Star clusters are privileged laboratories for studying the evolution of massive stars (OB stars). One particularly interesting question concerns the phases, during which the classical Be stars occur, which unlike HAe/Be stars, are not pre-main sequence objects, nor supergiants. Rather, they are extremely rapidly rotating B-type stars with a circumstellar decretion disk formed by episodic ejections of matter from the central star. To study the impact of mass, metallicity, and age on the Be phase, we observed SMC open clusters with two different techniques: 1) with the ESO-WFI in its slitless mode, which allowed us to find the brighter Be and other emission-line stars in 84 SMC open clusters 2) with the VLT-FLAMES multi-fiber spectrograph in order to determine accurately the evolutionary phases of Be stars in the Be-star rich SMC open cluster NGC 330. Based on a comparison to the Milky Way, a model of Be stellar evolution / appearance as a function of metallicity and mass / spectral type is developed, involving the fractional critical rotation rate as a key parameter.
We present the analysis of three faint clusters of the Small Magellanic Cloud RZ82, HW42 and RZ158. We employed the SOAR telescope instrument SAM with adaptive optics, allowing us to reach to V~23-24 mag, unprecedentedly, a depth sufficient to measure ages of up to about 10-12Gyr. All three clusters are resolved to their centres, and the resulting colour-magnitude diagrams (CMDs) allow us to derive ages of 3.9, 2.6, and 4.8Gyr respectively. These results are significantly younger than previous determinations (7.1, 5.0, and 8.3Gyr, respectively), based on integrated photometry or shallower CMDs…
Delta Scuti ($δ$ Sct) stars have been extensively studied in our Galaxy, but far less in extragalactic systems. Here we study the population of $δ$ Sct variables in NGC 419, an intermediate-age globular cluster of the Small Magellanic Cloud (SMC), using $g,r,i$ Gemini-S/GMOS time series observations. Our goal is to study the role of such variables in the cluster extended main-sequence turnoff (MSTO). We report the discovery of 54 $δ$ Sct stars and three eclipsing binaries in the NGC 419 field. We find only a handful of the $δ$ Sct stars at the MSTO of NGC 419 while the majority is fainter, ind…
We derived surface brightness profiles in the \emph{g} band for 170 Small Magellanic Cloud (SMC) star clusters (SCs) mainly located in the central region of the galaxy. We provide a set of homogeneous structural parameters obtained by fitting Elson, Fall \& Freeman (EFF) and King models. Through a careful analysis of their colour-magnitude diagrams (CMDs) we also supply the ages for a subsample of 134 SCs. For the first time, such a large sample of SCs in the SMC is homogeneously characterized in terms of their sizes, luminosities and masses, widening the probed region of the parameter space, …
The structure of the Small Magellanic Cloud (SMC) is very complex, in particular in the periphery that suffers more from the interactions with the Large Magellanic Cloud (LMC). A wealth of observational evidence has been accumulated revealing tidal tails and bridges made up of gas, stars and star clusters. Nevertheless, a full picture of the SMC outskirts is only recently starting to emerge with a 6D phase-space map plus age and metallicity using star clusters as tracers. In this work, we continue our analysis of another outer region of the SMC, the so-called West Halo, and combined it with th…
In this work we study 35 stellar clusters in the Small Magellanic Cloud (SMC) in order to provide their mean metallicities and ages. We also provide mean metallicities of the fields surrounding the clusters. We used Strömgren photometry obtained with the 4.1 m SOAR telescope and take advantage of $(b - y)$ and $m1$ colors for which there is a metallicity calibration presented in the literature. The spatial metallicity and age distributions of clusters across the SMC are investigated using the results obtained by Strömgren photometry. We confirm earlier observations that younger, more metal-ric…
Context. The interactions between the SMC and LMC created the Magellanic Bridge, a stream of gas and stars pulled out of the SMC towards the LMC about 150 Myr ago. The tidal counterpart of this structure, which should include a trailing arm, has been predicted by models but no compelling observational evidence has confirmed the Counter-Bridge so far. Aims. The main goal of this work is to find the stellar counterpart of the Magellanic Bridge and Counter-Bridge. We use star clusters in the SMC outskirts as they provide 6D phase-space vector, age and metallicity that help characterise the outski…
Massive stars are among the main cosmic engines driving the evolution of star-forming galaxies. Their powerful ionising radiation and stellar winds inject a large amount of energy in the interstellar medium. Furthermore, mass-loss ($\dot{M}$) through radiatively driven winds plays a key role in the evolution of massive stars. Even so, the wind mass-loss prescriptions used in stellar evolution models, population synthesis, and stellar feedback models often disagree with mass-loss rates empirically measured from the UV spectra of low metallicity massive stars. The most massive young star cluster…
Using spectra obtained with the VLT/FORS2 and Gemini-S/GMOS instruments we have investigated carbon, nitrogen and sodium abundances in a sample of red giants in the Small Magellanic Cloud cluster Kron 3. The metallicity and luminosity of this cluster are comparable to those of Galactic globular clusters although with a notably younger age of $\sim$ 6.5 Gyr. Specifically we have investigated the strengths of the CH ($λ$ 4300 A) and CN ($λ$ 3800, $λ$ 4215) molecular bands finding a bimodality of CN band-strengths and a CH/CN anti-correlation. Application of spectrum synthesis techniques reveals …
We set out to compare the age-metallicity relation (AMR) of massive clusters from Magellanic Cloud mass galaxies in the E-MOSAICS suite of numerical cosmological simulations with an amalgamation of observational data of massive clusters in the Large and Small Magellanic Clouds (LMC/SMC). We aim to test if: i) star cluster formation proceeds according to universal physical processes, suggestive of a common formation mechanism for young-massive clusters (YMCs), intermediate-age clusters (IACs), and ancient globular clusters (GCs); ii) massive clusters of all ages trace a continuous AMR; iii) the…
Star clusters as tracers of the perturbed southern outer disk of the Large Magellanic Cloud
Instituto Interdisciplinario de Ciencias Básicas (ICB), CONICET-UNCuyo（基础科学跨研究所（ICB），阿根廷国家科学研究委员会-门多萨国立大学）；Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)（阿根廷国家科学研究委员会）
Observations of massive stars in young open clusters (< ~8 Myr) have shown that a majority of them are in binary systems, most of which will interact during their life. Populations of massive stars older than ~20 Myr allow us to probe the outcome of such interactions after many systems have experienced mass and angular momentum transfer. Using multi-epoch integral-field spectroscopy, we investigate the multiplicity properties of the massive-star population in NGC 330 (~40 Myr) in the Small Magellanic Cloud to search for imprints of stellar evolution on the multiplicity properties. From six epo…
