Yellow supergiants as supernova progenitors: an indication of strong mass loss for red supergiants?

Abstract: The increasing observed number of supernova events allows for finding ever more frequently the progenitor star in archive images. In a few cases, the progenitor star is a yellow supergiant star. The estimated position in the Hertzsprung-Russell diagram of these stars is not compatible with the theoretical tracks of classical single star models. According to several authors, the mass-loss rates during the red supergiant phase could be underestimated. We study the impact of an increase of these mass-loss rates on the position of 12 to 15 M\odot stars at the end of their nuclear life, in order to reconcile the theoretical tracks with the observed yellow supergiant progenitors. We perform calculations of 12 to 15 M\odot rotating stellar models using the Geneva stellar evolution code. To account for the uncertainties in the mass-loss rates during the RSG phase, we increase the mass-loss rate of the star (between 3 and 10 times the standard one) during that phase and compare the evolution of stars undergoing such high mass-loss rates with models computed with the standard mass-loss prescription. We show that the final position of the models in the Hertzsprung-Russell diagram depends on the mass loss they undergo during the red supergiant phase. With an increased mass-loss rate, we find that some models end their nuclear life at positions that are compatible with the observed position of several supernova progenitors. We conclude that an increased mass-loss rate (whom physical mechanism still need to be clarified) allows single star models to reproduce simultaneously the estimated position in the HRD of the YSG SN progenitors, as well as the SN type.

• The paper investigates yellow supergiants as supernova progenitors, proposing that significantly increased mass-loss rates during the red supergiant phase can reconcile theoretical stellar models with observed progenitor locations.
• Using the Geneva stellar evolution code, the study simulated stellar models with 3 to 10 times higher mass-loss rates during the RSG phase, showing these enhanced rates align models with observed YSG progenitor locations on the Hertzsprung-Russell diagram.
• This research implies a need to revise mass-loss mechanisms for red supergiants, potentially explaining the observed lack of Type IIP supernovae from massive RSG stars and suggesting areas for future study.

Yellow Supergiants as Supernova Progenitors: Investigating Mass Loss in Red Supergiants

This paper by Cyril Georgy offers a detailed examination of yellow supergiants (YSGs) that act as progenitors for supernovae and suggests that current models underestimate the mass-loss rates during the red supergiant (RSG) phase. By analyzing stellar models with increased mass-loss rates, this work attempts to reconcile discrepancies between observed supernova progenitors and theoretical evolutionary tracks in the Hertzsprung-Russell diagram (HRD).

Study Motivation and Background

The detection of supernova events has increased significantly, providing valuable data about the progenitor stars. Traditionally, single-star evolution models locate these progenitors on the HRD either on the red supergiant branch or in the Wolf-Rayet (WR) star region. However, the observation of supernova progenitors like SN 2008ax, SN 1993J, SN 2008cn, SN 2009kr, and SN 2011dh, which are classified as yellow supergiants, presents a challenge to the classical models, suggesting a necessity for revised mass-loss prescriptions during the RSG phase.

Methodology

The study employs the Geneva stellar evolution code to simulate the evolution of rotating stellar models with an initial mass of 12 to 15 solar masses, $M_{\sun}$. The central hypothesis is investigated by increasing mass-loss rates during the RSG phase by factors of 3 to 10 times the standard mass-loss prescriptions. This computational framework allows for a comparison between models that follow the conventional mass-loss rates and those with augmented rates, assessing their final positions on the HRD.

Results

The study reveals that increased mass-loss rates significantly influence the evolutionary paths of the stars. Specifically, the enhanced rates cause stellar models to end their nuclear lives in positions on the HRD more consistent with observed YSG supernova progenitors' locations. The work indicates that by adopting higher mass-loss rates, theoretical models can simulate the conditions necessary for a single star to produce YSG progenitors compatible both in final position on the HRD and supernova type—fitting particularly well for SN types IIL and IIb.

Implications and Future Work

This research implies a need to revisit the mechanisms regulating mass loss during the RSG phase, with potential candidates like pulsation-driven winds or binary interactions being significant areas for future exploration. The models with increased mass loss also show promise in explaining the observed absence of type IIP supernovae coming from massive RSG stars.

Continued investigation is advised, focusing on further refinement of mass-loss mechanisms alongside a broader parameter study that includes various initial masses, rotations, and metallicities to enrich understanding and predictive accuracy.

In summary, while this study convincingly demonstrates that increased mass-loss rates align single-star models with observed YSG supernova progenitors, elucidating the exact physical processes underpinning such rates remains an open question requiring further empirical and theoretical scrutiny.