| 1. |
- Cabrera-Ziri, I., et al.
(författare)
-
Searching for globular cluster chemical anomalies on the main sequence of a young massive cluster
- 2020
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 495:1, s. 375-382
-
Tidskriftsartikel (refereegranskat)abstract
- The spectroscopic and photometric signals of the star-to-star abundance variations found in globular clusters seem to be correlated with global parameters like the cluster's metallicity, mass, and age. Understanding this behaviour could bring us closer to the origin of these intriguing abundance spreads. In this work we use deep HST photometry to look for evidence of abundance variations in the main sequence of a young massive cluster NGC 419 (similar to 10(5) M-circle dot, similar to 1.4 Gyr). Unlike previous studies, here we focus on stars in the same mass range found in old globulars (similar to 0.75-1 M-circle dot), where light elements variations are detected. We find no evidence for N abundance variations among these stars in the Un - B and U - B colour-magnitude diagrams of NGC 419. This is at odds with the N variations found in old globulars like 47 Tuc, NGC 6352, and NGC 6637 with similar metallicity to NGC 419. Although the signature of the abundance variations characteristic of old globulars appears to be significantly smaller or absent in this young cluster, we cannot conclude if this effect is mainly driven by its age or its mass.
|
|
| 2. |
- Martocchia, S., et al.
(författare)
-
Leveraging HST with MUSE : II. Na-abundance variations in intermediate age star clusters
- 2020
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 499:1, s. 1200-1211
-
Tidskriftsartikel (refereegranskat)abstract
- Ancient (>10 Gyr) globular clusters (GCs) show chemical abundance variations in the form of patterns among certain elements, e.g. N correlates with Na and anticorrelates with O. Recently, N abundance spreads have also been observed in massive star clusters that are significantly younger than old GCs, down to an age of similar to 2Gyr. However, so far N has been the only element found to vary in such young objects. We report here the presence of Na abundance variations in the intermediate age massive star clusters NGC 416 (similar to 6.5Gyr old) and Lindsay 1 (similar to 7.5Gyr old) in the Small Magellanic Cloud, by combining Hubble Space Telescope (HST) and European Southern Observatory Very Large Telescope MUSE observations. Using HST photometry, we were able to construct 'chromosome maps' and separate subpopulations with different N content, in the red giant branch of each cluster. MUSE spectra of individual stars belonging to each population were combined, resulting in high signal-to-noise spectra representative of each population, which were compared to search for mean differences in Na. We find a mean abundance variation of Delta[Na/Fe] = 0.18 +/- 0.04 dex for NGC 416 and Delta[Na/Fe] = 0.24 +/- 0.05 dex for Lindsay 1. In both clusters, we find that the population that is enhanced in N is also enhanced in Na, which is the same pattern to the one observed in ancient GCs. Furthermore, we detect a bimodal distribution of core-helium-burning red clump (RC) giants in the UV colour-magnitude diagram of NGC 416. A comparison of the stacked MUSE spectra of the two RCs shows the same mean Na abundance difference between the two populations. The results reported in this work are a crucial hint that star clusters of a large age range share the same origin: they are the same types of objects, but only separated in age.
|
|
| 3. |
- Saracino, S., et al.
(författare)
-
Leveraging HST with MUSE - I. Sodium abundance variations within the 2-Gyr-old cluster NGC 1978
- 2020
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 498:3, s. 4472-4480
-
Tidskriftsartikel (refereegranskat)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 similar 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 Delta[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.
|
|
