Wind-envelope interaction as the origin of the slow cyclic brightness variations of luminous blue variables
| Autor: | Grassitelli, Luca, Langer, Norbert, Mackey, Jonathan, Graefener, Goetz, Grin, Nathan, Sander, Andreas, Vink, Jorick |
|---|---|
| Rok vydání: | 2020 |
| Předmět: | |
| Zdroj: | A&A 647, A99 (2021) |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1051/0004-6361/202038298 |
| Popis: | Luminous blue variables (LBVs) are hot, very luminous massive stars displaying large quasi-periodic variations in brightness, radius,and photospheric temperature, on timescales of years to decades. The physical origin of this variability, called S Doradus cycle after its prototype, has remained elusive. Here, we study the feedback of stellar wind mass-loss on the envelope structure in stars near the Eddington limit. We perform a time-dependent hydrodynamic stellar evolutionary calculation, applying a stellar wind mass-loss prescription with a temperature-dependence inspired by the predicted systematic increase in mass-loss rates below 25 kK. We find that when the wind mass-loss rate crosses a well-defined threshold, a discontinuous change in the wind base conditions leads to a restructuring of the stellar envelope. The induced drastic radius and temperature changes, which occur on the thermal timescale of the inflated envelope, impose in turn mass-loss variations that reverse the initial changes, leading to a cycle that lacks a stationary equilibrium configuration. Our proof-of-concept model broadly reproduces the typical observational phenomenology of the S Doradus variability. We identify three key physical ingredients needed to trigger the instability: inflated envelopes in close proximity to the Eddington limit, a temperature range where decreasing opacities do not lead to an accelerating outflow, and a mass-loss rate that increases with decreasing temperature, crossing a critical threshold value within this temperature range. Our scenario and model provide testable predictions, and open the door for a consistent theoretical treatment of the LBV phase in stellar evolution, with consequences for their further evolution as single stars or in binary systems. Comment: A&A Accepted, 14 pages, many colorful figures |
| Databáze: | arXiv |
| Externí odkaz: |
|