Chromosome maps of young LMC clusters: an additional case of coeval multiple populations

ABSTRACT Recent studies have revealed that the multiple populations (MPs) phenomenon does not occur only in ancient and massive Galactic globular clusters (GCs), but it is also observed in external galaxies, where GCs sample a wide age range with respect to the Milky Way. However, for a long time, it was unclear whether we were looking at the same phenomenon in different environments or not. The first evidence that the MPs phenomenon is the same regardless of cluster age and host galaxy came out recently, when an intermediate-age cluster from the Small Magellanic Cloud, Lindsay 1, and a Galactic GC have been directly compared. By complementing those data with new images from the Hubble Space Telescope (HST), we extend the comparison to two clusters of different ages: NGC 2121 (∼2.5 Gyr) and NGC 1783 (∼1.5 Gyr), from the Large Magellanic Cloud. We find a clear correlation between the RGB (red giant branch) width in the pseudo-colour CF275W, F343N, F438W and the age of the cluster itself, with the older cluster having larger σ(CF275W, F343N, F438W)RGB and vice versa. Unfortunately, the σ values cannot be directly linked to the N-abundance variations within the clusters before properly taking account the effect of the first dredge-up. Such HST data also allow us to explore whether multiple star formation episodes occurred within NGC 2121. The two populations are indistinguishable, with an age difference of only 6 ± 12 Myr and an initial helium spread of 0.02 or lower. This confirms our previous results, putting serious constraints on any model proposed to explain the origin of the chemical anomalies in GCs.

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Leveraging HST with MUSE – I. Sodium abundance variations within the 2-Gyr-old cluster NGC 1978

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2748 ◽

2020 ◽

Vol 498 (3) ◽

pp. 4472-4480

Author(s):

S Saracino ◽

S Kamann ◽

C Usher ◽

N Bastian ◽

S Martocchia ◽

...

Keyword(s):

Globular Clusters ◽

Hubble Space Telescope ◽

Large Magellanic Cloud ◽

Host Galaxy ◽

Very Large Telescope ◽

Nearby Galaxies ◽

Red Giant ◽

Sodium Abundance ◽

Massive Clusters ◽

Cluster Age

ABSTRACT Nearly all of the well-studied ancient globular clusters (GCs), in the Milky Way and in nearby galaxies, show star-to-star variations in specific elements (e.g. He, C, N, O, Na, and Al), known as ‘multiple populations’ (MPs). However, MPs are not restricted to ancient clusters, with massive clusters down to ∼2 Gyr showing signs of chemical variations. This suggests that young and old clusters share the same formation mechanism but most of the work to date on younger clusters has focused on N variations. Initial studies even suggested that younger clusters may not host spreads in other elements beyond N (e.g. Na), calling into question whether these abundance variations share the same origin as in the older GCs. In this work, we combine Hubble Space Telescope (HST) photometry with Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) spectroscopy of a large sample of red giant branch (RGB) stars (338) in the Large Magellanic Cloud cluster NGC 1978, the youngest globular to date with reported MPs in the form of N spreads. By combining the spectra of individual RGB stars into N-normal and N-enhanced samples, based on the ‘chromosome map’ derived from HST, we search for mean abundance variations. Based on the NaD line, we find a Na difference of Δ[Na/Fe] = 0.07 ± 0.01 between the populations. While this difference is smaller than typically found in ancient GCs (which may suggest a correlation with age), this result further confirms that the MP phenomenon is the same, regardless of cluster age and host galaxy. As such, these young clusters offer some of the strictest tests for theories on the origin of MPs.

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Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud – V. Multiple populations in ancient globular clusters

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa822 ◽

2020 ◽

Vol 494 (2) ◽

pp. 1946-1955

Author(s):

Christina K Gilligan ◽

Brian Chaboyer ◽

Jeffrey D Cummings ◽

Dougal Mackey ◽

Roger E Cohen ◽

...

Keyword(s):

Globular Clusters ◽

Main Sequence ◽

Hubble Space Telescope ◽

Cluster Formation ◽

Large Magellanic Cloud ◽

Magellanic Cloud ◽

Wide Field ◽

Multiple Populations ◽

Show Evidence ◽

Advanced Camera For Surveys

ABSTRACT We examine four ancient Large Magellanic Cloud (LMC) globular clusters (GCs) for evidence of multiple stellar populations using the Advanced Camera for Surveys and Wide Field Camera 3 on the Hubble Space Telescope Programme GO-14164. NGC 1466, NGC 1841, and NGC 2257 all show evidence for a redder, secondary population along the main sequence. Reticulum does not show evidence for the presence of a redder population, but this GC has the least number of stars and Monte Carlo simulations indicate that the sample of main-sequence stars is too small to robustly infer whether a redder population exists in this cluster. The second, redder, population of the other three clusters constitutes $\sim 30-40{{\ \rm per\ cent}}$ of the total population along the main sequence. This brings the total number of ancient LMC GCs with known split or broadened main sequences to five. However, unlike for Hodge 11 and NGC 2210 (see Gilligan et al. (2019)), none of the clusters shows evidence for multiple populations in the horizontal branch. We also do not find evidence of a second population along the red giant branch.

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Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud – IV. Evidence for multiple populations in Hodge 11 and NGC 2210

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1174 ◽

2019 ◽

Vol 486 (4) ◽

pp. 5581-5599 ◽

Cited By ~ 5

Author(s):

Christina K Gilligan ◽

Brian Chaboyer ◽

Jeffrey D Cummings ◽

Dougal Mackey ◽

Roger E Cohen ◽

...

Keyword(s):

Globular Clusters ◽

Main Sequence ◽

Hubble Space Telescope ◽

Cluster Formation ◽

Stellar Populations ◽

Large Magellanic Cloud ◽

Magellanic Cloud ◽

Wide Field ◽

Horizontal Branch ◽

Advanced Camera For Surveys

Abstract We present a multiple population search in two old Large Magellanic Cloud (LMC) Globular clusters, Hodge 11 and NGC 2210. This work uses data from the Advanced Camera for Surveys and Wide Field Camera 3 on the Hubble Space Telescope from programme GO-14164 in Cycle 23. Both of these clusters exhibit a broadened main sequence with the second population representing (20 ± ∼5) per cent for NGC 2210 and (30 ± ∼5) per cent for Hodge 11. In both clusters, the smaller population is redder than the primary population, suggesting CNO variations. Hodge 11 also displays a bluer second population in the horizontal branch, which is evidence for helium enhancement. However, even though NGC 2210 shows similarities to Hodge 11 in the main sequence, there does not appear to be a second population on NGC 2210’s horizontal branch. This is the first photometric evidence that ancient LMC Globular clusters exhibit multiple stellar populations.

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Expanding the Time Domain of Multiple Populations: Evidence of Nitrogen Variations in the ∼1.5 Gyr Old Star Cluster NGC 1783

The Astrophysical Journal ◽

10.3847/2041-8213/ac424a ◽

2021 ◽

Vol 924 (1) ◽

pp. L2

Author(s):

Mario Cadelano ◽

Emanuele Dalessandro ◽

Maurizio Salaris ◽

Nate Bastian ◽

Alessio Mucciarelli ◽

...

Keyword(s):

Hubble Space Telescope ◽

Light Element ◽

Large Magellanic Cloud ◽

Chemical Abundance ◽

Multiple Populations ◽

Stellar Cluster ◽

Show Evidence ◽

Red Giant ◽

Color Combinations ◽

The Time Domain

Abstract We present the result of a detailed analysis of Hubble Space Telescope UV and optical deep images of the massive and young (∼1.5 Gyr) stellar cluster NGC 1783 in the Large Magellanic Cloud. This system does not show evidence of multiple populations (MPs) along the red giant branch (RGB) stars. However, we find that the cluster main sequence (MS) shows evidence of a significant broadening (50% larger than what is expected from photometric errors) along with hints of possible bimodality in the MP sensitive (m F343N − m F438W, m F438W) color–magnitude diagram (CMD). Such an effect is observed in all color combinations including the m F343N filter, while it is not found in the optical CMDs. This observational evidence suggests we might have found light-element chemical abundance variations along the MS of NGC 1783, which represents the first detection of MPs in a system younger than 2 Gyr. A comparison with isochrones including MP-like abundances shows that the observed broadening is compatible with a N abundance enhancement of Δ([N/Fe]) ∼ 0.3. Our analysis also confirms previous results about the lack of MPs along the cluster RGB. However, we find that the apparent disagreement between the results found on the MS and the RGB is compatible with the mixing effects linked to the first dredge up. This study provides new key information about the MP phenomenon and suggests that star clusters form in a similar way at any cosmic age.

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Mass-loss law for red giant stars in simple population globular clusters

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab568 ◽

2021 ◽

Vol 503 (1) ◽

pp. 694-703

Author(s):

M Tailo ◽

A P Milone ◽

E P Lagioia ◽

F D’Antona ◽

S Jang ◽

...

Keyword(s):

Mass Loss ◽

Stellar Evolution ◽

Globular Clusters ◽

Hubble Space Telescope ◽

Stellar Populations ◽

Chemical Compositions ◽

Multiple Populations ◽

Mass Losses ◽

Red Giant ◽

Stellar Masses

ABSTRACT The amount of mass lost by stars during the red-giant branch (RGB) phase is one of the main parameters to understand and correctly model the late stages of stellar evolution. Nevertheless, a fully comprehensive knowledge of the RGB mass-loss is still missing. Galactic Globular Clusters (GCs) are ideal targets to derive empirical formulations of mass-loss, but the presence of multiple populations with different chemical compositions has been a major challenge to constrain stellar masses and RGB mass-losses. Recent work has disentangled the distinct stellar populations along the RGB and the horizontal branch (HB) of 46 GCs, thus providing the possibility to estimate the RGB mass-loss of each stellar population. The mass-losses inferred for the stellar populations with pristine chemical composition (called first-generation or 1G stars) tightly correlate with cluster metallicity. This finding allows us to derive an empirical RGB mass-loss law for 1G stars. In this paper, we investigate seven GCs with no evidence of multiple populations and derive the RGB mass-loss by means of high-precision Hubble-Space Telescope photometry and accurate synthetic photometry. We find a cluster-to-cluster variation in the mass-loss ranging from ∼0.1 to ∼0.3 M⊙. The RGB mass-loss of simple-population GCs correlates with the metallicity of the host cluster. The discovery that simple-population GCs and 1G stars of multiple population GCs follow similar mass-loss versus metallicity relations suggests that the resulting mass-loss law is a standard outcome of stellar evolution.

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