Helium Enhancement in the Metal Rich Red Giants of Omega Centauri
arXiv:2005.06807 · doi:10.3847/1538-4357/ab93bd
Abstract
The helium-enriched (He-enriched) metal-rich red giants of Omega Centauri, discovered by Hema and Pandey using the low-resolution spectra from the Vainu Bappu Telescope (VBT) and confirmed by the analyses of the high-resolution spectra obtained from the HRS-South African Large Telescope (SALT) for LEID 34225 and LEID 39048, are reanalysed here to determine their degree of He-enhancement/hydrogen-deficiency (H-deficiency). The observed MgH band combined with model atmospheres with differing He/H ratios are used for the analyses. The He/H ratios of these two giants are determined by enforcing the fact that the derived Mg abundances from the MgI lines and from the subordinate lines of the MgH band must be same for the adopted model atmosphere. The estimated He/H ratios for LEID 34225 and LEID 39048 are 0.15+/-0.04 and 0.20+/-0.04, respectively, whereas the normal He/H ratio is 0.10. Following the same criteria for the analyses of the other two comparison stars (LEID 61067 and LEID 32169), a normal He/H ratio of 0.10 is obtained. The He/H ratio of 0.15-0.20 corresponds to a mass fraction of helium (Z(He)=Y) of about 0.375-0.445. The range of helium enhancement and the derived metallicity of the program stars are in line with those determined for Omega Cen blue main-sequence stars. Hence, our study provides the missing link for the evolutionary track of the metal-rich helium-enhanced population of Omega Centuari. This research work is the very first spectroscopic determination of the amount of He-enhancement in the metal-rich red giants of Omega Centauri using the MgI and MgH lines.
arXiv comment22 pages, 3 fugures, 1 table, Accepted for publication in the Astrophysical Journal
References in corpus (30)
- The chemical composition of the Sun
- A Triple Main Sequence in the Globular Cluster NGC 2808
- Omega Centauri: The Population Puzzle Goes Deeper
- The ACS Survey of Galactic Globular Clusters. XII. Photometric Binaries along the Main-Sequence
- Metallicities on the Double Main Sequence of omega Centauri Imply Large Helium Enhancement
- Multiple Stellar Populations in the Globular Cluster omega Centauri as Tracers of a Merger Event
- Chemical Abundances for 855 Giants in the Globular Cluster Omega Centauri (NGC 5139)
- The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XVI. The helium abundance of multiple populations
- The multiplicity of the subgiant branch of Omega Centauri: Evidence for prolonged star formation
- New evidence for the complex struscture of the RGB of Omega Cen
- The two metallicity groups of the globular cluster M22: a chemical perspective
- A WFC3/HST view of the three stellar populations in the Globular Cluster NGC6752
- An abundance analysis of bright giants in the globular cluster NGC 1851
- Helium enhanced stars and multiple populations along the horizontal branch of NGC2808: direct spectroscopic measurements
- The Abundance Spread Among Giants and Subgiants in the Globular Cluster Omega Centauri
- Sodium-Oxygen anticorrelation among Horizontal Branch Stars in the Globular Cluster M4
- New HST WFC3/UVIS observations augment the stellar-population complexity of omega Centauri
- The C+N+O abundance of Omega Centauri giant stars: implications on the chemical enrichment scenario and the relative ages of different stellar populations
- Multiple stellar populations in the Galactic globular cluster NGC 6752
- The Helium content of Globular Clusters: light element abundance correlations and HB morphology. I. NGC6752
- Multiple populations in globular clusters and their parent galaxies
- Direct Evidence for an Enhancement of Helium in Giant Stars in Omega Centauri
- The HST Large Program on Omega Centauri. I. Multiple stellar populations at the bottom of the main sequence probed in NIR-Optical
- Direct Evaluation of the Helium Abundances in Omega Centauri
- Hot Horizontal Branch stars in omega Centauri: clues about their origin from the cluster Color Magnitude Diagram
- The evolutionary status of the blue hook stars in Omega Centauri
- Spectral matching for abundances of 848 stars of the giant branches of the globular cluster ω Centauri
- Is the post-AGB star SAO 40039 mildly H-deficient?
- Discovery of relatively hydrogen-poor giants in the Galactic globular cluster Omega Centauri
- High resolution spectroscopy of the relatively hydrogen-poor metal rich giants in the globular cluster Omega Centauri