Spectroscopic Study of Red Giant Stars in Nine Open Clusters Reveals Mixing Processes
Astronomers analyzed the chemical compositions and radial velocities of 22 red giant stars across nine open clusters using high-resolution spectroscopy in visible and near-infrared wavelengths. The research focused on CNO abundances and carbon, nitrogen, and oxygen isotopic ratios to probe internal mixing mechanisms on the red giant branch. The findings support theoretical predictions about thermohaline and rotation-induced mixing, while also suggesting that variations in initial oxygen isotope abundances may be needed to fully explain observed dispersions.
A team of researchers conducted a spectroscopic analysis of 22 K-type giant stars drawn from nine open clusters — NGC188, NGC2682, NGC3680, NGC5822, IC4756, NGC6633, NGC3532, NGC6281, and NGC5460 — to investigate extra-mixing processes in evolved stars. High-resolution, high signal-to-noise spectra were obtained using the ESPaDOnS spectrograph at the Canada-France-Hawaii Telescope for NGC188 and the CRIRES spectrograph at the Very Large Telescope for the remaining clusters. The team measured CNO elemental abundances alongside 12C/13C, 16O/17O, and 16O/18O isotopic ratios, using standard spectral analysis tools including IRAF, Turbospectrum, and MOOG. Their results are broadly consistent with prior literature values for radial velocities and chemical abundances. The data support the occurrence of thermohaline mixing on the red giant branch and rotation-induced mixing on the main sequence, both with the mass dependence predicted by stellar evolution models. However, the observed dispersion in oxygen isotopic ratios suggests that variations in the initial abundances of 17O and 18O — potentially reflecting differences in cluster birth environments — may be required to fully account for the observations. The paper, accepted for publication in Monthly Notices of the Royal Astronomical Society, spans 28 pages and 12 figures.
What's missing
The study notes that variations in initial oxygen isotope abundances may explain observed dispersions but does not identify the specific astrophysical processes (e.g., nucleosynthetic enrichment history, Galactic chemical evolution gradients) that would drive such initial abundance variations.
What different sources said
- arXiv astro-phCenter
Spectroscopic analysis of RGB stars in nine open clusters
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