Uncovering Multiple Populations with Washington Photometry: I. The Globular Cluster NGC 1851

Abstract

The analysis of multiple populations (MPs) in globular clusters (GCs) has become a forefront area of research in astronomy. Multiple red giant branches (RGBs), subgiant branches (SGBs), and even main sequences (MSs) have now been observed photometrically in many GCs. UV photometry has been crucial in discovering and analyzing these MPs, but the Johnson U and the Stromgren and Sloan u filters that have generally been used are relatively inefficient and very sensitive to reddening and atmospheric extinction. In contrast, the Washington C filter is much broader and redder than these competing UV filters. Here we investigate the use of the Washington system to uncover MPs using only a 1-meter telescope. Our analysis of the well-studied GC NGC 1851 finds that the C filter is both very efficient and effective at detecting its previously discovered MPs in the RGB and SGB. Remarkably, we have also detected an intrinsically broad MS best characterized by two distinct but heavily overlapping populations that cannot be explained by binaries, field stars, or photometric errors. The MS distribution is in very good agreement with that seen on the RGB, with ~30% of the stars belonging to the second population. There is also evidence for two sequences in the red horizontal branch, but this appears to be unrelated to the MPs in this cluster. Neither of these latter phenomena have been observed previously in this cluster. The redder MS stars are also more centrally concentrated than the blue MS. This is the first time MPs in a MS have been discovered from the ground, and using only a 1-meter telescope. The Washington system thus proves to be a very powerful tool for investigating MPs, and holds particular promise for extragalactic objects where photons are limited.

25 pages, 10 figures

References in corpus (4)

• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• Spectroscopic and Photometric evidence of two stellar populations in the Galactic Globular Cluster NGC6121 (M4)
• The ACS Survey of Galactic Globular Clusters. III. The Double Subgiant Branch of NGC 1851
• A large C+N+O abundance spread in giant stars of the globular cluster NGC 1851

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• Multiple stellar populations of globular clusters from homogeneous Ca-Cn photometry. II. M5 (NGC 5904) and a new filter system
• A broad perspective on multiple abundance populations in the globular cluster NGC 1851
• Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud IV: Evidence for Multiple Populations in Hodge 11 and NGC 2210
• Blanco DECam Bulge Survey (BDBS) III: A new view of the double red clump in the Milky Way bulge through luminosity and color distribution
• Searching for multiple populations in star clusters using the China Space Station Telescope
• Searching for Multiple Populations in Ruprecht 106
• Intrinsic Metallicity Variation in the Intermediate Mass Type II Globular Cluster NGC 1261
• Stellar collisions in globular clusters: Constraints on the initial mass function of the first generation of stars
• Detecting unresolved binary stars in Euclid VIS images
• Photometric Detection of Multiple Populations in Globular Clusters Using Integrated Light
• Uncovering Multiple Populations in NGC 7099 (M 30) using Washington Photometry
• Mock Observations of Multiple Stellar Populations in Tidal Streams of Palomar 5 for the Chinese Space Station Survey Telescope
• C,T1,T2: A complementary method to detect Multiple Populations with the Washington filter system