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Cassiopeia A (Cas A) is one of the best studied young Galactic supernova remnants. While providing a rare opportunity to study in detail the remnant of a Type IIb supernova, questions remain regarding the nature of its progenitor, its mass-loss history, and its pre-SN evolution. Here we present an optical investigation of the circumstellar environment around Cas A and find clumpy and filamentary Halpha emission nebulosities concentrated 10-15 pc (10-15 arcminutes) to the north and east. First reported by Minkowski as a faint H II region, these nebulosities exhibit distinct morphological and spectroscopic properties relative to the surrounding diffuse emissions. Compared to neighboring H II regions, these nebulae show stronger [N II] 6548, 6583 A and [S II] 6716, 6731 A emissions relative to Halpha. We show that Cas A's highest-velocity ejecta knots are interacting with some of the closest projected emission nebulae, thus providing strong evidence that these nebulae lie at the same distance as the remnant. We interpret these surrounding nebulosities to be the remains of the progenitor's red supergiant wind which accumulated against the southern edge of a large extended H II region located north of Cas A. Our findings are consistent with the view that Cas A's progenitor underwent considerable mass-loss, first from a fast main-sequence wind, then from a slower, clumpy red supergiant wind, and finally from a brief high-velocity wind, like that from a yellow supergiant., Comment: 19 pages, 9 figures, accepted to ApJ

This is the second of two papers examining Spitzer Infrared Spectrograph (IRS) observations of the ultraluminous X-ray source (ULX) in Holmberg II. Here we perform detailed photoionization modeling of the infrared lines. Our analysis suggests that the luminosity and morphology of the [O IV] 25.89 $\mu$m emission line is consistent with photoionization by the soft X-ray and far ultraviolet (FUV) radiation from the accretion disk of the binary system and inconsistent with narrow beaming. We show that the emission nebula is matter-bounded both in the line of sight direction and to the east, and probably radiation-bounded to the west. A bolometric luminosity in excess of 10$^{40}$ erg s$^{-1}$ would be needed to produce the measured [O IV] flux. We use modeling and previously published studies to conclude that shocks likely contribute very little, if at all, to the high-ionization line fluxes observed in the Holmberg II ULX. Additionally, we find that the spectral type of the companion star has a surprisingly strong effect on the predicted strength of the [O IV] emission. This finding could explain the origin of [O IV] in some starburst systems containing black hole binaries., Comment: Accepted by ApJ

Using images centered around the 2.12 μm line of molecular hydrogen obtained with the Wide Field Infrared Camera on the Canada-France-Hawaii Telescope, we show that in spite of the different apparent morphologies, the Dumbbell Nebula and the Ring Nebula share the same intrinsic three-dimensional triple biconic structure.

Results are presented from a pilot survey of 3.3 micron PAH emission from planetary nebulae using FLITECAM, an instrument intended for airborne astronomy with SOFIA. The observations were made during ground-based commissioning of FLITECAM's spectroscopic mode at the 3-m Shane telescope at Lick Observatory. Direct-ruled KRS-5 grisms were used to give a resolving power (R)~1,700. Targets were selected from IRAS, KAO and ISO sources with previously observed PAH emission at longer wavelengths. AGB stars and PN with C/O ratios < 1 were also added to the target list in order to test PAH detection thresholds. In all, 20 objects were observed. PAH emission was detected in 11 out of 20 observed targets., 8 pages, 2 tables, 4 figures, accepted to ApJ

We present the first spatially resolved spectral study of an extragalactic pulsar wind nebula (PWN), that surrounding the 50 ms pulsar B0540-69.3 in the Large Magellanic Cloud, using the ACIS instrument on board the Chandra X-ray Observatory. The spectral properties of the PWN change at a radius of ~5'', corresponding to a shell detected optically in [O III]. Within this radius, the spectra are well characterized by a simple power law, whose spectral index varies strongly with radius, so that the effective size of the nebula decreases with increasing photon energy. These X-ray measurements support the idea that the [O III] shell represents an outer skin surrounding the wind nebula, analogous to that seen in the Crab Nebula. We use the size-energy relation and radial variability of the X-ray spectral index to estimate PWN parameters, including the radial dependence of the magnetic field, and the average ratio of electromagnetic to particle flux.

13 pags., 11 figs., 1 tab., Our imaging of the preplanetary nebula IRAS 19475+3119 (hereafter 119475) at 0.43 and 0.6 μm with HST reveals a quadrupolar nebula of size about 10.5″ × 4.7″, with two bipolar elongated lobes emanating from the center of the nebula. One of the bipolar lobes shows detailed point-symmetric structure with respect to the central star. A faint, surface brightness-limited, diffuse halo surrounds the lobes. Interferometric observations of the CO J = 1-0 line with OVRO at ∼8″ resolution show that the bulk of the emission comes from an unresolved molecular envelope expanding at 15 km s-1, resulting from the AGB progenitor's dense, slow wind. Weaker emission is seen from a fast bipolar outflow oriented along the longer and more tenuous pair of the sets of lobes. Optical spectroscopy reveals a complex Hα profile with a broad photospheric absorption feature and a narrow inverse P Cygni shaped core; comparison with previous data shows that the core profile shape varies dramatically with time. We find an unresolved source of millimeter-wave continuum emission in 119475, which together with previous submillimeter continuum measurements, implies a very substantial mass (roughly a few times 0.01 M⊙) of large (radius ≳1 mm), cold (∼30 K) dust grains in 119475. Combining our estimates of the circumstellar mass with the typical mass of a post-AGB star, we find that the main-sequence progenitor of 119475's central star had a mass ≳2.5 M⊙. We discuss the formation of 119475's quadrupolar nebula in the light of past and current ideas for the dramatic transformation of the morphology and kinematics of mass ejecta as AGB stars evolve into planetary nebulae. © 2007. The American Astronomical Society. All rights reserved., R. S. andM.M. thank NASA for partially funding this work by a NASA LTSA award (399-20-40-06); R. S. also received partial support for this work from NASA ADP award (399-20-00-08) and HST/GO awards (GO-09463.01-A and GO-09801.01-A) from the Space Telescope Science Institute, which is operated by theAURA, Inc., under NASA contract NAS5-26555). C. S. C. is partially funded for this work by National Science Foundation grant 9981546 to Owens Valley Radio Observatory, the Spanish MCyT under project AYA2003-2785, and the Astroscam project (Ref: S-0505 ESP-0237).

We present a multiwavelength study of the central region of the Carina Nebula, including Trumpler 16 and part of Trumpler 14. Our analysis of the Chandra X-Ray Observatory archival data led to the identification of 454 X-ray sources. These sources were then cross-identified with optical photometric and spectroscopic information available from the literature and with newly obtained near-infrared (JHKs) imaging observations. A total of 38 known OB stars are found to be X-ray emitters. All the O stars and early-B stars follow the nominal relation between the X-ray and bolometric luminosities, LX ~ 10-7Lbol. A few mid- to late-B stars are found to be associated with X-ray emission, likely attributable to T Tauri companions. We discovered 16 OB star candidates that suffer a large extinction in the optical wave bands. Some 300 sources have the X-ray and infrared characteristics of late-type pre-main-sequence stars. Our sample represents the most comprehensive census of the young stellar population in the Carina Nebula so far and should be useful for the study of the star formation history of this massive starburst region. We also report the finding of a compact (2' ? 4') group of 10 relatively bright X-ray sources, all of which are detected in the near-infrared wavelengths and are highly reddened. The group is spatially coincident with the dark V-shaped dust lane bisecting the Carina Nebula and may be part of an embedded association. The distribution of the young stellar groups surrounding the H II region associated with Trumpler 16 is consistent with the collect-and-collapse scenario of triggered star formation.

We present new images of the giant molecular cloud W3 obtained with the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer for Spitzer (MIPS) on board the Spitzer Space Telescope. The images encompass the star forming regions W3 Main, W3(OH), and a region that we refer to as the Central Cluster, which encloses the emission nebula IC 1795. We present a star count analysis of the point sources detected in W3. The star count analysis shows that the stellar population of the Central Cluster, when compared to that in the background, contains an over density of sources. The Central Cluster also contains an excess of sources with colors consistent with Class II young stellar objects (YSOs). An analysis of the color-color diagrams also reveals a large number of Class II YSOs in the Central Cluster. Our results suggest that an earlier epoch of star formation created the Central Cluster, created a cavity, and triggered the active star formation in the W3 Main and W3(OH) regions. We also detect a new outflow and its candidate exciting star.

Bright emission nebulae, or H II regions, around hot stars are readily seen in Hα light. However, the all-pervasive faint Hα emission has only recently been detected and mapped over the whole sky. Mostly the Hα emission observed along a line of sight is produced by ionized gas in situ. There are, however, cases where all or most of the Hα radiation is due to scattering by electrons or dust particles that are illuminated by an Hα-emitting source off the line of sight. Here we demonstrate that diffuse, translucent, and dark dust clouds at high Galactic latitudes are in many cases observed to have an excess of diffuse Hα surface brightness; i.e., they are brighter than the surrounding sky. We show that the majority of this excess surface brightness can be understood as light scattered off the interstellar dust grains. The source of incident photons is the general Galactic Hα background radiation impinging on the dust clouds from all over the sky.

Hubble Space Telescope images with the Wide Field Planetary Camera 2 of the young, oxygen-rich, Crab-like supernova remnant SNR0540-69.3 in the Large Magellanic Cloud (LMC) reveal details of the emission distribution and the relationship between the expanding ejecta and synchrotron nebula. The emission distributions appear very similar to those seen in the Crab nebula, with the ejecta located in a thin envelope surrounding the synchrotron nebula. The [O III] emission is more extended than other tracers, forming a faint "skin" around the denser filaments and synchrotron nebula, as also observed in the Crab. The [O III] exhibits somewhat different kinematic structure in long-slit spectra, including a more extended high-velocity emission halo not seen in images. Yet even the fastest expansion speeds in SNR 0540 s halo are slow when compared to most other young supernova remnants, though the Crab nebula has similar slow expansion speeds. We show a striking correspondence between the morphology of the synchrotron nebula observed in an optical continuum filter with that recently resolved in Chandra X-ray images. We argue that the multi-component kinematics and filamentary morphology of the optical emission-line features likely result from magnetic Rayleigh-Taylor instabilities that form as the synchrotron nebula expands and sweeps up ejecta, as seen in the Crab nebula. Our images and spectra help to refine our understanding of SNR 0540 in several more detailed respects: they confirm the identification of H(alpha)+[N II] in the red spectrum, they show that the systemic velocity of SNR 0540 is not significantly different from that of the LMC, and they hint at a lower Ne abundance than the Crab (potentially indicating a more massive progenitor star).

The mid-infrared emission from a photodissociation region (PDR) viewed edge-on in the Orion Nebula is examined through 8.7-20.6 ?m images and 8-13 ?m spectra. The polycyclic aromatic hydrocarbon (PAH) emission is located between the edges of H II regions and layers of [C I] emission, agreeing with PDR theory. Using a simple model, the spatial variations in the emission from PAHs detected at 8.6, 11.2, and 12.7 ?m are demonstrated to be directly proportional to the material column density and the intensity of the UV field. For a homogeneous, neutral cloud illuminated by a bright OB star, PDR theory predicts that the ultraviolet (UV) radiation is attenuated exponentially (e). The predicted UV attenuation is confirmed by observations of broad PAH emission features found at 8.6, 11.2, and 12.7 ?m. The PAH emission is found in cool regions having greater optical depths relative to regions where mid-infrared emission from ionized gas is observed. Through modeling we determine a gas density of 9.7 ? 104 cm-3. On large and small size scales, the relative strengths of the 8.6, 11.2, and 12.7 ?m PAH features at the bar of the Orion Nebula indicate that there is not a simple transition from ionized to neutral PAHs across the PDR.

We report the discovery of He II λλ4850 and 6545 Raman-scattered by atomic hydrogen in the high-resolution spectrum of the very compact and young planetary nebula IC 5117 obtained with the ESPaDOnS (Echelle Spectropolarimetric Device for the Observation of Stars) installed on the 3.6 m Canada-France-Hawaii Telescope. By adopting case B recombination atomic data and considering all the fine-structure emission components, we calculate the weighted averages for the line centers of the Raman-scattered features, as well as those for the emission lines He II λλ4859 and 6560 to determine redward velocity shifts of Δv4850 = +29 km s-1 and Δv6545 = +24 km s-1. We compute the Raman conversion efficiency by a Monte Carlo technique adopting a simple scattering geometry, in which the hot central star is surrounded by a hollow cylindrical H I region characterized by thickness T that is in turn parameterized by the H I column density. It is proposed that the central far-UV emission region is covered significantly by the neutral scattering region characterized by the H I column density N 4 × 1021 cm-2. The H I column density is higher by an order of magnitude than the value proposed from 21 cm radio observations. We briefly discuss the importance of Raman scattering as a probe of neutral material around a newly formed hot white dwarf and the mass-loss process occurring in the late stage of stellar evolution.

We report observations made with the SIMBA bolometer at SEST to measure the 1.2 mm continuum emission toward the Keyhole nebula. We have detected 1.2 mm emission toward the ionized gas filaments of the Car II radio source that is attributed to thermal free-free emission. Several compact 1.2 mm emission sources have also been identified and found to correspond to bright-rimmed molecular globules. Under the assumption that for these sources the 1.2 mm emission corresponds to dust, we find mass estimates in the range 3-19 M☉, which are consistent with previous molecular line measurements. The data also yield new 1.2 mm flux measurements at two different epochs during the cyclic brightness variation of η Carinae. No emission was detected toward the trademark dark keyhole of the nebula, consistent with it being cool molecular gas situated at the outskirts of the H II region.

We present the results of a spatio-kinematic study of the planetary nebula Menzel 1 using spectro-photometric mapping and a 3-D photoionization code. We create several 2-D emission line images from our long-slit spectra, and use these to derive the line fluxes for 15 lines, the Halpha/Hbeta extinction map, and the [SII] line ratio density map of the nebula. We use our photoionization code constrained by these data to derive the three-dimensional nebular structure and ionizing star parameters of Menzel 1 by simultaneously fitting the integrated line intensities, the density map, and the observed morphologies in several lines, as well as the velocity structure. Using theoretical evolutionary tracks of intermediate and low mass stars, we derive a mass for the central star of 0.63+-0.05 Msolar. We also derive a distance of 1050+_150 pc to Menzel 1.

We investigated spectroscopic data of the extended planetary nebula NGC 7026 in the wavelengths 3700-10,050 A, secured with the Hamilton Echelle Spectrograph at Lick Observatory. This optical wavelength spectrum has been analyzed along with the International Ultraviolet Explorer (IUE) UV spectral data. The diagnostic diagram indicates that the planetary nebula has very complex electron densities of N ~ 3000-10,000 cm-3. The electron temperatures are relatively low: around T = 8000-9500 K, probably as a result of an enhanced heavy elemental cooling. The electron temperature variation also indicates that the low-excitation line region is slightly higher than the high-excitation line regions perhaps as a result of the hardening of escaped UV ionizing photons into the outer shell part of low-excitation lines. We construct a photoionization model, with the central star of the planetary nebula at a temperature of Teff = 80,000 K, to fit most of the relatively strong line intensities and the observed physical conditions. With this photoionization model construction and with a semiempirical ionization correction method, we derived the elemental abundances of the nebula. Compared to the average or normal planetary nebula, most elemental abundances of He, C, N, O, Ne, S, Ar, and Cl appear to be enhanced.

We present Hubble Space Telescope STIS FUV images of the Lyα and FUV continuum emission of the luminous emission-line nebulae in two cooling-core clusters, A1795 and A2597. The Lyα and FUV continuum emission consist of a diffuse component (~60%) and more compact features (knots and filaments), which lie preferentially along the radio source edges. There are correlations between the FUV continuum flux and the emission-line fluxes of Lyα and Hα that imply that the brighter parts of the nebulae are ionized locally. We suggest that the FUV knots are star clusters with ongoing star formation of several solar masses per year. The bolometric luminosity of such a starburst (if absorbed by dust) would be detectable with the Spitzer Space Telescope MIPS. It appears that star formation occurs throughout the nebula, although it is strongly enhanced along the edges of the radio source. We find that young hot stars (e.g., O5) probably provide the bulk of the photons that ionize the nebula, although other sources of ionization may contribute in selected regions of the nebula. Constraints on diagnostic UV emission lines are consistent with photoionization from a starburst population and perhaps marginally with intermediate-velocity shocks, ~400 km s-1. We suggest that the mass accretion rates are comparable to the star formation rates (of order 10 M☉ yr-1). This is consistent with the lack of intermediate-temperature gas (

We report the detection, in archival ROSAT and ASCA observations, of X-ray emission from the direction of DA 495 (G65.7+1.2), a likely supernova remnant of uncertain classification but with similarities to the Crab Nebula. An unusual feature of the radio nebula is its annular morphology, with a flux minimum at the geometrical center. In the soft X-ray band, the ROSAT data resolve a compact source near the edge of the central radio hole ; the hard X-ray morphology, at the limit of ASCA's spatial resolution, is suggestive of extended plerionic emission dropping off from a central flux maximum coincident with the ROSAT source. The spectrum is well-described by a power-law with photon index approximately 1.7, and the X-ray flux is roughly constant with time. Taken together, this evidence suggests identification of the X-ray source with a magnetospherically active neutron star and its associated wind nebula. Timing analysis of the ASCA data yields only a weak upper bound on pulsations with periods longer than approximately 30 ms. These results reveal for the first time the high-energy engine that powers the synchrotron nebula, and strengthen the classification of DA 495 as a plerionic supernova remnant, one that may represent a late evolutionary stage of Crab-like nebulae.

We have searched the 30 Doradus nebula, a giant extragalactic H II region, for the presence of embedded supernova remnants using high-resolution radio, optical, and X-ray images. Radio images obtained at 6 and 3.5 cm with the Australia Telescope Compact Array have an angular resolution of ~2''. We compare our radio images with the optical images from the Cerro Tololo Inter-American Observatory to distinguish thermal and possible nonthermal components in the nebula. We have also mapped, for the first time, the extinction across the region at high angular resolution. We identify two sources as supernova remnant candidates in the nebula. Derived physical parameters for the adiabatic phase imply relatively young remnants (~103 yr) evolving in a very dense environment (102 cm-3). We compare our results with high-resolution data from the Chandra X-Ray Observatory, but with only a short exposure these preliminary X-ray data lack the sensitivity to resolve our supernova remnant candidates from intervening hot gas of the diffuse thermal X-ray component of the nebula.

We present a 100 ks observation of the Galactic supernova remnant 3C396 (G39.2-0.3) with the Chandra X-Ray Observatory that we compare to a 20cm map of the remnant from the Very Large Array. In the Chandra images, a nonthermal nebula containing an embedded pointlike source is apparent near the center of the remnant which we interpret as a synchrotron pulsar wind nebula surrounding a yet undetected pulsar. From the 2-10 keV spectrum for the nebula (N(sub H) = 5.3 plus or minus 0.9 x 10(exp 22) per square centimeter, GAMMA =1.5 plus or minus 0.3) we derive an unabsorbed x-ray flux of S(sub z)=1.62 x 10(exp -12) erg per square centimeter per second, and from this we estimate the spin-down power of the neutron star to be E(sup dot) = 7.2 x 10(exp 36) ergs per second. The central nebula is morphologically complex, showing bent, extended structure. The radio and X-ray shells of the remnant correlate poorly on large scales, particularly on the eastern half of the remnant, which appears very faint in X-ray images. At both radio and X-ray wavelengths the western half of the remnant is substantially brighter than the east.

We present observations of the bipolar nebula OH 231.8+4.2, made with the Hubble Space Telescope (HST) NICMOS camera, in three wide filter bands (F205W, F160W, and F110W). The images have excellent dynamic range after removal of low-level instrumental artifacts. In the F205W filter (λ ≈ 2.04 μm), we achieve a peak/rms of greater than 8000 with an angular resolution of 020 (FWHM). The combination of high dynamic range and angular resolution confirms previous observations but also reveals new features in the near-IR morphology of the nebula, which at these wavelengths is dominated by scattered light. The northern (approaching) lobe shows well-defined, limb-brightened edges. The central jet splits into two filaments and exhibits some curvature between the center of the nebula and the end of the northern lobe. The southern (receding) lobe has a diffuse, flocculent appearance without a sharply defined central jet, in contrast to the northern lobe. A sharpened version of the F205W image shows indications of turbulent structures both in the northern lobe and jet and in the southern lobe. A faint cylindrical halo of scattered light shows a sharp increase in surface brightness inside a radius of ~4'' from the center, possibly resulting from a transition from a spherical wind to a disk- or torus-like mass ejection, on the same timescale as the formation of the collimated fast wind seen in CO and HCO+ images. We calculate the extinction through the nebula from the measured near-IR colors and a silicate grain model. For a simple geometric model of a dense central disk, we estimate a disk mass (gas and dust) in the range 0.03-0.06 M☉, relatively insensitive to grain size. The circumstance of an asymptotic giant branch (AGB) star with a massive, highly collimated, high-velocity bipolar flow may be understood in terms of the model of Soker & Rappaport if the central star underwent a change in mass-loss properties from a (roughly) spherical AGB wind to equatorially enhanced mass loss beginning ~ × 103 yr ago. Supposing the presence of a dwarf companion in a suitable orbit, the bipolar nebula then is a consequence of a strong increase in mass loss as the central star evolves close to the tip of the AGB and will soon evolve to higher Teff and appear as a more typical proto-planetary nebula.

We present a detailed spectroscopic analysis of the peculiar nebula around RY Scuti using data from the Space Telescope Imaging Spectrograph (STIS) and various ground-based observatories. This massive contact binary may represent a rapid evolutionary phase in transition to a short-period WR+OB system, and it is surrounded by a young nebula with unusual geometry. The ionized nebula is only about 1'' across, so STIS has allowed us to spatially resolve the spectrum of the star from its circumstellar nebula for the first time. Combining STIS data with ground-based spectra at optical and infrared wavelengths solves some geometric ambiguities posed by previous images and reveals the kinematic relationship between the nebular geometry and RY Scuti's complex emission-line profiles. We offer a new determination of the systemic velocity of 20 ± 3 km s-1, and we estimate the distance to RY Scuti as 1.8 ± 0.1 kpc. Nebular lines show subtle phase-dependent variability in addition to expected changes in equivalent width due to eclipses of stellar continuum. These changes in equivalent width yield an updated ephemeris, but a previously suggested period change is still uncertain after considering these new data. The nebula contains roughly 0.003 M☉ of material that is He- and N-rich and probably O-deficient compared to solar abundances, indicating that CNO-processed material has reached the surface in at least one component of the binary system. Diagnostic line ratios suggest that the electron density and temperature in the nebula are 2 × 105 cm-3 and ~9500 K, respectively. There are concentrated regions of higher density as well; emission knots seen around the rings suggest that common envelope mass loss during massive contact binary evolution may be characterized by strong azimuthal asymmetry and sporadic mass ejection events.

We report the discovery of a planetary nebula in the globular cluster G169 of the giant elliptical galaxy NGC 5128, based on spectroscopy with the Magellan I Baade 6.5 m telescope at Las Campanas Observatory. G169 appears to be a typical metal-rich globular cluster in NGC 5128 with MV = -8.2. Its planetary nebula also appears to be a typical high-excitation bright planetary in NGC 5128 with m5007 = 24.3. This is the first time a planetary nebula is found in a globular cluster member of a giant elliptical galaxy. We predict that several new planetary nebulae should be present in the large spectroscopic samples of extragalactic globular clusters becoming available. The scientific potential of the study of extragalactic globular cluster planetary nebulae is discussed.

The Midcourse Space Experiment (MSX) Galactic plane survey discovered a nearly perfectly circular ring nebula around the suspected planetary nebula Wray 17-96. Using near-IR spectral typing and modeling of the mid-IR nebula, we find that Wray 17-96 is more likely a candidate to be a luminous blue variable (LBV) surrounded by a large spherical ejecta shell. It is very similar to the G79.29+0.46 LBV candidate in Cygnus and the Pistol Star. The K-band spectrum and the mid-IR data indicate a stellar temperature of 13,000 K. The most likely distance to the source is 4.5 kpc, leading to a luminosity of 1.8 × 106 L☉. We suggest that the nebula consists of multiple shells and that an evolution from oxygen-rich to carbon-rich chemistry may be indicated.

Author(s): De Gregorio, BT; Stroud, RM; Nittler, LR; Kilcoyne, ALD | Abstract: Geochemical indicators in meteorites imply that most formed under relatively oxidizing conditions. However, some planetary materials, such as the enstatite chondrites, aubrite achondrites, and Mercury, were produced in reduced nebular environments. Because of large-scale radial nebular mixing, comets and other Kuiper Belt objects likely contain some primitive material related to these reduced planetary bodies. Here, we describe an unusual assemblage in a dust particle from comet 81P/Wild 2 captured in silica aerogel by the NASA Stardust spacecraft. The bulk of this ∼20 μm particle is comprised of an aggregate of nanoparticulate Cr-rich magnetite, containing opaque sub-domains composed of poorly graphitized carbon (PGC). The PGC forms conformal shells around tiny 5-15 nm core grains of Fe carbide. The C, N, and O isotopic compositions of these components are identical within errors to terrestrial standards, indicating a formation inside the solar system. Magnetite compositions are consistent with oxidation of reduced metal, similar to that seen in enstatite chondrites. Similarly, the core-shell structure of the carbide + PGC inclusions suggests a formation via FTT reactions on the surface of metal or carbide grains in warm, reduced regions of the solar nebula. Together, the nanoscale assemblage in the cometary particle is most consistent with the alteration of primary solids condensed from a C-rich, reduced nebular gas. The nanoparticulate components in the cometary particle provide the first direct evidence from comets of reduced, carbon-rich regions that were present in the solar nebula.

This paper presents the first observations of molecular gas associated with the Wolf-Rayet ring nebula NGC 3199 around the WR star WR 18. This includes first observations of the molecules HCN, HCO+, CN, and HNC seen in any Wolf-Rayet ring nebula. Our observations immediately suggest the presence of high-density molecular gas (>104 cm-3) in the nebula with significant amounts of associated molecular gas, which is in the form of clumpy ejecta and/or interstellar material. Molecular CO gas was mapped across the optically bright portion of the nebula and out into the diffuse ionized component using the 12CO J = 1 → 0 line. CO gas is not seen within the optically bright rim of NGC 3199 but adjacent to it. The optical emission rim therefore appears to mark regions of photodissociation. Velocity components in the CO data are consistent with those seen in high-resolution optical spectra of the Hα line but extend beyond the visible emission. A prior suggestion of the formation of the nebula via a bow shock appears unlikely since Hipparcos measurements show the proper motion of WR 18 is almost at right angles to the direction required for the bow shock model. Instead, line splitting toward the north of the nebula suggests that a possible blowout of the Wolf-Rayet wind through surrounding ejecta may be responsible for some of the velocity features observed. Preliminary estimates of molecular abundances in the nebula seen toward the central star are significantly higher than for the interstellar medium and are similar to those in planetary nebulae, although CN is distinctly underabundant in comparison to the very high values found in many planetary nebulae. The abundances found are consistent with the idea that at least a portion of the molecular material is associated with ejecta from the central star.

We present new observations of the deuterium and hydrogen Balmer lines in the Orion Nebula. There is a real variation in the deuterium-to-hydrogen line ratios across the nebula, being greatest in the emission from the largest proplyd (Orion 244-440). We also present the results of a detailed model for the emission of these lines, the hydrogen lines being the result of photoionization and recombination while the deuterium lines are produced by fluorescent excitation of the upper energy states by the far-UV radiation from θ1 Ori C. Comparison of the observations and predictions of the line intensities shows good agreement, both in the strength of the reference lines at Hβ and also in the differences of the Balmer decrement for the two atoms. The fact that both the deuterium and hydrogen emissions arise from mechanisms that count the near-ultraviolet (deuterium) and photoionizing ultraviolet (hydrogen) photons from the dominant star means that there is little prospect of similar observations being useful for determination of D/H abundances in H II regions.

Using the density and temperature profiles resulting from a two-dimensional turbulent model of the solar nebula as well as an appropriate law for the time variation of the disk accretion rate, we integrate the equation of diffusion that rules the evolution of the D/H ratio in H2O and HCN throughout the nebula. By fitting D/H measured in LL3 meteorites and comets or inferred in proto-Uranian and proto-Neptunian ices, we constrain the parameters of the model, namely, the initial accretion rate (0), the initial radius of the turbulent disk RD, and the α-coefficient of turbulent viscosity, and we find 2 × 10-6 < (0) < 10-5 M☉ yr-1, 12.8 < RD < 39 AU, and 0.006 < α < 0.04. Under the assumption that cometary cores are homogeneous, the microscopic icy grains that subsequently formed cometesimals were produced in the Uranus-Neptune region and no later than 3.5 × 105 yr. The epochs of the formation of Jupiter and Saturn cannot be lower than 0.7 and 5.7 Myr, respectively, after the formation of the Sun. Uranus and Neptune were completed after the dissipation of the nebula. The enrichment in volatiles with respect to the solar abundance measured by the Galileo probe in Jupiter may result from the trapping of these gases in the form of clathrate hydrates in the feeding zone of the forming planet.

We analyze (archival) Space Telescope Imaging Spectrograph long-slit Hα spectra of the proto-planetary nebula He 3-1475. We find two remarkable blueshifted absorption features arising from the inner ~5 × 1016 cm of the nebula, revealing the presence of two different winds outflowing at high velocity from the central star. The kinematic age of these winds is only tens of years. We find that the fast wind is flowing with velocities in the range ~150-1200 km s-1 whereas the ultrafast wind is moving much faster (up to 2300 km s-1). The latter is highly collimated (length/width 7) close to the central star (~1016 cm) along a direction different from previous mass ejection axes and shows a radially increasing velocity. We identify the ultrafast wind with a "pristine" post-asymptotic giant branch (post-AGB) outflow that has not been (strongly) altered by its interaction with the AGB envelope. We discuss the implications of the spatiokinematic structure of this wind for current theories of the formation and shaping of planetary nebulae.

We present a detailed modeling of the two broad bands observed at 6825 \AA\ and 7082 \AA\ in Sanduleak's star, a controversial object in the Large Magellanic Cloud. These bands are known to originate from Raman-scattering of O VI $\lambda\lambda$ 1032 and 1038 photons with atomic hydrogen and are only observed in bona fide symbiotic stars. Our high-resolution spectrum obtained with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph at the Magellan-Clay Telescope reveals, quite surprisingly, that the profiles of the two bands look very different: while the Raman 6825 \AA\ band shows a single broad profile with a redward extended bump, the Raman 7082 \AA\ band exhibits a distinct triple-peak profile. Our model suggests that the O VI emission nebula can be decomposed into a red, blue and central emission regions from an accretion disk, a bipolar outflow and a further compact, optically thick region. We also perform Monte Carlo simulations with the aim of fitting the observed flux ratio $F(6825)/F(7082) \sim 4.5$, which indicate that the neutral region in Sanduleak's star is characterized by the column density $N_{HI} \sim 1 \times 10^{23} {\rm\ cm^{-2}}$., Comment: 11 pages, 5 figures, accepted for publication in ApJ

We present a study of molecular-hydrogen absorption lines in the continuum spectra of three early-type stars in the Carina Nebula, HD 93129a, HD 93250, and HD 303308, made with the Berkeley Extreme and Far-Ultraviolet Spectrometer (BEFS) on the ORFEUS telescope in 1993 September. The instrument possesses an intermediate spectral resolving power (λ/Δλ = 3000) over the wavelength range λλ390-1170.We derive column densities for the H2 rotational levels up to J'' = 6 and estimate the kinetic temperature and the UV radiation fields at the surface of the clouds in the nebula. All three stars show strong H2 absorption features, indicating that the Carina Nebula contains abundant molecular hydrogen. The UV radiation field strength seems to be correlated with the angular distance of the target star from η Car, implying that the clouds might be located close to η Car. We derive the absolute distances between the clouds and η Car, which are in good agreement with the angular positions of these stars. We also examine the morphology of the Carina Nebula based on the present result, as well as previous CO observations, and derive the conversion factor N(H2)/W(12CO) in this region.

In the nebula OH 231.8+4.2 we have observed SO and SO2 millimeter-wave emission lines having a wide range of excitation energy. The extent of the SO emission was also mapped. Rotation diagrams were derived from these observations, and we deduced the rotation temperatures and relative abundances of SO and SO2 for three different velocity ranges corresponding to the spherical mass-loss envelope and the blue and red lobes of the bipolar outflow. The rotation temperatures for SO and SO2 are higher in the expanding envelope than in the outflow lobes. Subject to modeling uncertainties, the relative abundances of both molecules in the lobes are slightly enhanced by factors 2-5 times relative to the values in the envelope.

We report high-resolution (27 × 19) CO J = 2-1 line imaging of the young planetary nebula M1-16 that reveals the shaping of its neutral envelope by collimated outflows or jets. An extended (~50'') envelope of molecular gas surrounds the compact (3'') ionized nebula and dominates the mass of circumstellar material (~0.12 M☉). Multiple bipolar outflows, prominent at optical wavelengths, have pierced the envelope from the center, disrupting a significant fraction of the molecular gas. The outflows have excavated cavities along the bipolar axes, with CO velocities up to ~30 km s-1 in the cavity walls, and have produced point-symmetric lobes of molecular gas by entrainment. These features, imprinted by the outflows on the neutral gas, will appear as characteristics of the ionized nebula as the envelope becomes more fully ionized. The outflow-envelope interactions seen in M1-16 exemplify the shaping mechanism of a wide class of planetary nebulae at early stages of their formation.

We report the discovery of a collimated bipolar outflow emerging from a visible disk around the proto-planetary nebula IRAS 17106-3046. The radius of the disk, estimated to be 2500 AU at a distance of 4 kpc, is too large for it to be a Keplerian disk created by accretion. The radial intensity profile of the disk suggests that it is consistent with an expanding torus. In contrast to the open-end, butterfly-like lobes commonly seen in bipolar planetary nebulae, the lobes of IRAS 17106-3046 have pointed ends, suggesting a recently formed jet breaking out of the lobes. IRAS 17106-3046 therefore could represent the earliest stage of the bipolar-shaping process during the transition from an asymptotic giant branch star to a planetary nebula.

We present Her imaging and molecular-line (CO) observations of He 2-113, an object which belongs to a rare class of planetary nebulae with Wolf-Rayet type central stars.

We report the discovery of extended X-ray emission from the planetary nebula BD +30°3639. Analysis of the ROSAT HRI image shows clearly that BD +30°3639 has extended X-ray emission which is well fitted with a Gaussian source of σ = 17-28 (95.4% confidence interval). This size is consistent with being the same as that of the optical nebula as imaged by the Hubble Space Telescope. BD +30°3639 therefore represents the best case for the detection of a shocked-stellar-wind bubble in planetary nebulae.

We present a sensitive radio image of the nebula associated with the luminous blue variable star HR Carinae. This nebula is small and difficult to observe optically because of the presence of the bright star. The radio image shows the filaments in the outer regions of the nebula as seen in optical coronagraphic images. The core of the nebula is elongated north-south on the sky. A compact source associated with HR Car is clearly detected at the western edge of the nebula, but the nebula is very asymmetric with respect to the star, lying almost entirely to the east. The inner nebula shows no evidence for the bipolar structure inferred to exist from observations of the outer nebula: the symmetry axes in the inner nebula are 45° away from the bipolar axes. If the compact radio emission at the location of the star is a classical stellar wind source, we estimate a mass-loss rate for ionized gas of 1.8 × 10-5 M☉ yr-1. The mass in the central core of the nebula is about 0.3 M☉, while the outer nebula may contain as much as 0.5 M☉. We believe that a colliding winds explanation of the nebula is unlikely; a symbiotic-like explanation in which ionization of neutral ejecta is provided by a hot companion star may be possible if the companion star is on the far side of the nebula and heavily extincted, but it is not clear whether the properties required of this star are compatible with the fact that it is not detected in a 10 μm image. A B0 V companion without much dust may be consistent with the data.

We present a parameter study for the optical, low-ionization [O I] λ6300, λ6363, and λ5577 and the [S II] λ6731 and λ6716 lines emitted by photodissociation regions (PDRs). We assume in these models that the PDR has a plane-parallel, semi-infinite geometry and is illuminated from one side. The PDR models are characterized by the total hydrogen density 104 cm-3 ≤ n ≤ 107 cm-3 and the strength of the FUV field G0 in terms of the Habing field 103 < G0 < 107. Oxygen and singly ionized sulfur are excited thermally in the outer hot PDR layers due to collisions with electrons and atomic hydrogen. [O I] photons are also produced in the photodissociation of OH. We apply the results of the parameter study to the protoplanetary disks in Orion, layers between H II regions and molecular clouds, low-ionization nuclear emission-line regions, T Tauri stars, and planetary nebulae. We discuss the extent to which PDRs dominate or contribute to the observed [O I] and [S II] emission in these different objects.

We investigate the effects of photoexcitation of [N I] and [O I] lines by stellar continuum radiation under nebular conditions. It is found that the [N I] optical lines at 5198 and 5200 A are affected by fluorescence in many objects, including the Orion Nebula. [O I] lines are much less sensitive to fluorescence, except under conditions of low temperatures (≤5000 K) and high-radiation fields. Furthermore, it is shown that recent diagnostics by Esteban et al. of the physical conditions of partially ionized zones in Orion using combinations of [N I] and [O I] are unreliable because the lines from these species are likely to come from different regions. The hypothesis about different conditions in [N I]- and [O I]/[Fe II]-emitting regions is supported by the lack of correlation between these lines in samples of planetary nebulae, supernova remnants, and Herbig-Haro objects.

We have measured the spectral line intensities of the metal poor planetary nebula IC 4634. Using a photo-ionization model calculation, we try to fit the the optical and UV region spectra, i.e., Hamilton Echelle and IUE observations. From direct images, one expects complicated density variations, but the model predicts a range in densities that may be smaller than actually exist. We find N(sub epsilon) approximates 5000 /cubic meter. In spite of the geometrical complexity of the S shaped double-lobed structure, the simple photoionization model with a spherical symmetry can fit most emission lines, fairly well. The derived chemical composition has been compared with previous estimates and also with the Sun - The metallicity in IC 4634 appears to be lower than in the Sun or the average planetary nebula. The most likely temperature of the central ionizing source of IC 4634 appears to be about 55,000 K. We find a central star mass of about 0.55 Solar Mass from comparison with theoretical evolutionary tracks.

We have obtained narrowband images of the young planetary nebula Hubble 12 showing [Fe II] line emission in bipolar bubbles near the core. Bright [Fe II] emission is strong evidence for shocks, suggesting the presence of a high-velocity wind emanating from the central star. We compare our data to previously published images of Hubble 12—finding similar structures in hydrogen recombination and free-free emission—and we propose three possible interpretations of the data: that the bubbles indicate the inner shock of the fast wind, that the [Fe II] emission is evidence of the outer shock of an episodic wind, or that the emission is cooling line radiation from a photodissociation region. We argue that the first two interpretations are more likely, since the [Fe II] emission must be shock excited.

We present a fully sampled map of the Helix Nebula in the 1.3 mm CO J = 2-1 line, made using the Caltech Submillimeter Observatory. The angular resolution is 31'', and the velocity resolution is 1.5 km s-1. The CO emission is found to extend over a region ~1000'' × 800'' and delineates the well-known double ring or "helix" seen in optical images of the ionized gas. Our observations provide the first complete view of the global kinematics of the envelope and reveal the three-dimensional structure of the gas. The helix is seen to be an expanding, equatorial ring around the ionized nebula, with arcs extending to higher latitudes and exhibiting remarkable point symmetries about the central star. The molecular gas is fragmented into many small condensations with narrow line widths (~1 km s-1). The close relationship found between the structure of the envelope and the ionized nebula underscores the important role of neutral gas in determining the morphology of planetary nebulae. The point symmetries provide evidence for early shaping of the envelope by bipolar outflows or jets.

Using the NRAO 140 Foot Telescope, we have confirmed our earlier detection of 3He in the planetary nebula NGC 3242 made with the 100 m radio telescope of the Max-Planck-Institut fur Radioastronomie. Both spectrometers show that the observed 3He+ hyperfine line has a double-peaked structure. This line shape naturally arises if NGC 3242 is modeled as a dense core surrounded by a very low density expanding shell. The observed 3He+ emission suggests an abundance by number of 3He/H = (2–5) × 10-4, which is more than an order of magnitude higher than typically found in Galactic H II regions.

We report Hubble Space Telescope observations of variability within the reflection nebulosity of HH 30, a compact bipolar nebula which is a nearly edge-on accretion disk system.

H92α and He92α recombination lines and λ3.6 cm continuum observations have been carried out with the Very Large Array (synthesized beam 68 × 42, PA 74°) toward the polypolar planetary nebula NGC 2440. The H92α and He92α lines have been detected, for the first time in this nebula, over a region of θ14'' around its geometric center. The λ3.6 cm continuum emission is detected over a region of 65'' × 40'', similar in extent to the optical emission. Physical parameters of the nebula have been derived for the region in which the recombination lines were detected. From the line to continuum ratio, an electron temperature of 16,000 K and a single ionized helium abundance Y+0.14 are obtained. A relative extinction map of NGC 2440 has also been obtained from the ratio of the λ3.6 cm continuum and Hα images. A higher relative extinction in the central region traces the dense and dusty environment of an apparent central "toroid." The velocity field obtained from the H92α line suggests that the central toroidal structure has a distorted, noncircular shape. The polypolar characteristics of this nebula are discussed and compared with those of similar objects.

A detailed analysis of archival individual and co-added low- and high-dispersion IUE spectra of the planetary nebula NGC 40 has been performed, using NEWSIPS extracted spectra. More than 50 emission lines and numerous absorption features have been identified, and emission-line fluxes and equivalent widths were measured. Terminal wind velocities from P Cygni profiles and electron densities were redetermined. Several inconsistencies were found in earlier works for this peculiar low-excitation planetary that is excited by a 90,000 K "O VI sequence" WC8 star. The detection of Fe II lines that are resonantly excited by the O VI λ1031 line supports the O VI classification for the central star.

Based on ISO short-wavelength spectrograph (SWS) + long-wavelength spectrograph (LWS) observations, IRAS 16594-4656 is identified as a new member of the rare class of C-rich proto-planetary nebulae with the 21 ?m dust feature in emission. In addition, the major polycyclic aromatic hydrocarbon (PAH) emission bands at 3.3, 6.2, 7.7, 8.6, and 11.3 ?m are detected, together with unusually strong features at 12.6 and 13.4 ?m, very rarely observed, attributed to PAH species with a high degree of hydrogenation. The shapes and relative intensities of the various features found are consistent with a mixed population of transient decomposition products of large hydrogenated amorphous carbonaceous (HAC) grains, consisting of fullerenes with different degrees of hydrogenation, which we suggest to be the main carriers of the strong 21 ?m feature, and a combination of small and large partially dehydrogenated cationic PAH molecules excited by the visible radiation coming from the central star. Additional features corresponding to crystalline silicates (mostly pyroxenes) are also tentatively detected, together with a possible very broad unidentified emission feature centered around 30 ?m, previously reported as appearing in combination with the 21 ?m feature in other proto-planetary nebulae candidates. The combination of features corresponding to O-rich and C-rich dust grains, if real, would suggest a recent change to a C-rich chemistry in the outer envelope of IRAS 16594-4656. With the help of optical ground-based spectroscopy and recently obtained Hubble Space Telescope (HST) images, we identify IRAS 16594-4656 as a new transition object between the asymptotic giant branch (post-AGB) and the planetary nebula (PN) stage. The ground-based optical spectrum shows only the Balmer lines in emission and a faint, probably shock-excited, [O I] emission over a very red continuum where strong, probably circumstellar, diffuse interstellar absorption bands (DIBs) at 5780 and 6281-6284 ? are clearly seen. HST WFPC2 continuum images reveal the presence of a bright central star surrounded by a bipolar reflection nebula with a multiple-axis morphology and a maximum size of ~5''?11''.

Combined Infrared Space Observatory Short-Wavelength Spectrometer and Long-Wavelength Spectrometer spectroscopy is presented of the late WC-type planetary nebula nucleus CPD -56°8032 and its carbon-rich nebula. The extremely broad coverage (2.4-197 μm) enables us to recognize the clear and simultaneous presence of emission features from both oxygen- and carbon-rich circumstellar materials. Removing a smooth continuum highlights bright emission bands characteristic of polycyclic aromatic hydrocarbons in the 3-14 μm region, bands from crystalline silicates longward of 18 μm, and the 43 and 62 μm bands of crystalline water ice. We discuss the probable evolutionary state and history of this unusual object in terms of (a) a recent transition from an O-rich to a C-rich outflow following a helium shell flash or (b) a carbon-rich nebular outflow encountering an O-rich comet cloud.

The bipolar proto-planetary nebula IRAS 17441-2411 (the "Silkworm Nebula") was observed with the Hubble Space Telescope. By fitting the observed spectral energy distribution and the V-band image by a two-dimensional radiation transfer model, we derive the properties of the circumstellar wind and a proposed circumstellar "disk." We suggest that bipolar structures are probably more common than actually observed, because objects with similar intrinsic structures may simply appear stellar because of their orientation in the sky.

We present high-quality (subarcsecond) optical narrowband CCD images of the planetary nebula NGC 6881, which reveal a highly collimated bipolar structure. A careful examination of the [N II] image and of the [N II]/[O III] and [N II]/Hα ratio images shows that NGC 6881 is a quadrupolar planetary nebula, that is, a twice bipolar planetary nebula, each pair of lobes having a different symmetry axis. In addition, a striking knotty, looplike structure has been discovered in the southeast extreme of the nebula. Its appearance strongly suggests a precessing jetlike structure. Kinematical information of the different morphological features confirms the proposed nature of this nebula. The bright core is a ring that is collimating the bipolar lobes, while the looplike structure turns out to be a precessing jet. Assuming a simple ballistic model, an age of 7400d yr (d is the distance in kpc) is worked out, which can be compared with the computed age of the inner lobes of 400d yr. The precession period is 3800d yr. An upper limit of the ionized mass ejected (1.8 × 10-5d5/2 M☉) in the precessing jet has also been calculated.

With the Hubble Space Telescope's Wide Field Planetary Camera 2 we have obtained a deep, Hα image of the relatively young ejection-type nebula M1-67 around the runaway Population I Wolf-Rayet star WR 124 (WN 8). This image shows a wealth of complex detail, some of which have never been seen before in such a nebula. In particular, large arcs of nebulosity extend around the central star yet with no overall global shell structure to the nebula and no clear bipolar signature as claimed by Sirianni et al. In addition, numerous bright, mostly unresolved knots of emission, each 10-4 M☉, occur in the inner part of the nebula, often surrounded by what appear to be their own local "wind" diffuse bubbles. Is this the first direct evidence of spatially resolved hot clumps being ejected from a hot central star?