The nature of the companion in the Wolf-Rayet system EZ Canis Majoris

Context. EZ Canis Majoris is a classical Wolf-Rayet star whose binary nature has been debated for decades. It was recently modeled as an eccentric binary with a periodic brightening at periastron of the emission originating in a shock heated zone near the companion. Aims. The focus of this paper is to further test the binary model and to constrain the nature of the unseen close companion by searching for emission arising in the shock-heated region. Methods. We analyze over 400 high resolution International Ultraviolet Explorer spectra obtained between 1983 and 1995 and XMM-Newton observations obtained in 2010. The light curve and radial velocity (RV) variations were fit with the eccentric binary model and the orbital elements were constrained. Results. We find RV variations in the primary emission lines with a semi-amplitude K1 ∼ 30 km s−1 in 1992 and 1995, and a second set of emissions with an anti-phase RV curve with K2 ∼ 150 km s−1. The simultaneous model fit to the RVs and the light curve yields the orbital elements for each epoch. Adopting a Wolf-Rayet mass M1 ∼ 20 M⊙ leads to M2 ∼ 3−5 M⊙, which implies that the companion could be a late B-type star. The eccentric (e = 0.1) binary model also explains the hard X-ray light curve obtained by XMM-Newton and the fit to these data indicates that the duration of maximum is shorter than the typical exposure times. Conclusions: The anti-phase RV variations of two emission components and the simultaneous fit to the RVs and the light curve are concrete evidence in favor of the binary nature of EZ Canis Majoris. The assumption that the emission from the shock-heated region closely traces the orbit of the companion is less certain, although it is feasible because the companion is significantly heated by the WR radiation field and impacted by the WR wind.

SPECTRAL BEHAVIOR OF THE SYMBIOTIC NOVA HM SGE IN THE ULTRAVIOLET

Ultraviolet observations of the symbiotic nova HM Sge were obtained from the International Ultraviolet Explorer (IUE) through the interval from 1980 - 1992. Three line profiles demonstrating the variations of some emission lines at different dates are presented. We determined the reddening of HM Sge from the 2200 Å absorption feature; the estimated value is E(B − V ) = 0.34 ± 0.02. We studied CIV at 1550 Å, He II 1640 Å, and CIII] at 1909 Å produced in the wind from the hot star. The line flux variations at different dates could be explained in terms of the variations of temperature in the emitting region as a result of mass loss variations. The IUE observations can be explained by the models of Girard & Willson (1987); Formiggini et al. (1995).

Photometric and Spectroscopic Studies of the Intermediate -Polar Cataclysmic System DQ Her

We report the results of spectral and photometric observations of DQ Her. Available spectra from International Ultraviolet Explorer (IUE), Hubble Space Telescope Faint Object Spectrograph (HST - FOS) and CCD photometry of one night were used. Some profiles revealing the variations of some spectral lines at different times are presented. There is variation with time for photometric observations and the brightness of DQ Her is changed from 14 mag. to 17.7 mag with clear display of burst. The ultraviolet luminosity for emitting region is in the range of (1.9x1031erg s−1). The mass accretion rate is in the range of (3.5x10−12M⊙yr−1). The line flux modulations at different times can be explained in terms of the accretion curtain model for intermediate polars, Kim & Beuermann (1996).

Ultraviolet Spectroscopic Investigation of HU Aqr and AN UMa with the Data from HST and IUE

We present ultraviolet spectroscopic study of two polar systems, HU Aqr and AN UMa, observed with the Hubble Space Telescope’s Space Telescope Imaging Spectrograph (STIS) and Faint Object Spectrograph (FOS) and with the International Ultraviolet Explorer (IUE) during the period 1979–2003, to diagnose the ultraviolet fluxes of CIV 1550 Å and He II 1640 Å emission lines originating in an accretion stream during different orbital phases. The reddening of two systems is determined from the 2200 Å absorption feature. Different spectra for both systems, showing the variations in line fluxes at different orbital phases, are presented. We concentrated on calculating the line fluxes of CIV and He II emission lines. From HST and IUE data, we derived accretion luminosities and accretion rates for the two systems. The average temperature of the accretion stream for HU Aqr and AN UMa is about 5000 K and 6000 K, respectively. Our results show that there are variations in line fluxes, accretion luminosities and accretion rates with time for the two systems. These modulations are attributed to the variations of both density and temperature as a result of a changing rate of mass transfer from the secondary star to the primary star. These results from the HST and IUE observations support the irradiation model producing sufficient ultraviolet flux for orbital modulations.

CO-to-H2 Abundance Ratio of the Foreground Gas of the Carina Nebula

We analyze CO and H2 absorption lines of the foreground molecular cloud in the Carina nebula. We use HST-STIS (Hubble Space Telescope - Space Telescope Imaging Spectrograph) & IUE (International Ultraviolet Explorer) INES data to analyze the A-X (v=0→2) absorption band of CO for several hot stars toward the Carina nebula, while 9 stars of them have FUSE (Far Ultraviolet Spectroscopic Explorer) spectra to analyze the (v=0→4) vibrational band in the Lyman series of H2. The column densities of CO and H2 varies in the vicinity of N(CO) ~ 1013cm−2 and N(H2) ~ 1019cm−2, respectively. The resultant CO-to-H2 abundance ratio is about 10−6. We investigate the variation of the abundance ratio according to the relative position of the target stars to morphology the molecular cloud in the Carina nebula.

UV Radiation in Different Stellar Systems

We have studied the UV radiation in the range 180 to 330 nm emitted by several stars with planetary systems, in order to determine the constraints on the habitable zones posed by the radiation levels. The observations were taken from the International Ultraviolet Explorer (IUE) and the Hubble Space Telescope (HST) satellites database. The stellar sample was chosen to cover the range of what are usually called solar-type stars, from late F to K stars. We found that the planets discovered around Epsilon Eridani and 16 Cyg B are within both the optical and UV habitable zones.