A deep proper-motion survey in Kapteyn selected areas. I. Survey description and first results for stars in the tidal tail of Sagittarius and in the Monoceros Ring

We describe a high-precision, deep (to V similar to 19-21), absolute proper-motion survey that samples similar to 50 lines of sight in the Kapteyn selected areas along declination zones -15 degrees, 0 degrees, and 15 degrees. In many fields the astrometric baseline reaches nearly a century. We demonstrate that these data provide typical per star precisions between similar to 1 and 3 mas yr(-1) to the above magnitude limits, with the absolute reference frame established by numerous extragalactic sources in each survey field. Combined with existing and ongoing photometric and radial velocity surveys in these fields, these astrometric data will enable, among other things, accurate detailed dynamical modeling of satellite interactions with our Galaxy. In this contribution we describe the astrometric part of our survey and show preliminary results along the trailing tail of the Sagittarius dwarf galaxy, and in the Monoceros Ring region.