Two Distinct Red Giant Branches in the Globular Cluster NGC 288

Abstract

We report the presence of two distinct red giant branches (RGBs) in the globular cluster NGC 288 from the narrow-band calcium and Strömgren b & y photometry obtained at the CTIO 4m Blanco telescope. The RGB of NGC 288 is clearly split into two in the hk [=(Ca - b) - (b - y)] index, while the split is not shown in the b - y color. Unlike other globular clusters with multiple populations reported thus far, the horizontal branch of NGC 288 is only mildly extended. Our stellar population models show that this and the presence of two distinct RGBs in NGC 288 can be reproduced if slightly metal-rich (Δ[m/H] $\approx$ 0.16) second generation stars are also enhanced in helium by small amount (ΔY $\approx$ 0.03) and younger by ~ 1.5 Gyrs. The RGB split in hk index is most likely indicating that the second generation stars were affected by supernovae enrichment, together with the pollutions of lighter elements by intermediate-mass asymptotic giant branch stars or fast-rotating massive stars. In order to confirm this, however, spectroscopy of stars in the two distinct RGB groups is urgently required.

Accepted for publication in the Astrophysical Journal Letters

References in corpus (7)

• Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters
• Spectroscopic and Photometric evidence of two stellar populations in the Galactic Globular Cluster NGC6121 (M4)
• The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy
• The double Subgiant Branch of NGC 1851: the role of the CNO abundance
• Comparing CN and CH Line Strengths in a Homogeneous Spectroscopic Sample of 8 Galactic Globular Clusters
• MCAO near-IR photometry of the Globular Cluster NGC 6388: MAD observations in crowded fields
• On the Origin of Bimodal Horizontal-Branches in Massive Globular Clusters: The Case of NGC 6388 and NGC 6441

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