O. Cardona

Spectroscopic binaries in the Orion Nebula cluster

A search was made for spectroscopic binaries among the 26 brightest members of this very young cluster. Orbital elements are given for four binaries (three known binaries, one newly discovered), and one star is a probable binary. In agreement with published predictions from n-body simulations for binary formation by capture, it is found that the spectroscopic binaries have long periods (median of 20 days), have low-mass companions, are not rotating synchronously with their orbital motions even for a period of 6.5 days, and are probably not concentrated toward the cluster center more than are the massive single stars. The binary frequency is probably normal for a cluster with a high mean rotational velocity. 38 refs.

A 2.3 Day Periodic Variability in the Apparently Single Wolf-Rayet Star WR 134: Collapsed Companion or Rotational Modulation?

The apparently single WN 6 type star WR 134 (HD 191765) is distinguished among the Wolf-Rayet star population by its strong, presumably cyclical (≈2.3 day) spectral variations. A true periodicity—which is still very much debated—would render WR 134 a prime candidate for harboring either a collapsed companion or a rotating, large-scale, inhomogeneous outflow. We have carried out an intensive campaign of spectroscopic and photometric monitoring of WR 134 from 1989 to 1997 in an attempt to reveal the true nature of this object. This unprecedentedly large data set allows us to confirm unambiguously the existence of a coherent 2.25±0.05 day periodicity in the line-profile changes of He II λ4686, although the global pattern of variability is different from one epoch to another. This period is only marginally detected in the photometric data set. Assuming the 2.25 day periodic variability to be induced by orbital motion of a collapsed companion, we develop a simple model that aims to investigate (1) the effect of this strongly ionizing, accreting companion on the Wolf-Rayet wind structure, and (2) the expected emergent X-ray luminosity. We argue that the predicted and observed X-ray fluxes can only be matched if the accretion on the collapsed star is significantly inhibited. Additionally, we performed simulations of line-profile variations caused by the orbital revolution of a localized, strongly ionized wind cavity surrounding the X-ray source. A reasonable fit is achieved between the observed and modeled phase-dependent line profiles of He II λ4686. However, the derived size of the photoionized zone substantially exceeds our expectations, given the observed low-level X-ray flux. Alternatively, we explore rotational modulation of a persistent, largely anisotropic outflow as the origin of the observed cyclical variability. Although qualitative, this hypothesis leads to greater consistency with the observations.

THE WOLF-RAYET BINARY V444 CYGNI UNDER THE SPECTROSCOPIC MICROSCOPE. II. PHYSICAL PARAMETERS OF THE WOLF-RAYET WIND AND THE ZONE OF WIND COLLISION

New, extensive, high signal-to-noise, phase-dependent optical spectroscopy, along with simultaneous narrowband continuum photometry, leads to restrictions on the electron temperature and density in the wind close to the Wolf-Rayet component of the eclipsing binary V444 Cygni (WN5 + O6 V-III). Detailed study of the phase dependence of the equivalent widths and line profiles of the W-R star reveals significant ionization stratification in the W-R wind. Our previous discussion of the wind-wind collision effects on He I lines is extended to He II lines. We find that (1) the wind-wind collision zone is detached from the surface of the O star; (2) the radiation field of the O star does not inhibit the initial acceleration of the W-R wind; however, it does brake the flow just prior to entrance into the collision zone; (3) the shocked gas experiences rapid, tcool (2-4) × 104 s, and profound cooling via radiative losses, leading to high compression of the postshock gas.

Coupled Line-Profile and Continuum Variations in EZ Canis Majoris: Implications for the Driving Mechanism of Global Wind Structures in Wolf-Rayet Winds

EZ CMa is an apparently unusual Wolf-Rayet star of the nitrogen sequence that exhibits strong variations on a period of 3.77 days with coherency lasting typically about 10 cycles. We have used an extensive set of optical spectroscopic observations to investigate a possible link between its line-profile and photometric continuum variability. Despite the strong epoch dependency of the variations, a persistent correlation is found between changes in the wind line profiles (N V λλ4604, 4620 in particular) and in continuum flux emanating near the stellar core. We suggest that these observations give further support to the idea that the physical conditions prevailing in the vicinity of the stars photosphere have a significant impact on the wind structure and that a spatial dependence of these conditions at the base of the outflow induces the formation of azimuthal wind structures in EZ CMa. The epoch-dependent nature of the variability could be related to long-term behavior of corotating magnetic structures, although pulsational instabilities constitute a viable alternative.

Confirmation among visual multiples of an increase of Ap stars with age

Open clusters with ages below certain threshold values contain no Ap stars and those with greater ages contain numbers of Ap stars that apparently increase with age. But in view of the few young clusters studied, the data could also be interpreted in terms of random differences in the frequencies of Ap stars between individual clusters, rather than an age effect. We therefore obtained data on 77 field visual multiple systems (that originated from many different clusters and associations) in which the primaries are O5-Al stars and the secondaries occur in the absolute magnitude range of the Ap stars. Again spectral classification shows no Ap stars in systems with ages < or =10/sup 6/ yr and a steady increase in Ap stars thereafter. The numerical agreement with the cluster data is good, confirming that the cluster data are exhibiting a real age effect.

The nature of the visual companions of Ap and Am stars

Classification des etoiles dans 43 multiples visuelles ayant des primaires Ap ou Am. On compte la fraction de systemes ayant des secondaires Ap ou Am

The Wind-Wind Collision Region of the Wolf-Rayet Binary V444 Cygni: How Much Optical Line Emission Does It Produce?

We model the emission-line profile variations that are expected to be produced by physical and wind eclipses in the Wolf-Rayet (W-R + O) binary system V444 Cyg. A comparison of the theoretical profiles with the He II 4686 A line observed in V444 Cyg allows us to isolate the effects that are likely to be due to the wind-wind collision region in this particular line. We estimate that the wind-wind collision region contributes no more than ~12% of the equivalent width of the emission line, with smaller values during elongations, when part of the shock cone is being eclipsed by the O star. The upper limit implies a maximum contribution from the wind-wind collision region of ~1 × 1035 ergs s-1 to the total luminosity of He II 4686 A line. Using the analytical solution of Canto et al., we find that the bulk of this emission arises along the shock cone walls where the flow velocity is ~800 km s-1, at a distance of ~8 R☉ from the O stars surface, and at θ = 65°-75° from the line joining the centers of the two stars, with origin in the O star. The derived surface density of this region is σ = 0.22 g cm-2, which, together with the He II 4686 A luminosity, indicates that the thickness of the shock lies in the range 2-10 × 1010 cm and the total density is 1-6 × 1012 cm-3.

The Wolf-Rayet Stars HD 4004 and HD 50896: Two of a Kind

We present the results of the analysis of 151 spectra of the Wolf-Rayet star HD 4004 (WR1) obtained in 1999 and in 2005. The line-profile variability is found to be periodic, with P = 7.684 days, and to have characteristics that are very similar to those of another variable WR star, HD 50896 (WR6). The similarities point toward a common physical phenomenon in both systems. Of the scenarios that can explain the observations, such as colliding winds in two stars with similar wind momenta and the ejection of streams or jets from two opposite locations on the stellar surface, the latter seems more likely due to the lack of observational evidence for a strong wind-bearing companion.

CYCLICAL SPECTRAL AND PHOTOMETRIC VARIATIONS OF THE APPARENTLY SINGLE WOLF-RAYET STAR WR 134

Evidence is presented for the existence of a 2.3 day periodicity in the line-profile changes of the apparently singleWolf-Rayet star WR 134. This cyclical variability may be induced either by the presence of an orbiting collapsed companion, or by the rotational modulation of a largely inhomogeneous outflow.

Confirmation of a 2.3-Day Periodicity in the Wolf-Rayet Star WR 134: A Twin of EZ CMa?

We confirm the existence of the 2 . d 25 ± 0 . d 05 periodicity in the line-profile changes of the apparently single Wolf-Rayet star WR 134 that was first proposed by McCandliss et al. (1994). This period dominates the skewness, centroid, and FWHM variations of He II λ4686 in spectra obtained in 1992 and 1993. Furthermore, the line-profile changes demonstrate a coherent, although complex, pattern of variability when phased with this period. Loss of coherency on a ~ monthly time scale is also observed.