1 Introduction

The STIS CCD camera on-board Hubble Space Telescope has been providing an unique view of faint galaxies. The characteristics of this instrument which offers good depth, excellent resolution and a good sampling of the HST PSF, together with the possibility of obtaining data using the parallel observing mode, makes it a suitable instrument for studies such as the STIS Parallel Shear Survey (hereafter refered as SPSS), whose main goal is the study of cosmic shear on scales below one arcminute. Data for this program started to be collected on September 24th, 2000, within the scope of an HST GO cycle 9 parallel proposal (8562 and 9248, P.I.: P. Schneider) and up to date, more than 500 different pointings have been obtained. The use of STIS CCD imaging in the CLEAR filter mode allows to combine good spatial resolution (originally 0.05'' per pixel) with very deep exposures since the CCD is un-filtered and sensitive to wavelengths between 2500 and 11 000 Å (Pirzkal et al. 2001). We report in this paper the discovery of a conspicuous alignment of galaxies in a deep exposure obtained with that program. This field contains several high-ellipticity galaxies which seem oriented around a point near the center of the field giving a striking visual impression that caught our attention. Also, there are several fainter galaxies in this field which also contribute to the visual impression of an alignment of galaxies. We used the aperture mass technique and an analysis of the most elliptical objects in the field to try to quantify the significance of this effect and test the visual impression. Section 2 describes our data and the reduction procedure. The core of Sect. 3 presents the aperture mass analysis, discussing the significance of the peak of mass obtained and the errors on its position. Section 4 presents the most elongated objects in the field, and discusses their orientation with respect to the peak found with the aperture mass technique. We discuss also in this part the similar characteristics of 2 of these candidate arclets that could be compatible with being multiply imaged. Finally, Sect. 5 summarizes and discusses the indications presented in the paper which, taken together, could make a case for the presence of a possible underluminous lens in this field.