complex photometric behavior whose explanation apparently requires regions with enhanced elemental abundances whose geometry is not that of spots at the magnetic poles; this is in accord with the magnetic diffusion hypothesis (Shore & Adelman 1974, 1976) as the magnetic latitude at which maximum elemental abundance occurs does not necessarily have to be at the poles.

Osawa (1965) classified HD 192913 as a silicon star. It is one of the sharpest-lined Si stars with v sin i of 14 km s^-1 (Preston 1971). Differential FCAPT uvby photometry of HD 192913 by Adelman & Knox (1994) resulted in a period of 16.829 $\pm$ 0.002 days, a value which is close to previous studies by Bartolini et al. (1974), Winzer (1974), Schoneich et al. (1976), and Musielok et al. (1980). This star shows an asymmetric single wave photometric variability with the broad minimum showing evidence for two sub-minima. Optical spectrophotometry (Adelman 1982) showed a definite $\lambda$5200 feature while the other three spectrophotometric anomalies are absent (Adelman & Pyper 1993). Ryabchikova et al. (1990) concluded that the metal lines change with the photometric period.