The Leo IV dwarf spheroidal galaxy: color-magnitude diagram and pulsating stars

TL;DR

This study presents the first color-magnitude diagram and variable star analysis of the Leo IV dwarf galaxy, revealing its stellar population, distance, and Oosterhoff classification through RR Lyrae stars.

Contribution

First detailed photometric and variable star study of Leo IV, including its color-magnitude diagram and pulsating star population analysis.

Findings

Identified three RR Lyrae and one SX Phoenicis star in Leo IV.

Determined the galaxy's distance as approximately 154 kpc.

Found RR Lyrae stars suggest an Oosterhoff type II classification.

Abstract

We present the first V, B-V color-magnitude diagram of the Leo IV dwarf spheroidal galaxy, a faint Milky Way satellite recently discovered by the Sloan Digital Sky Survey. We have obtained B,V time-series photometry reaching about half a magnitude below the Leo IV turnoff, which we detect at V= 24.7 mag, and have performed the first study of the variable star population. We have identified three RR Lyrae stars (all fundamental-mode pulsators, RRab) and one SX Phoenicis variable in the galaxy. In the period-amplitude diagram the Leo IV RR Lyrae stars are located close to the loci of Oosterhoff type I systems and the evolved fundamental-mode RR Lyrae stars in the Galactic globular cluster M3. However, their mean pulsation period, $<P{\rm ab}>$=0.655 days, would suggest an Oosterhoff type II classification for this galaxy. The RR Lyrae stars trace very well the galaxy's horizontal branch, setting its average magnitude at $<V_{\rm RR}>= 21.48 \pm 0.03$ mag (standard deviation of the mean). This leads to a distance modulus of $\mu_{0}=20.94 \pm 0.07$ mag, corresponding to a distance of $154 \pm 5$ kpc, by adopting for the Leo IV dSph a reddening $E(B-V) = 0.04 \pm 0.01$ mag and a metallicity of [Fe/H] = -2.31 $\pm$ 0.10.