Multiple Populations of the Large Magellanic Cloud Globular Cluster NGC 2257: No Major Environmental Effect on the Formation of Multiple Populations of Old Globular Clusters in the Large Magellanic Cloud

Abstract How the environment of the host galaxy affects the formation of multiple populations (MPs) in globular clusters (GCs) is one of the outstanding questions in near-field cosmology. To understand the true nature of the old GC MPs in the Large Magellanic Cloud (LMC), we study the Ca–CN–CH photometry of the old metal-poor LMC GC NGC 2257. We find the predominantly first-generation-dominated populational number ratio of n (FG): n (SG) = 61:39(±4), where FG and SG denote the first and second generations, respectively. Both the FG and SG have similar cumulative radial distributions, consistent with the idea that NGC 2257 is dynamically old. We obtain [Fe/H] hk = −1.78 ± 0.00 dex( σ = 0.05 dex), and our metallicity is ∼0.2 dex larger than that from the high-resolution spectroscopy by others, due to their significantly lower temperatures by ∼−200 K. The NGC 2257 FG shows a somewhat larger metallicity variation than the SG, the first detection of such a phenomenon in an old LMC GC, similar to Galactic GCs with MPs, strongly suggesting that it is a general characteristic of GCs with MPs. Interestingly, the NGC 2257 SG does not show a helium enhancement compared to the FG. Our results for the Galactic normal GCs exhibit that the degree of carbon and nitrogen variations is tightly correlated with the GC mass, while NGC 2257 exhibits slightly smaller variations in its mass. We show that old LMC GCs follow the same trends as the Galactic normal GCs in the Δ W CF336W,F438W,F814W , N FG / N tot , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mi>M</mml:mi> <mml:mo>/</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> </mml:math> domains. Our result indicates that the environment of the host galaxy did not play a major role in the formation and evolution of GC MPs.