487 research outputs found
The Progenitor of SN 1987A
Spatially resolved IUE spectra (1150 to 2000 A) taken at the position of SN 1987A in March 1987 show that the 12th mag B3 I star Sk -69 deg 202 disappeared. Only the fainter companion stars (Star 2 and Star 3) are present near the site of the supernova. It is concluded that Sk -69 deg 202 exploded to produce SN 1987A. The known characteristics of Sk -69 deg 202 are consistent with the interpretation that the progenitor was a relatively compact star, having a high-velocity low-density stellar wind prior to the outburst. Recent IUE spectra of SN 1987A (May 1988) show no evidence that Sk -69 deg 202 still exists inside the expanding ejecta
The complete visual light curve of SN 1987A: Thirteen months of FES observations
Visual brightness measurements of SN 1987A are being obtained with the IUE acquisition camera and star tracker Fine Error Sensor, (FES) as part of each ultraviolet observation. Due to IUE's around-the-clock operation and lack of clouds, the FES record of SN 1987A provides the most complete set of visual photometry of the supernova made by any single instrument. The data illustrate the photometric limitations of the FES (+ or - 0.03 mag). Use of differential photometric methods are recommended for IUE observers desiring accurate photometry from FES measurements made during their observing shifts
IUE observations of the 1987 superoutburst of the dwarf nova Z Cha
Low resolution IUE observations of the dwarf nova Z Cha during superoutburst are presented. These cover most of the development of the outburst and have sufficient time resolution to probe continuum and line behavior on orbital phase. The observed modulation on this phase is very similar to that observed in the related object OY Car. The results imply the presence of a cool spot on the edge of the edge of the accretion disk, which periodically occults the brighter inner disk. Details of the line behavior suggest that the line originated in an extended wind-emitting region. In contrast to archive spectra obtained in normal outburst, the continuum is fainter and redder, indicating that the entire superoutburst disk may be geometrically thicker than during a normal outburst
Cepheid Masses: FUSE Observations of S Mus
S Mus is the Cepheid with the hottest known companion. The large ultraviolet
flux means that it is the only Cepheid companion for which the velocity
amplitude could be measured with the echelle mode of the HST GHRS.
Unfortunately, the high temperature is difficult to constrain at wavelengths
longer than 1200 \AA because of the degeneracy between temperature and
reddening. We have obtained a FUSE spectrum in order to improve the
determination of the temperature of the companion. Two regions which are
temperature sensitive near 16,000 K but relatively unaffected by H
absorption (940 \AA, and the Ly wings) have been identified. By
comparing FUSE spectra of S Mus B with spectra of standard stars, we have
determined a temperature of 17,000 500 K. The resultant Cepheid mass is
6.0 0.4 M. This mass is consistent with main sequence
evolutionary tracks with a moderate amount of convective overshoot.Comment: accepted to Ap
Identification of a Class of Low-Mass Asymptotic Giant Branch Stars Struggling to Become Carbon Stars in the Magellanic Clouds
We have identified a new class of Asymptotic Giant Branch (AGB) stars in the
Small and Large Magellanic Clouds (SMC/LMC) using optical to infrared
photometry, light curves, and optical spectroscopy. The strong dust production
and long-period pulsations of these stars indicate that they are at the very
end of their AGB evolution. Period-mass-radius relations for the
fundamental-mode pulsators give median current stellar masses of 1.14 M_sun in
the LMC and 0.94 M_sun in the SMC (with dispersions of 0.21 and 0.18 M_sun,
respectively), and models suggest initial masses of <1.5 M_sun and <1.25 M_sun,
respectively. This new class of stars includes both O-rich and C-rich
chemistries, placing the limit where dredge-up allows carbon star production
below these masses. A high fraction of the brightest among them should show S
star characteristics indicative of atmospheric C/O ~ 1, and many will form
O-rich dust prior to their C-rich phase. These stars can be separated from
their less-evolved counterparts by their characteristically red J-[8] colors.Comment: 16 pages, 18 figures, accepted for publication in Ap
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