Metallicities and ages of stellar populations at a high Galactic latitude field

TL;DR

This study analyzes stellar metallicities and ages at high Galactic latitudes using $UBVRI$ data, revealing a mostly uniform abundance distribution with some halo stream contamination, and discusses the limitations of UVX methods for distant halo stars.

Contribution

It provides a recalibrated UVX method for estimating metallicities and ages of stars in a high-latitude field, comparing vertical abundance distributions with previous studies.

Findings

Abundance distribution is mostly uniform with [Fe/H] = -0.8 for thick disk and -1.4 for halo.

Presence of outliers suggests possible halo stream contamination.

UVX method has limited sensitivity for very metal-poor distant halo stars.

Abstract

We present an analysis of $UBVRI$ data from the Selected Area SA 141. By applying recalibrated methods of measuring ultraviolet excess (UVX), we approximate abundances and absolute magnitudes for 368 stars over 1.3 square degrees out to distances over 10 kpc. With the density distribution constrained from our previous photometric parallax investigations and with sufficient accounting for the metallicity bias in the UVX method, we are able to compare the vertical abundance distribution to those measured in previous studies. We find that the abundance distribution has an underlying uniform component consistent with previous spectroscopic results that posit a monometallic thick disk and halo with abundances of $[Fe/H]$ = $-$0.8 and $-$1.4, respectively. However, there are a number of outlying data points that may indicate contamination by more metal-rich halo streams. The absence of vertical abundance gradients in the Galactic stellar populations and the possible presence of interloping halo streams would be consistent with expectations from merger models of Galaxy formation. We find that our UVX method has limited sensitivity in exploring the metallicity distribution of the distant Galactic halo, owing to the poor constraint on the $UBV$ properties of very metal-poor stars. The derivation of metallicities from broadband $UBV$ photometry remains fundamentally sound for the exploration of the halo but is in need of both improved calibration and superior data.