Rosina C. Iping

Cepheid Masses: FUSE Observations of S Muscae*

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 A 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 that are temperature sensitive near 16,000 K but relatively unaffected by H2 absorption (940 A and the Lyβ 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 resulting Cepheid mass is 6.0 ± 0.4 M☉. This mass is consistent with main-sequence evolutionary tracks with a moderate amount of convective overshoot.

A COORDINATED X-RAY AND OPTICAL CAMPAIGN OF THE NEAREST MASSIVE ECLIPSING BINARY, δ ORIONIS Aa. I. OVERVIEW OF THE X-RAY SPECTRUM

We present an overview of four deep phase-constrained Chandra HETGS X-ray observations of δ Ori A. Delta Ori A is actually a triple system that includes the nearest massive eclipsing spectroscopic binary, δ Ori Aa, the only such object that can be observed with little phase-smearing with the Chandra gratings. Since the fainter star, δ Ori Aa2, has a much lower X-ray luminosity than the brighter primary (δ Ori Aa1), δ Ori Aa provides a unique system with which to test the spatial distribution of the X-ray emitting gas around δ Ori Aa1 via occultation by the photosphere of, and wind cavity around, the X-ray dark secondary. Here we discuss the X-ray spectrum and X-ray line profiles for the combined observation, having an exposure time of nearly 500 ks and covering nearly the entire binary orbit. The companion papers discuss the X-ray variability seen in the Chandra spectra, present new space-based photometry and ground-based radial velocities obtained simultaneously with the X-ray data to better constrain the system parameters, and model the effects of X-rays on the optical and UV spectra. We find that the X-ray emission is dominated by embedded wind shock emission from star Aa1, with little contribution from the tertiary star Ab or the shocked gas produced by the collision of the wind of Aa1 against the surface of Aa2. We find a similar temperature distribution to previous X-ray spectrum analyses. We also show that the line half-widths are about 0.3−0.5 times the terminal velocity of the wind of star Aa1. We find a strong anti-correlation between line widths and the line excitation energy, which suggests that longer-wavelength, lower-temperature lines form farther out in the wind. Our analysis also indicates that the ratio of the intensities of the strong and weak lines of Fe xvii and Ne x are inconsistent with model predictions, which may be an effect of resonance scattering.

Phase‐resolved FUV Spectra of Massive Binaries

We present FUV observations of massive binary systems in the Galaxy, LMC and SMC. The binaries are High Mass X‐ray binaries and double‐line spectroscopic binaries. Many are eclipsing systems, with well‐determined orbits and periods in the range 1.6–12 days. The far‐UV spectra are used to determine spectrometric changes with phase and terminal velocities from species tracing a range of wind ionization states. We observed each system more than once to sample different orbital phases and spectral variability. All systems show significant changes in the P‐Cygni wind profiles with phase.

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 O VI emission. However, O VI emission was detected in 2000–2001 with a narrow line width (FWHM<35 km s−1) and a heliocentric radial velocity of +280 km s−1. 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.

Search for O VI Emission from the Shocked Circumstellar Ring of SN 1987A

A search for O VI 1032‐38 A emission from the circumstellar shock interaction zones of SN 1987A was made with the FUSE satellite. The shock interaction of supernova ejecta with the dense inner ring began in the mid‐1990s. Broad (FWHM ∼ 300 km s−1) emission from optical coronal lines (e.g. [Fe X], [Fe XI], and [Fe XIV]) has emerged and increased exponentially in strength. O VI emission is expected to track the coronal lines and is expected to be the primary cooling transition for the million‐degree shocked gas. In the most recent FUSE observation of SN 1987A, June 2004, a weak broad O VI feature may be present. An upper limit on the intrinsic O VI flux is ∼ 1 × 10−13 erg cm−2 s−1 (corrected for foreground Galactic and LMC extinction). A follow‐up observation of planned for mid‐2007.

Cepheid Masses: FUSE Observations of S Mus

S Mus is the Cepheid with the hottest known companion. As a benefit, the large ultraviolet flux made it 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 A because of the degeneracy between temperature and reddening. We have now obtained a FUSE spectrum in order to determine the temperature of the companion better. We have identified two regions which are temperature sensitive near 16 000 K, but are relatively unaffected by H 2 absorption (940 A, and the Ly β wings). By comparing S Mus B with other FUSE spectra, we have determined a temperature of 17 000 K. The resultant Cepheid mass is 6.0 ± 0.4 M ⊙

FUSE observations of Luminous Blue Variables

P Cyg, AG Car, HD 5980 and η Car were observed with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. FUSE covers the spectral range from 980 A to 1187 A at a resolution of 0.05 A. In this paper we discuss the far-UV properties of these LBVs and explore their similarities and differences. The FUSE observations of P Cyg and AG Car, both spectral type B2pe, are very similar. The atmospheres of both η Car and HD 5980 appear to be somewhat hotter and have much higher ionization stages (Si iv, S iv, and P v) in the FUSE spectrum than P Cyg and AG Car. There is a very good agreement between the FUSE spectrum of P Cygni and the model atmosphere computed by John Hillier with his code cmfgen. The FUSE spectrum of η Car, however, does not agree very well with existing model spectra.