The Multiplicity of the Subgiant Branch of ω Centauri: Evidence for Prolonged Star Formation

By S. Villanova, G. Piotto, Ivan R. King, Joseph M. Anderson, L. Bedin, R. Gratton, Santi Cassisi, Y. Momany, Andrea Bellini, A. Cool and 2 more. 2007

172 citations recorded by the source corpus.

We combine spectroscopic and photometric data for subgiant stars of ω Cen to extract results that neither data set could have provided on its own. GIRAFFE@VLT spectra of 80 stars at R = 6400 give metallicities for all of them and abundances of C, N, Ca, Ti, and Ba for a subset of them. The photometric data, which have unusually high accuracy, come from a ~10 × 10 arcmin2 mosaic of HST ACS images centered on the cluster center and on multicolor images of a ~34 × 33 arcmin2 field, taken with the WFI@ESO2.2m camera. Stars with [Fe/H] < -1.25 have a large magnitude spread on the flat part of the SGB. We interpret this as empirical evidence for an age spread, and from theoretical isochrones we derive a relative age for each star. Within the SGB region we identify four distinct stellar groups: (1) an old, metal-poor group ([Fe/H] ~ -1.7); (2) an old, metal-rich group ([Fe/H] ~ -1.1); (3) a young (up to 4-5 Gyr younger than the old component) metal-poor group ([Fe/H] ~ -1.7); (4) a young, intermediate-metallicity ([Fe/H] ~ -1.4) group, on average 1-2 Gyr younger than the old metal-poor population, and with an age spread that we cannot properly quantify with the present sample. In addition, many SGB stars are spread between the intermediate-metallicity and metal-rich branches. We tentatively propose connections between the SGB stars and both the multiple main-sequence and the red giant branches. Finally, we discuss the implications of the multiple stellar populations on the formation and evolution of ω Cen. The spread in age within each population establishes that the original system must have had a composite nature.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/d6b6b4a9cd2836503e352e0249172b35bb40ef59

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In Astronomy and Astrophysics

1. Jay Anderson
2. A. Milone
3. G. Piotto
4. C. Conroy
5. L. Bedin
6. Aaron Dotter
7. A. Renzini
8. H. Baumgardt

In Instrumentation

1. Jay Anderson
2. G. Piotto
3. A. Milone
4. L. Bedin
5. F. D’Antona
6. Aaron Dotter
7. A. Renzini
8. A. Aparicio

Citations in the corpus

• CHEMICAL ABUNDANCES FOR 855 GIANTS IN THE GLOBULAR CLUSTER OMEGA CENTAURI (NGC 5139) (2010, background): “Instead, the [X/H] ratios for all elements analyzed so far are found to vary by at least a factor of ten as well (e.g., Cohen 1981; Paltoglou & Norris 1989; Norris & Da Costa 1995; Smith et al. 2000; Cunha et al. 2002; Johnson et al. 2009; Villanova et al. 2009; Cunha et al. 2010; Stanford et al. 20”
• Spectroscopic and photometric evidence of two stellar populations in the Galactic globular cluster NGC 6121 (M 4) (2008, background): “More recently, Villanova et al. (2007) showed that the two main sequences split in at least four sub giant branches (SGB) which must be connected in some way to the multiplicity of RGBs identified by Lee et al. (1999) and Pancino et al. (2000).”
• Origin of multiple stellar populations in globular clusters and their helium enrichment (2008, background): “…kind of studies are now possible thanks to the high multiplex multiobject spectrographs at 8–10 m class telescopes, such as for example the Fibre Large Array Multi Element Spectrograph (FLAMES) at the Very Large Telescope (VLT) (Sollima et al. 2005; Carretta et al. 2006; Villanova et al. 2007).”
• The ACS Survey of Galactic Globular Clusters. III. The Double Subgiant Branch of NGC 1851 (2007, background): “…as a bimodal He abundance; see Bedin et al. 2004; Norris 2004; Piotto et al. 2005) and in a multiplicity of SGBs (interpreted in terms of large age variations, 31 Gyr; see Villanova et al. 2007 and references therein), which implies at least four different stellar groups within the same cluster.”
• An Abundance Analysis of Bright Giants in the Globular Cluster NGC 1851 (2007, background): “While this unpalatable scenario would be a challenge to explain, Villanova et al. (2007) find that the most metal-rich subgiant stars in q Centauri are among the oldest stars in the cluster.”
• Multiple stellar populations in Magellanic Cloud clusters - I. An ordinary feature for intermediate age globulars in the LMC? (2008, methodology): “…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 al. 2008a), Based on observations with the NASA/ESA…”
• 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): “4.4, where Piotto et al. (2005) and Villanova et al. (2007) found that the more metal rich, Heenriched stars also have a higher Ba content.”
• Photometric signatures of multiple stellar populations in galactic globular clusters (2011, background): “A weakly populated third main-sequence, redder than the two others, was found by Villanova et al. (2007) and definitely confirmed on the basis of an accurate WFC3 photometry by Bellini et al. (2010).ω Cen is also known for hosting at least four subgiant (Lee et al. 2005; Sollima et al. 2005;…”
• Scaled solar tracks and isochrones in a large region of the Z-Y plane I. From the ZAMS to the TP-A (2008, background): “According to Piotto et al. (2005) and Villanova et al. (2007), only greatly enhanced helium can explain the color difference Send offprint requests to: G. Bertelli, e-mail: gianpaolo.bertelli@oapd.inaf.it between the two main sequences inω Cen.”
• Multiple Stellar Populations in Three Rich Large Magellanic Cloud Star Clusters (2008, background): “NGC 2808 possesses a triple main sequence split, suggesting two helium-enriched populations (Piotto et al. 2007); while NGC 1851 and NGC 6388 show clear splits in their SGBs, possibly indicative of populations with ages ∼ 1 Gyr apart, or of sizeable intracluster variations in chemical composition (M”
• Formation and dynamical evolution of multiple stellar generations in globular clusters (2008, background): “In ω Cen the “normal” MS is actually made up of sequences with different metal content, as also shown by the complexity of the subgiant branch(es) (e.g. Villanova et al. 2007).”
• From star clusters to dwarf galaxies: the properties of dynamically hot stellar systems (2008, methodology): “However, this is not necessarily the case for the stars in MCOs, as the examples of ω Cen (e.g. Kayser et al. 2006; Villanova et al. 2007) and G1 (Meylan et al. 2001) show.”
• NEW LIMITS ON AN INTERMEDIATE-MASS BLACK HOLE IN OMEGA CENTAURI. I. HUBBLE SPACE TELESCOPE PHOTOMETRY AND PROPER MOTIONS (2009, methodology): “Villanova et al. (2007) then measured metallicities for stars in the two populations and found that the bluer stars were indeed more metal rich than the redder stars, in line with the Helium explanation.”