Engineering topics

Jewitt, D. C.

Publications and source records attributed to Jewitt, D. C..

11 records

NASA NTRS1998

Deuterium in comet C/1995 O1 (Hale-Bopp): detection of DCN

Deuterated hydrogen cyanide (DCN) was detected in a comet, C/1995 O1 (Hale-Bopp), with the use of the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. The inferred deuterium/hydrogen (D/H) ratio in hydrogen cyanide (HCN) is (D/H)HCN = (2.3 +/- 0.4) x 10(-3). This ratio is higher than the D/H ratio found in cometary water and supports the interstellar origin of cometary ices. The observed values of D/H in water and HCN imply a kinetic temperature >/=30 +/- 10 K in the fragment of interstellar cloud that formed the solar system.

Non-NASA Center↗

NASA NTRS1998

A determination of the HDO/H2O ratio in comet C/1995 O1 (Hale-Bopp)

Deuterated water (HDO) was detected in comet C/1995 O1 (Hale-Bopp) with the use of the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. The inferred D/H ratio in Hale-Bopp's water is (3.3 +/- 0.8) x 10(-4). This result is consistent with in situ measurements of comet P/Halley and the value found in C/1996 B2 (Hyakutake). This D/H ratio, higher than that in terrestrial water and more than 10 times the value for protosolar H2, implies that comets cannot be the only source for the oceans on Earth.

NASA Discipline Exobiology↗

NASA NTRS1987

Surface brightness profiles of 10 comets

CCD photometric observations of the comae of 10 comets, obtained at the 4-m and 2.1-m telescopes at KPNO during 1985-1986 using filters centered at 700.5, 650.0, or 546.0 nm, are reported. The data are presented in extensive tables and graphs and characterized in detail. The radial surface brightness profiles are shown to be steeper than predicted by an idealized spherically symmetric steady-state comet model, the steepness increasing with the projected distance from the nucleus. These profiles are attributed, on the basis of Monte Carlo simulations, to imperfect coupling between the sublimated gas and the optically dominant grains of the coma.

Jewitt, D. C.↗

NASA NTRS1986

Optical investigation of Comet Halley

The optical properties of comet p/Halley are being investigated. Initial research has revealed the basic characteristics of the nucleus and provided unique insights into the formation and structure of the coma and the plasma tail. The study is among the most intensive conducted for any comet. The results from comet p/Halley may be useful in the interpretation of results from other comets.

Jewitt, D. C.↗

NASA NTRS1986

Halos around planetary nebulae

Preliminary results of a CCD survey designed to detect and investigate faint halos around planetary nebulae are reported. A TI 800 x 800 pixel CCD was used to take deep exposures of 44 planetary nebulae. The exposures were obtained through an H-alpha filter at the Cassegrain focus of the Palomar 1.5 m telescope. Spatial resolutions of 1 to 2 arcsec were obtained across 400 arcsec wide fields. The images, which are in many cases considerably deeper than any previously taken, reveal numerous planetary nebula halos. About two-thirds of the studied nebulae possess extensive outer halos, here defined as any extended emission beyond the 10 percent isophote. Ionized sulphur electron density measurements show that in some nebulae, the mass in the halo is comparable to the mass contained in the primary H II region. The data have been used to place constraints on the mode of origin of the halos. It is likely that the halos originate either by dynamical separation of a single ejected shell of gas or by the ejection of two or more such shells from the central star. It is possible but less likely that the halos are caused by excitation of the preplanetary stellar wind and improbable that the halos represent reflection nebulae.

Jewitt, D. C.↗

NASA NTRS1983

Distribution of forbidden neutral carbon emission in the ring nebula (NGC 6720)

The spatial distribution of forbidden C I 9823, 9850 A emission in NGC 6720 is reported. Like forbidden O I, the forbidden C I radiation appears enhanced in the region of the bright filaments. A few percent of the carbon atoms in the filaments are neutral. The neutral fraction is consistent with ionization equilibrium calculations made under the assumption of complete shielding of direct stellar radiation by hydrogen. The observed carbon lines are excited by photoelectrons produced from hydrogen by the nebular diffuse radiation field. The forbidden C I observations confirm that the filaments in NGC 6720 are regions of locally enhanced shielding.

Jewitt, D. C.↗

NASA NTRS1982

Visual and infrared observations of the distant Comets P/Stephan-Oterma /1980g/, Panther /1980u/, and Bowell /1980b/

The paper reports combined visual imagery and spectroscopy, near-infrared spectroscopy, and broadband infrared photometry of comets P/Stephan-Oterma (1980g), Bowell (1980b), and Panther (1980u) at intermediate heliocentric distances. The visual data indicate the existence of solid grains in extended halos around the nuclei of the three comets. Broadband near-infrared and thermal infrared measurements of Comet Panther suggest the presence of 2-4-micron-radius particles in the coma which most likely contain molecules incorporating the N-H bond, but which are more complex and less volatile than NH3. Such molecules can be produced in the grains by cosmic-ray reprocessing. Near infrared spectral features identical to those seen in comet Panther similary suggest the presence of a molecule incorporating the N-H bond in comet Bowell.

Jewitt, D. C.↗

NASA NTRS1982

The rings of Jupiter

The properties of the Jovian ring system are reviewed. The system has three morphologically distinct components. The bright ring is planar and circular. It merges into the faint sheet component at its inner edge. A broad halo of ring particles envelops the bright ring and the faint sheet, extending some 10,000 km above and below the plane of the bright ring, and apparently extending down to the atmosphere of the planet. The system is bounded on the outside by the small satellite Adrastea (1979 J1). The micrometer-sized ring particles observed at large phase angles may be generated by the erosion of parent bodies within the bright ring. The parent bodies probably lie in the size range 1 m to 1 km. Small particles may decay into the faint sheet under the action of Poynting-Robertson and other drag forces. Ring particles will maintain a net electric potential with respect to the ambient plasma, due to several charging processes in operation in the Jovian magnetosphere. Particles with diameters less than 0.4 micron may be lifted into the halo by an interaction with the Jovian magnetic field.

Jewitt, D. C.↗

NASA NTRS1981

Ground-based observations of the Jovian ring and inner satellites

Ground-based 0.9-micron observations of the Jovian ring and inner satellites are reported. The ring observations substantially confirm those obtained by the Voyager spacecraft. The first ground-based detection of 1979J2 suggests a geometric albedo of about 0.10 and a new value for its orbit period of 16 hr 11 min 23.5 + or - 0.5 sec.

Jewitt, D. C.↗

NASA NTRS1981

Spectra of the Jovian ring and Amalthea

Measurements made between 0.887 and 2.4 microns demonstrate that the Jovian ring and Amalthea have similar reflection spectra. The spectra, in particular the ratio of the 0.9- to 2.2-micron reflectivities, are inconsistent with those expected from water, ammonia, or methane frosts, but are consistent with reflection from large rock bodies.

Neugebauer, G.↗

NASA NTRS1979

Discovery of a new Jupiter satellite

During detailed analysis of Voyager 2 pictures of the Jupiter ring, a starlike object was identified in the plane of the ring. The same object was subsequently found on a higher-resolution frame and proved to be a satellite of Jupiter. This satellite has a circular orbit whose radius is 1.8 Jupiter radii, a period of 7 hours and 8 minutes, and a diameter of less than 40 kilometers. It is located at the outer edge of the Jupiter ring.

Jewitt, D. C.↗