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We present in this second paper the results of our intensive spectroscopic campaign to search for binaries via periodic radial-velocity (RV) variations among Wolf-Rayet (WR) stars for the Large Magellanic Cloud (LMC). We observed 61 nitrogen-rich WNE stars in the LMC. Along with the results of Bartzakos, Moffat & Niemela on the carbon/oxygen-rich WR stars, 2/3 of the WR population of the LMC (134 stars in total) has now been investigated for periodic RV variability. We have also retrieved time-dependent photometric data in the public domain from the OGLE and MACHO projects, as well as X-ray data from ROSAT and Chandra satellites, to provide additional constraints on the binary character. For each of our sample stars, we discuss its observational properties: RV variations, (periodic) photometric variability, X-ray luminosity, spectral classification, abundance of hydrogen, runaway status and lineprofile variations (LPVs). For the binaries we discuss additional properties, such as windwind collision (WWC) effects, and the orbital parameters. With this large sample, we discuss the global properties of the WNE population, which is expected to be the most sensitive to binary evolution with respect to the influence of metallicity. To emphasize the relevance of the binary frequency test for the stellar evolution of massive stars in the LMC, we review their observational properties and provide new and meaningful evolutionary classes, which reconcile observational and theoretical definitions. Finally, we draw an overall evolutionary scheme for massive-star evolution, with respect to the three main ingredients of stellar evolution: mass, metallicity and rotation.

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 Montréal 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.

We have obtained Chandra ACIS-S observations of NGC 6543, the Cat's Eye Nebula. The X-ray emission from NGC 6543 is clearly resolved into a point source at the central star and diffuse emission confined within the central elliptical shell and two extensions along the major axis. Spectral analysis of the diffuse component shows that the abundances of the X-ray-emitting gas are similar to those of the fast (1,750 km s −1 ) stellar wind but not those of the nebula. Furthermore, the temperature of this gas is ∼1.7×10 6 K, which is 100 times lower than the expected post-shock temperature of the fast stellar wind. The combination of low temperature and wind abundances is puzzling. The thermal pressure of this hot gas is about twice the pressure in the cool nebular shell; thus, the hot gas plays an essential role in the ongoing evolution of the nebula. Subject headings: planetary nebulae: general -planetary nebulae: individual (NGC 6543) -X-rays: ISM -stars: winds 1. Introduction Optical emission-line images of planetary nebulae (PNs) reveal a fascinating range of morphologies (e.g., the Hubble Space Telescope gallery of PNs 4 ), indicating complex internal structures in the nebulae. Among these PNs, NGC 6543, also known as the Cat's Eye Nebula, has perhaps the most interesting morphology. As reported by Reed et al. (1999), the Hα and [O III] λ5007 line images of NGC 6543 are similar, showing an inner shell surrounded by an envelope with multiple, interlocking, semi-circular features. The [N II] 4

We have carried out an intensive spectroscopic campaign to search for binaries via periodic radial velocity (RV) variations among all the nitrogen-rich WN Wolf-Rayet (WR) stars in the Small Magellanic Cloud (SMC), and all WNE stars in the Large Magellanic Cloud (LMC). We present in this first paper the results for the SMC. Along with the results of Bartzakos et al. on the only carbon/oxygen-rich WR star (AB8, WO4+O4), the whole WR population of the SMC (11 stars) has now been investigated intensively for periodic RV variability. We have also retrieved time-dependent photometric data in the public domain from the OGLE and MACHO projects, and X-ray data from the ROSAT and Chandra archives, to provide additional constraints on the binary character. Contrary to theoretical expectations that predict a virtually 100 per cent binary frequency in the SMC, we find a normal (∼40 per cent) WR binary frequency in this galaxy. We also find the clear presence of hydrogen in the winds of the single WR stars in the SMC, even for the stars with an early spectral subtype. We discuss the possible reasons and implications of this for stellar evolution of massive stars in such a low-metallicity environment, e.g. the influence of rotation versus the necessity of a very high initial mass of the progenitors for single stars, and the possible past occurrence of Roche lobe overflow for binaries.

We report the results from a homogeneous analysis of the X-ray (Chandra ACIS) data available for a sample of 51 LINER galaxies selected from the catalogue by Carrillo et al. (1999, Rev. Mex. Astron. Astrofis., 35, 187) and representative of the population of bright LINER sources. The nuclear X-ray morphology has been classified by their nuclear compactness in the hard band (4.5-8.0 keV) into 2 categories: active galactic nuclei (AGN) candidates (with a clearly identified unresolved nuclear source) and starburst (SB) candidates (without a clear nuclear source). Sixty percent of the total sample are classified as AGNs, with a median luminosity of L X (2−10 keV) = 2.5 × 10 40 erg s −1 , which is an order of magnitude higher than for SB-like nuclei. The spectral fitting allows us to conclude that most of the objects need a non-negligible power-law contribution. When no spectral fitting can be performed (data with a low signal-to-noise ratio), the color-color diagrams allow us to roughly estimate physical parameters, such as column density, temperature of the thermal model, or spectral index for a power-law, and therefore to better constrain the origin of the X-ray emission. The X-ray morphology, the spectra, and the color-color diagrams together allow us to conclude that a high percentage of LINER galaxies, at least ≈60%, could host AGN nuclei, although contributions from high-mass X-ray binaries or ultra-luminous X-ray sources cannot be ruled out for some galaxies.

This paper presents a homogeneous study of abundances in a sample of 79 northern galactic planetary nebulae whose morphological classes have been uniformly determined. Ionic abundances and plasma diagnostics were derived from selected optical line strengths in the literature, and elemental abundances were