Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “STELLAR ACTIVITY”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

A STRING OF RADIO EMISSION ASSOCIATED WITH IRAS 16562-3959: A COLLIMATED JET EMANATING FROM A LUMINOUS MASSIVE YOUNG STELLAR OBJECT

We report the discovery, made using the Australia Telescope Compact Array, of a remarkable string of radio emission toward IRAS 16562-3959, a luminous infrared source with a bolometric luminosity of 7.0 x 10{sup 4} L{sub sun}. The radio emission arises from a compact, bright central component, two inner lobes which are separated by about 7'' and symmetrically offset from the central source, and two outer lobes which are separated by about 45''. The emission from the central object has a spectral index between 1.4 and 8.6 GHz of 0.85 {+-} 0.15, consistent with free-free emission from a thermal jet. The radio emission from the lobes has spectral indices in the range characteristic of thermal emission. We suggest that the emission from the lobes arises in shocks resulting from the interaction of a collimated wind with the surrounding medium. The radio string is located within a massive dense molecular core, and is associated with extended green emission (Spitzer three-color), Herbig-Haro-type emission (2MASS K{sub s} band), and OH maser sites-all phenomena readily observed toward sites of massive star formation. We conclude that the massive core hosts a high-mass star in an early stage of evolution in which it is undergoing the ejection of a powerful collimated stellar wind, showing that jets found in the formation of low-mass stars are also produced in high-mass stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

RADIO AND X-RAY OBSERVATIONS OF THE TYPE Ic SN 2007gr REVEAL AN ORDINARY, NON-RELATIVISTIC EXPLOSION

We present extensive radio and X-ray observations of the nearby Type Ic SN 2007gr in NGC 1058 obtained with the Very Large Array (VLA) and the Chandra X-ray Observatory and spanning 5 to 150 days after explosion. Through our detailed modeling of these data, we estimate the properties of the blast wave and the circumstellar environment. We find evidence for a freely expanding and non-relativistic explosion with an average blast wave velocity, v-bar {approx}0.2c, and a total internal energy for the radio emitting material of E {approx} 2 x 10{sup 46} erg assuming equipartition of energy between electrons and magnetic fields ({epsilon}{sub e} = {epsilon}{sub B} = 0.1). The temporal and spectral evolution of the radio emission points to a stellar wind-blown environment shaped by a steady progenitor mass loss rate of M-dot {approx}6x10{sup -7} M{sub sun} yr{sup -1} (wind velocity, v{sub w} = 10{sup 3} km s{sup -1}). These parameters are fully consistent with those inferred for other SNe Ibc and are in line with the expectations for an ordinary, homologous SN explosion. Our results are at odds with those of Paragi et al. who recently reported evidence for a relativistic blast wave in SN 2007gr based on their claim that the radio emission was resolved away in a low signal-to-noise Very Long Baseline Interferometry (VLBI) observation. Here we show that the exotic physical scenarios required to explain the claimed relativistic velocity-extreme departures from equipartition and/or a highly collimated outflow-are excluded by our detailed VLA radio observations. Moreover, we present an independent analysis of the VLBI data and propose that a modest loss of phase coherence provides a more natural explanation for the apparent flux density loss which is evident on both short and long baselines. We conclude that SN 2007gr is an ordinary Type Ibc supernova.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

MASSIVE STAR FORMATION OF THE SGR A EAST H II REGIONS NEAR THE GALACTIC CENTER

A group of four compact H II regions associated with the well-known 50 km s{sup -1} molecular cloud is the closest site of on-going star formation to the dynamical center of the Galaxy, at a projected distance of {approx}6 pc. We present a study of ionized gas based on the [Ne II] (12.8 {mu}m) line, as well as multi-frequency radio continuum, Hubble Space Telescope Pa{alpha}, and Spitzer Infrared Array Camera observations of the most compact member of the H II group, Sgr A East H II D. The radio continuum image at 6 cm shows that this source breaks up into two equally bright ionized features, D1 and D2. The spectral energy distribution of the D source is consistent with it being due to a 25 {+-} 3 M{sub sun} star with a luminosity of 8 {+-} 3 x 10{sup 4} L{sub sun}. The inferred mass, effective temperature of the UV source, and the ionization rate are compatible with a young O9-B0 star. The ionized features D1 and D2 are considered to be ionized by UV radiation collimated by an accretion disk. We consider that the central massive star photoevaporates its circumstellar disk on a timescale of 3 x 10{sup 4} years giving a mass flux {approx}3 x 10{sup -5} M{sub sun} yr{sup -1} and producing the ionized material in D1 and D2 expanding in an inhomogeneous medium. The ionized gas kinematics, as traced by the [Ne II] emission, is difficult to interpret, but it could be explained by the interaction of a bipolar jet with surrounding gas along with what appears to be a conical wall of lower velocity gas. The other H II regions, Sgr A East A-C, have morphologies and kinematics that more closely resemble cometary flows seen in other compact H II regions, where gas moves along a paraboloidal surface formed by the interaction of a stellar wind with a molecular cloud.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

A MODEL OF MIRA'S COMETARY HEAD/TAIL ENTERING THE LOCAL BUBBLE

We model the cometary structure around Mira as the interaction of an asymptotic giant branch stellar wind from Mira A with a streaming environment. Our simulations introduce the following new element: we assume that after 200 kyr of evolution in a dense environment, Mira entered the Local Bubble (low-density coronal gas). As Mira enters the bubble, the head of the comet expands quite rapidly, while the tail remains well collimated for a >100 kyr timescale. The result is a broad-head/narrow-tail structure that resembles the observed morphology of Mira's comet. The simulations were carried out with our new adaptive grid code WALICXE, which is described in detail.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

SPIRALING OUT OF CONTROL: THREE-DIMENSIONAL HYDRODYNAMICAL MODELING OF THE COLLIDING WINDS IN {eta} CARINAE

Three-dimensional adaptive mesh refinement hydrodynamical simulations of the wind-wind collision between the enigmatic supermassive star {eta} Car and its mysterious companion star are presented which include radiative driving of the stellar winds, gravity, optically thin radiative cooling, and orbital motion. Simulations with static stars with a periastron passage separation reveal that the preshock companion star's wind speed is sufficiently reduced so that radiative cooling in the postshock gas becomes important, permitting the runaway growth of nonlinear thin-shell instabilities (NTSIs) which massively distort the wind-wind collision region (WCR). However, large-scale simulations, which include the orbital motion of the stars, show that orbital motion reduces the impact of radiative inhibition and thus increases the acquired preshock velocities. As such, the postshock gas temperature and cooling time see a commensurate increase, and sufficient gas pressure is preserved to stabilize the WCR against catastrophic instability growth. We then compute synthetic X-ray spectra and light curves and find that, compared to previous models, the X-ray spectra agree much better with XMM-Newton observations just prior to periastron. The narrow width of the 2009 X-ray minimum can also be reproduced. However, the models fail to reproduce the extended X-ray minimum from previous cycles. We conclude that the key to explaining the extended X-ray minimum is the rate of cooling of the companion star's postshock wind. If cooling is rapid then powerful NTSIs will heavily disrupt the WCR. Radiative inhibition of the companion star's preshock wind, albeit with a stronger radiation-wind coupling than explored in this work, could be an effective trigger.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

THE NASA-UC ETA-EARTH PROGRAM. II. A PLANET ORBITING HD 156668 WITH A MINIMUM MASS OF FOUR EARTH MASSES

We report the discovery of HD 156668 b, an extrasolar planet with a minimum mass of M{sub P} sin i = 4.15 M{sub +}. This planet was discovered through Keplerian modeling of precise radial velocities from Keck-HIRES and is the second super-Earth to emerge from the NASA-UC Eta-Earth Survey. The best-fit orbit is consistent with circular and has a period of P = 4.6455 days. The Doppler semi-amplitude of this planet, K = 1.89 m s{sup -1}, is among the lowest ever detected, on par with the detection of GJ 581 e using HARPS. A longer period (P {approx} 2.3 years), low-amplitude signal of unknown origin was also detected in the radial velocities and was filtered out of the data while fitting the short-period planet. Additional data are required to determine if the long-period signal is due to a second planet, stellar activity, or another source. Photometric observations using the Automated Photometric Telescopes at Fairborn Observatory show that HD 156668 (an old, quiet K3 dwarf) is photometrically constant over the radial velocity period to 0.1 mmag, supporting the existence of the planet. No transits were detected down to a photometric limit of {approx}3 mmag, ruling out transiting planets dominated by extremely bloated atmospheres, but not precluding a transiting solid/liquid planet with a modest atmosphere.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

A LIGHT-CURVE MODEL OF THE SYMBIOTIC NOVA PU Vul (1979): A VERY QUIET EXPLOSION WITH LONG-LASTING FLAT PEAK

We present a light-curve model of the symbiotic nova PU Vul (Nova Vulpeculae 1979) that shows a long-lasting flat peak with no spectral indication of wind mass loss before decline. Our quasi-evolution models consisting of a series of static solutions explain both the optical flat peak and ultraviolet (UV) light curve simultaneously. The white dwarf mass is estimated to be {approx}0.6 M{sub sun}. We also provide a new determination of the reddening, E(B - V) = 0.43 {+-} 0.05, from UV spectral analysis. Theoretical light-curve fitting of UV 1455 A provides the distance of d = 3.8 {+-} 0.7 kpc.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

STAR FORMATION ASSOCIATED WITH THE SUPERNOVA REMNANT IC443

We have performed submillimeter and millimeter observations in CO lines toward supernova remnant (SNR) IC443. The CO molecular shell coincides well with the partial shell of the SNR detected in radio continuum observations. Broad emission lines and three 1720 MHz OH masers were detected in the CO molecular shell. The present observations have provided further evidence in support of the interaction between the SNR and the adjoining molecular clouds (MCs). The total mass of the MCs is 9.26 x 10{sup 3} M{sub sun}. The integrated CO line intensity ratio (R{sub I{sub CO(3-2)}/I{sub CO(2-1)}}) for the whole MC is between 0.79 and 3.40. The average value is 1.58, which is much higher than previous measurements of individual Galactic MCs. Higher line ratios imply that shocks have driven into the MCs. We conclude that high R{sub I{sub CO(3-2)}/I{sub CO(2-1)}} is identified as a good signature of the SNR-MC interacting system. Based on the IRAS Point Source Catalog and the Two Micron All Sky Survey near-infrared database, 12 protostellar object and 1666 young stellar object (YSO) candidates (including 154 classical T Tauri stars and 419 Herbig Ae/Be stars) are selected. In the interacting regions, the significant enhancement of the number of protostellar objects and YSOs indicates the presence of some recently formed stars. After comparing the characteristic timescales of star formation with the age of IC443, we conclude that the protostellar objects and YSO candidates are not triggered by IC443. For the age of the stellar winds shell, we have performed our calculation on the basis of a stellar wind shell expansion model. The results and analysis suggest that the formation of these stars may be triggered by the stellar winds of the IC443 progenitor.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

JET PROPAGATIONS, BREAKOUTS, AND PHOTOSPHERIC EMISSIONS IN COLLAPSING MASSIVE PROGENITORS OF LONG-DURATION GAMMA-RAY BURSTS

We investigate the following by two-dimensional axisymmetric relativistic hydrodynamical simulations: (1) jet propagations through an envelope of a rapidly rotating and collapsing massive star, which is supposed to be a progenitor of long-duration gamma-ray bursts (GRBs); (2) breakouts and subsequent expansions into stellar winds; and (3) the accompanying photospheric emissions. We find that if the envelope rotates uniformly almost at the mass shedding limit, its outer part eventually stops contracting when the centrifugal force becomes large enough. Then another shock wave is formed, propagates outward, and breaks out of the envelope into the stellar wind. Whether the jet or the centrifugal bounce-induced shock breaks out earlier depends on the timing of jet injection. If the shock breakout occurs earlier, owing to a later injection, the jet propagation and subsequent photospheric emissions are affected substantially. We pay particular attention to observational consequences of the difference in the timing of jet injection. We calculate optical depths to find the location of photospheres, extracting densities, and temperatures at appropriate retarded times from the hydrodynamical data. We show that the luminosity and observed temperature of the photospheric emissions are both much lower than those reported in previous studies. Although luminosities are still high enough for GRBs, the observed temperatures are lower than the energy at the spectral peak expected by the Yonetoku relation. This may imply that energy exchanges between photons and matter are terminated deeper inside or that some non-thermal processes are operating to boost photon energies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

GAMMA-RAY EMISSION OF ACCELERATED PARTICLES ESCAPING A SUPERNOVA REMNANT IN A MOLECULAR CLOUD

We present a model of gamma-ray emission from core-collapse supernovae (SNe) originating from the explosions of massive young stars. The fast forward shock of the supernova remnant (SNR) can accelerate particles by diffusive shock acceleration (DSA) in a cavern blown by a strong, pre-SN stellar wind. As a fundamental part of nonlinear DSA, some fraction of the accelerated particles escape the shock and interact with a surrounding massive dense shell producing hard photon emission. To calculate this emission, we have developed a new Monte Carlo technique for propagating the cosmic rays (CRs) produced by the forward shock of the SNR, into the dense, external material. This technique is incorporated in a hydrodynamic model of an evolving SNR which includes the nonlinear feedback of CRs on the SNR evolution, the production of escaping CRs along with those that remain trapped within the remnant, and the broadband emission of radiation from trapped and escaping CRs. While our combined CR-hydro-escape model is quite general and applies to both core collapse and thermonuclear SNe, the parameters we choose for our discussion here are more typical of SNRs from very massive stars whose emission spectra differ somewhat from those produced by lower mass progenitors directly interacting with a molecular cloud.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

WHAT DRIVES THE EXPANSION OF GIANT H II REGIONS?: A STUDY OF STELLAR FEEDBACK IN 30 DORADUS

Observations show that star formation is an inefficient and slow process. This result can be attributed to the injection of energy and momentum by stars that prevents free-fall collapse of molecular clouds. The mechanism of this stellar feedback is debated theoretically; possible sources of pressure include the classical warm H II gas, the hot gas generated by shock heating from stellar winds and supernovae, direct radiation of stars, and the dust-processed radiation field trapped inside the H II shell. In this paper, we measure observationally the pressures associated with each component listed above across the giant H II region 30 Doradus in the Large Magellanic Cloud. We exploit high-resolution, multi-wavelength images (radio, infrared, optical, ultraviolet, and X-ray) to map these pressures as a function of position. We find that radiation pressure dominates within 75 pc of the central star cluster, R136, while the H II gas pressure dominates at larger radii. By contrast, the dust-processed radiation pressure and hot gas pressure are generally weak and not dynamically important, although the hot gas pressure may have played a more significant role at early times. Based on the low X-ray gas pressures, we demonstrate that the hot gas is only partially confined and must be leaking out the H II shell. Additionally, we consider the implications of a dominant radiation pressure on the early dynamics of 30 Doradus.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

ACCRETION OF A TERRESTRIAL-LIKE MINOR PLANET BY A WHITE DWARF

We present optical and infrared characterization of the polluted DAZ white dwarf GALEX J193156.8+011745. Imaging and spectroscopy from the ultraviolet to the thermal infrared indicate that this white dwarf hosts excess infrared emission consistent with the presence of an orbiting dusty debris disk. In addition to the five elements previously identified, our optical echelle spectroscopy reveals chromium and manganese and enables restrictive upper limits on several other elements. Synthesis of all detections and upper limits suggests that GALEX J193156.8+011745 has accreted a differentiated parent body. We compare the inferred bulk elemental composition of the accreted parent body to expectations for the bulk composition of an Earth-like planet stripped of its crust and mantle and find relatively good agreement. At least two processes could be important in shaping the final bulk elemental composition of rocky bodies during the late phases of stellar evolution: irradiation and interaction with the dense stellar wind.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

X-RAY EMISSION AND DYNAMICS FROM LARGE DIAMETER SUPERBUBBLES: THE CASE OF THE N70 SUPERBUBBLE

The morphology, dynamics, and thermal X-ray emission of the superbubble N70 are studied by means of three-dimensional hydrodynamic simulations carried out with the YGUAZU-A code. We consider three possible scenarios: the superbubble being the product of a single supernova remnant, of the stellar winds from an OB association, or of the joint action of stellar winds and a supernova (SN) event. Our results show that, in spite of the fact that all scenarios produce bubbles with the observed physical size, only those in which the bubble is driven by stellar winds and an SN event successfully explain the general morphology, dynamics, and X-ray luminosity of N70. Our models predict temperatures in excess of 10{sup 8} K at the interior of the superbubble; however, the density is too low and thermal X-ray emission above 2 keV is too faint to be detected.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

GLOBAL SELF-SIMILAR PROTOSTELLAR DISK/WIND MODELS

The magnetocentrifugal disk wind mechanism is the leading candidate for producing the large-scale, bipolar jets commonly seen in protostellar systems. I present a detailed formulation of a global, radially self-similar model for a non-ideal disk that launches a magnetocentrifugal wind. This formulation generalizes the conductivity tensor formalism previously used in radially localized disk models. The model involves matching a solution of the equations of non-ideal magnetohydrodynamics (MHD) describing matter in the disk to a solution of the equations of ideal MHD describing a 'cold' wind. The disk solution must pass smoothly through the sonic point, the wind solution must pass smoothly through the Alfven point, and the two solutions must match at the disk/wind interface. This model includes for the first time a self-consistent treatment of the evolution of magnetic flux threading the disk, which can change on the disk accretion timescale. The formulation presented here also allows a realistic conductivity profile for the disk to be used in a global disk/wind model for the first time. The physical constraints on the model solutions fix the distribution of the magnetic field threading the disk, the midplane accretion speed, and the midplane migration speed of flux surfaces. I present a representative solution that corresponds to a disk in the ambipolar conductivity regime with a nominal neutral-matter-magnetic-field coupling parameter that is constant along field lines, matched to a wind solution. I conclude with a brief discussion of the importance of self-similar disk/wind models in studying global processes such as dust evolution in protostellar systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

XMM-NEWTON X-RAY AND ULTRAVIOLET OBSERVATIONS OF THE FAST NOVA V2491 Cyg DURING THE SUPERSOFT SOURCE PHASE

Two XMM-Newton observations of the fast classical nova V2491 Cyg were carried out in short succession on days 39.93 and 49.62 after discovery, during the supersoft source (SSS) phase, yielding simultaneous X-ray and UV light curves and high-resolution X-ray spectra. The first X-ray light curve is highly variable, showing oscillations with a period of 37.2 minutes after an extended factor of three decline lasting {approx}3 hr, while the second X-ray light curve is less variable. The cause of the dip is currently unexplained and has most likely the same origin as similar events in the early SSS light curves of the novae V4743 Sgr and RS Oph, as it occurred on the same timescale. The oscillations are not present during the dip minimum and also not in the second observation. The UV light curves are variable but contain no dips and no period. High-resolution X-ray spectra are presented for four intervals of differing intensity. All spectra are atmospheric continua with deep absorption lines and absorption edges. Two interstellar lines of O I and N I are clearly seen at their rest wavelengths, while a large number of high-ionization absorption lines are found at blueshifts indicating an expansion velocity of 3000-3400 km s{sup -1}, which does not change significantly during the epochs of observation. Comparisons with the slower nova V4743 Sgr and the symbiotic recurrent nova RS Oph are presented. The SSS spectrum of V4743 Sgr is much softer with broader and more complex photospheric absorption lines. The ejecta are extended, allowing us to view a larger range of the radial velocity profile. Meanwhile, the absorption lines in RS Oph are as narrow as in V2491 Cyg, but they are less blueshifted. A remarkable similarity in the continua of V2491 Cyg and RS Oph is found. The only differences are smaller line shifts and additional emission lines in RS Oph that are related to the presence of a dense stellar wind from the evolved companion. Three unidentified absorption lines are present in the X-ray spectra of all three novae, with projected rest wavelengths 26.05 A, 29.45 A, and 30.0 A. No entirely satisfactory spectral model is currently available for the soft X-ray spectra of novae in outburst, and careful discussion of assumptions is required.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

DETAILED X-RAY LINE PROPERTIES OF {theta}{sup 2} Ori A IN QUIESCENCE

We investigate X-ray emission properties of the peculiar X-ray source {theta}{sup 2} Ori A in the Orion Trapezium region using more than 500 ks of HETGS spectral data in the quiescent state. The amount of exposure provides tight constraints on several important diagnostics involving O, Ne, Mg, and Si line flux ratios from He-like ion triplets, resonance line ratios of the H- and He-like lines, and line widths. Accounting for the influence of the strong UV radiation field of the O9.5V star, we can now place the He-like line origin well within two stellar radii of the O-star's surface. The lines are resolved with average line widths of 341 {+-} 38 km s{sup -1}. In the framework of standard wind models, this likely implies a rather weak wind with moderate post-shock velocities. The emission measure distribution of the X-ray spectrum, as reported previously, includes very high temperature components which are not easily explained in this framework. The X-ray properties are also not consistent with coronal emissions from an unseen low-mass companion nor with typical signatures from colliding wind interactions. The properties are more consistent with X-ray signatures observed in the massive Trapezium star {theta}{sup 1} Ori C which has recently been successfully modeled with a magnetically confined wind model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

AN XMM-NEWTON STUDY OF THE BRIGHT, NEARBY SUPERNOVA REMNANT G296.1-0.5

We present a detailed study of the supernova remnant (SNR) G296.1-0.5, performed using observations with the European Photon Imaging Camera (EPIC) and Reflection Grating Spectrometer instruments of the XMM-Newton satellite. G296.1-0.5 is a bright remnant that displays an incomplete multiple-shell morphology in both its radio and X-ray images. We use a set of observations toward G296.1-0.5, from three distinct pointings of EPIC, in order to perform a thorough spatial and spectral analysis of this remnant, and hence determine what type of progenitor gave rise to the supernova explosion, and describe the evolutionary state of the SNR. Our XMM-Newton observations establish that the spectral characteristics are consistent across the X-ray bright regions of the object and are best described by a model of the emission from a nonequilibrium ionization collisional plasma. The study reveals that the emission from the shell is characterized by an excess of N and an underabundance of O, which is typical of wind material from red supergiant and Wolf-Rayet stars. Additionally, we have detected transient X-ray source 2XMMi J115004.8-622442 at the edge of the SNR whose properties suggest that it is the result of stellar flare, and we discuss its nature in more detail.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

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 {approx} 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 {approx}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 {approx}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 high-precision 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.

79 ASTRONOMY AND ASTROPHYSICS↗