S. V. Marchenko

Large-scale wind structures in OB supergiants: a search for rotationally modulated Hα variability ⋆

We present the results of a long-term monitoring campaign of the Hline in a sample of bright OB-supergiants (O7.5-B9) that aims at detecting rotationally modulated changes potentially related to the existence of large-scale wind structures. A total of 22 objects were monitored during 36 nights spread over 6 months in 2001-2002. Co- ordinated broad-band photometric observations were also obtained for some targets. Conspicuous evidence for variability in His found for the stars displaying a fea- ture contaminated by wind emission. Most changes take place on a daily time-scale, although hourly variations are also occasionally detected. Convincing evidence for a cyclical pattern of variability in Hhas been found in 2 stars: HD 14134 and HD 42087 (periodic signals are also detected in other stars, but independent confirmation is re- quired). Rotational modulation is suggested from the similarity between the observed recurrence time-scales (in the range 13-25 days) and estimated periods of stellar rota- tion. We call attention to the atypical case of HD 14134 which exhibits a clear 12.8-d periodicity both in the photometric and in the spectroscopic data sets. This places this object among a handful of early-type stars where one may observe a clear link between extended wind structures and photospheric disturbances. Further modelling may test the hypothesis that azimuthally-extended wind streams are responsible for the patterns of spectral variability in our target stars.

Hydrogen in the atmosphere of the evolved WN3 Wolf–Rayet star WR 3: defying an evolutionary paradigm?

WR 3 is the brightest very early-type WN star in the sky. Based on several years of timeresolved spectroscopy and precision photometry on various time-scales, we deduce that WR 3 is most likely a single, weak-lined star of type WN3ha (contrary to its current catalogue-type of WN3 + O4), with H lines occurring both in emission and absorption in its wind. This conclusion is confirmed and strengthened via detailed modelling of the spectrum of WR 3. Given the similarity of WR 3 with numerous H-rich WNE stars in the Large Magellanic Cloud and especially the Small Magellanic Cloud, and its location towards the metal-deficient exterior of the Galaxy, we conclude that rotationally induced meridional circulation probably led to the apparently unusual formation of this hot Galactic WN star with enhanced hydrogen. Although we cannot completely rule out the possibility of a binary with a low orbital inclination and/or long period, we regard this latter possibility as highly unlikely. Ke yw ords: stars: abundances ‐ stars: individual: W R3‐ stars: Wolf‐Rayet.

Spectroscopic study of the long-period dust-producing WC7pd+O9 binary HD 192641

We present the results of an optical spectroscopic study of the massive Wolf-Rayet binary HD192641=WR137. These 1986-2000 data cover the dust-formation maximum in 1997. Combining all available measurements of radial velocities, we derive, for the first time, a spectroscopic orbit with period 4766 ± 66 days (13.05 ± 0.18 years). The resulting masses, adopting i=67 ◦ , are MO=20 ± 2M⊙ for the O component and MW R=4.4 ± 1.5M⊙ for the WR component. These appear, respectively, ∼ normal and on the low side for the given spectral types. Analysis of the intense multi-site spectroscopic monitoring in 1999 shows that the CIII λ5696 and CIV λ5802/12 lines have the highest intrinsic variability levels. The periodogram analysis yields a smallamplitude modulation in the absorption troughs of the CIV λ5802/12 and HeI λ5876 lines with a period of 0.83 days, which could be related either to pulsations or largescale rotating structures as seen in the WN4 star EZ Canis Majoris (WR6). Wavelet analysis of the strong emission lines of CIII λ5696 and CIV λ5802/12 enabled us to isolate and follow for several hours small structures (emission subpeaks) associated with density enhancements within the wind of the Wolf-Rayet star. Cross-correlating the variability patterns seen in different lines, we find a weak but significant correlation between the varability in emission lines with different ionization potential, i.e. in lines formed at different distances from the WR stellar core. Adopting a β wind-velocity law, from the motion of individual subpeaks we find β ∼ 5, which is significantly larger than the canonical value β ≃ 1 found in O-star winds.

Orbitally modulated dust formation by the WC7+O5 colliding-wind binary WR 140

We present high-resolution infrared (2–18 μm) images of the archetypal periodic dust-making Wolf–Rayet binary system WR 140 (HD 193793) taken between 2001 and 2005, and multi-colour (J–[19.5]) photometry observed between 1989 and 2001. The images resolve the dust cloud formed by WR 140 in 2001, allowing us to track its expansion and cooling, while the photometry allows tracking the average temperature and total mass of the dust. The combination of the two data sets constrains the optical properties of the dust, and suggests that they differ from those of the dust made by the WC9 dust-makers, including the classical pinwheel, WR 104. The photometry of individual dust emission features shows them to be significantly redder in (nbL–[3.99]) , but bluer in ([7.9]–[12.5]), than the binary, as expected from the spectra of heated dust and the stellar wind of a Wolf–Rayet star. The most persistent dust features, two concentrations at the ends of a bar of emission to the south of the star, were observed to move with constant proper motions of 324 ± 8 and 243 ± 7 mas yr^−1. Longer wavelength (4.68 and 12.5 μm) images show dust emission from the corresponding features from the previous (1993) periastron passage and dust formation episode, showing that the dust expanded freely in a low-density void for over a decade, with dust features repeating from one cycle to the next. A third persistent dust concentration to the east of the binary (the arm) was found to have a proper motion ∼320 mas yr^−1, and a dust mass about one-quarter that of the bar. Extrapolation of the motions of the concentrations back to the binary suggests that the eastern arm began expansion four to five months earlier than those in the southern bar, consistent with the projected rotation of the binary axis and wind-collision region (WCR) on the sky. A comparison of model dust images and the observations constrains the intervals when the WCR was producing sufficiently compressed wind for dust nucleation in the WCR, and suggests that the distribution of this material was not uniform about the axis of the WCR, but more abundant in the following edge in the orbital plane.

The Quadruple Wolf-Rayet System GP Cephei: Spectral Types, Masses, Mass-Loss Rate, and Colliding Winds

We have reevaluated the orbital elements for each pair of the quadruple (W-R+O) + (O+O) stellar system GP Cep and propose new spectral types WN6o/WCE + O3-6, B0: I + B1: V-III. It is shown that there is only one Wolf-Rayet (W-R) star in GP Cep, contrary to a previous claim. A rate of change = 1.3 ± 0.2 s yr-1 is determined for the W-R+O pair, which leads to a new period of 6.6887 days and to a W-R mass-loss rate of (0.8-3.0) × 10-5 M☉ yr-1. Masses for this pair are estimated to be MW-R 6 M☉ and MO 21 M☉. The effects of wind-wind collision in the W-R+O pair are studied. It is shown that even after allowing for dilution by the OB components of the quadruple system, these effects are not as strong as in the binary V444 Cygni (WN5+O6, P = 4.212 days). In GP Cep, the phase-dependent, relatively weak excess emission does not originate in the arms of the bow shock cone. Rather, it emerges from the extra heated portion of the W-R wind facing the hot O companion. The trailing bow shock arm is clearly seen, however, as an enhanced He I absorption component near quadrature at phase ~0.73. An anomalous blueshifted He I absorption is present at phase ~0.9, as is also seen in V444 Cyg, in the WC8+O9 I/O8 III binary γ Velorum and in the LBV-cotype binary R81 (B2.5 Iab:e). A 3.5 day orbit for the eclipsing B star pair is confirmed.

Population I Wolf-Rayet Runaway Stars: The Case of WR124 and its Expanding Nebula M1-67

In 1997 and 2008 we used the WFPC2 camera on board the Hubble Space Telescope to obtain two sets of narrow-band Hα images of the runaway Wolf-Rayet (WR) star WR 124 surrounded by its nebula M1-67. This two-epoch imaging provides an expansion parallax and thus a practically assumption-free geometric distance to the nebula, d = 3.35 ± 0.67 kpc. Combined with the global velocity distribution in the ejected nebula, this confirms the extreme runaway status of WR 124. WR stars embedded within such ejection nebulae at the point of core collapse would produce different supernova characteristics from those expected for stars surrounded by wind-filled cavities. In galaxies with extremely low ambient metallicity, Z ≤ 10–3 Z ☉, γ-ray bursts originating from fast-moving runaway WR stars may produce afterglows which appear to be coming from regions with a relatively homogeneous circumburst medium.

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.