Planetary nebulae (PNe) are expected to have a ~10 super(5) K interface layer between the > or =, slanted10 super(6) K inner hot bubble and the ~10 super(4) K optical nebular shell. The PN structure ...and evolution, and the X-ray emission, depend critically on the efficiency of the mixing of material at this interface layer. However, neither its location nor its spatial extent have ever been determined. Using high-spatial resolution HST STIS spectroscopic observations of the N v ambda lambda1239,1243 lines in the Cat's Eye Nebula (NGC 6543), we have detected this interface layer and determined its location, extent, and physical properties for the first time in a PN. We confirm that this interface layer, as revealed by the spatial distribution of the N v lambda 1239 line emission, is located between the hot bubble and the optical nebular shell. We estimate a thickness of 1.5 x 10 super(16) cm and an electron density of ~200 cm super(-3) for the mixing layer. With a thermal pressure of ~2 x 10 super(-8) dyn cm super(-2), the mixing layer is in pressure equilibrium with the hot bubble and ionized nebular rim of NGC 6543.
Massive stars can alter physical conditions and properties of their ambient interstellar dust grains via radiative heating and shocks. The H II regions in the Large Magellanic Cloud (LMC) offer ideal ...sites to study the stellar energy feedback effects on dust because stars can be resolved, and the galaxy's nearly face-on orientation allows us to unambiguously associate H II regions with their ionizing massive stars. The Spitzer Space Telescope survey of the LMC provides multi-wavelength (3.6-160 mum) photometric data of all H II regions. To investigate the evolution of dust properties around massive stars, we have analyzed spatially resolved IR dust emission from two classical H II regions (N63 and N180) and two simple superbubbles (N70 and N144) in the LMC. We produce photometric spectral energy distributions (SEDs) of numerous small subregions for each region based on its stellar distributions and nebular morphologies. We use DustEM dust emission model fits to characterize the dust properties. Color-color diagrams and model fits are compared with the radiation field (estimated from photometric and spectroscopic surveys). Strong radial variations of SEDs can be seen throughout the regions, reflecting the available radiative heating. Emission from very small grains drastically increases at locations where the radiation field is the highest, while polycyclic aromatic hydrocarbons (PAHs) appear to be destroyed. PAH emission is the strongest in the presence of molecular clouds, provided that the radiation field is low.
We present a 1.42 deg2 mosaic of diffuse X-ray emission in the Great Nebula in Carina from the Chandra X-ray Observatory Advanced CCD Imaging Spectrometer camera. After removing >14,000 X-ray point ...sources from the field, we smooth the remaining unresolved emission, tessellate it into segments of similar apparent surface brightness, and perform X-ray spectral fitting on those tessellates to infer the intrinsic properties of the X-ray-emitting plasma. By modeling faint resolved point sources, we estimate the contribution to the extended X-ray emission from unresolved point sources and show that the vast majority of Carina's unresolved X-ray emission is truly diffuse. Line-like correlated residuals in the X-ray spectral fits suggest that substantial X-ray emission is generated by charge exchange at the interfaces between Carina's hot, rarefied plasma and its many cold neutral pillars, ridges, and clumps.
Nine supergiant shells (SGSs) have been identified in the Large Magellanic Cloud (LMC) based on H alpha images, and 23 SGSs have been reported based on H I 21 cm line observations, but these sets do ...not always identify the same structures. We have examined the physical structure of the optically identified SGSs using H I channel maps and P-V diagrams to analyze the gas kinematics. There is good evidence for seven of the nine optically identified SGSs to be true shells. Of these seven H alpha SGSs, four are the ionized inner walls of H I SGSs, while three are an ionized portion of a larger and more complex H I structure. All of the H alpha SGSs are identified as such because they have OB associations along the periphery or in the center, with younger OB associations more often found along the periphery. After roughly 12 Myr, if no new OB associations have been formed, a SGS will cease to be identifiable at visible wavelengths. Thus, the presence and location of ionizing sources is the main distinction between shells seen only in H I and those also seen in H alpha . Based on our analysis, H alpha observations alone cannot unambiguously identify SGSs, especially in distant galaxies.
Detailed 4.8 and 8.6 GHz radio images of the entire Large Magellanic Cloud with half-power beamwidths of 33'' at 4.8 GHz and 20'' at 8.6 GHz have been obtained using the Australia Telescope Compact ...Array. A total of 7085 mosaic positions were used to cover an area of 6° on a side. Full polarimetric observations were made. These images have sufficient spatial resolution (~8 and 5 pc, respectively) and sensitivity (3 s of 1 mJy beam-1) to identify most of the individual supernova remnants and H II regions and also, in combination with available data from the Parkes 64 m telescope, the structure of the smooth emission in that galaxy. In addition, limited data using the sixth antenna at 4.5-6 km baselines are available to distinguish bright point sources (<3'' and 2'', respectively) and to help estimate sizes of individual sources smaller than the resolution of the full survey. The resulting database will be valuable for statistical studies and comparisons with X-ray, optical, and infrared surveys of the LMC with similar resolution.
Abstract
The Large and Small Magellanic Clouds (LMC and SMC) are the largest satellite galaxies of the Milky Way and close enough to allow for a detailed exploration of their structure and formation ...history. The Survey of the MAgellanic Stellar History (SMASH) is a community Dark Energy Camera (DECam) survey of the Magellanic Clouds using ∼50 nights to sample over ∼2400 deg
2
centered on the Clouds at ∼20% filling factor (but with contiguous coverage in the central regions) and to depths of ∼24th mag in
ugriz
. The primary goals of SMASH are to map out the extended stellar peripheries of the Clouds and uncover their complicated interaction and accretion history as well as to derive spatially resolved star formation histories of the central regions and create a “movie” of their past star formation. Here we announce the second SMASH public data release (DR2), which contains all 197 fully calibrated DECam fields including the main body fields in the central regions. The DR2 data are available through the Astro Data Lab hosted by the NSF’s National Optical-Infrared Astronomy Research Laboratory. We highlight three science cases that make use of the SMASH DR2 data and will be published in the future: (1) preliminary star formation histories of the LMC, (2) the search for Magellanic star clusters using citizen scientists, and, (3) photometric metallicities of Magellanic Cloud stars using the DECam
u
-band.
ABSTRACT
We present the statistical methods that have been developed to analyse the OzDES reverberation mapping sample. To perform this statistical analysis we have created a suite of customizable ...simulations that mimic the characteristics of each source in the OzDES sample. These characteristics include: the variability in the photometric and spectroscopic light curves, the measurement uncertainties, and the observational cadence. By simulating the sources in the OzDES sample that contain the C iv emission line, we developed a set of criteria that rank the reliability of a recovered time-lag depending on the agreement between different recovery methods, the magnitude of the uncertainties, and the rate at which false positives were found in the simulations. These criteria were applied to simulated light curves and these results used to estimate the quality of the resulting Radius–Luminosity relation. We grade the results using three quality levels (gold, silver, and bronze). The input slope of the R–L relation was recovered within 1σ for each of the three quality samples, with the gold standard having the lowest dispersion with a recovered a R–L relation slope of 0.454 ± 0.016 with an input slope of 0.47. Future work will apply these methods to the entire OzDES sample of 771 AGN.
We present Spitzer Space Telescope spectroscopy of the CO2 ice absorption feature at 15.2 Delta *mm toward 41 high-mass young stellar objects in the Large Magellanic Cloud (LMC). As the shape of the ...CO2 absorption profile is a measure of both the composition and thermal history of the ice, we have performed a decomposition of the spectral profiles to determine the nature of the CO2 ice. We fit the absorption profiles to laboratory analogues of ice spectra with two different methods: (1) a five-component fit with polar and apolar ices and (2) a two-component fit with a polar and an annealed H2O:CH3OH:CO2 ice mixture. Many of the LMC sources have a pronounced double peak in their CO2 feature profiles analogous to that seen from pure CO2 or annealed CO2 laboratory ice mixtures; these represent the first direct detections of the characteristic double peak in an extragalactic environment. Fits to annealed laboratory ices suggest that the ices around massive LMC young stellar objects (YSOs) have been warmed and thermally processed. We find that a majority of the CO2 is embedded in a polar ice matrix; however, the observations suggest that a lower fraction of CO2 is locked in polar ices in the LMC compared to the Milky Way, which is in agreement with the proposed lower LMC abundance of water ice. In addition, we find that the ices are best fit with laboratory ice mixtures composed of less than 50% methanol, and most absorption spectra can be fit by ices with no methanol. Finally, we corroborate mounting evidence of an enhanced CO2 ice abundance in the LMC relative to the Milky Way, and determine a CO2/H2O ratio of 0.33 ? 0.01 by combining the column densities of these observations with those in the literature.
Two types of dust disks have been discovered around white dwarfs (WDs): small dust disks within the Roche limits of their WDs and large dust disks around hot WDs extending to radial distances of ...10-10 super(2) AU. The majority of the latter WDs are central stars of planetary nebulae (CSPNs). We have therefore used archival Spitzer Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS) observations of PNs to search for CSPNs with IR excesses and to make a comparative investigation of dust disks around stars at different evolutionary stages. We have examined available images of 72 resolved PNs in the Spitzer archive and found 56 of them large enough for the CSPN to be resolved from the PN. Among these, only 42 CSPNs are visible in IRAC and/or MIPS images and selected for photometric measurements. From the spectral energy distributions (SEDs) of these CSPNs, we find 19 cases with clear IR excess. Of these, seven are WC-type stars, two have apparent visual companions that account for the observed excess emission, two are symbiotic CSPNs, and in eight cases the IR excess originates from an extended emitter, likely a dust disk. For some of these CSPNs, we have acquired follow-up Spitzer MIPS images, Infrared Spectrograph spectra, and Gemini NIRI and Michelle spectroscopic observations. The SEDs and spectra show a great diversity in the emission characteristics of the IR excesses, which may imply different mechanisms responsible for the excess emission. For CSPNs whose IR excesses originate from dust continuum, the most likely dust production mechanisms are (1) breakup of bodies in planetesimal belts through collisions and (2) formation of circumstellar dust disks through binary interactions. A better understanding of post-asymptotic giant branch binary evolution as well as debris disk evolution along with its parent star is needed to distinguish between these different origins. Future observations to better establish the physical parameters of the dust disks and the presence of companions are needed for models to discern between the possible dust production mechanisms.
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