Optical observations of the ultrahigh-excitation Wolf-Rayet star Sanduleak 3

Recombination lines of O VII, O VIII, and C V have been identified in the optical spectrum of an O VI Wolf-Rayet star, representing the first non-X-ray detection of these ions in astronomical spectra and implying excitation energies in excess of 800 eV. Rapid variations on a time scale of about 150 s have been observed in the profile of one of the O VII lines

High-Resolution Observations of Interstellar NA i and CA II Absorption Lines toward the Scorpius OB1 Association

Observations of Na I and Ca II in absorption toward 22 stars in the Sco OB1 region, obtained at resolution R = 100,000 with a coude echelle spectrograph and 3.3-m camera on the 1.9-m telescope at Mt. Stromlo Observatory during 1986, are reported. The data are presented in extensive tables and graphs and analyzed in detail. Features discussed include (1) strong absorption at heliocentric velocities between 0 and -20 km/sec, (2) sharp discrete components with blueshifted velocities of up to -50 km/sec, and (3) some absorption at positive heliocentric velocities up to +20 km/sec. The (Na I)/(Ca II) ratios are found to be 4-200 for component (1), near 1 for component (2), and 0.4 or less for component (3)

Photoionization modelling based on HST images of Magellanic Cloud planetary nebulae – I. SMC N 2 and SMC N 5

We construct fully self-consistent, detailed photoionization models for two planetary nebulae (PNe) in the Small Magellanic Cloud (SMC), namely SMC N 2 and SMC N 5, to fit optical and UV spectrophotometric observations as well as HST Faint Object Camera (FOC) narrow-band images taken in the light of Hβ. The derived density structure shows that both PNe have a central cavity surrounded by a shell of decreasing density described by a parabolic curve. For both nebulae, our models fail to reproduce the HST images taken in the light of the [O III] λ 5007 line, in the sense that the observed [O III] λ 5007 surface brightness decreases more slowly outside the peak emission than predicted. An effective temperature of Teff = 111 500 K, a stellar surface gravity of log g = 5.45 and a luminosity of L* = 8430 Lʘ are derived for the central star of SMC N2; similarly Teff = 137 500 K, log g = 6.0 and L* = 5850 Lʘ are derived for SMC N 5. SMC N 2 is optically thin and has a total nebular mass (H plus He) of 0.180 Mʘ, while SMC N 5 is optically thick and has an ionized gas mass of 0.194 Mʘ. Using the H-burning SMC metal abundance (Z = 0.004) evolutionary tracks calculated by Vassiliadis & Wood, core masses of 0.674 Mʘ and 0.649Mʘ are derived for SMC N 2 and SMC N 5, respectively. Similarly, from the He-burning evolutionary tracks of Vassiliadis & Wood for progenitor stars of mean LMC heavy-element abundance (Z = 0.008), we find Mc = 0.695 and 0.675 Mʘ for SMC N 2 and SMC N 5, respectively. We find that Hβ images are needed if one is to derive accurate stellar luminosities directly from photoionization modelling. However, in the absence of an Hβ image, photoionization models based on [O III] images (and nebular line intensities) yield accurate values of Teff and log g, which in turn allow reliable stellar masses and luminosities to be derived from a comparison with theoretical evolutionary tracks. We show that the correct nebular ionized mass can be deduced from the nebular Hβ flux, provided the mean nebular density given by the C III] λ 1909/λ 1907 ratio is also known

Hubble Space Telescope Images of Magellanic Cloud Planetary Nebulae: Data and Correlations across Morphological Classes

The morphology of planetary nebulae (PNs) provides an essential tool for understanding their origin and evolution, since it reflects both the dynamics of the gas ejected at the tip of the asymptotic giant branch phase and the central-star energetics. Here we study the morphology of 27 Magellanic Cloud planetary nebulae (MCPNs) and present an analysis of their physical characteristics across morphological classes. Similar studies have been successfully carried out for Galactic PNs but were compromised by the uncertainty of individual PN distances. We present our own Hubble Space Telescope (HST) Faint Object Camera (FOC) images of 15 MCPNs acquired through a narrowband [O III] λ5007 filter. We use the Richardson-Lucy deconvolution technique on these pre-COSTAR images to achieve post-COSTAR quality. Three PNs imaged before and after COSTAR confirm the high reliability of our deconvolution procedure. We derive morphological classes, dimensions, and surface photometry for all of these PNs. We have combined this sample with HST/PC1 images of 15 MCPNs, three of which are in common with the FOC set acquired by Dopita et al., to obtain the largest MCPNs sample ever examined from the morphological viewpoint. By using the entire database, supplemented with published data from the literature, we have analyzed the properties of the MCPNs and compared them to a typical, complete Galactic sample. Morphology of the MCPNs is then correlated with PN density, chemistry, and evolution

Atomic and Molecular Interstellar Absorption Lines toward the High Galactic Latitude Stars HD 141569 and HD 157841 at Ultra-High Resolution

We present ultra-high-resolution (0.32 km s-1) spectra obtained with the 3.9 m Anglo-Australian Telescope (AAT) and Ultra-High-Resolution Facility (UHRF) of interstellar Na I D1, Na I D2, Ca II K, K I, and CH absorption toward two high Galactic latitude stars HD 141569 and HD 157841. We have compared our data with 21 cm observations obtained from the Leiden/Dwingeloo H I survey. We derive the velocity structure and column densities of the clouds represented by the various components and identify the clouds with ISM structures seen in the region at other wavelengths. We further derive abundances, linear depletions, and H2 fractional abundances for these clouds wherever possible. Both stars are located in regions of IRAS 100 μm emission associated with high Galactic latitude molecular clouds (HLCs): HD 141569 lies, in projection, close to MBM 37 and the Lynds dark cloud L134N, whereas HD 157841 is in the vicinity of the MBM 151. Toward HD 141569 we detect two components in our UHRF spectra: a weak, broad b = 4.5 km s-1 component at -15 km s-1, seen only in Ca II K absorption, and another component at 0 km s-1, seen in Na I D1, Na I D2, Ca II K, K I, and CH absorption. The cloud represented by the -15 km s-1 component is warm and may be located in a region close to the star. The cloud represented by the 0 km s-1 component has a Ca linear depletion δ(Ca) = 1.4 × 10-4 and shows evidence for the presence of dust, consistent with strong 100 μm emission seen in this region. The H2 fractional abundance f(H2) derived for this cloud is 0.4, which is typically what is observed toward HLCs. We conclude that this 0 km s-1 cloud is associated with MBM 37 and L134N based on the presence of dust and molecular gas (CH) and good velocity agreement with CO emission from these two clouds. This places HD 141569 beyond MBM 37 and L134N, which are estimated to be at ≈ 110 pc. In the case of the HD 157841 sight line, a total of six components are seen on our UHRF spectra in Na I D1, Na I D2, Ca II K, K I, and CH absorption. Two of these six components are seen only in a single species. The cloud represented by the components at 1.85 km s-1 has a Ca linear depletion δ(Ca) = 2.8 × 10-4, indicating the presence of dust. The f(H2) derived for this cloud is 0.45, and there is good velocity agreement with CO emission from MBM 151. To the best of our knowledge, this 1.85 km s-1 component toward HD 157841 is the first one found to have relative line widths that are consistent with pure thermal broadening only. We associate the 1.85 km s-1 cloud seen in our UHRF spectra with MBM 151 and conclude that HD 157841 must lie beyond ~200 pc, the estimated distance to MBM 151

Planetary Nebulae as Probes of Stellar Evolution and Populations

Planetary Nebulae (PNe) have been used satisfactory to test the effects of stellar evolution on the Galactic chemical environment. Moreover, a link exists between nebular morphology and stellar populations and evolution. We present the latest results on Galactic PN morphology, and an extension to a distance unbiased and homogeneous sample of Large Magellanic Cloud PNe. We show that PNe and their morphology may be successfully used as probes of stellar evolution and populations.Comment: to appear in: Chemical Evolution of the Milky Way: stars versus clusters, ed. F. Giovannelli and F. Matteucci, Kluwer (2000), in pres

Imaging of Four Planetary Nebulae in the Magellanic Clouds Using the Hubble Space Telescope Faint Object Camera

Using the Faint Object Camera on-board the Hubble Space Telescope, we have obtained images of four planetary nebulae (PNe) in the Magellanic Clouds, namely N2 and N5 in the SMC and N66 and N201 in the LMC. Each nebula was imaged through two narrow-band filters isolating [O III] λ5007 and Hβ, for a nominal exposure time of 1000 s in each filter. Significant detail is evident on the raw images and, after deconvolution using the Richardson-Lucy algorithm, structures as small as 0.06" are easily discernible. In [O III], SMC N5 shows a circular ring structure, with a peak-to-peak diameter of 0.26" and a FWHM of 0.35", while SMC N2 shows an elliptical ring structure with a peak-to-peak diameter of 0.26" x 0.21" (FWHM 0.40" x 0.35"). The expansion ages corresponding to the observed structures in SMC N2 and N5 are of the order of 3000 yr. Such low ages appear more easy to reconcile with helium-burning rather than hydrogen-burning central star evolutionary tracks. LMC N201 is very compact, with a FWHM of 0.21" in Hβ. The Type I PN LMC N66 is a multipolar nebula, with the brightest part having an extent of about 2" and with fainter structures extending over 4". The [O III] image reveals structures unprecedented for a planetary nebula, with several bright knots and faint loops visible outside the two main bright lobes

The Distances of the Magellanic Clouds

The present status of our knowledge of the distances to the Magellanic Clouds is evaluated from a post-Hipparcos perspective. After a brief summary of the effects of structure, reddening, age and metallicity, the primary distance indicators for the Large Magellanic Cloud are reviewed: The SN 1987A ring, Cepheids, RR Lyraes, Mira variables, and Eclipsing Binaries. Distances derived via these methods are weighted and combined to produce final "best" estimates for the Magellanic Clouds distance moduli.Comment: Invited review article to appear in ``Post Hipparcos Cosmic Candles'', F. Caputo & A. Heck (Eds.), Kluwer Academic Publ., Dordrecht, in pres