Yervant Terzian

FLIERs and Other Microstructures in Planetary Nebulae. IV. Images of Elliptical PNs from the Hubble Space Telescope

?????We report new results from high spatial resolution Wide Field Planetary Camera 2 imaging studies of FLIERs and other microstructures in the planetary nebulae NGC 3242, 6826, 7009, and 7662. Most FLIERs have head-tail morphologies, with the tails pointing outward from the nucleus. Ionization gradients that decrease with distance from the nebular center are ubiquitous. These are consistent with an ionization front in neutral knots of density ?104 cm-3. Can neutral knots account for the properties of FLIERs? We compare two broad classes of possible explanations for FLIERs with the new images: high-speed bullets ramming through the shells of planetary nebulae, and photoevaporated gas swept by winds into head-tail shapes. Both classes of models fail basic consistency tests. Hence an entirely new conceptual paradigm is needed to account for the phenomenology of FLIERs.

Hubble Space Telescope Measurements of the Expansion of NGC 6543: Parallax Distance and Nebular Evolution*

The optical expansion parallax of NGC 6543 has been detected and measured using two epochs of HST images separated by a time baseline of only three years. We have utilized three separate methods of deriving the angular expansion of bright fiducials, the results of which are in excellent agreement. We combine our angular expansion estimates with spectroscopically obtained expansion velocities to derive a distance to NGC 6543 of 1001

New OH/IR stars from color-selected IRAS sources. 3: A complete survey

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FLIERs and Other Microstructures in Planetary Nebulae. III.

269 pc. The deduced kinematic age of the inner bright core of the nebula is 1039

Planetary nebulae expansion distances

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The scale height of the galactic free electron cloud

259 years; however, the kinematic age of the polar caps that surround the core is larger - perhaps the result of deceleration or earlier mass ejection. The morphology and expansion patterns of NGC 6543 provide insight into a complex history of axisymmetric, interacting stellar mass ejections.

Hubble Space Telescope Expansion Parallaxes of the Planetary Nebulae NGC 6578, NGC 6884, NGC 6891, and IC 2448*

We present the results of 1612 MHz observations conducted at the Arecibo Observatory of 571 color-selected sources from the IRAS Point Source Catalog. Of these sources we detect 132, 113 for the first time. This is the third part of an Arecibo survey of color-selected IRAS sources. The earlier two parts together detected a total of 268 sources of 1612 MHz emission. An analysis of the properties of the OH/IR stars detected in all three parts of the survey is included. In particular we compute the limiting 1612 MHz peak flux of the entire survey to be approximately ˜40 mJy. The correlation between the IRAS infrared fluxes and the 1612 MHz flux of the 132 sources detected in part III of the survey is smaller than that found in the earlier parts of the survey. This is to be expected from the intrinsic variability of OH/IR stars and the longer time gap between the 1612 MHz observations and the IRAS measurements. We identify a subset of 54 stars as being near the tangent point of the galactic rotation curve. Using the kinematical distances to these stars we find that the efficiency of momentum transfer varies exponentially with the (25-12) micrometer color, consistent with the stellar outflow being driven by radiation pressure. Further the IR pump efficiency increases with increasing optical depth of the circumstellar shell, as expected for radiative pumping. The bolometric luminosity function is found to decrease sharply above L Bol =5600 L solar luminosity, and the 1612 MHz luminosity function shows a corresponding falloff above L 1612 =1.8 × 10 −8 solar luminosity. We also find direct confirmation of the expectation that sources with large expansion velocity are more luminous than sources with small expansion velocity.

Dynamics of binary galaxies. I: Wide pairs

Long-slit spectroscopic observations along the major axes of four planetary nebulae with interesting jets and FLIERs (Hb 4, IC 4634, NGC 6369, and NGC 7354) have been conducted with the Palomar 5 m telescope. Chemical abundances and physical conditions (n, T) in microstructures were derived along their structural axes. No evidence of conspicuous shock activity or N/O abundance anomalies is seen in most cases, unlike some earlier studies of similar features in other planetary nebulae. Microstructures seem to be a heterogeneous class of structures aside from their low ionization and generally supersonic motions.

The Timescale Correlation Method: Distances to Planetary Nebulae with Halos

We present two epochs of λ6 cm VLA maps of the planetary nebulae NGC 7027 and BD+30-3639 with subarsecond angular resolution. By taking advantage of the high dynamic range possible with the VLA as well as the almost 6 yr time baseline between the two epochs, we have constructed difference maps that show the signature characteristic of the radial expansion of the ionization front surrounding the nebulae. We have combined these results with the Doppler expansion velocities to estimate the distance to both objects. Our results indicate that D NGC 7027 =703±95 pc and D BD+30 =2680±810 pc

PLANETARY NEBULAE EXPANSION DISTANCES: III

Accurate distance measurements toward sixty-one pulsars in and around the disk of the Galaxy show a mean electron density for the interstellar medium of ∼ 0.033 ± 0.002 cm -3 . The additional discovery of 29 pulsars in globular clusters at high galactic latitudes indicates an electron scale height of between 0.53 and 0.84 kpc. The number of photons available for ionization of the ISM is calculated and compared with the number of photons that theory predicts are required for the degree of ionization observed. It is found that UV photons from OB stars, supernovae, and planetary nebulae are sufficient to produce the necessary power, but only if the fraction of photons that are used to maintain the ionized gas approaches 40%, and only if the majority of the electron gas is found at a temperature of ∼10 4 K