The evolution of Red Supergiants to supernova in the LMC cluster NGC 2100 (1608.03895v1)

Abstract: The mass loss rates of red supergiants (RSGs) govern their evolution towards supernova and dictate the appearance of the resulting explosion. To study how mass-loss rates change with evolution we measure the mass-loss rates (\mdot) and extinctions of 19 red supergiants in the young massive cluster NGC2100 in the Large Magellanic Cloud. By targeting stars in a coeval cluster we can study the mass-loss rate evolution whilst keeping the variables of mass and metallicity fixed. Mass-loss rates were determined by fitting DUSTY models to mid-IR photometry from WISE and Spitzer/IRAC. We find that the \mdot\ in red supergiants increases as the star evolves, and is well described by \mdot\ prescription of de Jager, used widely in stellar evolution calculations. We find the extinction caused by the warm dust is negligible, meaning the warm circumstellar material of the inner wind cannot explain the higher levels of extinction found in the RSGs compared to other cluster stars. We discuss the implications of this work in terms of supernova progenitors and stellar evolution theory. We argue there is little justification for substantially increasing the \mdot\ during the RSG phase, as has been suggested recently in order to explain the absence of high mass Type IIP supernova progenitors. We also argue that an increase in reddening towards the end of the RSG phase, as observed for the two most evolved cluster stars, may provide a solution to the red supergiant problem.

The Evolution of Red Supergiants to Supernova in the LMC Cluster NGC 2100: A Study of Mass Loss Rates

The research paper discusses the evolution and mass loss rates of Red Supergiants (RSGs) in the Large Magellanic Cloud's (LMC) cluster NGC 2100, offering insights into their path towards becoming supernovae (SNe). By examining 19 RSGs in this coeval cluster, the paper aims to determine how mass-loss rates change as RSGs evolve, while keeping the variables of mass and metallicity constant.

Key Findings

• Mass-Loss Rates and Luminosity: The paper establishes a positive correlation between mass-loss rates and stellar luminosity, implying that mass loss increases substantially as RSGs evolve. The most luminous stars observed in the sample exhibit the highest mass-loss rates, suggesting that the mass-loss mechanism becomes stronger over time.
• Comparison with Prescriptions: The paper's observations are well modeled by existing mass-loss rate prescriptions, particularly those by de Jager (dJ88) and Reimers, commonly employed in stellar evolution calculations. These prescriptions were found to fit the data reliably, suggesting no need for significant revisions unless variable metallicity or mass effects are considered.
• Extinction Levels: The intrinsic extinction caused by circumstellar dust was found to be negligible, with an estimated optical extinction of $A_V$ derived from the models being approximately 0.01 mag. Nonetheless, isochrone fitting indicates that RSGs possess additional intrinsic extinction estimated to be $A_V$ ≈ 0.5 mag, not accounted for by inner dust winds.
• Enhanced Reddening: The paper identifies enhanced reddening in two of the most evolved stars in the sample, suggesting increased optical extinction. When considering this reddening as intrinsic extinction, a significant effect on inferred progenitor masses for Type II-P Supernovae is observed, potentially resolving discrepancies known as the "red supergiant problem."

Technical Implications

The paper provides valuable data on the increase in mass-loss rates with RSG evolution, sustaining the relevance of standard mass-loss rate prescriptions in predicting evolution paths for stars of sub-solar metallicity. The observation of enhanced reddening in more evolved RSGs poses questions about the extent to which circumstellar dust impacts extinction measurements and mass estimations. The confirmation of significant intrinsic extinction in RSGs has practical implications for how progenitor masses to SNe are estimated, thus addressing gaps in understanding massive stellar evolution.

Future Directions

Given the findings, further studies on RSGs at solar metallicity and in clusters with higher initial mass may yield insights applicable to broader mass-loss prescriptions, enhancing the accuracy of SNe progenitor mass evaluations. By addressing inconsistencies with theoretical predictions, future research could contribute to resolving longstanding ambiguities in stellar astrophysics, particularly concerning the lifecycle of massive stars in various environments.

Conclusion

This paper contributes significantly to the understanding of mass-loss processes in RSGs. By combining empirical modeling with optical and infrared observations, the paper provides robust insights into the evolution of massive stars and their ultimate fate as supernovae. As a focal point for addressing issues such as the "red supergiant problem," these findings have substantial implications for astrophysical models, serving as a springboard for future research in stellar evolution.