ﻻ يوجد ملخص باللغة العربية
Stars which start their lives with spectral types O and early-B are the progenitors of core-collapse supernovae, long gamma-ray bursts, neutron stars, and black holes. These massive stars are the primary sources of stellar feedback in star-forming galaxies. At low metallicities, the properties of massive stars and their evolution are not yet fully explored. Here we report a spectroscopic study of 320 OB stars in the Small Magellanic Cloud. The data, which we obtained with the ESO Very Large Telescope, were analyzed using state-of-the-art stellar atmosphere models. We find that stellar winds of our sample stars are much weaker than theoretically expected. The stellar rotation rates show a bi-modal distribution. The well-populated upper Hertzsprung-Russell diagram including our sample OB stars from SMC Wing as well as additional evolved stars all over SMC from the literature shows a strict luminosity limit. The comparison with single-star evolutionary tracks suggests a dichotomy in the fate of massive stars in the SMC. Only stars with Minit<30M$_{odot}$ seem to evolve from the main sequence to the cool side of the HRD to become a red supergiant and to explode as type II-P supernova. In contrast, stars with Minit>30M$_{odot}$ appear to stay always hot and might evolve quasi chemically homogeneously, finally collapsing to relatively massive black holes. However, we find no indication that chemical mixing is correlated with rapid rotation. We report extended star-formation episodes in a quiescent low-density region of the Wing, which is progressing stochastically. We measure the key parameters of stellar feedback and establish the links between the rates of star formation and supernovae. Our study reveals that in metal-poor environments the stellar feedback is dominated by core-collapse supernovae in combination with winds and ionizing radiation supplied by a few of the most massive stars.
The supergiant ionized shell SMC-SGS 1 (DEM 167), located in the outer Wing of the Small Magellanic Cloud (SMC), resembles structures that originate from an energetic star-formation event and later stimulate star formation as they expand into the amb
We study the evolution, rotation, and surface abundances of O-type dwarfs in the Small Magellanic Cloud. We analyzed the UV and optical spectra of twenty-three objects and derived photospheric and wind properties. The observed binary fraction of the
We present synthetic spectra and SEDs computed along evolutionary tracks at Z=1/5 Zsun and Z=1/30 Zsun, for masses between 15 and 150 Msun. We predict that the most massive stars all start their evolution as O2 dwarfs at sub-solar metallicities. The
The rich SMC star cluster NGC419 has recently been found to present both a broad main sequence turn-off and a dual red clump of giants, in the sharp colour-magnitude diagrams (CMD) derived from the High Resolution Channel of the Advanced Camera for S
Deep HST/ACS photometry of the young cluster NGC 602, located in the remote low density wing of the Small Magellanic Cloud, reveals numerous pre-main sequence stars as well as young stars on the main sequence. The resolved stellar content thus provid