Evidence of globular cluster abundance anomalies in the SMC intermediate-age cluster Kron 3

Salgado, C.; Costa, G. S. Da; Yong, David; Salinas, R.; Norris, John E.; Mackey, A. D.; Marino, A. F.; Milone, A. P.

doi:10.1093/mnras/stac1724

Cited by 5 publications

(1 citation statement)

References 85 publications

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“…Instead of a simple population of coeval stars formed from a chemically homogeneous protocluster cloud, individual GCs associated with the Milky Way and to several galaxies of the Local Group host stars formed with large variations of their content in C, N, O, Na, and Al, with Mg also varying in the most massive and/or most metal-poor Galactic GCs (Cohen 1978;Peterson 1980;Carretta et al 2009Carretta et al , 2010Mészáros et al 2015Mészáros et al , 2020Pancino et al 2017;Schiavon et al 2017;Wang et al 2017;O'Malley & Chaboyer 2018;Mucciarelli et al 2009;Schiavon et al 2013;Dalessandro et al 2016;Carretta et al 2017;Niederhofer et al 2017;Gilligan et al 2019;Milone et al 2020;Vanaraj et al 2021;Leath et al 2022;Larsen et al 2022). Hints for the presence of MSP with similar characteristics are also found in intermediate-age (down to ∼ 2 Gyr) massive star clusters in the Magellanic Clouds (Hollyhead et al 2017(Hollyhead et al , 2019Saracino et al 2020;Martocchia et al 2020Martocchia et al , 2021Asa'd et al 2022;Cadelano et al 2022;Salgado et al 2022). While the epoch when the clusters formed is thus not critical for MSP to be present, the mass of the cluster is.…”

Section: Introductionmentioning

confidence: 94%

Search strategies for supermassive stars in young clusters and application to nearby galaxies

A.¹,

D.²,

Messa³

et al. 2023

A&A

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Context. Supermassive stars (SMS) with masses M 10 3 − 10 4 M , formed by runaway collisions in young, massive, and dense star clusters have been invoked as a possible solution to the puzzles raised by the presence of multiple stellar populations and peculiar abundance patterns observed in globular clusters. However, such objects have not been observed so far. Aims. We developed observational strategies to search for SMS hosted within young massive clusters (thought to be the precursors of globular clusters, GCs), which could be applicable in a relatively general fashion, using both photometric and spectroscopic observations. Methods. We used theoretical predictions of spectra of SMS and SMS-hosting clusters, together with predictions from standard simple stellar populations to examine their impact on color-color diagrams and on individual optical spectral lines (primarily Hydrogen emission and absorption lines). As a first step, we apply our search strategies to a sample of ∼ 3000 young star clusters (YSC) from two nearby galaxies with multi-band observations from the HST and optical integral-field spectroscopy obtained with MUSE on the Very Large Telescope. Results. We focus on models for SMS with large radii (corresponding to T eff 7000 K), which predict strong Balmer breaks, and construct proper color-color diagrams to select the corresponding SMS-hosting cluster candidates. We show that their spectrophotometric properties are similar to that of normal clusters with ages of a few hundred Myr, which would, however, show signs of composite stellar populations, in particular the presence of nebular lines ( Hα and others). Examining the photometry, overall SEDs, and the spectra of ∼ 100 clusters with strong Balmer breaks, we have found several objects with peculiar SEDs, the presence of emission lines, or other peculiar signatures. After careful inspection of the available data, we do not find good candidates of SMS-hosting clusters. In most cases, the composite spectra can be explained by multiple clusters or H ii regions inside the aperture covered by the spectra, by contamination from a Planetary Nebula or diffuse gas, or by improper background subtraction. Furthermore, most of our candidate clusters are too faint to host SMS. Conclusions. We demonstrate a search strategy for SMS by applying it to a sample of YSCs in two nearby galaxies. Our method can be applied to larger samples and also extended to higher redshift with existing and upcoming telescopes. It should thus provide an important test for GC formation scenarios invoking such extreme stars.

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Section: Introductionmentioning

confidence: 94%

Search strategies for supermassive stars in young clusters and application to nearby galaxies

A.¹,

D.²,

Messa³

et al. 2023

A&A

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Synthetic stellar spectra for studying multiple populations in globular clusters

Branco,

Coelho,

Lançon

et al. 2024

A&A

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Most Galactic globular clusters (GCs) harbour multiple populations of stars (MPs) that are composed of at least two generations: the first generation is characterised by a standard α-enhanced metal mixture, as observed in field halo stars of the Milky Way, and the second generation displays an anti-correlated CN–ONa chemical abundance pattern in combination with an enhanced helium fraction. Adequate collections of stellar spectra are needed to characterize the effect of these changes in the stellar abundance on the integrated light of GCs. We present a grid of synthetic stellar spectra to cover the atmospheric parameters relevant to old stellar populations at four subsolar metallicities and two abundance patterns that are representative of the first and second generations of stars in GCs. The integrated spectra of the populations were computed using our stellar grid and empirical stellar populations, namely, colour-magnitude diagrams from the literature for Galactic GCs. The spectra range from 290 to 1000 nm, where we measured the effect on several spectrophotometric indices due to the surface abundance variations attributed to MPs. We find non-negligible effects of the MPs on the spectroscopic indices that are sensitive to C, N, Ca, or Na, and on the Balmer indices; we also describe how MPs modify specific regions in the near-UV and near-IR that can be measured with narrow or medium photometric passbands. The effects vary with metallicity. A number of these changes remain detectable even when we account for the stochastic fluctuations due to the finite nature of the stellar population cluster.

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A high-resolution spectroscopic search for multiple populations in the 2 Gyr old cluster NGC 1846

Nordlander

Costa

et al. 2022

Monthly Notices of the Royal Astronomical Society

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We present detailed C, O, Na, Mg, Si, Ca, Ti, V, Fe, Zr, Ba, and Eu abundance measurements for 20 red giant branch (RGB) stars in the LMC star cluster NGC 1846 ([Fe/H] = -0.59). This cluster is 1.95 Gyr old and lies just below the supposed lower age limit (2 Gyr) for the presence of multiple populations in massive star clusters. Our measurements are based on high and low-resolution VLT/FLAMES spectra combined with photometric data from HST. Corrections for non-local thermodynamic equilibrium effects are also included for O, Na, Mg, Si, Ca, Fe and Ba. Our results show that there is no evidence for multiple populations in this cluster based on the lack of any intrinsic star-to-star spread in the abundances of Na and O: we place 95 per cent confidence limits on the intrinsic dispersion for these elements of ≤0.07 and ≤0.09 dex, respectively. However, we do detect a significant spread in the carbon abundances, indicating varying evolutionary mixing occurring on the RGB that increases with luminosity. Overall, the general abundance patterns for NGC 1846 are similar to those seen in previous studies of intermediate-age LMC star clusters and field stars.

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Evidence of globular cluster abundance anomalies in the SMC intermediate-age cluster Kron 3

Cited by 5 publications

References 85 publications

Search strategies for supermassive stars in young clusters and application to nearby galaxies

Search strategies for supermassive stars in young clusters and application to nearby galaxies

Synthetic stellar spectra for studying multiple populations in globular clusters

A high-resolution spectroscopic search for multiple populations in the 2 Gyr old cluster NGC 1846

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