P. Eenens

The Organizing Committee

Graçaliz Pereira Dimuro – General Chair Universidade Federal do Rio Grande – FURG, Brazil Luciana Foss – General Chair Universidade Federal de Pelotas – UFPEL, Brazil Eder Gonçalves – Local Chair Universidade Federal do Rio Grande – FURG, Brazil Raquel de Miranda Barbosa – Local Chair Universidade Federal do Rio Grande – FURG, Brazil Leila Ribeiro – Program Committee Chair Universidade Federal do Rio Grande do Sul – UFGRS, Brazil Lucio Mauro Duarte – Program Committee Chair Universidade Federal do Rio Grande do Sul – UFRGS, Brazil Marilton Sanchotene de Aguiar Universidade Federal de Pelotas – UFPEL, Brazil Simone André da Costa Cavalheiro Universidade Federal de Pelotas – UFPEL, Brazil

The Unusual 2001 Periastron Passage in the “Clockwork” Colliding-Wind Binary WR 140

We follow, using both optical spectroscopy and photometry, the ‘‘ textbook ’’ colliding-wind WR+O binary WR 140 through and between the periastron passages of 1993 and 2001. An extensive collection of high-quality spectra allows us to derive precise orbital elements for both components simultaneously. We confirm the extremely high eccentricity of the system, e ¼ 0:881 � 0:005, find an excellent match of the newly derived period to the previous estimates, P ¼ 2899:0 � 1:3 days, and improve the accuracy of the time of periastron passage, T0 ¼ HJD 2; 446; 147:4 � 3:7. Around periastron, at orbital phases � � 0:995 1:015, additional emission components appear on the tops of the broad Wolf-Rayet emission lines of relatively low ionization potential. The phase-dependent behavior of these excess line emissions points to their origin in the wind-wind collision zone, which allows us to place some limits on the orbital inclination of the system, i ¼ 50 � � 15 � , and half-opening angle of the bow shock cone, � ¼ 40 � � 15 � . The relatively sudden appearance and disappearance of the extra emission components probably signify a rapid switch from an adiabatically to a radiatively dominated regime and back again. Multiyear UBV photometry provides one more surprise: in 2001 at � ¼ 0:02 0:06, the system went through a series of rapid, eclipse-like events. Assuming these events to be related to an episode of enhanced dust formation at periastron, we estimate the characteristic size of the dust grains to be a � 0:07 lm. Subject headings: binaries: spectroscopic — stars: early-type — stars: individual (WR 140) — stars: Wolf-Rayet On-line material: machine-readable tables

Early-type stars in the young open cluster IC 1805 - II. The probably single stars HD 15570 and HD 15629, and the massive binary/triple system HD 15558

Aims. We address the issue of the multiplicity of the three brightest early-type stars of the young open cluster IC 1805, namely HD 15570, HD 15629 and HD 15558. Methods. For the three stars, we measured the radial velocity by fitting Gaussian curves to line profiles in the optical domain. In the case of the massive binary HD 15558, we also used a spectral disentangling method to separate the spectra of the primary and of the secondary in order to derive the radial velocities of the two components. These measurements were used to compute orbital solutions for HD 15558. Results. For HD 15570 and HD 15629, the radial velocities do not present any significant trend attributable to a binary motion on time scales of a few days, nor from one year to the next. In the case of HD 15558 we obtained an improved SB1 orbital solution with a period of about 442 days, and we report for the first time on the detection of the spectral signature of its secondary star. We derive spectral types O5.5III(f) and O7V for the primary and the secondary of HD 15558. We tentatively compute a first SB2 orbital solution although the radial velocities from the secondary star should be considered with caution. The mass ratio is rather high, i.e. about 3, and leads to very extreme minimum masses, in particular for the primary object. Minimum masses of the order of 150 ± 50 – – – – – –

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.

Early-type stars in the young open cluster NGC 2244 and in the Monoceros OB2 association - I. The multiplicity of O-type stars

Aims. We present the results obtained from a long-term spectroscopic campaign devoted to the multiplicity of O-type stars in the young open cluster NGC 2244 and in the Mon OB2 association. Methods. Our spectroscopic monitoring was performed over several years, allowing us to probe different time-scales. For each star, several spectral diagnostic tools are applied, in order to s earch for line shifts and profile variations. We also measure the projected rotational velocity and revisit the spectral classificatio n. Results. In our sample, several stars were previously considered as spectroscopic binaries, though only a few scattered observations were available. Our results now reveal a more complex situation. Our study identifies two new spectroscopic binaries (HD 46149 in NGC 2244 and HD 46573 in Mon OB2). The first object is a long-period double-lined spectroscopic binary, though the exact value of its period remains uncertain and the second object is classi fied as an SB1 system with a period of about 10.67 days but the ti me series of our observations do not enable us to derive a unique orbital solution for this system. We also classify another star as variable in radial velocity (HD 46150) and we detect line profile variati ons in two rapid rotators (HD 46056 and HD 46485). Conclusions. This spectroscopic investigation places a firm lower limit ( 17%) on the binary fraction of O-stars in NGC 2244 and reveals the lack of short-period O+OB systems in this cluster. In addition, a comparison of these new results with two other wellstudied clusters (NGC 6231 and IC 1805) puts forward possible hints of a relation between stellar density and binarity, w hich could provide constraints on the theories about the formation and early evolution of hot stars.

A multiwavelength investigation of the massive eclipsing binary Cygnus OB2 #5

Context. The properties of the early-type binary Cyg OB2 #5 have been debated for many years and spectroscopic and photometric investigations yielded conflicting results. Aims. We have attempted to constrain the physical properties of the binary by collecting new optical and X-ray observations. Methods. The optical light curves obtained with narrow-band continuum and line-bearing filters are analysed and compared. Optical spectra are used to map the location of the He ii λ 4686 and Hα line-emission regions in velocity space. New XMM-Newton as well as archive X-ray spectra are analysed to search for variability and constrain the properties of the hot plasma in this system. Results. We find that the orbital period of the system slowly changes though we are unable to discriminate between several possible explanations of this trend. The best fit solution of the continuum light curve reveals a contact configuration with the secondary star being significantly brighter and hotter on its leading side facing the primary. The mean temperature of the secondary star turns out to be only slightly lower than that of the primary, whilst the bolometric luminosity ratio is found to be 3.1. The solution of the light curve yields a distance of 925 ± 25 pc much lower than the usually assumed distance of the Cyg OB2 association. Whilst we confirm the existence of episodes of higher X-ray fluxes, the data reveal no phase-locked modulation with the 6.6 day period of the eclipsing binary nor any clear relation between the X-ray flux and the 6.7 yr radio cycle. Conclusions. The bright region of the secondary star is probably heated by energy transfer in a common envelope in this contact binary system as well as by the collision with the primary’s wind. The existence of a common photosphere probably also explains the odd mass-luminosity relation of the stars in this system. Most of the X-ray, non-thermal radio, and possibly γ-ray emission of Cyg OB2 #5 is likely to arise from the interaction of the combined wind of the eclipsing binary with at least one additional star of this multiple system.

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.

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.

The Wolf-Rayet Binary WR 141 (WN5o + O5 V-III) Revisited

ABSTRACT We combine all previously published radial velocity measurements of the spectroscopic binary WR 141 with new CCD data from 1988–1989 and 1992, complemented by polarimetric broadband measurements from 1989. This enables us to refine the orbital elements [ \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

9 Sagittarii: uncovering an O-type spectroscopic binary with an 8.6 year period

P=21.6895