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Huggins, P. J.

Publications and source records attributed to Huggins, P. J..

34 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Neutral carbon in the Egg Nebula (AFGL 2688)

A search for sub-mm C I emission from seven stars that are surrounded by dense molecular gas shells has led to the detection, in the case of the 'Egg Nebula' (AFGL 2688), of an 0.9 K line implying a C I/CO value greater than 5. The material surrounding this star must be extremely carbon-rich, and it is suggested that the apparently greater extent of the C I emission region may be due to the effects of the the galactic UV field on the shell's chemistry, as suggested by Huggins and Glassgold (1982).

Huggins, P. J.↗
NASA NTRS1983

Atomic and molecular hydrogen in the circumstellar envelopes of late-type stars

The distribution of atomic and molecular hydrogen in the expanding circumstellar envelopes of cool evolved stars is discussed. The main concern is to evaluate the effects of photodestruction of H2 by galactic UV radiation, including shielding of the radiation by H2 itself and by dust in the envelope. One of the most important parameters is the H/H2 ratio which is frozen out in the upper atmosphere of the star. For stars with photospheric temperatures greater than about 2500 K, atmospheric models suggest that the outflowing hydrogen is mainly atomic, whereas cooler stars should be substantially molecular. In the latter case, photodissociation of H2 and heavy molecules contribute to the atomic hydrogen content of the outer envelope. The presented estimates indicate that atomic hydrogen is almost at the limit of detection in the C-rich star IRC + 10216, and may be detectable in warmer stars. Failure to detect it would have important implications for the general understanding of circumstellar envelopes.

Glassgold, A. E.↗
NASA NTRS1983

Neutral carbon in the Egg Nebula (AFGL 2688)

A search for sub-mm C I emission from seven stars that are surrounded by dense molecular gas shells led to the detection, in the case of the "Egg Nebula' (AFGL 2688), of an 0.9 K line implying a C I/CO value greater than 5. The material surrounding this star must be extremely carbon-rich, and it is suggested that the apparently greater extent of the C I emission region may be due to the effects of the galactic UV field on the shell's chemistry, as suggested by Huggins and Glassgold (1982).

Beichman, C. A.↗
NASA NTRS1982

The photoproduction of circumstellar OH maser shells

The structure of OH shells formed from the photodestruction of H2O by ambient UV photons in the thick, expanding envelopes around cool evolved stars is investigated. The properties of the shells are governed mainly by the envelope shielding which in turn is primarily controlled by the mass-loss rate M. The peak OH densities and column densities through the shells are, respectively, slowly decreasing and increasing functions of M. The characteristic radii of the shells also depend on M, increasing from about 4(15) cm for M = 1(-6) solar mass/yr to about 1(17) cm for M = 1(-4) solar mass/yr; this dependence is well matched by recent observational data, and lends support to the OH photoproduction mechanism.

Huggins, P. J.↗
NASA NTRS1982

Symposium on the Orion Nebula to Honor Henry Draper, New York University, New York, NY, December 4, 5, 1981, Proceedings

The present conference on astronomical studies of the Orion Nebula covers molecular clouds in Orion, the use of the nebula's cloak as a model for gas super-shells around OB associations, optical and UV data concerning the nebula's physical conditions, the presence of atomic carbon in Orion, large scale distribution of far-IR and sub-mm line emission, star formation studies in the IR, gas dynamics in the circumstellar nebula of the Becklin-Neugebauer source, maser sources and far-IR CO line emission in Orion-KL, and synthesis maps of mm molecular lines. Also discussed are Orion's star distributions, core region nebular condensations, energetic molecular flows in star-forming cloud cores, IR observations of HH objects, compact continuum radio sources, the SiO maser, shock waves, and the chemical evolution of OB associations.

Glassgold, A. E.↗
NASA NTRS1982

Simultaneous observations of the BL Lacertae object I Zw 187

Two sets of simultaneous spectra consisting of data obtained with radio, IR, optical, UV and X-ray telescopes were obtained 10 months apart for the X-ray bright BL Lac object IZw 187. In addition, nonsimultaneous observations were made in several of the aforementioned observing bands in order to detect flux variations and galactic light contamination was removed from all observations. The BL Lac component is found to have a weak 3000 A bump superposed on an IR-optical-UV spectrum of slope 0.9. Consistent with the arising of the IR-through-X-ray continuum from a single synchrotron source, the X-ray data fall on or near an extrapolation of this power law. No flux variations have been detected in the flat radio spectrum. Optical and X-ray fluxes are observed to vary by a factor not greater than three, and the shortest variability time scales in these bands are comparable at about one week.

Bregman, J. N.↗
NASA NTRS1982

Simultaneous multifrequency observations of BL Lac objects and violently variable quasars

Ultraviolet spectra simultaneous with radio, infrared, optical, and X-ray measurements were obtained for three BL Lac objects and one violently variable quasar during several epochs (0735+178, BL Lac, IZw-187, and 3C446). A feature common to these objects is that the radio-mm continuum must steepen in the far-infrared region in order to connect smoothly to the IR-UV continuum. This indicates that synchrotron emission becomes optically thick in the mm or far-infrared region. The continuum of 3C446 and BL Lac steepen quite rapidly between the IR and UV spectra with slopes near unity. The X-ray emission in BL Lac, 3C446, and 0735+178 has a different origin from the IR-UV radiation, probably from the inverse Compton process. However, the synchrotron radiation is the probable source of X-ray emission in the X-ray bright BL Lac object IZw-187. In IZw-187, most of the energy emerges in the UV - X-ray region, while for the other sources, most of the energy emerges in the far infrared region.

Bregman, J. N.↗
NASA NTRS1982

Multifrequency observations of the quasar 1156+295

The recent outburst in the quasar 1156+295 was discovered in the course of optical monitoring made in preparation for IUE observations in April 1981. Short and long wavelength spectra were obtained on three occasions when the object was very bright, and which were separated in time by intervals of 4 and 60 days. The UV continuum in all cases is a steeply falling power law, with slope close to -2.0. No spectral features are apparent in the UV. Closely simultaneous observations were made by our collaborators at radio, infrared, and optical frequencies. The continuum is less steep at optical and infrared frequencies, and the overall spectra show little change in shape with time.

Glassgold, A. E.↗
NASA NTRS1982

The photochemistry of carbon-rich circumstellar shells

The effect of ambient ultraviolet photons on the chemical structure of carbon-rich, circumstellar envelopes is investigated with a simple formulation of the time-dependent, photochemical rate equations valid for optically thick shells. Molecules injected into the shielded inner envelope are broken down when they reach the outer regions where ambient ultraviolet photons can penetrate. A quantitative description of the abundance variations is obtained for the case of uniform expansion by detailed consideration of the shielding of the radiation by the dust and molecules of the envelope. Representative results are presented to illustrate the role of shielding in defining the extent of molecular envelopes, the formation of C I and C II shells by photodestruction of carbon-bearing molecules, and the development of layered chemical structures from the photobreakup of polyatomic molecules. Photochemistry makes the outer parts of thick, carbon-rich envelopes into complex regions containing radicals, ions, and atoms which are of considerable observational and theoretical interest.

Huggins, P. J.↗
NASA NTRS1981

Abundance of atomic carbon /C I/ in dense interstellar clouds

The abundance of interstellar neutral atomic carbon is investigated by means of its ground state fine-structure line emission at 492 GHz using the 91.5 cm telescope of NASAs Kuiper Airborne Observatory. Atomic carbon is found to be very abundant in dense interstellar molecular clouds with column densities of about 10 to the 19th per sq cm. Because the observations have considerably greater column densities than current theories of carbon chemistry, it is suggested that the physical conditions of these clouds are not as simple as assumed in the models. Various situations are discussed which would lead to large C I abundances, including the possibility that the chemical lifetimes of the clouds are relatively short.

Phillips, T. G.↗
NASA NTRS1981

Detection of Lyman continuum absorption in the BL Lacertae object PKS 0735+178

The detection of the Lyman edge in the BL Lac object PKS 0735+178 at the absorption red shift determined by optical measurements leads to a lower limit for the column density of atomic hydrogen, N(H I) not less than 4(17)/sq cm. The Lyman-alpha absorption line appears to have been detected, but only an approximate upper limit can be obtained from the data, of the order of 2(19)/sq cm. This amount of atomic hydrogen is less than that for a line of sight through the disk of a normal spiral galaxy. It is suggested that the absorbing material exists either in the halo of a galaxy or in the tenuous, extended, gaseous disk of a galaxy.

Bregman, J. N.↗
NASA NTRS1981

Temperatures of galactic molecular clouds showing CO self-absorption

The CO J = 2-1 line has been observed and, in most cases, mapped in 10 star-forming molecular clouds (W3, NGC 1333, NGC 2071, Mon R2, CRL 961, Rho Oph, W49N, W51A, DR 21, and Cep A). The CO J = 3-2 line has been observed in W3 and DR 21. The CO lines from all these sources are strongly self-absorbed. By comparing the present results with published CO(1-0) line profiles, it is found that large corrections to the temperatures of the cloud cores, as measured by the CO(1-0) lines, are required. The corrections for self-absorption bring the CO brightness temperatures into closer agreement with the grain temperatures inferred from far-IR photometry.

Phillips, T. G.↗
NASA NTRS1981

Simultaneous observations of active galactic nuclei with IUE

The IUE observations of four active nuclei were coordinated with radio, infrared, and X-ray measurements to obtain simultaneous determinations of their continuous spectra. The results for the BL Lac objects 0735+178 and I Zw 187 indicate sufficient UV and X-ray fluxes to ionize any gas. Comparison of the X-ray measurements with the extrapolated optical UV continuum show a definite X-ray excess for I Zw 187 but none for the other BL Lac object.

Bregman, J. N.↗
NASA NTRS1980

Detection of the 610 micron /492 GHz/ line of interstellar atomic carbon

The ground-state transition of neutral atomic carbon, 3P1-3P0, has been detected in the interstellar medium at the frequency of 492.162 GHz determined in the laboratory by Saykally and Evenson (1980). The observations were made from the NASA Kuiper Airborne Observatory using an InSb heterodyne bolometer receiver. The line was detected as strong emission from eight molecular clouds and apparently provides a widely useful probe of the interstellar medium.

Phillips, T. G.↗