Variable Stars in the Newly Discovered Milky Way Dwarf Spheroidal Satellite Canes Venatici I

TL;DR

This study identifies variable stars in Canes Venatici I, estimates its distance, and characterizes its stellar populations, revealing a mainly old galaxy with some younger stars and a likely intermediate Oosterhoff type.

Contribution

It provides the first detailed analysis of variable stars and stellar populations in Canes Venatici I, including distance measurement and population complexity.

Findings

23 RR Lyrae stars identified

Distance estimated at 210 kpc

Galaxy hosts a complex stellar population

Abstract

We have identified 23 RR Lyrae stars and 3 possible Anomalous Cepheids among 84 candidate variables in the recently discovered Canes Venatici I dwarf spheroidal galaxy. The mean period of 18 RRab type stars is <Pab> = 0.60 +/-0.01 days. This period, and the location of these stars in the period-amplitude diagram, suggest that Canes Venatici I is likely an Oosterhoff-intermediate system. The average apparent magnitude of the RR Lyrae stars <V> = 22.17 +/-0.02 is used to obtain a precision distance estimate of 210 +7/-5 kpc, for an adopted reddening E(B-V)=0.03 mag. We present a B,V color-magnitude diagram of Canes Venatici I that reaches V about 25 mag, and shows that the galaxy has a mainly old stellar population with a metal abundance near [Fe/H] = -2.0 dex. The width of the red giant branch and the location of the candidate Anomalous Cepheids on the color-magnitude diagram may indicate that the galaxy hosts a complex stellar population with stars from about 13 Gyr to as young as about 0.6 Gyr.