I. Cabrera-Ziri

A general abundance problem for all self-enrichment scenarios for the origin of multiple populations in globular clusters

A number of stellar sources have been advocated as the origin of the enriched material required to explain the abundance anomalies seen in ancient globular clusters (GCs). Most studies to date have compared the yields from potential sources (asymptotic giant branch stars (AGBs), fast rotating massive stars (FRMS), high mass interacting binaries (IBs), and very massive stars (VMS)) with observations of specific elements that are observed to vary from star-to-star in GCs, focussing on extreme GCs such as NGC 2808, which display large He variations. However, a consistency check between the results of fitting extreme cases with the requirements of more typical clusters, has rarely been done. Such a check is particularly timely given the constraints on He abundances in GCs now available. Here we show that all of the popular enrichment sources fail to reproduce the observed trends in GCs, focussing primarily on Na, O and He. In particular, we show that any model that can fit clusters like NGC 2808, will necessarily fail (by construction) to fit more typical clusters like 47 Tuc or NGC 288. All sources severely over-produce He for most clusters. Additionally, given the large differences in He spreads between clusters, but similar spreads observed in Na–O, only sources with large degrees of stochasticity in the resulting yields will be able to fit the observations. We conclude that no enrichment source put forward so far (AGBs, FRMS, IBs, VMS - or combinations thereof) is consistent with the observations of GCs. Finally, the observed trends of increasing [N/Fe] and He spread with increasing cluster mass cannot be resolved within a self-enrichment framework, without further exacerbating the mass budget problem.

Constraining Globular Cluster Formation Through Studies of Young Massive Clusters: I. A lack of ongoing star formation within young clusters

We present a survey of 130 Galactic and extragalactic young massive clusters (YMCs, 10 4 < M/M⊙ < 10 8 , 10 < t/Myr < 1000) with integrated spectroscopy or resolved stellar photometry (40 presented here and 90 from the literature) and use the sample to search for evidence of ongoing star-formation within the clusters. Such episodes of secondary (or continuous) star-formation are predicted by models that attempt to explain the observed chemical and photometric anomalies observed in globular clusters as being due to the formation of a second stellar population within an existing first population. Additionally, studies that have claimed extended star-formation histories within LMC/SMC intermediate age clusters (1-2 Gyr), also imply that many young massive clusters should show ongoing star-formation. Based on visual inspection of the spectra and/or the colour-magnitude diagrams, we do not find evidence for ongoing star-formation within any of the clusters, and use this to place constraints on the above models. Models of continuous star-formation within clusters, lasting for hundreds of Myr, are ruled out at high significance (unless stellar IMF variations are invoked). Models for the (nearly instantaneous) formation of a secondary population within an existing first generation are not favoured, but are not formally discounted due to the finite sampling of age/mass-space.

Constraining globular cluster formation through studies of young massive clusters – II. A single stellar population young massive cluster in NGC 34

Currently there are two competing scenarios to explain the origin of the stellar population in globular clusters (GCs). The main difference between them is whether or not multiple events of star formation took place within GCs. In this paper we present the star formation history (SFH) of Cluster 1, a massive young cluster in NGC 34

Constraining globular cluster formation through studies of young massive clusters - V. ALMA observations of clusters in the Antennae

(\sim10^7\mbox{ M}_\odot)

The Search for Multiple Populations in Magellanic Cloud Clusters II: The Detection of Multiple Populations in Three Intermediate-Age SMC Clusters

. We use DynBaS, a spectrum fitting algorithm, to retrieve the SFH and find that Cluster 1 is consistent with a single stellar population of solar metallicity with an age of

Is the escape velocity in star clusters linked to extended star formation histories? Using NGC 7252: W3 as a test case

100\pm30

A young cluster with an extended main-sequence turnoff: confirmation of a prediction of the stellar rotation scenario

Myr and a mass of

Searching for GC-like abundance patterns in young massive clusters

1.9\pm0.4\times10^7\mbox{ M}_\odot

The search for multiple populations in Magellanic Cloud Clusters – III. No evidence for multiple populations in the SMC cluster NGC 419

. These results are in conflict with the expectations/predictions of the scenarios that invoke extended or multiple episodes within 30--100 Myr of the initial star-formation burst in young massive clusters.

A high fraction of Be stars in young massive clusters: evidence for a large population of near-critically rotating stars

Some formation scenarios that have been put forward to explain multiple populations within Globular Clusters (GCs) require that the young massive cluster have large reservoirs of cold gas within them, which is necessary to form future generations of stars. In this paper we use deep observations taken with Atacama Large Millimeter/sub-millimeter Array (ALMA) to assess the amount of molecular gas within 3 young (50 − 200 Myr) massive (� 106 M⊙) clusters in the Antennae galaxies. No significant CO(3–2) emission was found associated with any of the three clusters. We place upper limits for the molecular gas within these clusters of � 1 × 105 M⊙ (or < 9% of the current stellar mass). We briefly review different scenarios that propose multiple episodes of star formation and discuss some of their assumptions and implications. Our results are in tension with the predictions of GC formation scenarios that expect large reservoirs of cool gas within young massive clusters at these ages.