AGB Stars in the Fornax Dwarf Spheroidal Galaxy

TL;DR

This study investigates the asymptotic giant branch stars in the Fornax dwarf galaxy using infrared observations, identifying variable stars, analyzing their properties, and deriving a precise distance estimate consistent with other methods.

Contribution

It provides a detailed characterization of AGB stars in Fornax, including variable star properties and a refined distance measurement using Mira period-luminosity relations.

Findings

Identification of 7 Mira variables and 10 semi-regular variables in Fornax.

Derived a distance modulus of 20.69 for Fornax, consistent with other estimates.

Isochrone models reproduce many observed AGB characteristics.

Abstract

We report on a multi-epoch study of the Fornax dwarf spheroidal galaxy, made with the Infrared Survey Facility, over an area of about 42'x42'. The colour-magnitude diagram shows a broad well-populated giant branch with a tip that slopes down-wards from red to blue, as might be expected given Fornax's known range of age and metallicity. The extensive AGB includes seven Mira variables and ten periodic semi-regular variables. Five of the seven Miras are known to be carbon rich. Their pulsation periods range from 215 to 470 days, indicating a range of initial masses. Three of the Fornax Miras are redder than typical LMC Miras of similar period, probably indicating particularly heavy mass-loss rates. Many, but not all, of the characteristics of the AGB are reproduced by isochrones from Marigo et al. for a 2 Gyr population with a metallicity of Z=0.0025. An application of the Mira period-luminosity relation to these stars yields a distance modulus for Fornax of 20.69+/-0.04 (internal), +/-0.08 (total) (on a scale that puts the LMC at 18.39 mag) in good agreement with other determinations. Various estimates of the distance to Fornax are reviewed.