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The Role of Asteroseismology in Understanding Mass Loss in Red Giants

Sibel Örtel, Mutlu Yıldız

TL;DR

This study uses six APOKASC-2 red giants to constrain mass loss during the RGB by constructing interior models with MESA and comparing predicted asteroseismic properties ($Δν$, $ν_{max}$, $ΔΠ_1$) against observations. By exploring grids over initial mass $M_0$, initial metallicity $Z_0$, and mass-loss efficiency $η$ under Reimers’ law, the authors show that mass loss is required for these stars to occupy their observed RGB/RC positions, with $ΔM_{ m RGB}$ in the range $0.1$–$0.3~M_igodot$ and ages around $9$–$9.5$ Gyr. They demonstrate that mass loss increases with metallicity and decreases with higher initial mass, and that asteroseismic constraints can distinguish RC from RGB-descending interiors, though degeneracies persist. For two RC stars, RC models provide excellent fits to $Δν$, $ΔΠ_1$, and $T_{ m eff}$, while several RGB-descending stars require substantial mass loss to avoid unrealistically old ages from mass-conservative histories. Overall, the work underscores the power of asteroseismology to quantify RGB mass loss and to resolve evolutionary states, guiding future precision improvements with more complete seismic diagnostics.

Abstract

Red giant stars play a key role in advancing our understanding of stellar mass loss. However, its initial mass and the amount of mass lost during this phase remain uncertain. In this study, we investigate the asteroseismic signatures of mass loss and the parameters that influence it. We examine six stars identified as red giant branch (RGB) stars in the APOKASC-2 catalog. Assuming these stars are on their first ascent of the RGB, we construct interior models. The resulting model ages are significantly older than the age of the Galaxy, indicating that these stars are likely experiencing mass loss and evolving toward the red clump (RC) phase. The minimum possible initial masses are estimated using the mass-metallicity diagram, from which we infer that the minimum mass lost by these stars ranges from $0.1$-$0.3{\rm M}_{\odot}$. Models constructed with an initial minimum mass yield the maximum possible age of the star. The ages of these models fall within the range of 9-9.5Gyr. For two stars, asteroseismic parameters confirm RC classification. Due to degeneracies in the HR diagram, distinguishing between internal structure models is challenging; however, asteroseismic constraints provide clear differentiation. Although mass-loss and mass-conservation models have similar $M$, $R$, and $T_{\rm eff}$ values, $Δν$s determined from the $l$=0 modes in the mass-loss models are 5-10$\%$ higher than observed. This discrepancy may arise from differences in internal structure. Finally, evolutionary model grids are used to examine how initial mass and $Z$ affect mass loss. Mass loss increases with increasing metallicity and decreases with increasing initial mass, regardless of the adopted value of $η$.

The Role of Asteroseismology in Understanding Mass Loss in Red Giants

TL;DR

This study uses six APOKASC-2 red giants to constrain mass loss during the RGB by constructing interior models with MESA and comparing predicted asteroseismic properties (, , ) against observations. By exploring grids over initial mass , initial metallicity , and mass-loss efficiency under Reimers’ law, the authors show that mass loss is required for these stars to occupy their observed RGB/RC positions, with in the range – and ages around – Gyr. They demonstrate that mass loss increases with metallicity and decreases with higher initial mass, and that asteroseismic constraints can distinguish RC from RGB-descending interiors, though degeneracies persist. For two RC stars, RC models provide excellent fits to , , and , while several RGB-descending stars require substantial mass loss to avoid unrealistically old ages from mass-conservative histories. Overall, the work underscores the power of asteroseismology to quantify RGB mass loss and to resolve evolutionary states, guiding future precision improvements with more complete seismic diagnostics.

Abstract

Red giant stars play a key role in advancing our understanding of stellar mass loss. However, its initial mass and the amount of mass lost during this phase remain uncertain. In this study, we investigate the asteroseismic signatures of mass loss and the parameters that influence it. We examine six stars identified as red giant branch (RGB) stars in the APOKASC-2 catalog. Assuming these stars are on their first ascent of the RGB, we construct interior models. The resulting model ages are significantly older than the age of the Galaxy, indicating that these stars are likely experiencing mass loss and evolving toward the red clump (RC) phase. The minimum possible initial masses are estimated using the mass-metallicity diagram, from which we infer that the minimum mass lost by these stars ranges from -. Models constructed with an initial minimum mass yield the maximum possible age of the star. The ages of these models fall within the range of 9-9.5Gyr. For two stars, asteroseismic parameters confirm RC classification. Due to degeneracies in the HR diagram, distinguishing between internal structure models is challenging; however, asteroseismic constraints provide clear differentiation. Although mass-loss and mass-conservation models have similar , , and values, s determined from the =0 modes in the mass-loss models are 5-10 higher than observed. This discrepancy may arise from differences in internal structure. Finally, evolutionary model grids are used to examine how initial mass and affect mass loss. Mass loss increases with increasing metallicity and decreases with increasing initial mass, regardless of the adopted value of .

Paper Structure

This paper contains 20 sections, 5 equations, 9 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Asteroseismic and Spectroscopic Data for Six Red Giants
  3. Modelling Method
  4. Properties of MESA inlist
  5. Red giant stars
  6. Mini Helium Flashes
  7. Effects of Metallicity and Initial Mass on Stellar Mass Loss
  8. Mass-Metallicity diagram
  9. Model results and Discussions
  10. Red Clump Models for KIC 5526130 and KIC 6131884
  11. Asteroseismic Analysis of Red Giant Stars
  12. Individual Notes on Red Giant Stars
  13. KIC 5526130
  14. KIC 6131884
  15. KIC 6521069
  16. ...and 5 more sections

Figures (9)

  • Figure 1:
  • Figure 2: $L$ and $\Delta\Pi_1$ variations of an internal structure model constructed for KIC 5526130. (a) The HR diagram shows the track followed by the star when it reaches the RC region. (b) $L$ and $\Delta\Pi_1$ are plotted logarithmically against age. Here, the change during the mini helium flash is shown. (c) The $L$ and $\Delta\Pi_1$ changes in the phase where regular helium burning starts after the mini helium flash are given.
  • Figure 3: $\Delta\Pi_1$–$\Delta\nu$ diagram. The 1.05 $M_\odot$ model shows the evolutionary path of the stellar interior. The pre-ZACHeB phase is marked with black crosses, while the stable core helium-burning phase is shown as a red solid line. The background circles represent the values determined by Vrard et al. (2016) for 6111 stars, with the color variation indicating stellar mass.
  • Figure 4: Initial mass ($M_0$) and metallicity ($Z_0$) are plotted against the amount of mass loss ($\Delta M$). The top panel shows the models constructed with $\eta=0.20$ (filled circle). As $M_0$ decreases, the mass loss increases, while as $Z_0$ increases, the mass loss increases. In the bottom panel, models constructed with $\eta=0.20$ (filled circle), 0.50 (filled triangle) and 0.85 (filled square) are given together. The effects of $M_0$, $Z_0$ and $\eta$ on mass loss are investigated together.
  • Figure 5: $Z_s$ is plotted against $M$. The six stars examined are shown as filled circles. In the background, RGB stars from the APOKASC-2 catalog are represented by crosses, and the two sides of the triangle are indicated by open circles Yıldız2023. All six stars lie to the left of this boundary.
  • ...and 4 more figures