Nicole St-Louis

A spectroscopic survey of WNL stars in the Large Magellanic Cloud: general properties and binary status

We report the results of an intense, spectroscopic survey of all 41 late-type, nitrogen-rich Wolf-Rayet (WR) stars in the Large Magellanic Cloud (LMC) observable with ground-based telescopes. This survey concludes the decade-long effort of the Montreal Massive Star Group to monitor every known WR star in the Magellanic Clouds except for the six crowded WNL stars in R136, which will be discussed elsewhere. The focus of our survey was to monitor the so-called WNL stars for radial velocity (RV) variability in order to identify the short- to intermediate-period (P ≤ 200 d) binaries among them. Our results are in line with results of previous studies of other WR subtypes, and show that the binary frequency among LMC WNL stars is statistically consistent with that of WNL stars in the Milky Way. We have identified four previously unknown binaries, bringing the total number of known WNL binaries in the LMC to nine. Since it is very likely that none but one of the binaries is classical, helium-burning WNL star, but rather superluminous, hence extremely massive, hydrogen-burning object, our study has dramatically increased the number of known binaries harbouring such objects, and thus paved the way to determine their masses through model-independent, Keplerian orbits. It is expected that some of the stars in our binaries will be among the most massive known. With the binary status of each WR star now known, we also studied the photometric and X-ray properties of our program stars using archival MACHO photometry as well as Chandra and ROSAT data. We find that one of our presumably single WNL stars is among the X-ray brightest WR sources known. We also identify a binary candidate from its RV variability and X-ray luminosity which harbours the most luminous WR star known in the Local Group.

The Luminous Eclipsing SMC OB + WN Binary HD 5980 before and during the Recent LBV-like Outburst: An Extreme Case of Colliding Winds

The 1994 LBV-(luminous blue variable)like outburst of one of the luminous, hot components of the binary HD 5980 made it the brightest star in the Small Magellanic Cloud for an interval of 5 months. The most intriguing question to arise from this event is the following: Why did the HD 5980 spectrum change from an H-poor WN3 with veiled OB absorption lines about 20 yr ago to an H-rich WN11 without central absorption lines during the outburst? In an attempt to answer this apparent enigma, we present and analyze new phase-dependent spectroscopic, polarimetric, and light-curve observations. Together with other published data, these new observations allow us to improve the orbital parameters considerably, except for the radial velocity amplitudes and hence the masses, which are only roughly constrained. Especially important in HD 5980 is the strong collision of the two nearly equal pre-outburst winds. The emission-line spectrum generated by the collision tends to mask the underlying line spectra of both components when the system is relatively quiescent. We argue that the pre-erupting system consists of a very luminous but moderately massive H-rich O type supergiant, possibly with emission lines, and a low-mass, H-poor, relatively faint WN companion, whose lines are mostly drowned out by wind collision emission, the spectrum of which largely imitates that of a WNE star. It was the O supergiant that erupted in a normal way as an H-rich, visually bright WN11 star. In this way, the need for peculiar evolutionary scenarios (e.g., rapid evolution from a faint, low-mass, H-poor WNE star to a luminous, H-rich WNL star) is avoided.

Discovery of a magnetic field in the O9 sub‐giant star HD 57682 by the MiMeS Collaboration★

We report the detection of a strong, organized magnetic field in the O9IV star HD 57682, using spectropolarimetric observations obtained with ESPaDOnS at the 3.6-m Canada-France-Hawaii Telescope within the context of the Magnetism in Massive Stars (MiMeS) Large Programme. From the fitting of our spectra using non-local thermodynamic equilibrium model atmospheres, we determined that HD 57682 is a 17(-9)(+19)M(circle dot) star with a radius of 7.0(-1.8)(+2.4)R(circle dot) and a relatively low mass-loss rate of 1.4(-0.95)(+3.1) x 10(-9) M-circle dot yr(-1). The photospheric absorption lines are narrow, and we use the Fourier transform technique to infer v sin i = 15 +/- 3 km s(-1). This v sin i implies a maximum rotational period of 31.5 d, a value qualitatively consistent with the observed variability of the optical absorption and emission lines, as well as the Stokes V profiles and longitudinal field. Using a Bayesian analysis of the velocity-resolved Stokes V profiles to infer the magnetic field characteristics, we tentatively derive a dipole field strength of 1680(-356)(+134)G. The derived field strength and wind characteristics imply a wind that is strongly confined by the magnetic field.

A first orbital solution for the very massive 30 Dor main-sequence WN6h+O binary R145

We report the results of a spectroscopic and polarimetric study of the massive, hydrogen-rich WN6h stars R144 (HD 38282 = BAT99-118 = Brey 89) and R145 (HDE 269928 = BAT99-119 = Brey 90) in the Large Magellanic Cloud. Both stars have been suspected to be binaries by previous studies (R144: Schnurr et al.; R145: Moffat). We have combined radial-velocity (RV) data from these two studies with previously unpublished polarimetric data. For R145, we were able to establish, for the first time, an orbital period of 158.8 d, along with the full set of orbital parameters, including the inclination angle i, which was found to be i = 38° ± 9°. By applying a modified version of the shift-and-add method developed by Demers et al., we were able to isolate the spectral signature of the very faint line companion star. With the RV amplitudes of both components in R145, we were thus able to estimate their absolute masses. We find minimum masses M WR sin 3 i = 116 ± 33 M ⊙ and M o sin 3 i = 48 ± 20 M ⊙ for the WR and the O component, respectively. Thus, if the low-inclination angle were correct, resulting absolute masses of the components would be at least 300 and 125 M ⊙ , respectively. However, such high masses are not supported by brightness considerations when R145 is compared to systems with known very high masses such as NGC 3603-A1 or WR20a. An inclination angle close to 90° would remedy the situation, but is excluded by the currently available data. More and better data are thus required to firmly establish the nature of this puzzling, yet potentially very massive and important system. As to R144, however, the combined data sets are not sufficient to find any periodicity.

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.

Wind inhomogeneities in Wolf-Rayet stars. IV. Using clumps to probe the wind structure in the WC8 star HD 192103

We present the most intensive, high-quality spectroscopic monitoring of optical Wolf-Rayet emission lines ever obtained. The Wolf-Rayet star HD 192103 (\WR 135; subtype WC8) was observed in the 5650¨5840 regime alternately from both the William Herschel Telescope and the Canada-France- Ae Hawaii Telescope. The —nal data consist of a series of 197 spectra spread over 64 hr, each with a resolv- ing power j/*j ^ 20,000 and a signal-to-noise ratio in the continuum ^450 per 3 pixel resolution element. We clearly and unambiguously identify stochastic, structured patterns of intrinsic variability at the 1%¨2% level of the line —ux in the broad C III j5696 emission line. The j5801/12 doublet emission is also found to be variable at the 0.2%¨0.5% level of the line —ux. We —nd a correlation between the variability patterns observed in C III and C IV, which suggests a signi—cant overlap in the emission volumes of these transitions, although C IV is known to arise somewhat closer to the star. We attempt to reproduce the observed line pro—le variation patterns using a simple phenomenological model, which assumes the wind to be fully clumped. With a minimal set of assumptions, we are able to reproduce both the shape and the variability in the C III j5696 emission pro—le. We show that the variability pattern provides constraints on the radial extent of WR 135ˇs wind where C III is produced, as well as on the local wind acceleration rate. However, our simple clump model does not reproduce the lower variability in the C IV doublet unless we assume the C IV emission to occur in a much larger volume than C III, implying that signi—cant C IV emission occurs farther out in the wind than C III. We suggest that while some C IV emission might occur farther out, possibly because of reionization from shocks, a more likely explanation is that wind clumping signi—cantly increases with distance from the star, leading to larger variability levels in C III, formed farther out than most of C IV. Alternatively, optical depth eUects and/or local ionization gradients within clumps could conspire to attenuate clumping eUects in the C IV emis- sion line while enhancing them in the C III line.

Oscillations in the massive wolf-rayet star WR 123 with the MOST satellite

We present the results of intensive visual-broadband photometric monitoring of the highly variable WN8 Wolf-Rayet star WR 123, obtained by the MOST (Microvariability and Oscillations of STars) satellite. This first Canadian astronomical space telescope observed WR 123 for 38 days nonstop during 2004 June and July. Fourier analysis shows that no periodic signal is stable for more than several days in the low-frequency domain (f < 1 day-1), where most of the stochastic power is contained. Also, no significant variability is seen in the high-frequency domain (10 day-1 < f < 1400 day-1) down to the level of 0.2 mmag, an order of magnitude lower than theoretical predictions for strange-mode pulsations. On the other hand, there seems to be a relatively stable 9.8 hr periodic signal present throughout the whole run. This period is probably too short to represent the axial rotation of the star, unless it is related to multiple substructures equidistantly spread along the stellar equator. It is also too short to be orbital in nature; it is more likely to be related to pulsational instablilities (although with a much longer period than expected), thus finally revealing a possible fundamental driver behind the highly variable wind of this object, and others of similar type.

Ultraviolet observations of selective wind eclipses in Gamma Velorum and evidence for colliding winds

We present a study of high-resolution ultraviolet spectra of the WC8+O9I binary system γ Velorum. The data consist of Copernicus U2 (λλ=912-1450 A) and V2 (λλ=1700-3250 A) spectra secured during two separate binary cycles in 1977 and 1980, together with 40 IUE high-resolution SWP (λλ=1150-2050 A) and 30 LWR (λλ= 1850-3250 A) spectra, secured at many binary phases during six orbital cycles in 1978 and 1979. These data reveal substantial UV spectral variations confined to resonance and low-excitation lines of Si II, Si III, Si IV, C II, C III, C IV, S IV, and Fe IV. These variations are found to be strongly dependent on binary phase and highly repeatable from one binary cycle to another

WR 110: a single Wolf–Rayet star with corotating interaction regions in its wind?

A 30 day contiguous photometric run with the Microvariability and Oscillations of STars (MOST) satellite on the WN5-6b star WR 110 (HD 165688) reveals a fundamental periodicity of P = 4.08 ± 0.55 days along with a number of harmonics at periods P/n, with n ≈ 2, 3, 4, 5, and 6, and a few other possible stray periodicities and/or stochastic variability on timescales longer than about a day. Spectroscopic radial velocity studies fail to reveal any plausible companion with a period in this range. Therefore, we conjecture that the observed light-curve cusps of amplitude ∼0.01 mag that recur at a 4.08 day timescale may arise in the inner parts, or at the base, of a corotating interaction region (CIR) seen in emission as it rotates around with the star at constant angular velocity. The hard X-ray component seen in WR 110 could then be a result of a high velocity component of the CIR shock interacting with the ambient wind at several stellar radii. Given that most hot, luminous stars showing CIRs have two CIR arms, it is possible that either the fundamental period is 8.2 days or, more likely in the case of WR 110, there is indeed a second weaker CIR arm for P = 4.08 days, that occurs ∼two-thirds of a rotation period after the main CIR. If this interpretation is correct, WR 110 therefore joins the ranks with three other single WR stars, all WN, with confirmed CIR rotation periods (WR 1, WR 6, and WR 134), albeit with WR 110 having by far the lowest amplitude photometric modulation. This illustrates the power of being able to secure intense, continuous highprecision photometry from space-based platforms such as MOST. It also opens the door to revealing low-amplitude photometric variations in other WN stars, where previous attempts have failed. If all WN stars have CIRs at some level, this could be important for revealing sources of magnetism or pulsation in addition to rotation periods.

VLT/SINFONI time-resolved spectroscopy of the central, luminous, H-rich WN stars of R136

ABSTRACT Using the Very Large Telescope’s Spectrograph for INtegral Field Observation in theNear-Infrared (VLT/SINFONI), we have obtained repeated AO-assisted, NIR spec-troscopy of the six central luminous, Wolf-Rayet (WR) stars in the core of the veryyoung (∼ 1 Myr), massive and dense cluster R136, in the Large Magellanic Cloud(LMC). We also de-archived available images that were obtained with the HubbleSpace Telescope’s Space Telescope Imaging Spectrograph (HST/STIS), and extractedhigh-quality, differential photometry of our target stars to check for any variabilityrelated to binary motion.Previous studies, relying on spatially unresolved, integrated, optical spectroscopy,had reported that one of these stars was likely to be a 4.377-day binary. Our studyset out to identify the culprit and any other short-period system among our targets.However, none displays significant photometric variability, and only one star, BAT99-112 (R136c), located on the outer fringe of R136, displays a marginal variability in itsradial velocities; we tentatively report an 8.2-day period. The binary status of BAT99-112 is supported by the fact that it is one of the brightest X-ray sources among allknown WR stars in the LMC, consistent with it being a colliding-wind system. Follow-up observations have been proposed to confirm the orbital period of this potentiallyvery massive system.Key words: binaries: general – stars: evolution – stars: fundamental parameters