We present in this work secondary catalogs up to mV al \, ~ \, 13 based on the Tycho reference frame (ESA, 1997) for 12 selected low-extinction fields towards the galactic bulge. The observations have been performed with the Askania-Zeiss Meridian Circle equiped with a CCD camera, located at the Abrahão de Moraes Observatory (Valinhos, Brazil) and operated by the Institute of Astronomy and Geophysics, São Paulo University. The presented catalog, though not complete, has been designed to help in intensive search programmes (e.g. microlensing and variable searches) and therefore the selected standards have a high astrometric and photometric (V band, approximately) quality. The mean precisions obtained were 0.0018ˢ in α, $0.013''$ in δ, 0.030 for the standard deviation in magnitude and 0.0042 for the magnitude when weighted with the error bars in each night (in the mean, 42 stars for the catalog of each window).
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Dominici et al. (1999) studied this question.