Search

The FUSE data for 287 OB stars in the Magellanic Clouds are an unprecedented resource to investigate the behavior of the stellar winds as a function of spectral type, luminosity class, and metallicity. The smaller extinction and interstellar absorption relative to Galactic counterparts render the MC sample more powerful, especially below 1100 Å. IUE provided a comparable Galactic sample at longer UV wavelengths, but HST has yet to do the same in the MCs. An initial FUSE atlas of 47 objects published in 2002 charted several basic trends, including the luminosity (or wind-density) sensitivity of the S IV, P V, and C III profiles, analogous to the previously unique Si IV behavior at longer UV wavelengths; this effect is due to the relatively low ionization of these species except for P V, for which the much lower abundance prevents saturation at lower luminosities. Now we are augmenting our sample by about 150 more objects, to provide better coverage of the parameters and redundancy at some spectral types, as well as to investigate categories of peculiar objects. Some outstanding early results are increased representation of the earliest spectral types (O2–O4), and the extension of the CNO dichotomy between O2 and ON2 spectra to the superionized O VI profiles. This work and subsequent quantitative modeling will improve our understanding of stellar winds, massive stellar evolution, and the integrated spectra of distant starbursts. [ABSTRACT FROM AUTHOR]

We have obtained Chandra HRC-S/LETG spectroscopy of the prototypical supersoft source CAL 83 in the Large Magellanic Cloud. The data reveal a very rich absorption line spectrum from the hot white dwarf photosphere. We have recently completed the analysis of the Chandra spectrum and of an earlier XMM-Newton RGS spectrum of CAL 83 with new non-LTE line-blanketed model atmospheres that explicitly include 74 ions of the 11 most abundant species. We have successfully matched the Chandra and XMM-Newton spectra, and have thus derived the basic stellar parameters of the hot white dwarf. In particular, we have obtained the first direct spectroscopic evidence that the white dwarf is massive (M > 1M⊙). We also found no spectral signatures of a wind from the white dwarf. These results provide direct support for supersoft sources as likely progenitors of SN Ia. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

We compare predicted Type Ib/c supernova (SNIb/c) rates with the observed long-duration Gamma-Ray-Burst (GRB) rates both locally and as a function of redshift, by assuming different star formation histories in galaxies of different morphological types. Due to the high star formation in spheroids at high redshift, we predict a large number of GRBs beyond z > 7. Moreover, based on our studies and on the current LAT performance, an estimate of the detection possibility of this burst population is presented. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We report the result of the 2–5 μm spectroscopy of massive young stellar objects (YSOs) in the Large Magellanic Cloud (LMC) using the infrared satellite AKARI. Absorption features of H2O, CO2 and CO ices are detected toward these extragalactic YSOs, and derived CO2/H2O ratio in the LMC showed a higher value than galactic YSOs. In this proceeding, we discuss the difference of a chemical conditions around extragalactic YSOs. [ABSTRACT FROM AUTHOR]