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New Paper: Evolved Massive Stars at Low-metallicity III. A Source Catalog for the Large Magellanic Cloud
Evolved Massive Stars at Low-metallicity III. A Source Catalog for the Large Magellanic Cloud
Ming Yang, Alceste Z. Bonanos, Biwei Jiang, Jian Gao, Panagiotis Gavras, Grigoris Maravelias, Shu Wang, Xiao-Dian Chen, Man I Lam, Yi Ren, Frank Tramper, Zoi T. Spetsieri
New paper on the circumstellar environment of the B[e] supergiant LHA 120-S 35
Resolving the clumpy circumstellar environment of the B[e] supergiant LHA 120-S 35
Andrea F. Torres, Lydia S. Cidale, Michaela Kraus, María L. Arias, Rodolfo H. Barbá, Grigoris Maravelias, Marcelo Borges Fernandes
B[e] supergiants (SGs) are massive post-main-sequence stars, surrounded by a complex circumstellar (CS) environment. The aim of this work is to investigate the structure and kinematics of the CS disc of the B[e] SG LHA 120-S 35. We used high-resolution optical spectra obtained in different years to model the forbidden emission lines and determine the kinematical properties of their line-forming regions, assuming Keplerian rotation. We also used low-resolution near-infrared (IR) spectra to explore the variability of molecular emission. LHA 120-S 35 displays spectral variability in both optical and IR regions. The P-Cygni line profiles of H I, as well as those of Fe II and O I, suggest the presence of a strong bipolar clumped wind. We distinguish density enhancements in the P-Cygni absorption component of the first Balmer lines, which show variations in both velocity and strength. The P-Cygni profile emission component is double-peaked, indicating the presence of a rotating CS disc. We also observe line-profile variations in the permitted and forbidden features of Fe II and O I. In the IR, we detect variations in the intensity of the H I emission lines as well as in the emission of the CO band-heads. Moreover, we find that the profiles of each [Ca II] and [O I] emission lines contain contributions from spatially different (complete or partial) rings. Globally, we find evidence of detached multi-ring structures, revealing density variations along the disc. We suggest that LHA 120-S 35 has passed through the red-supergiant (RSG) phase and evolves back bluewards in the Hertzsprung-Russell diagram. The formation of the complex CS structure could be the result of the wind-wind interactions of the post-RSG wind with the previously ejected material from the RSG. However, the presence of a binary companion can not be excluded. Finally, we find that LHA 120-S 35 belongs to a young stellar cluster.
New Paper on star clusters in the Large Magellanic Cloud
A novel method to automatically detect and measure the ages of star clusters in nearby galaxies: Application to the Large Magellanic Cloud
T. Bitsakis, P. Bonfini, R. A. Gonzalez-Lopezlira, V. H. Ramirez-Siordia, G. Bruzual, S. Charlot, G. Maravelias, D. Zaritsky
We present our new, fully-automated method to detect and measure the ages of star clusters in nearby galaxies, where individual stars can be resolved. The method relies purely on statistical analysis of bservations and Monte-Carlo simulations to define stellar overdensities in the data. It decontaminates the cluster color-magnitude diagrams and, using a revised version of the Bayesian isochrone fitting code of Ramirez-Siordia et al., estimates the ages of the clusters. Comparisons of our estimates with those from other surveys show the superiority of our method to extract and measure the ages of star clusters, even in the most crowded fields. An application of our method is shown for the high-resolution, multi-band imaging of the Large Magellanic Cloud. We detect 4850 clusters in the 7 deg2 we surveyed, 3451 of which have not been reported before. Our findings suggest multiple epochs of star cluster formation, with the most probable occurring ~310 Myr ago. Several of these events are consistent with the epochs of the interactions among the Large and Small Magellanic Clouds, and the Galaxy, as predicted by N-body numerical simulations. Finally, the spatially resolved star cluster formation history may suggest an inside-out cluster formation scenario throughout the LMC, for the past 1 Gyr.
How big a star can be?
It seems that this question has no final answer yet. Although the recent models were claiming that no star bigger than 100-150 solar masses can exist, there is evidence that a star close to 300 solar masses exists in the Large Magellanic Cloud. One star, R136a1 (from the young cluster RMC 136a or R136), is considered to have a mass ~265 solar masses (with a birthweight close to 320 solar masses).
More on ESO’s announcement (eso1030) & the paper (2010arXiv1007.3284C / Crowther P.A. et al, The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150Msolar stellar mass limit, MNRAS, 408, p 731, 2010)