1 Introduction

The properties of the local interstellar medium has been probed by several different techniques. As a result, there are evidences that the solar vicinity is a relatively depleted volume with an irregular shape. Such volume is usually called the Local Bubble and may be surrounded, at least in some directions, by large interstellar structures composing the surface of other bubbles, like the Loop I Bubble which is seen toward the whole fourth galactic quadrant. Among the techniques usually used to investigate the interstellar medium one may mention the measurement of the linear polarization of starlight, one of the most readily observable phenomena arising from the partial alignment of the aspherical interstellar dust grains. Although the alignment mechanism is not fully understood, it is clear that the galactic magnetic field is responsible for this alignment, with the long axes of the grains tending to become orientated perpendicular to the field lines.

The knowledge of the linear polarization of starlight is important because it provides information on grain properties and also on the galactic magnetic field. The distribution of polarization vectors with respect to galactic coordinates has been investigated by a number of authors (Axon & Ellis 1976, and references therein), of which the most extensive data sets are those published by Mathewson & Ford (1970) and Klare et al.(1972). On the other hand, high precision polarimetry has been used by some authors to investigate the nearby low column volume (Tinbergen 1982; Leroy 1993a).

In this paper we introduce UBV linear polarization measurements collected for 361 A- and F-type stars with accurate distance and colour excess determination. A search in the available literature showed that only five of them have previous polarimetric measurements.