A New Tool for Studying Galactic

We here describe a new synthetic catalogue generator , based on a statistical model of the Galaxy, and use it to model the spatial and kinematic distribution of a subset of the Hipparcos Catalogue, speciically OB stars in the plane of the Galaxy. To accurately model this stellar population a method is developed which does not make the usual assumption of uniformity across the eld. This population is shown to be best described by a non-axisymmetric spatial distribution. Many of the Galactic parameters are found by a manual adjustment to recover the observed properties of the selected Hipparcos sample. 1. MOTIVATION Circumstances dictate that our determination of the large scale structure of our Galaxy be indirect, as we view it from an uniquely internal perspective. Therefore studies of the stellar components of the Milky Way have relied upon Galactic models that give a statistical description of the stellar distribution, and the synthetic catalogues produced from them (Bahcall & Soniera 1980, Robin & Cr ez e 1986, Ratnatunga et al. 1989). The parameters and components of the model will presumably describe physically meaningful stellar populations. Here we present a model of a single stellar component of our Galaxy: the young OB stars in the direction of the anti-center. We have chosen this population in order to study the warp of the Galaxy, as we expect this young population to trace the gaseous warp that has long been known from HI observations. Evidence of the Galactic Warp is investigated in Smart et al. (1997, hereafter SDL), as well as a detailed description of the Hipparcos data set that was studied; here we present our synthetic catalogue generation program and the stellar distribution model upon which it is based. The challenges of modeling this stellar component include its large eld upon the sky (70 < l < 290), its sparseness (0.07 per square degree), its natural location at low galactic latitudes and the consequential importance of absorption. To meet these challenges we present a synthetic catalogue generation program which is designed to build stellar catalogues over large regions of the sky without the usual assumption of uniformity across the eld or sub-elds, but instead generates the spatial distribution accurately throughout the entire volume. We also show that the distribution of our chosen young stellar population is better described by a non-axisymmetric distribution then the usual axisymmetric model. Absorption is calculated from a model …