- ID:
- ivo://CDS.VizieR/J/AJ/159/50
- Title:
- Identifying multiple populations in M71 using CN
- Short Name:
- J/AJ/159/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have observed their cyanogen CN features at ∼3800 and 4120Å as well as the CH band at ∼4300Å for 145 evolved stars in the Galactic globular cluster M71 using the multi-object spectrograph, Hydra, on the Wisconsin-Indiana-Yale- NOAO-3.5 m telescope. We use these measurements to create two δCN indices finding that both distributions are best fit by two populations: a CN-enhanced and CN-normal. We find that 42%±4% of the red giant branch stars in our sample are CN-enhanced. The percentage of CN-enhanced is 40%±13% for the asymptotic giant branch and 33%±9% for the horizontal branch stars (HB stars), which suggests there are no missing second generation stars at these stages of stellar evolution. The two generations also separate in magnitude and color on the HB, which allows us to find the difference in He abundance between the two populations by fitting appropriate zero-age horizontal branches. The broad range of distances from the cluster's center covered by our sample allows us to study the dependence of the ratio of the number of first to second population stars on the distance from the cluster's center, and we find that this ratio does not vary radially and that the two populations are spatially mixed. Finally, we compare our identification of multiple populations with the classification based on the Na-O anti-correlation and the Hubble Space Telescope UV photometry, and we find good agreement with both methods.
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- ID:
- ivo://CDS.VizieR/J/other/Nat/498.198
- Title:
- Na abundances in NGC6752
- Short Name:
- J/other/Nat/498.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The asymptotic giant branch (AGB) phase is the final stage of nuclear burning for low-mass stars. Although Milky Way globular clusters are now known to harbour (at least) two generations of stars, they still provide relatively homogeneous samples of stars that are used to constrain stellar evolution theory. It is predicted by stellar models that the majority of cluster stars with masses around the current turn-off mass (that is, the mass of the stars that are currently leaving the main sequence phase) will evolve through the AGB phase. Here we report that all of the second-generation stars in the globular cluster NGC 6752 - 70 per cent of the cluster population - fail to reach the AGB phase. Through spectroscopic abundance measurements, we found that every AGB star in our sample has a low sodium abundance, indicating that they are exclusively first-generation stars. This implies that many clusters cannot reliably be used for star counts to test stellar evolution timescales if the AGB population is included. We have no clear explanation for this observation.
