The variable mass-loss in low-mass red giant stars: Chromospheric motion across stellar evolution in 47 Tuc
Abstract
Mass-Loss (ML) is a critical process that remains poorly understood despite its broad implications across astrophysics. Our current knowledge is insufficient to reproduce ML consistently across stars, particularly in cool, low-mass giants, where the time-variable nature of chromospheres (CHR) ---the region where most physical phenomena powering ML in this regime are expected to occur--- is poorly constrained. We characterize the relevant timescales of CHR variability in red giants and explore correlations with intrinsic stellar properties. We analyze the first large temporal spectroscopic monitoring of CHR variability using the Hα line in red giants belonging to the globular cluster NGC 104 (47 Tuc) using FLAMES/GIRAFFE data. We find that Hα variations increase on average and span a wider range of values with luminosity, together with a systematic blueshift of the line core indicative of outflows for log(L/L⊙) ≳ 2.4, alongside deeper cores consistent with increased CHR optical depth. The characteristic timescale required to observe variations in the Hα profile is approximately one day, showing a flat trend with luminosity. While shorter-timescale variations remain consistent with statistical uncertainties, a possible increase toward dimmer stars is found. These trends appear similarly correlated with luminosity and effective temperature. No further correlation is found with different cluster populations, nor are significant differences observed between AGB and RGB stars. The outflow trends closely match previous observations across a wide metallicity range. We discuss whether these observations reflect changes in Hα sensitivity to the winds, a genuine atmospheric transition driven by changes in heating efficiency, or continued CHR expansion with geometrically dominated Hα formation.
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BibTeX
@misc{baeza2026variable,
title = {{The variable mass-loss in low-mass red giant stars: Chromospheric motion across stellar evolution in 47 Tuc}},
author = {Ian Baeza and L. Monaco and H. Frelijj and Y. Momany and L. Sbordone and S. Zaggia and I. Yegorova and I. Saviane and A. Mucciarelli and K. Ohnaka and M. Gómez},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.06957},
eprint = {2610.06957},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.06957},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The variable mass-loss in low-mass red giant stars: Chromospheric motion across stellar evolution in 47 Tuc
AU - Ian Baeza
AU - L. Monaco
AU - H. Frelijj
AU - Y. Momany
AU - L. Sbordone
AU - S. Zaggia
AU - I. Yegorova
AU - I. Saviane
AU - A. Mucciarelli
AU - K. Ohnaka
AU - M. Gómez
PY - 2026
DA - 2026/10/03
PB - arXiv
DO - 10.48550/arxiv.2610.06957
UR - https://arxiv.org/abs/2610.06957
AB - Mass-Loss (ML) is a critical process that remains poorly understood despite its broad implications across astrophysics. Our current knowledge is insufficient to reproduce ML consistently across stars, particularly in cool, low-mass giants, where the time-variable nature of chromospheres (CHR) ---the region where most physical phenomena powering ML in this regime are expected to occur--- is poorly constrained. We characterize the relevant timescales of CHR variability in red giants and explore correlations with intrinsic stellar properties. We analyze the first large temporal spectroscopic monitoring of CHR variability using the Hα line in red giants belonging to the globular cluster NGC 104 (47 Tuc) using FLAMES/GIRAFFE data. We find that Hα variations increase on average and span a wider range of values with luminosity, together with a systematic blueshift of the line core indicative of outflows for log(L/L_⊙) ≳ 2.4, alongside deeper cores consistent with increased CHR optical depth. The characteristic timescale required to observe variations in the Hα profile is approximately one day, showing a flat trend with luminosity. While shorter-timescale variations remain consistent with statistical uncertainties, a possible increase toward dimmer stars is found. These trends appear similarly correlated with luminosity and effective temperature. No further correlation is found with different cluster populations, nor are significant differences observed between AGB and RGB stars. The outflow trends closely match previous observations across a wide metallicity range. We discuss whether these observations reflect changes in Hα sensitivity to the winds, a genuine atmospheric transition driven by changes in heating efficiency, or continued CHR expansion with geometrically dominated Hα formation.
ER -