Structure and kinematics of the interstellar medium around WR 142a: Searching for traces of the action of stellar wind

Based on our Hα interferometric observations and CO data, we analyze the structure and kinematics of the gas in an extended region of the Cygnus arm around the recently discovered star WR 142a. We have established that WR 142a and the ionized hydrogen in its immediate neighborhood are associated with the complex of molecular clouds observed in a region with l ～ 78°–80°30′, b ～ 2°–3°20′, and V _LSR ～ 4–16 km s^?1. Traces of the action of the stellar wind from WR 142a on the ambient gas have been found to the northeast of the star in a region devoid of dense absorbing foreground clouds. These include very weak thin gas and dust filaments as well as high-velocity components of the Hα profile, which can be interpreted as a possible expansion of the shell swept up by the wind with a velocity as high as 50–80 km s^?1. Giant regions of reduced CO emission dominated by high-velocity motions of ionized hydrogen have been detected. Stars of the Cyg OB2 association and the cluster NGC 6910 can be responsible for these motions.     

Galactic distribution of WR stars

The recent VIIth Catalogue of Galactic Wolf-Rayet Stars lists 227 Population I WR stars, comprising 127 WN, 87 WC, 10 WN/WC and 3 WO stars. Additional discoveries bring the census to 234 WR stars. A re-determination of the optical photometric distances and the galactic distribution of WR stars shows in the solar neighbourhood a projected surface density of 2.7 WR stars per kpc², a N _WC/N _WN number ratio of 1.3, and a WR binary frequency of 40 %.The galactocentric distance (R _WR) distribution per subtype showsR _WN and R _WC decreasing with WN and WC subtypes. This revised version was published online in September 2006 with corrections to the Cover Date.     

The line-of-sight velocities of OB associations and molecular clouds in a wide solar neighborhood: The streaming motions of stars and gas in the Perseus arm

We compare the line-of-sight velocities of stars in OB associations within 3 kpc of the Sun and the molecular clouds closest to them. The Perseus arm is used as an example to show that the line-of-sight velocity ranges in which OB-association stars, molecular clouds, and H II regions ionized by these association stars are observed overlap. The streaming motions produced by density waves in the (l, V_LSR) plane were found to lead to an inversion of the distances to objects of the Perseus arm and the interarm space beyond this arm.     

Modelling the spectra of colliding winds in the Wolf–Rayet WC7+O binaries WR 42 and WR 79

We have obtained complete phase coverage of the WC7+O binaries WR 42 = HD 97152 and WR 79 = HD 152270 with high signal-to-noise ratio (S/N), moderate-resolution spectra. Remarkable orbital phase-locked profile variations of the C  iii λ 5696 line are observed and interpreted as arising from colliding wind effects. Within this scenario, we have modelled the spectra using a purely geometrical model that assumes a cone-shaped wind–wind interaction region which partially wraps around the O star. Such modelling holds the exciting promise of revealing a number of interesting parameters for WR+O binaries, such as the orbital inclination, the streaming velocity of material in the interaction region and the ratio of wind momentum flux. Knowledge of these parameters in turn leads to the possibility of a better understanding of WR star masses, mass-loss rates and wind region characteristics.     

Structure and evolution of single WR stars

New computations of massive stars follow the evolution up to advanced stages and include:

-A large and flexible nuclear network consisting of 174 nuclear species that are linked by 1742 nuclear reactions.

-Semiconvection, overshooting and mass loss.

-Modern rates for both strong and weak interaction processes as well as the latest rates for the neutrino processes.

-Improved grid distribution and a large number of grid points.

The nuclear network and the diffusion equation are solved for each time step during the whole evolution. In this way the accuracy of nuclear yields and chemical abundances are mainly limited by uncertainties in the diffusion coefficient found from the convection theories. Several instability mechanisms may affect the mass loss rates of massive stars and thereby the structure and abundances of WR stars. Due to heavy mass loss at the LBV and WR stages, the masses at the pre-SN stage may be less than 5M _⊙. Yields and abundances throughout the stars are discussed together with the amount of all elements expelled.     

Neutral hydrogen around the oxygen-sequence Wolf-Rayet star WR 102 and the nebula G2.4+1.4

We carried out the first 21-cm line observations of an extended region around the Wolf-Rayet star WR 102 and the associated nebula G2.4+1.4 with the RATAN-600 radio telescope. An irregular H I shell was identified. Its maximum expansion velocity reaches ～50 km s^?1, and its outer diameter (at a distance of 3 kpc) is 56 pc. The mechanical luminosity of the stellar wind required to produce the observed shell is estimated to be ～0.8×10³⁸ erg s^?1; the age of the shell is ～3.4×10⁵ yr. We compare the inferred parameters of the H I shell with the structure and kinematics of the ionized nebula and with the dust distribution in the region.     

Properties of Wolf-Rayet stars in eclipsing binary systems

The results of investigations of a number of eclipsing Wolf-Rayet binaries are presented. The ‘core’ radiuses, the ‘core’ temperatures and masses of WR stars in the eclipsing WR+OB binary systems V 444 Cyg, CX Cep, CQ Cep, and CV Ser are obtained (see Table I). The results obtained from the light curves analysis of the V 444 Cyg in the range λλ2460 Å-3.5μ give strong evidence for the Beals (1944) model of WR phenomenon. The chromospheric-coronal effects in the WN5 extended atmosphere are not observed up to a distance ofr?20R _⊙. In the Hertzsprung—Russell diagram all the WR stars lie on the left side from the main sequence between the main sequence and the sequence of uniform helium stars (see Figure 9). Their locations are close to those of the helium remnants formed as a result of mass exchange in massive close binary systems. The period variations in the systems V 444 Cyg and CQ Cep have been discovered and a reliable value of the mass loss rateM=10^?5 M _⊙yr^?1 is obtained, for the two WR stars. The results of the photometric and spectroscopic investigations of the WR stars with low mass companions (post X-ray binary stage?) are presented too (see Table II). The masses of the companions are (1–2)M _⊙, their optical luminosity is ～10³⁶, erg s^?1 which implies that these companions cannot be the normal stars. It is possible that these companions are neutron stars accreting from the stellar wind of the WR stars. Low values of the X-ray luminosities of such WR stars with low mass companions imply that the accretion of matter in such systems is distinct from the accretion process in classical X-ray binary systems. It is noted also that the parameters of low massive companions coupled with WR stars are close to those of helium stars.     

Spectropolarimetric observations of WR 137

We present high signal-to-noise spectropolarimetry of the WC7+OB star WR 137 (HD 192641) covering the spectral range from 3600Å to 1.1µm. The polarization spectrum shows unambiguous evidence for an intrinsic polarization vector.     

Further results on the line-profile variability of WR 134

We discuss a few conclusions previously derived from the analysis of the lineprofile variability of the Wolf-Rayet star WR 134; some details are made more explicit. In addition, we present a new set of data and briefly comment on recent results deduced from its analysis.     

Detection of H2 emission towards the wolf-rayet nebula NGC 2359

We report the first detection of molecular hydrogen emission in the vicinity of a Wolf-Rayet star and nebula. The spatial distribution of the excited molecular gas is filamentary and is not correlated with the distribution of the ionised gas as traced by optical emission lines. The typical H₂ surface brightness in the filaments is 5× 10^–5 ergs s^–1 cm^–2 str^–1. We demonstrate that the excitation mechanism can be shocks or fluorescence from the strong ultraviolet flux of the WR star.     

Shaping planetary nebulae: is it different for [WR] stars?

This review discusses the physics of the formation of planetarynebulae around low mass WR stars, or [WR] stars. It especially focuseson the differences which can be expected due to the differentcharacter of the fast winds from these [WR] stars. Their fast windsare more massive and are highly H deficient and metal enrichedcompared to the winds of normal central stars of planetarynebulae. This is expected to lead to faster expansion velocities forthe nebulae and a longer momentum-driven phase in the evolution of thewind-driven bubble, leading to more turbulent nebulae. Theobservational evidence also shows that the process which produces the[WR] stars is unlikely to influence the onset of aspherical mass loss,something which can be used as a test for models for aspherical massloss from AGB and post-AGB stars. Finally it is shown that thenebular characteristics rule out a very late He shell flash as theorigin of most [WR] stars.     

Colliding stellar wind models with non-equilibrium ionization: X-rays from WR 147

The effects of non-equilibrium ionization are explicitly taken into account in a numerical model which describes colliding stellar winds (CSW) in massive binary systems. This new model is used to analyse the most recent X-ray spectra of the WR+OB binary system WR 147. The basic result is that it can adequately reproduce the observed X-ray emission (spectral shape, observed flux) but some adjustment in the stellar wind parameters is required. Namely (i) the stellar wind velocities must be higher by a factor of 1.4–1.6 and (ii) the mass loss must be reduced by a factor of ∼2. The reduction factor for the mass loss is well within the uncertainties for this parameter in massive stars, but given the fact that the orbital parameters (e.g. inclination angle and eccentricity) are not well constrained for WR 147, even smaller corrections to the mass loss might be sufficient. Only CSW models with non-equilibrium ionization and equal (or nearly equal) electron and ion post-shock temperature are successful. Therefore, the analysis of the X-ray spectra of WR 147 provides evidence that the CSW shocks in this object must be collisionless .     

WR 7a: a V Sagittae or a qWR star?

The star WR 7a, also known as SPH 2, has a spectrum that resembles that of V Sagittae stars although no O  vi emission has been reported. The Temporal Variance Spectrum – TVS – analysis of our data shows weak but strongly variable emission of O  vi lines which is below the noise level in the intensity spectrum.
Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is   P _phot= 0.227(±14) d  , while radial velocities suggest a period of   P _spec= 0.204(±13) d  . One-day aliases of these periods can not be ruled out. We call attention to similarities with HD 45166 and DI Cru (= WR 46), where multiple periods are present. They may be associated to the binary motion or to non-radial oscillations.
In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N  v 4604 Å  absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system.     

Two-dimensional spectroscopy of double-barred galaxies

We describe the results of our spectroscopy for a sample of barred galaxies whose inner regions exhibit an isophotal twist commonly interpreted as a secondary bar. The line-of-sight velocity fields of the ionized gas and stars and the light-of-sight velocity dispersion fields of the stars were constructed from two-dimensional spectroscopy with the 6-m Special Astrophysical Observatory telescope. We detected various types of noncircular motions of ionized gas: radial flows within large-scale bars, counterrotation of the gas and stars at the center of NGC 3945, a polar gaseous disk in NGC 5850, etc. Our analysis of the optical and near-infrared galaxy images (both ground-based and those from the Hubble Space Telescope) revealed circumnuclear minispirals in five objects. The presence of an inner (secondary) bar in the galaxy images is shown to have no effect on the circumnuclear kinematics of the gas and stars. Thus, contrary to popular belief, the secondary bar is not a dynamically decoupled galactic structure. We conclude that the so-called double-barred galaxies are not a separate type of galaxy but are a combination of objects with distinctly different morphologies of their circumnuclear regions.     

WR 38/38a and the ratio of total-to-selective extinction in Carina

A reanalysis of the (seemingly very distant) open cluster Shorlin 1, the group of stars associated with WR 38 and WR 38a, is made on the basis of existing UBV and JHK _s observations for cluster members. The 2MASS observations, in particular, imply a mean cluster reddening of E _B−V =1.45±0.07 and a distance of 2.94±0.12 kpc. The reddening agrees with the UBV results provided that the local reddening slope is described by E _U−B /E _B−V =0.64±0.01, but the distance estimates in the 2MASS and UBV systems agree only if the ratio of total-to-selective extinction for the associated dust is R=A _V /E _B−V =4.0±0.1. Both results are similar to what has been obtained for adjacent clusters in the Eta Carinae region by similar analyses, which suggests that “anomalous” dust extinction is widespread through the region, particularly for groups reddened by relatively nearby dust. Dust associated with the Eta Carinae complex itself appears to exhibit more “normal” qualities. The results have direct implications for the interpretation of distances to optical spiral arm indicators for the Galaxy at ℓ=287°–291°, in particular the Carina arm here is probably little more than ∼2 kpc distant, rather than 2.5–3 kpc distant as implied in previous studies. Newly-derived intrinsic parameters for the two cluster Wolf-Rayet stars WR 38 (WC4) and WR 38a (WN5) are in good agreement with what is found for other WR stars in Galactic open clusters, which was not the case previously.     

Kinematics and Dynamics of the Galactic Halo from RR Lyrae Variable Stars

Based on a sample of RR Lyrae variable stars including more than 9000 objects with proper motions and distances, we have investigated the kinematics of the Galactic halo from the two-dimensional velocity field. We have used both the proper motions deduced independently by us from the positional data taken from all-sky catalogues in a time interval up to 65 years and the proper motions taken from the Gaia DR2 catalogue. In addition, we have also studied the halo kinematics from the three-dimensional velocity field of ~850 RR Lyrae variables with distances, proper motions, and line-of-sight velocities. The kinematic parameters describing the velocity field have been estimated by the maximum-likelihood method; their change with Galactocentric distance has been investigated. The radial velocity dispersion in spherical coordinates σ_r ≈ 160?170 km s^?1 exceeds its values from previous papers approximately by 20 km s^?1, while the anisotropy parameter β ≈ 0.68?0.72 agrees satisfactorily with previous studies. When estimating the rotation velocity of the population of RR Lyrae stars, we identified the inner and outer halos with weak prograde and retrograde rotations, respectively.     

Kinematics of gas and stars in circumnuclear star-forming regions of early-type spirals

We present high-resolution (R～20,000) spectra in the blue and the far red of circumnuclear star-forming regions (CNSFRs) in three early-type spirals (NGC3351, NGC2903 and NGC3310), which have allowed the study of the kinematics of the stars and the ionized gas in these structures and, for the first time, the derivation of their dynamical masses for the first two. In some cases, these regions, about 100 to 150 pc in size, are composed of several individual star clusters with sizes between 1.5 and 4.9 pc, estimated from Hubble Space Telescope images. The stellar dispersions have been obtained from the Calcium triplet (CaT) lines at λ λ 8494, 8542, 8662 Å, while the gas velocity dispersions have been measured by means of Gaussian fits to the Hβ and [Oiii]λ 5007 Å lines in the high-dispersion spectra. Values of the stellar velocity dispersions are between 30 and 68 km?s^?1. We apply the virial theorem to estimate dynamical masses of the clusters, assuming that systems are gravitationally bounded and spherically symmetric, and using previously measured sizes. The measured values of the stellar velocity dispersions yield dynamical masses of the order of 10⁷ to 10⁸ M_⊙ for the entire CNSFRs. Stellar and gas velocity dispersions are found to differ by about 20 to 30 km?s^?1, with the Hβ emission lines being narrower than both the stellar lines and the [Oiii]λ 5007 Å lines. The douby-ionized oxygen, on the other hand, exhibits velocity dispersions comparable to those of the stars or, in some cases, even larger. We have found indications of the presence of two different kinematical components in the ionized gas of the regions. We have mapped the velocity field in the central kpc of the spiral galaxies NGC3351 and NGC2903. For the first object, the radial velocity curve shows deviations from circular motions for the ionized hydrogen consistent with its infall towards the central regions of the galaxy, at a velocity of about 25 km?s^?1. For NGC3310, we present preliminary results for the velocity dispersions for one of the two observed slit position angles, two CNSFRs and the nucleus.     

Ionized gas towards galactic centre — Constraints from low-frequency recombination lines

Observations of the H272α recombination line towards the galactic centre show features near V_LSR= 0, −50 and + 36 kms⁻¹. We have combined the parameters of these features with the available H166α measurements to obtain the properties of the ionized gas present along the line of sight and also in the ‘3 kpc arm’. For the line-of-sight ionized gas we get an electron density around 7 cm⁻³ and a pathlength through it ∼ 10–60 pc. The emission measure and the electron temperature are in the range 500–2900 pc cm⁻⁶ and 2000–6000 K. respectively. The ionized gas in the 3 kpc arm has an electron density of 30 cm⁻³ and extends over 9 pc along the line of sight if we assume an electron temperature of 10⁴ K. Using the available upper limit to the intensity of the H351α recombination line, we show that the distributed ionized gas responsible for the dispersion of pulsar signals should have a temperature >4500 K. and a minimum filling factor of 20 per cent. We also show that recombination lines from the ‘warm ionized’ gas proposed by McKee & Ostriker (1977) should be detectable in the frequency range 100–150 MHz towards the galactic centre with the sensitivity available at present.     

Searches for the shell swept up by the stellar wind from Cyg OB2

We investigated the kinematics of ionized gas in an extended (20°×15°) region containing the X-ray Superbubble in Cygnus with the aim of finding the shell swept up by a strong wind from Cyg OB2. Hα observations were carried out with high angular and spectral resolutions using a Fabry-Perot interferometer attached to the 125-cm telescope at the Crimean Observatory of the Sternberg Astronomical Institute. We detected high-velocity gas motions, which could result from the expansion of the hypothetical shell at a velocity of 25–50 km s^?1. Given the number of OB stars increased by Knödlseder (2000) by an order of magnitude, Cyg OB2 is shown to possess a wind that is strong enough [L _w ? (1–2) × 10³⁹ erg s^?1] to produce a shell comparable in size to the X-ray Superbubble and to a giant system of optical filaments. Based on our measurements and on X-ray and infrared observations, we discuss possible observational manifestations of the shell swept up by the wind.     

Ionization stratification in [WR] winds

We summarize currently available evidence for ionization stratification in the winds of [WR] stars and point out that ionization stratification may be important to explain with radiation-driven wind theory the winds of [WR] stars, while also providing an empirical tool to investigate [WR] wind structures.