Southern Standard Stars for the u'g'r'i'z' System:

An Introduction

The Sloan Digital Sky Survey (SDSS) is a five-color imaging survey with spectroscopic follow-up of the Northern Galactic Cap region, approximately one-quarter of the entire sky. During the first phase of the SDSS (SDSS-1) during the 5 year period from 2000 to 2005, the SDSS obtained five-color imaging data for approximately 100 million objects and the positions for each of these objects. Using the colors and magnitudes the survey selected approximately 1 million objects for spectroscopic follow-up observations. These objects were primarily galaxies and quasars and the spectra enable us to obtain distances to them, thus allowing us to build a 3-D map of the northern Galactic cap. However, roughly half of the objects in the imaging survey are stars in our own Galaxy. Furthermore, the second phase of the SDSS (SDSS-2) has a large stellar and Galactic Structure component. There are several survey projects in both SDSS-1 and SDSS-2 designed for looking at the more interesting of these stars as well as the mundane ones. However, to make sense of all this, we have to define what we mean when we say a star is a certain brightness or has a certain color.

We use well-observed, non-varying stars called "standard stars" to make these definitions. The SDSS uses a group of 158 standard stars spread around the northern sky that are used as the basis of the magnitude (or brightness) and color (difference in magnitudes between two different colored filters) determinations for the survey objects. This information is then used to select, based on color and brightness, the spectroscopic candidates for the survey.

All that is well and good but, the northern standard stars are really only useful in the northern hemisphere. So, we have embarked on this project to create a set of standard stars in the SDSS u'g'r'i'z' filter system for the southern hemisphere. This project will take approximately four years to gather enough observations to assign magnitudes (brightnesses) to the set of selected stars.

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