Super-Helium-rich Populations and the Origin of Extreme Horizontal-Branch Stars in Globular Clusters

Lee, Young-Wook; Joo, Seok-Joo; Han, Sang-Il; Chung, Chul; Ree, Chang H.; Sohn, Young-Jong; Kim, Yong-Cheol; Yoon, Suk-Jin; Yi, Sukyoung K.; Demarque, P.

doi:10.1086/428944

Cited by 212 publications

(245 citation statements)

References 19 publications

Supporting

Mentioning

229

Contrasting

Order By: Relevance

“…(vii) In conclusion, we show that a satisfactory compari-Authors Age ∆Age Ferraro et al (2004) 15 Gyr ∼ +2 Gyr Freyhammer et al (2005) 12 ÷ 13 Gyr ∼ +4 Gyr Lee et al (2005) 13 Gyr −1.5 Gyr Sollima et al (2005) 16.0 Gyr ∼ 0 ÷ 1 Gyr Stanford et al (2006) 13.5 Gyr −(2 ÷ 4) Gyr Joo & Lee (2013) 13.1 Gyr −1.7 Gyr Villanova et al (2014) 12.1 Gyr > ±2 Gyr This work 13 Gyr 0 ÷ −0.5 Gyr Table 3. Summary of isochrones fitting estimates of the maximum age difference among the populations in ω Centauri.…”

Section: Discussionsupporting

confidence: 53%

“…The first studies, until 10 years ago, gave disparate results. In some cases, the MSa is found to be older than the the main populations by 2-4 Gyr (Ferraro et al 2004;Freyhammer et al 2005), while Sollima et al (2005) discuss that the MSa can be so helium rich to be coeval with the others, and Lee et al (2005) find the MSa younger by ∼1.5 Gyr, using similar hypothesis concerning helium enhancement. Many other dating works came out, based on disparate methods of age determination (see Table 5 in Stanford et al 2006), and we do not consider them here.…”

Section: Introductionmentioning

confidence: 82%

See 1 more Smart Citation

The mosaic multiple stellar populations in ω Centauri: the horizontal branch and the main sequence

Tailo

Criscienzo

D’Antona

et al. 2016

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

We interpret the stellar population of ω Centauri by means of a population synthesis analysis, following the most recent observational guidelines for input metallicities, helium and [(C+N+O)/Fe] contents. We deal at the same time with the main sequences, sub-giant and horizontal branch data. The reproduction of the observed color magnitude features is very satisfying and bears interesting hints concerning the evolutionary history of this peculiar stellar ensemble. Our main results are: 1) no significant spread in age is required to fit the colour-magnitude diagram. Indeed we can use coeval isochrones for the synthetic populations, and we estimate that the ages fall within a ∼ 0.5 Gyr time interval; in particular the most metal rich population can be coeval (in the above meaning) with the others, if its stars are very helium-rich (Y∼0.37) and with the observed CNO enhancement ([(C+N+O)/Fe] = + 0.7); 2) a satisfactory fit of the whole HB is obtained, consistent with the choice of the populations providing a good reproduction of the main sequence and sub giant data. 3) the split in magnitude observed in the red HB is well reproduced assuming the presence of two stellar populations in the two different sequences observed: a metal poor population made of stars evolving from the blue side (luminous branch) and a metal richer one whose stars are in a stage closer to the zero age HB (dimmer branch). This modelization also fits satisfactorily the period and the [Fe/H] distribution of the RR Lyrae stars.

show abstract

Section: Discussionsupporting

confidence: 53%

Section: Introductionmentioning

confidence: 82%

The mosaic multiple stellar populations in ω Centauri: the horizontal branch and the main sequence

Tailo

Criscienzo

D’Antona

et al. 2016

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

show abstract

“…2). These values are in excellent agreement with the results obtained by Norris (2004), Piotto et al (2005), Lee et al (2005) and Sollima et al (2007) by means of isochrone analysis.…”

Section: Application To Globular Clusterssupporting

confidence: 92%

Revisiting the helium abundance in globular clusters with multiple main sequences

2009

View full text Add to dashboard Cite

Abstract. For nearby K dwarfs, the broadening of the observed Main Sequence at low metallicities is much narrower than expected from isochrones with the standard helium-to-metal enrichment ratio ΔY /ΔZ ∼ 2. A much higher value, of order 10, is formally needed to reproduce the observed broadening, but it returns helium abundances in awkward contrast with Big Bang Nucleosynthesis. This steep enrichment ratio resembles, on a milder scale, the very high ΔY /ΔZ estimated from the multiple Main Sequences observed in some metal-poor Globular Clusters. We argue that a revision of low Main Sequence stellar models, suggested from nearby stars, could help to reduce the overwhelmingly high ΔY /ΔZ deduced so far for those clusters. Under the most favourable assumptions, the estimated helium content for the enriched populations may decrease from Y 0.4 to as low as Y 0.3, with intermediate values being plausible.

show abstract

“…We covered a range of masses from 0. (Y = 0.25, 0.27, 0.33, 0.38, 0.42) that simulate different helium enrichments up to the very high values supposed for some stellar samples in multipopulation clusters (Lee et al 2005;Villanova et al 2007;Piotto et al 2007;Piotto 2009), while the last one follows the often adopted linear helium-to-metal enrichment law given by:…”

Section: Database Description: Stellar Tracks and Isochronesmentioning

confidence: 99%

The Pisa Stellar Evolution Data Base for low-mass stars

Dell’Omodarme

Valle

Degl’Innocenti

et al. 2012

A&A

View full text Add to dashboard Cite

Context. The last decade showed an impressive observational effort from the photometric and spectroscopic point of view for ancient stellar clusters in our Galaxy and beyond, leading to important and sometimes surprising results. Aims. The theoretical interpretation of these new observational results requires updated evolutionary models and isochrones spanning a wide range of chemical composition so that the possibility of multipopulations inside a stellar cluster is also taken also into account. Methods. With this aim we built the new "Pisa Stellar Evolution Database" of stellar models and isochrones by adopting a welltested evolutionary code (FRANEC) implemented with updated physical and chemical inputs. In particular, our code adopts realistic atmosphere models and an updated equation of state, nuclear reaction rates and opacities calculated with recent solar elements mixture. Results. A total of 32 646 models have been computed in the range of initial masses 0.30 ÷ 1.10 M for a grid of 216 chemical compositions with the fractional metal abundance in mass, Z, ranging from 0.0001 to 0.01, and the original helium content, Y, from 0.25 to 0.42. Models were computed for both solar-scaled and α-enhanced abundances with different external convection efficiencies. Correspondingly, 9720 isochrones were computed in the age range 8÷15 Gyr, in time steps of 0.5 Gyr. The whole database is available to the scientific community on the web. Models and isochrones were compared with recent calculations available in the literature and with the color-magnitude diagram of selected Galactic globular clusters. The dependence of relevant evolutionary quantities, namely turn-off and horizontal branch luminosities, on the chemical composition and convection efficiency were analyzed in a quantitative statistical way and analytical formulations were made available for reader's convenience. These relations can be useful in several fields of stellar evolution, e.g. evolutionary properties of binary systems, synthetic models for simple stellar populations and for star counts in galaxies, and chemical evolution models of galaxies.

show abstract

Super-Helium-rich Populations and the Origin of Extreme Horizontal-Branch Stars in Globular Clusters

Cited by 212 publications

References 19 publications

The mosaic multiple stellar populations in ω Centauri: the horizontal branch and the main sequence

The mosaic multiple stellar populations in ω Centauri: the horizontal branch and the main sequence

Revisiting the helium abundance in globular clusters with multiple main sequences

The Pisa Stellar Evolution Data Base for low-mass stars

Contact Info

Product

Resources

About