期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 439, 期 2, 页码 1588-1595出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stu030
关键词
stars: Population II; globular clusters: individual: NGC 6121
资金
- Australian Research Council [DP120100475]
- PRIN-INAF
- PRIN MIUR
- project 'The Chemical and Dynamical Evolution of the Milky Way and Local Group Galaxies' [prot. 2010LY5N2T]
- Science and Technology Facilities Council [ST/J001600/1] Funding Source: researchfish
- STFC [ST/J001600/1] Funding Source: UKRI
The M 4 Core Project with HST is designed to exploit the Hubble Space Telescope (HST) to investigate the central regions of M 4, the Globular Cluster closest to the Sun. In this paper we combine optical and near-infrared photometry to study multiple stellar populations in M 4. We detected two sequences of M-dwarfs containing similar to 38 per cent (MSI) and similar to 62 per cent (MSII) of MS stars below the main-sequence (MS) knee. We compare our observations with those of NGC 2808, which is the only other GCs where multiple MSs of very low-mass stars have been studied to date. We calculate synthetic spectra for M-dwarfs, assuming the chemical composition mixture inferred from spectroscopic studies of stellar populations along the red giant branch, and different helium abundances, and we compare predicted and observed colours. Observations are consistent with two populations, one with primordial abundance and another with enhanced nitrogen and depleted oxygen.
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