Radial distribution of the multiple stellar populations in $\mathsf{\omega}$ Centauri

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

“…of MpIII stars, which has been shown to be more centrally concentrated in the cluster (Bellini et al 2009). …”

Section: Discussionmentioning

confidence: 99%

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

“…Interestingly, fainter than M B ∼ 5.7, isochrones for the "standard" and the "extreme" heavy-element mixtures are essentially identical when the same values of Y and [Fe/H] ZAHB loci Figure 2. Comparison of several ZAHB loci for the indicated properties with the horizontal-branch stars in ω Cen having M B < 3.2 (from Bellini et al 2009) on the assumption of the reddening and distance modulus that were assumed in the previous figure, as noted. As mentioned in the text, the predicted colors had to be increased by +0.04 mag in order for the models to reproduce the HB population in the blue tail satisfactorily.…”

Section: Color-magnitude Diagram Considerationsmentioning

confidence: 94%

FROM THE COLOR-MAGNITUDE DIAGRAM OF Ω CENTAURI AND (SUPER-)ASYMPTOTIC GIANT BRANCH STELLAR MODELS TO a GALACTIC PLANE PASSAGE GAS PURGING CHEMICAL EVOLUTION SCENARIO

Herwig

VandenBerg

Navarro

et al. 2012

ApJ

View full text Add to dashboard Cite

We have investigated the color-magnitude diagram of ω Centauri and find that the blue main sequence (bMS) can be reproduced only by models that have a of helium abundance in the range Y = 0.35-0.40. To explain the faint subgiant branch of the reddest stars ("MS-a/RG-a" sequence), isochrones for the observed metallicity ([Fe/H] ≈ −0.7) appear to require both a high age (∼ 13 Gyr) and enhanced CNO abundances ([CNO/Fe] ≈ 0.9). Y ≈ 0.35 must also be assumed in order to counteract the effects of high CNO on turnoff colors, and thereby to obtain a good fit to the relatively blue turnoff of this stellar population. This suggest a short chemical evolution period of time (< 1 Gyr) for ω Cen. Our intermediate-mass (super-)AGB models are able to reproduce the high helium abundances, along with [N/Fe] ∼ 2 and substantial O depletions if uncertainties in the treatment of convection are fully taken into account. These abundance features distinguish the bMS stars from the dominant [Fe/H] ≈ −1.7 population. The most massive super-AGB stellar models (M ZAMS ≥ 6.8 M , M He,core ≥ 1.245 M ) predict too large N-enhancements, which limits their role in contributing to the extreme populations. In order to address the observed central concentration of stars with He-rich abundance we show here quantitatively that highly He-and N-enriched AGB ejecta have particularly efficient cooling properties. Based on these results and on the reconstruction of the orbit of ω Cen with respect to the Milky Way we propose the galactic plane passage gas purging scenario for the chemical evolution of this cluster. The bMS population formed shortly after the purging of most of the cluster gas as a result of the passage of ω Cen through the Galactic disk (which occurs today every ∼ 40Myrs for ω Cen) when the initial-mass function of the dominant population had "burned" through most of the Type II supernova mass range. AGB stars would eject most of their masses into the gas-depleted cluster through low-velocity winds that sink to the cluster core due to their favorable cooling properties and form the bMS population. In our discussion we follow our model through four passage events, which could explain not only some key properties of the bMS, but also of the MS-a/RGB-a and the s-enriched stars.

show abstract

“…Further studies on MSPs have shown that they exhibit different spatial (ω Cen Bellini et al 2009;several GCs Lardo et al 2011;47 Tuc Nataf et al 2011;M15 Larsen et al 2015) and dynamical signatures (47 Tuc Richer et al 2013 andKučinskas, Dobrovolskas &Bonifacio 2014). However, Dalessandro et al (2014) found that the different populations in NGC 6362 share the same radial distribution which is the first evidence of fully spatially mixed MSPs ever observed in a GC.…”

Section: Introductionmentioning

confidence: 92%

Dynamical constraints on the origin of multiple stellar populations in globular clusters

Khalaj¹,

Baumgardt²

2015

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

We have carried out a large grid of N -body simulations in order to investigate if massloss as a result of primordial gas expulsion can be responsible for the large fraction of second generation stars in globular clusters (GCs) with multiple stellar populations (MSPs). Our clusters start with two stellar populations in which 10% of all stars are second generation stars. We simulate clusters with different initial masses, different ratios of the half-mass radius of first to second generation stars, different primordial gas fractions and Galactic tidal fields with varying strength. We then let our clusters undergo primordial gas-loss and obtain their final properties such as mass, half-mass radius and the fraction of second generation stars. Using our N -body grid we then perform a Monte Carlo analysis to constrain the initial masses, radii and required gas expulsion time-scales of GCs with MSPs. Our results can explain the present-day properties of GCs only if (1) a substantial amount of gas was present in the clusters after the formation of second generation stars and (2) gas expulsion time-scales were extremely short ( 10 5 yr). Such short gas expulsion time-scales are in agreement with recent predictions that dark remnants have ejected the primordial gas from globular clusters, and pose a potential problem for the AGB scenario. In addition, our results predict a strong anti-correlation between the number ratio of second-generation stars in GCs and the present-day mass of GCs. So far, the observational data show only a significantly weaker anti-correlation, if any at all.

show abstract

Radial distribution of the multiple stellar populations in $\mathsf{\omega}$ Centauri

Cited by 115 publications

References 76 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

FROM THE COLOR-MAGNITUDE DIAGRAM OF Ω CENTAURI AND (SUPER-)ASYMPTOTIC GIANT BRANCH STELLAR MODELS TO a GALACTIC PLANE PASSAGE GAS PURGING CHEMICAL EVOLUTION SCENARIO

Dynamical constraints on the origin of multiple stellar populations in globular clusters

Contact Info

Product

Resources

About