On the Enhancement of Mass Loss in Cepheids Due to Radial Pulsation. II. The Effect of Metallicity

TL;DR

This study models pulsation-driven mass loss in Cepheids across different metallicities, revealing that lower metallicity Cepheids may experience higher mass loss rates, affecting their infrared brightness and Period-Luminosity relations.

Contribution

It applies a pulsation-driven mass loss model to Cepheids with varying metallicities, highlighting the counterintuitive increase in mass loss at lower metallicities.

Findings

Mass loss may be larger for lower metallicity Cepheids.

Mass-loss rates vary from 10^{-9} to 10^{-7} solar masses per year.

Infrared brightness increases by about a magnitude due to mass loss.

Abstract

It has been observed that Cepheids in the Magellanic Clouds have lower masses for the same luminosity than those in the Milky Way. The model, from Neilson & Lester (2008), of pulsation-driven mass loss for Cepheids is applied to theoretical models of Cepheids with metallicity consistent with the Milky Way and Large and Small Magellanic Clouds. The mass-loss model is analyzed using the metallicity correction of the Period-Luminosity relation to compare the ratio of mass loss of Cepheids with lower metallicity to that of Cepheids with solar metallicity. It is determined that mass loss may be larger for the lower metallicity Cepheids, counterintuitive to radiative driving estimates. Also the mass-loss rates of theoretical Cepheid models are found to be up to $5\times 10^{-9}$ for Galactic Cepheids, $5\times 10^{-8}$ for Large Magellanic Cloud Cepheids, and $2\times 10^{-7}M_\odot /yr$ for Small Magellanic Cloud Cepheids. It is argued that mass loss increases as metallicity decreases for Cepheids with periods less than 20 days and that mass loss decreases for longer periods. Assuming dust forms in the wind of a Cepheid at some distance, the infrared excess of the models is computed, finding the infrared brightness is approximately a magnitude larger due to mass loss. The infrared magnitudes are compared to recently published Period-Luminosity relations as a test of our predictions.