ω Centauri: The Population Puzzle Goes Deeper

By L. Bedin, G. Piotto, Jay Anderson, Santi Cassisi, Ivan R. King, Y. Momany, G. Carraro. 2004

306 citations recorded by the source corpus.

We present Hubble Space Telescope observations that show a bifurcation of colors in the middle main sequence of the globular cluster ω Centauri. We see this in three different fields, observed with different cameras and filters. We also present high-precision photometry of a central Advanced Camera for Surveys field, which shows a number of main-sequence turnoffs and subgiant branches. The double main sequence, the multiple turnoffs and subgiant branches, and other population sequences discovered in the past along the red giant branch of this cluster add up to a fascinating but frustrating puzzle. We suggest various explanations, none of them very conclusive.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/230249b6e3a2b6c6421345d99dde5630e5af6437

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In Astronomy and Astrophysics

1. R. Gratton
2. E. Carretta
3. A. Bragaglia
4. Jay Anderson
5. G. Piotto
6. F. D’Antona
7. L. Bedin
8. A. Milone

In Instrumentation

1. R. Gratton
2. E. Carretta
3. A. Bragaglia
4. F. D’Antona
5. Jay Anderson
6. G. Piotto
7. L. Bedin
8. A. Milone

Citations in the corpus

• The two metallicity groups of the globular cluster M 22: a chemical perspective (2011, background): “Photometric evidence of multiple stellar populations has been recently observed in many GCs in the form of multiple main sequences (Bedin et al. 2004, Piotto et al. 2007, Anderson et al. 2009, and Milone et al. 2010), split sub-giant branches (Milone et al. 2008, and Piotto 2009), and multiple…”
• Multiple populations in globular clusters (2012, background): “Carretta et al. (2010b) were the first to demonstrate that the Na-O anticorrelation is more extended at intermediate than at low metallicities in ω Cen and M 54, the two most massive globular clusters in the Milky Way, both showing a large dispersion in iron abundance.”
• Synthetic stellar photometry – I. General considerations and new transformations for broad-band systems (2014, background): “While broad-band photometry can be easily used to map and study extended stellar populations and/or large fractions of the sky, also at faint magnitudes (e.g., Stetson et al. 1998; Bedin et al. 2004; Ivezić et al. 2007; Saito c© 0000 RAS ar X iv :1 40 7.”
• Intrinsic iron spread and a new metallicity scale for globular clusters (2009, background): “Ramirez & Cohen 2002; Carretta et al. 2004; Piotto et al. 2005) and photometric (e.g. Bedin et al. 2004) observations convincingly showed that the observed pattern of chemical composition is present also among unevolved stars on the subgiant branch and the main sequence.”
• The dynamical distance and intrinsic structure of the globular cluster ω Centauri (2005, background): “Furthermore, multiple stellar populations can be identified (e.g. Freeman & Rodgers 1975; Lee et al. 1999; Pancino et al. 2000; Bedin et al. 2004).”
• Evidence for two early accretion events that built the Milky Way stellar halo (2019, background): “However, ω Centauri hosts multiple stellar populations with different heavy element abundances enriched by supernovae, as well as spreads in the light elements (see e.g., Bedin et al. 2004; D’Antona et al. 2011; D’Orazi et al. 2011; Joo & Lee 2013).”
• The fraction of second generation stars in globular clusters from the analysis of the horizontal branch (2008, methodology): “In addition, we try to model better the EBT2 and EBT3 (in the definition by Bedin et al. 2004) blue clumps, which contain the extreme HB (D’Cruz et al. 2000; Brown et al. 2001) and the “blue hook” stars (Moehler et al. 2004), respectively, and compare also simulations based on HST ultraviolet and…”
• Properties of stellar generations in globular clusters and relations with global parameters (2010, background): “Multiple main sequences attributed to populations with different He fraction Y have recently been found in some GCs (ω Cen, see Bedin et al. 2004, and NGC 2808, Piotto et al. 2007).”
• Origin of multiple stellar populations in globular clusters and their helium enrichment (2008, background): “Then came the discovery that also its main sequence (MS) splits into two parallel sequences, with the bluer one being more metal rich by nearly a factor of 2, hence indicating a higher helium abundance (Bedin et al. 2004; Norris 2004; Piotto et al. 2005).”
• NEW LIMITS ON AN INTERMEDIATE-MASS BLACK HOLE IN OMEGA CENTAURI. I. HUBBLE SPACE TELESCOPE PHOTOMETRY AND PROPER MOTIONS (2009, background): “Anderson (2002) found and Bedin et al. (2004) confirmed that the main sequence clearly bifurcates into a red and blue branch below V ∼ 20.”
• A double stellar generation in the globular cluster NGC 6656 (M 22): Two stellar groups with different iron and s-process element abundances (2009, background): “…in the photometric precision of data from HST images, provide evidence of multimodal sequences in the color-magnitude diagrams (CMD) of some GCs (Bedin et al. 2004; Piotto et al. 2007; Milone et al. 2008; and Piotto et al. in preparation) further confirming that at least in some GCs, there is…”
• THE ABUNDANCES OF NEUTRON-CAPTURE SPECIES IN THE VERY METAL-POOR GLOBULAR CLUSTER M15: A UNIFORM ANALYSIS OF RED GIANT BRANCH AND RED HORIZONTAL BRANCH STARS (2011, background): “Detections of multiple main sequences and giant branches in globular clusters (GC; e.g. ωCen, NGC 2808, and NGC 1851; Bedin et al. 2004(9), Piotto et al. 2007(72), Han et al. 2009(42)) have challenged the notion that these objects are uniformly mono-metallic stellar systems of unique age.”
• Formation and dynamical evolution of multiple stellar generations in globular clusters (2008, background): “…two clusters, ω Cen and NGC 2808, in which the MS morphology shows that a non negligible fraction of the stars (∼25% in ω Cen , ∼15% in NGC 2808) populate a “blue MS” which can only be interpreted as a very heliumrich MS (Bedin et al. 2004; Norris 2004; Piotto et al. 2005; D’Antona et al. 2005b).”
• The second and third parameters of the horizontal branch in globular clusters (2010, background): “…HB, suchas that observed e.g., in NGC 2808 (D’Antona et al. 2005); (iii) Very accurate photometric data detect multiple main sequences in some GCs (Bedin et al. 2004; Piotto et al. 2007) that can only be explained by assuming large variations in the He content (Norris et al. 2004; Piotto et al.…”
• Spectroscopic and photometric evidence of two stellar populations in the Galactic globular cluster NGC 6121 (M 4) (2008, background): “In a sense, the findings by Pancino et al. (2000), Bedin et al. (2004), Piotto et al. (2005), Villanova et al. (2007) and Sollima et al. (2007) could simply be considered additional evidence that ω Cen is so peculiar that it might not be a GC.”
• Re-evaluating old stellar populations (2018, background): “These have revealed examples of clusters with a broad or bifurcated main sequence (e.g. Bedin et al. 2004), which is not expected from single-aged simple stellar populations, and, in many cases, also blue stragglers - surviving luminous blue stars which appear younger than the rest of the…”
• Abundance patterns of multiple populations in globular clusters: a chemical evolution model based on yields from AGB ejecta (2010, background): “…clusters (ω Cen and NGC 2808) were recognized to have a large fraction of main sequence stars (∼25% in ω Cen , ∼15% in NGC 2808) in a “blue MS” which could only be interpreted as a very helium rich MS (Bedin et al. 2004; Norris 2004; Piotto et al. 2005; D’Antona et al. 2005; Piotto et al. 2007) 1.”
• THE HUBBLE SPACE TELESCOPE UV LEGACY SURVEY OF GALACTIC GLOBULAR CLUSTERS. I. OVERVIEW OF THE PROJECT AND DETECTION OF MULTIPLE STELLAR POPULATIONS (2014, background): “After almost a decade since the firstbreakthrough (Bedin et al. 2004), our current understanding can be summarized as follows: • Ubiquity.”
• Multiple stellar populations in Magellanic Cloud clusters - I. An ordinary feature for intermediate age globulars in the LMC? (2008, background): “Thus far, photometry has revealed multiple stellar populations in a few Galactic globular clusters (GGCs) i.e. Omega Centauri (Anderson 1997; Bedin et al. 2004; Piotto et al. 2005; Sollima et al. 2007, Villanova et al. 2007), NGC 2808 (D’Antona et al. 2005; Piotto et al. 2007), NGC 1851 (Milone et…”