A new optical reddening model for the Solar neighborhood: Galactic Structure through low-latitude starcounts from the Guide Star Catalogue

A new optical reddening model for the Solar neighborhood is presented. The model makes use of the large-scale properties of the dust layer in the Galaxy, and of the observed clumpiness in its distribution, and it is used to compute starcounts in the plane of the Galaxy, which are compared to the observed counts from the Guide Star Catalogue (GSC) for a few representative regions having a range of reddening values. These comparisons provide a good test case in a wide variety of conditions with regards to both the amount and distribution of the reddening material along the line-of-sight. This is the first systematic study of low-Galactic latitude starcounts from the perspective of a Galactic structure and reddening model, and it is demonstrated that the model can be used to obtain meaningful starcount estimates in the plane of the Milky-Way. Our best-fit model to three (out of six) selected regions yields a distance of the Sun from the symmetry plane of the Galaxy of Z_Sun=27 +/- 3 (3 sigma) pc, while the disk's scale-length is found to be H_Disk= 6 +/- 2 (3 sigma) kpc. While the derived value for Z_Sun is quite sensitive to the adopted scale-height of disk stars, no big dependency of H_Disk on this parameter is found. The accuracy of the reddening and starcounts model opens the possibility of using it to estimate and compare observations of diffuse starlight to constrain the major structural parameters of the Galaxy, and to compute the distance distribution of stars self-consistently with the starcounts, in order to derive corrections to absolute parallax.