Limits on O VI Emission from the Shocked Circumstellar Gas of SN 1987A

The Far Ultraviolet Spectroscopic Explorer (FUSE) was used to search for emission from the shock interaction of the ejecta of SN 1987A with its circumstellar material. FUSE observations of SN 1987A between 2000 and 2007 did not detect broad OVI emission. However, OVI emission was detected in 2000-2001 with a narrow line width (FWHM <35 kms t ) and a heliocentric radial velocity of +280 km/s. This places the emitting gas at rest relative to the supernova and is interpreted as emission from unshocked circumstellar gas. This narrow emission had disappeared in 2007 (and possibly earlier) as a result of the advancing shock overtaking the H II region that was flash ionized by the supernova explosion in 1987

Detection of a Hot Binary Companion of η\eta Carinae

We report the detection of a hot companion of $\eta$ Carinae using high resolution spectra (905 - 1180 \AA) obtained with the Far Ultraviolet Spectroscopic Explorer (\fuse) satellite. Observations were obtained at two epochs of the 2024-day orbit: 2003 June during ingress to the 2003.5 X-ray eclipse and 2004 April several months after egress. These data show that essentially all the far-UV flux from \etacar shortward of \lya disappeared at least two days before the start of the X-ray eclipse (2003 June 29), implying that the hot companion, \etaB, was also eclipsed by the dense wind or extended atmosphere of \etaA. Analysis of the far-UV spectrum shows that \etaB is a luminous hot star. The \nii \wll1084-1086 emission feature suggests that it may be nitrogen-rich. The observed far-UV flux levels and spectral features, combined with the timing of their disappearance, is consistent with \etacar\ being a massive binary system

Physical Conditions in Circumstellar Gas surrounding SN 1987A 12 Years After Outburst

Two-dimensional spectra of Supernova 1987A were obtained on 1998 November 14-15 (4282 days after outburst) with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST). The slit sampled portions of the inner circumstellar ring at the east and west ansae as well as small sections of both the northern and southern outer rings. The temperature and density at these locations are estimated by nebular analysis of [N II], [O III], and [S II] emission line ratios, and with time-dependent photoionization/recombination models. The results from these two methods are mutually consistent. The electron density in the inner ring is ~ 4000 cm-3 for S II, with progressively lower densities for N II and O III. The electron temperatures determined from [N II] and [O III] line ratios are ~11,000 K and \~22,000 K, respectively. These results are consistent with evolutionary trends in the circumstellar gas from similar measurements at earlier epochs. We find that emission lines from the outer rings come from gas of lower density (n_e \la 2000 cm-3) than that which emits the same line in the inner ring. The N/O ratio appears to be the same in all three rings. Our results also suggest that the CNO abundances in the northern outer ring are the same as in the inner ring, contrary to earlier results of Panagia et al. (1996). Physical conditions in the southern outer ring are less certain because of poorer signal-to-noise data. The STIS spectra also reveal a weak Ha emission redshifted by ~100 km s-1 at p.a. 103\arcdeg that coincides with the recently discovered new regions that are brightening (Lawrence et al. 2000). This indicates that the shock interaction in the SE section of the inner ring commenced over a year before it became apparent in HST images.Comment: 25 pages, 6 figures, to appear in December 1, 2000 Astrophysical Journa

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$_2$ absorption (940 \AA, and the Ly $\beta$ 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 $\pm$ 500 K. The resultant Cepheid mass is 6.0 $\pm$ 0.4 M$_\odot$. This mass is consistent with main sequence evolutionary tracks with a moderate amount of convective overshoot.Comment: accepted to Ap

The Chandra Delta Ori Large Project: Occultation Measurements of the Shocked Gas in the Nearest Eclipsing O-Star Binary

Delta Ori is the nearest massive, single-lined eclipsing binary (O9.5 II+OB, P=5^{d}.7324). High resolution X-ray spectrometry offers a unique opportunity to geometrically measure the dynamics of the shocked gas around the primary star. We summarize our recent campaign of phase-constrained high-resolution X-ray spectra obtained with the CHANDRA/HETGS plus high-precision photometry with MOST. These observations provide local measurement of the distribution of the embedded, X-ray emitting shocks in the wind of an O star via radial velocity variations and occultation effects, along with standard f/i ratio diagnostics, and enable us to look for correlations with the broad-band photometric variability. We discuss how these observations can help determine the primary star's clumping-corrected mass loss rate, and resolve critical uncertainties in our understanding of the connection between stellar and mass loss parameters