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Constraining intrinsic S-type AGB masses and third dredge-up using pulsation

Y. L. Mori, A. I. Karakas, S. W. Campbell

TL;DR

This study tackles the uncertain lower mass limit for third dredge-up (TDU) on the TP-AGB by leveraging intrinsic S-type AGB stars as constraints. It combines pulsation-based mass estimates from overtone periods, Gaia DR3 distances, and multiple luminosity determinations with grids of detailed TP-AGB and linear pulsation models to derive initial masses. The results reveal a mass distribution peaking near $1.4\,M_{igodot}$ and include stars down to about $1.0\,M_{igodot}$, challenging the conventional minimum mass for TDU and suggesting revisions to convective mixing or overshoot in current models. The work also highlights uncertainties in luminosities, pulsation-mode assignments, and mass-loss treatment, and discusses implications for population synthesis and the role of binarity and non-radial pulsations in AGB evolution.

Abstract

The lowest mass at which the third dredge-up (TDU) occurs for thermally-pulsing asymptotic giant branch (TP-AGB) stars remains a key uncertainty in detailed stellar models. S-type AGB stars are an important constraint on this uncertainty as they have C/O ratios between 0.5 and 1, meaning they have only experienced up to a few episodes of TDU. AGB stars are also long-period variable stars, pulsating in low order radial pulsation modes. In this paper we estimate the initial masses of a large literature sample of intrinsic S-type AGB stars, by analysing their visual light curves, estimating their luminosities with Gaia DR3 parallax distances and finally comparing to a grid of detailed stellar models combined with linear pulsation models. We find that the initial mass distribution of intrinsic S-type stars peaks at 1.3 to 1.4 \Msun, depending on model assumptions. There also appear to be stars with initial masses down to 1 solar mass, which is in conflict with current detailed stellar models. Additionally, we find that though the mass estimates for semiregular variable stars pulsating in higher order radial modes are precise, the Mira variables pulsating in the fundamental mode present challenges observationally from uncertain parallax distances, and theoretically from the onset of increased mass-loss and the necessity of non-linear pulsation models.

Constraining intrinsic S-type AGB masses and third dredge-up using pulsation

TL;DR

This study tackles the uncertain lower mass limit for third dredge-up (TDU) on the TP-AGB by leveraging intrinsic S-type AGB stars as constraints. It combines pulsation-based mass estimates from overtone periods, Gaia DR3 distances, and multiple luminosity determinations with grids of detailed TP-AGB and linear pulsation models to derive initial masses. The results reveal a mass distribution peaking near and include stars down to about , challenging the conventional minimum mass for TDU and suggesting revisions to convective mixing or overshoot in current models. The work also highlights uncertainties in luminosities, pulsation-mode assignments, and mass-loss treatment, and discusses implications for population synthesis and the role of binarity and non-radial pulsations in AGB evolution.

Abstract

The lowest mass at which the third dredge-up (TDU) occurs for thermally-pulsing asymptotic giant branch (TP-AGB) stars remains a key uncertainty in detailed stellar models. S-type AGB stars are an important constraint on this uncertainty as they have C/O ratios between 0.5 and 1, meaning they have only experienced up to a few episodes of TDU. AGB stars are also long-period variable stars, pulsating in low order radial pulsation modes. In this paper we estimate the initial masses of a large literature sample of intrinsic S-type AGB stars, by analysing their visual light curves, estimating their luminosities with Gaia DR3 parallax distances and finally comparing to a grid of detailed stellar models combined with linear pulsation models. We find that the initial mass distribution of intrinsic S-type stars peaks at 1.3 to 1.4 \Msun, depending on model assumptions. There also appear to be stars with initial masses down to 1 solar mass, which is in conflict with current detailed stellar models. Additionally, we find that though the mass estimates for semiregular variable stars pulsating in higher order radial modes are precise, the Mira variables pulsating in the fundamental mode present challenges observationally from uncertain parallax distances, and theoretically from the onset of increased mass-loss and the necessity of non-linear pulsation models.

Paper Structure

This paper contains 39 sections, 3 equations, 21 figures, 3 tables.

Table of Contents

  1. INTRODUCTION
  2. SAMPLE SELECTION
  3. METHODS
  4. Light curves and pulsation modes
  5. Light curve analysis
  6. Pulsation mode assignment
  7. Luminosities
  8. Distances and dust extinction
  9. Bolometric corrections based on empirical relations
  10. Bolometric corrections based on SED fitting
  11. Luminosity comparisons and outliers
  12. Grids of stellar models
  13. Detailed AGB stellar models
  14. Radial pulsation models
  15. Pulsation period evolution during the TP-AGB
  16. ...and 24 more sections

Figures (21)

  • Figure 1: Period-luminosity diagrams for the OGLE III Collection of LPVs in the LMC, the ASAS-SN g-band catalogue of LPVs, and the Gaia DR3 catalogue of LPVs. Lines are from trabucchi_semi-regular_2021, and denote the boundaries adopted for sequence C$'$ (first overtone mode, blue dash dot) and sequence C (fundamental mode, red solid) for the LMC PL diagram. We also include lines denoting sequence A (2nd overtone mode, green dashed). We mark the approximate luminosity of the RGB tip (purple dashed line). In the ASAS-SN and Gaia DR3 panels, sequence C appears to be offset with respect to the boundaries; this may be an effect of uncertain Gaia DR3 parallax distances bailer-jones_estimating_2021 for the more evolved, brighter stars pulsating in the fundamental mode.
  • Figure 2: Example ASAS-SN light curves for three Tc-rich S-type stars. Top: Semiregular variable CD$-$29$^{\circ}$5912 (Hen 4-44), middle: SRa variable V441 Cyg (Hen 4-227), bottom: Mira variable V600 Car (Hen 4-109).
  • Figure 3: Example light curve analysis and mode assignment for Tc-rich S star CD$-$29$^{\circ}$5912. Top panel: OGLE period-luminosity diagram, and the periods from the periodogram at the absolute W$_{\text{JK}}$ magnitude of CD$-$29$^{\circ}$5912. Top panel inset: Phased light curve showing the 62 d peak period from the periodogram. Middle panel: Lomb-Scargle periodogram of the g-band ASAS-SN light curve. Red horizontal dotted line is the power at which the false alarm probability is 10$^{-7}$, and the peaks above this threshold are labelled with the corresponding period. The 62 d period lies in between pulsation sequences B and C$'$, is thus assigned to the first overtone mode. Bottom panel: Window power spectrum of the light curve, showing structure at $\sim$ 1 yr (371 d).
  • Figure 4: Luminosity functions derived for the sample, using the kerschbaum_bolometric_2010 bolometric corrections (left) and VOSA SED fitting (right).
  • Figure 5: Comparison of residuals between the luminosities derived in this paper and the S21 sample.
  • ...and 16 more figures