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Papers by J Patrick Harrington

Monthly Notices of the Royal Astronomical Society, 1977

Monthly Notices of the Royal Astronomical Society, 1974

We present new HST/WFPC2 imagery for the planetary nebula (PN) NGC 6818. Observations were made i... more We present new HST/WFPC2 imagery for the planetary nebula (PN) NGC 6818. Observations were made in line filters F437N, F487N, F502N, and F656N plus continuum filter F547M. The primary goal was to develop a high spatial resolution (approx. 0.1 in.) map of the intrinsic line ratio [O III] 4363/5007 and thereby evaluate the electron temperature (T(sub e)) and the mean-square T(sub e) variation (t(sup 2) across the PN. In this process we developed an extinction map from the F487N (H(beta)) and F656N (H(alpha)) images by comparing the observed line ratios in each pixel to the theoretical ratio and computing a c(H(beta)) map which was used to correct the observed 4363/5007 ratios for reddening. We also adjust for the continuum contribution to the line filter data. We present color-coded pictures of the reddening (c(H(beta))) map, the [O III] T(sub e) map, as well as our determinations of t(sup 2). The T(sub e) map shows a decline from approx. 14000 K in the inner regions to approx. 11000 K at the outer edge. Such a radial T(sub e) gradient is expected for a high-excitation nebula with a prominent He(++) zone such as NGC 6818. A composite of images taken in 3 filters (F656N, red; F487N, blue; and F502N, [O III] 5007, green) shows a roughly spherical outer envelope as well as a brighter vase-shaped interior "bubble". There is a prominent orifice to the North and a smaller one to the South, along the major axis, possibly caused by a blow-out from a fast wind. This nebula has an appearance remarkably similar to that of the PN NGC 3918 previously imaged with HST by H. Bond. We note from the continuum images (F547M) two stars in the nebular field that are fainter than the prominent central star; these are roughly 2-4 sec. N and NE of the central star. Further study is needed to establish whether or not there may be a physical association of either star with the central star.

Proceedings of the International Astronomical Union, 1997

Proceedings of the International Astronomical Union, 2014

Continuum scattering by free electrons can be significant in early type stars, while in late type... more Continuum scattering by free electrons can be significant in early type stars, while in late type stars Rayleigh scattering by hydrogen atoms or molecules may be important. Computer programs used to construct models of stellar atmospheres generally treat the scattering of the continuum radiation as isotropic and unpolarized, but this scattering has a dipole angular dependence and will produce polarization. We review an accurate method for evaluating the polarization and limb darkening of the radiation from model stellar atmospheres. We use this method to obtain results for: (i) Late type stars, based on the MARCS code models (Gustafsson et al. 2008), and (ii) Early type stars, based on the NLTE code TLUSTY (Lanz and Hubeny 2003). These results are tabulated at http://www.astro.umd.edu/~jph/Stellar_Polarization.html While the net polarization vanishes for an unresolved spherical star, this symmetry is broken by rapid rotation or by the masking of part of the star by a binary companio...

We obtained high-resolution images of the planetary nebula BD+30°3639 using the HST WFPC2 instrum... more We obtained high-resolution images of the planetary nebula BD+30°3639 using the HST WFPC2 instrument and the VLA telescope. Images were obtained in the emission lines Hbeta , Halpha , HeIlambda 5876, [O III]lambda 5007, [O II]lambda 3727, [O I]lambda 6300, [N II]lambda 6584, [S III]lambda 9532, [S II]lambda 6717,6731 and in the optically-thin radio continuum. These images reveal detailed structure

International Conference on Next Generation Web Services Practices (NWeSP'05)

BPEL provides a language for the formal specification of business processes and business interact... more BPEL provides a language for the formal specification of business processes and business interaction protocols. In business transactions non-repudiation is a serious security issue in which any involved party denies having participated in a transaction. In this paper we propose and verify novel non-repudiation protocols for business transactions in a number of scenarios and specify them in BPEL. Our proposed protocols fulfill the requirements of security, fairness, protection and timeliness.

Astrophysics and Space Science Library, 1987

Dust can be included in the photoionization models of planetary nebulae; the dust temperatures re... more Dust can be included in the photoionization models of planetary nebulae; the dust temperatures resulting from the radiation field within the models can be evaluated and the resulting thermal IR emission compared to observations. We use a model of NGC 3918 to illustrate the behavior of various grain materials (graphite, amorphous carbon, silicates, and iron). We also present a model of IC 418 with graphite grains in both the ionized zone and in a surrounding thick, neutral shell.

The Astrophysical Journal, 1976

Theoretical models have been constructed of planetary nebulae illuminated by central stars which ... more Theoretical models have been constructed of planetary nebulae illuminated by central stars which are evolving on a time scale comparable with the cooling time of the nebular gas. The emission line spectra of the models have been compared with the spectrum of the planetary nebula surrounding FG Sge. The observed spectrum can be reproduced by that of a nebular shell

The Encyclopedia of Astronomy and Astrophysics

American Art Journal, 1990

Lecture Notes in Computer Science, 2006

The emerging autonomic computing technology has been hailed by worldwide researchers and professi... more The emerging autonomic computing technology has been hailed by worldwide researchers and professionals in academia and industry. Besides four key capabilities, well known as self-CHOP, we propose an additional self-regulating capability to explicitly emphasize the policy-driven self-manageability and dynamic policy derivation and enactment. Essentially, these five capabilities, coined as Self-CHROP, define an autonomic system along with other minor properties. Trusted computing targets guaranteed secured systems. Self-protection alone does not ensure the trustworthiness in autonomic systems. The new trend is to integrate both towards trusted autonomic computing systems. This paper presents a comprehensive survey of the autonomic and trusted computing paradigms and a preliminary conceptual architecture towards trustworthy autonomic grid computing.

Bulletin of the …, 1998