Asymptotic Giant Branch Stars in the Leo I Dwarf Spheroidal Galaxy

TL;DR

This study identifies and analyzes 26 AGB variable stars in Leo I, revealing their age range, distribution, and dust obscuration events, and uses their properties to estimate the galaxy's distance.

Contribution

First detailed characterization of AGB variables in Leo I, including periods, amplitudes, and implications for stellar evolution and galaxy distance measurement.

Findings

AGB stars span a wide age range from 1.6 to over 10 Gyr.

Distance modulus of Leo I determined as 21.80 ± 0.12 mag.

Old Miras found in outer regions, testing stellar evolution models.

Abstract

Twenty six Asymptotic Giant Branch (AGB) variables are identified in the Local Group galaxy Leo I. These include 7 Mira and 5 semi-regular variables for which periods, amplitudes and mean magnitudes are determined. The large range of periods for the Miras, 158<P<523 days, suggests an AGB spanning a significant age range. The youngest must be around 1.6 Gyr while the oldest could be 10 Gyr or more. Two of these old Miras are found in the outer regions of Leo I (over 490 arcsec from the centre) where stars on the extended AGB are rare. They could provide an interesting test of third dredge-up and mass loss in old stars with low metallicity and are worth further detailed investigation. At least two stars, one a Mira, the other an irregular variable, are undergoing obscuration events due to dust ejection. An application of the Mira period-luminosity relation to these stars yields a distance modulus for Leo I of (m-M)=21.80 \pm 0.11 mag (internal), \pm 0.12 (total) (on a scale that puts the LMC at 18.39 mag) in good agreement with other determinations.