# Milky Way tomography with the SkyMapper Southern Survey: I: Atmospheric parameters and distances of one million red giants

## TL;DR

This paper presents a photometric method to determine atmospheric parameters and distances for nearly one million red giant stars using SkyMapper data, Gaia parallaxes, and spectroscopic surveys, enabling detailed Galactic studies.

## Contribution

The study introduces a novel photometric approach to estimate stellar parameters and distances for large samples of red giants, combining SkyMapper data with Gaia and spectroscopic surveys.

## Key findings

- Achieved ~80 K precision for T_eff, ~0.18 dex for [Fe/H], and ~0.35 dex for log g.
- Median distance uncertainty of 16% for distant stars using photometric methods.
- Derived parameters for nearly one million red giants from SkyMapper DR1.1.

## Abstract

Accurate determinations of atmospheric parameters (effective temperature $T_{\rm eff}$, surface gravity log $g$ and metallicity [Fe/H]) and distances for large complete samples are of vital importance for various Galactic studies. We have developed a photometric method to select red giant stars and estimate their atmospheric parameters from the photometric colors provided by the SkyMapper Southern Survey (SMSS) data release (DR) 1.1, using stars in common with the LAMOST Galactic spectroscopic surveys as a training set. Distances are estimated with two different approaches: one based on the Gaia DR2 parallaxes for nearby ($d \leq 4.5$ kpc) bright stars and another based on the absolute magnitudes predicted by intrinsic color $(g-i)_0$ and photometric metallicity [Fe/H] for distant ($d > 4.5$ kpc) faint stars. Various tests show that our method is capable of delivering atmospheric parameters with a precision of $\sim$80 K for $T_{\rm eff}$, $\sim$0.18 dex for [Fe/H] and $\sim$0.35 dex for log $g$, but with a significant systematic error at log $g \sim$ 2.3. For distances delivered from $(g-i)_0$ and photometric [Fe/H], our test with the member stars of globular clusters show a median uncertainty of 16 per cent with a negligible zero-point offset. Using this method, atmospheric parameters and distances of nearly one million red giant stars are derived from SMSS DR1.1. Proper motion measurements from Gaia DR2 are available for almost all of the red giant stars, and radial velocity measurements from several large spectroscopic surveys are available for 44 per cent of these. This sample will be accessible online at https://yanghuang0.wixsite.com/yangh/research .