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Astron. Astrophys. 330, 910-936 (1998)

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A new optical reddening model for the solar neighborhood

Galactic structure through low-latitude starcounts from the Guide Star Catalogue

R.A. Méndez 1 and W.F. van Altena 2

1 European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748, Garching b. München, Germany (e-mail: rmendez@eso.org)
2 Yale University Observatory, P.O. Box 208101, New Haven, CT 06520-8101, USA (e-mail: vanalten@astro.yale.edu)

Received 19 February 1997 / Accepted 13 August 1997

Abstract

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.

We find that it is possible to predict starcounts in the range [FORMULA] with a mean accuracy of 15% or better for total samples of several thousand stars at [FORMULA], and for total reddening at 1 kpc of up to [FORMULA]  mag.

Self-consistency checks indicate that a differential optical absorption of 0.5 mag/kpc is adequate to reproduce, with our model, the available reddening maps in the distance range [FORMULA]  kpc.

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 [FORMULA]  pc, while the disk's scale-length is found to be [FORMULA]  kpc. While the derived value for [FORMULA] is quite sensitive to the adopted scale-height of disk stars, no big dependency of [FORMULA] on this parameter is found. These values should be taken, of course, with caution because of the inherent uncertainties in modeling optical starcounts in the presence of patchy reddening material.

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.

Key words: techniques: photometric – surveys – stars: distances – ISM: dust, extinction – Galaxy: fundamental parameters – Galaxy: structure

Present address: Cerro Tololo Inter-American Observatory, Casilla 603, La Serena, Chile, e-mail: rmendez@noao.edu

Send offprint requests to: R.A. Méndez

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This article was processed by the author using Springer-Verlag LATEX A&A style file L-AA version 3.

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© European Southern Observatory (ESO) 1998

Online publication: January 27, 1998
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