1 Introduction

The Ae and A type shell stars which constitute a small group with less than one hundred members, seems to be an extension of the well studied Be stars into the domain of lower temperatures. These stars have received less attention than the hotter Be type stars, as their variations are less spectacular than the changes in Be type stars and might be slower. Difficulties for describing the variations come from that most of the descriptions are only verbal descriptions, without recourse to measures (equivalent widths), which makes studies of variability rather uncertain.

A-type shell stars are of great interest since shell characteristics appear in three types of A-type objects, namely stars with Infrared (IRAS)excess (Jaschek et al. 1991), $\lambda$ Boo stars (Andrillat et al. 1995) and $\b$ Pic objects. A better knowledge of the known shell stars should thus enable astronomers to improve the status of the frontier cases and to better delimit object categories. For example are shell systems an intermediate step toward $\b$ Pic type systems?

The present paper provides some quantitative data for the red and infrared regions. We previously studied these stars (Jaschek et al. 1988, 1991), in both the photographic and the near infrared regions.