Pulsation-Initiated Mass Loss in Luminous Blue Variables: A Parameter Study

TL;DR

This study investigates how pulsations triggered by opacity changes near the iron bump can initiate mass loss in luminous blue variables, providing insights into the conditions leading to their outbursts.

Contribution

It presents a parameter study identifying conditions under which pulsation-driven mass loss occurs in LBVs, focusing on the effects of composition on pulsation amplitude and outburst likelihood.

Findings

Higher helium abundance reduces pulsation amplitude.

Lower metallicity increases likelihood of outburst-like behavior.

Pulsation amplitude correlates with outburst potential.

Abstract

Luminous blue variables (LBVs) are characterized by semi-periodic episodes of enhanced mass-loss, or outburst. The cause of these outbursts has thus far been a mystery. One explanation is that they are initiated by kappa-effect pulsations in the atmosphere caused by an increase in luminosity at temperatures near the so-called ``iron bump'' (T ~ 200,000 K), where the Fe opacity suddenly increases. Due to a lag in the onset of convection, this luminosity can build until it exceeds the Eddington limit locally, seeding pulsations and possibly driving some mass from the star. We present some preliminary results from a parameter study focusing on the conditions necessary to trigger normal S-Dor type (as opposed to extreme eta-Car type) outbursts. We find that as Y increases or Z decreases, the pulsational amplitude decreases and outburst-like behavior, indicated by a large, sudden increase in photospheric velocity, becomes likes likely.