SDSS Absolute Magnitudes for Thin Disc Stars based on Trigonometric Parallaxes

TL;DR

This paper develops a new luminosity-colour relation for thin disc main-sequence stars using trigonometric parallaxes, matching Hipparcos and 2MASS data, and calibrates SDSS absolute magnitudes based on colour indices.

Contribution

It introduces a novel calibration method for SDSS absolute magnitudes of thin disc stars using combined astrometric and photometric data.

Findings

Calibrated SDSS absolute magnitudes for thin disc stars.

Provided transformation equations between 2MASS and SDSS photometries.

Enhanced understanding of space densities for bright stars in SDSS.

Abstract

We present a new luminosity-colour relation based on trigonometric parallaxes for thin disc main-sequence stars in SDSS photometry. We matched stars from the newly reduced Hipparcos catalogue with the ones taken from 2MASS All-Sky Catalogue of Point Sources, and applied a series of constraints, i.e. relative parallax errors ($\sigma_{\pi}/\pi\leq0.05$), metallicity ($-0.30\leq[M/H]\leq0.20$ dex), age ($0\leq t \leq 10$ Gyr) and surface gravity ($\log g>4$), and obtained a sample of thin disc main-sequence stars. Then, we used our previous transformation equations (Bilir et al. 2008a) between SDSS and 2MASS photometries and calibrated the $M_{g}$ absolute magnitudes to the $(g-r)_{0}$ and $(r-i)_0$ colours. The transformation formulae between 2MASS and SDSS photometries along with the absolute magnitude calibration provide space densities for bright stars which saturate the SDSS magnitudes.