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Hubble Space Telescope Observations of

the Role of Planetary Nebulae in the

Chemical Evolution of the Large Magellanic Cloud

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Hubble Space Telescope Observations of

Planetary Nebulae in the Magellanic Clouds III:

Ultraviolet Spectroscopy Using the Faint Object Spectrograph

by E. Vassiliadis, M.A. Dopita, R.C. Bohlin, J.P. Harrington, H.C. Ford, S.J. Meatheringham, P.R. Wood, T.P. Stecher, and S.P. Maran

Submitted to: Astrophysical Journal

Short Abstract : Ultraviolet FOS grating and PRISM data are coupled to ground-based spectroscopy to provide 1150 - 8000 angstrom spectroscopy for eight planetary nebulae in the LMC and four in the SMC. Spectra of six nebulae are compared with archival IUE observations. Nebular densities derived from O IV] and Si III] emission line ratios are found to be larger than densities derived from the visible [O II] or [S II] ratios, indicating that the regions nearest the star are denser. The C/O ratio appears to be anti-correlated with the N/O ratio, suggesting that hot bottom burning processes operated during the AGB phase. Si emission is detected only in the four Type I objects.

Subject Headings: Galaxies: Magellanic Clouds - planetary nebulae: general - ultraviolet:spectra

For text and figures:

PNIII

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Hubble Space Telescope Observations of

Planetary Nebulae in the Magellanic Clouds IV:

[O III] Images and Evolutionary Ages

by M. A. Dopita , E. Vassiliadis, S. J. Meatheringham, R. C. Bohlin, H. C. Ford, J. P. Harrington, P. R. Wood, T. P. Stecher, and S. P. Maran

Accepted by the Astrophysical Journal

Abstract : The Planetary Camera of the Hubble Space Telescope has been used to obtain images in the [O III] l5007? line for a sample of 15 planetary nebulae in the Magellanic Clouds chosen to eliminate any selection bias in either excitation class or in flux (for log F(Hb) > -13.7 erg.cm-2s-1). These images are used to derive the physical dimensions, the spatial structure and the kinematic ages of the nebulae. The raw images were deconvolved using the Richardson-Lucy Image Restoration Algorithm, and based on extensive tests of model images, a limit of 100 iterations of the algorithm was adopted. The restored images show clear evidence for size evolution across the H-R Diagram. The younger, low excitation, compact planetary nebulae tend to be systematically smaller than photoionisation models based on ground-based data would predict, suggesting these planetary nebulae have a central reservoir of dense atomic and molecular gas. This gas lies close to the central star and is undergoing ionisation and being accelerated into outflow. Planetary Nebulae previously classified as nitrogen-rich objects with massive central stars (Peimbert Type I), show the bipolar ТbutterflyУ symmetry that is also a characteristic of their Galactic counterparts. The derived kinematic ages range from less than 1000 years up to almost 5000 years, but show little sign of systematic increase along the evolutionary tracks. The true ages of the larger objects are systematically underestimated because of acceleration of the nebular shell during its lifetime. Using both the empirical fit that we had previously derived for the expansion velocity as a function of the position on the H-R Diagram, and the theoretical evolutionary tracks of the central star, we have derived two semi-empirical estimates for the evolutionary timescales based upon the nebular size, and the measured dynamical age. If these evolutionary timescales are to be consistent with the evolutionary age derived from theory, then He-burners outnumber H-burners in the approximate ratio 2:1. Subject Headings: galaxies: Magellanic Clouds ___ nebulae: planetary___ nebulae: structure ___ stars: evolution

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Spectral Signatures of Fast Shocks I:

Low Density Model Grid

by Michael A. Dopita and Ralph S. Sutherland

Accepted by Astrophysical Journal Supplements

Abstract : A high velocity radiative shock provides an efficient means to generate a strong local UV photon field. The optical emission from the shock and precursor region is then dominated by the photoionized gas, rather than by the cooling region, and the total optical and UV emission scales as the mechanical energy flux through the shock. In addition, for reasonable values of the magnetic field, such shocks become supported by magnetic pressure in the photoionization / recombination zone of the shock. The effect of the limited compression factor has a profound influence on the output spectrum. Models without precursors apply to unresolved shocks in gas-poor environments, or to fast shocks in individually resolved filaments of supernova remnants. Models with precursors should be applicable to unresolved structures in gas-rich environments. In this paper, we present extensive tabular results designed to be of maximum utility to observationalists, for a grid of low-density steady-flow models covering the shock velocity range 150 ? Vs ? 500 km.s-1, and magnetic parameter 0 ? B / n1/2 ? 4 чG.cm-3/2. In the next paper of this series, we will apply these models to diagnostic plots for narrow line regions of AGN.

Subject Headings: Galaxies: active, seyfert - hydrodynamics -ISM:supernova remnants - radiation mechanisms:thermal - shock waves

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Spectral Signatures of Fast Shocks II:

Diagnostic Diagrams

by Michael A. Dopita and Ralph S. Sutherland

Accepted by Astrophysical Journal

Abstract: In the first paper we presented a low-density grid of models of high velocity photoionising radiative shocks, including magnetic pressure support in the photoionization / recombination zone. Here we apply these models to the line ratios observed in narrow line emission regions in active galaxies. From a set of line diagnostic diagrams, we find that LINER galaxies, narrow line radio galaxies and cooling flow emission regions can be modelled in terms of fast shocks in a relatively gas poor environment. Emission from a photoionised precursor of the shock is either weak or absent. On the other hand, the narrow line regions associated with Seyfert 2 and 1.5 galaxies and the energetic luminous IR galaxies can be understood as fast shocks in a gas rich environment, where the EUV photons produced in the shock are fully, or mostly, absorbed in the shock precursor HII region. For LINER-like objects, shock velocities required range from 150 to 500 km.s-1, but the Seyfert specta require shocks typically in the range 300 to 500 km.s-1. These figures are comparable to the observed line widths in both these classes of object. The magnetic parameter which characterises these shocks is about 2 < B/n1/2 < 4 чG.cm3/2, typical of the general interstellar medium. Our fast shock models are capable of explaining the long standing Тtemperature problemУ of AGN, in which the electron temperatures observed are found to be systematically higher than predicted by photoionisation models. For Seyferts, the pre-shock densities are clearly higher than the 1 cm-3 used in the model grid. Finally, we find evidence that nitrogen is enhanced above solar values in both Seyfert and in LINER nuclei.

Subject Headings: Atomic Processes - Galaxies : Active, Cooling Flows, Jets, Seyfert, Starburst - Line : Formation - MHD - Radiation Mechanisms : Thermal - Shock Waves

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POST:ККA Polar Stratospheric

Telescope for the Antarctic

Michael A. Dopita, Mount Stromlo and Siding Spring Observatories, Institute of Advanced Studies, The Australian National University Holland C. Ford, The Johns Hopkins University, Baltimore, MD John Bally, University of Colorado, Boulder, CO and Pierre Bely, Space Telescope Science Institute, Baltimore, MD*

Accepted by Publication of the Astronomical Society of Australia

Abstract: The tropopause, typically at 16 to 18 km altitude at the lower latitudes, dips down to only 8 km in the polar regions, allowing access to the cold, dry and nonturbulent lower stratosphere by tethered aerostats. These can float as high as 12 km, have long operating lifetimes, and are extremely reliable. In contrast to free-flying balloons, they can stay on station for weeks at a time, and payloads can be safely recovered for maintenance and adjustment and relaunched in a matter of hours. We propose to use such a platform, located first near Fairbanks, Alaska and, later, in the Antarctic, to operate a new technology 4-m telescope with diffraction-limited performance in the near infrared. Thanks to the low ambient temperature (~200 K), thermal emission from the optics is of the same order as that of the zodiacal light in the 2 to 3 чm band. Since this wavelength interval is the darkest part of the zodiacal light spectrum from optical wavelengths to 100 чm, the combination of high resolution images and a very dark sky make it the spectral region of choice for observing galaxies, QSOs and clusters of galaxies at the formation epoch of galaxies.

Subject Headings: Antarctic Astronomy - Atmospheric Effects - Balloons - Infrared: General - Telescopes

* co-investigators or contributors to this Project also include: Ronald Allen (ST ScI), Robert Ashford (TCOM), Frank Bartko (Denver, Colorado), Robert Brown, (ST ScI), Richard Burg (The Johns Hopkins U.), Chris Burrows (ST ScI), Mark Clampin (ST ScI), JamesCrocker (ST ScI), Charles Cox (ITEK), Charles Deere (Uni. of Alaska), George Hartig (ST ScI), Garth Illingworth (U. of California), Richard McCray (U. of Colorado), Steven Meyer (U. of Chicago), Max Nein (MSFC), Colin Norman (The Johns Hopkins U.), Larry Petro (ST ScI), Charles Telesco (MSFC), James Tilley (Ball Aerospace Corp.), Roger Thompson (U. of Arizona), and Richard White (ST ScI)

Text of Paper II- 40 Kb

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