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At least 685 records · Page 38
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NASA NTRS1985

Selection effects against small comets

Everhart's (1967) formulation is used to determine the correlation between the probability of discovering a comet and the size of its nuclear radius. The analysis is concentrated on comets that are not more than two or three hundred meters in diameter; hence, heliocentric variations in cometary brightness can be neglected. The effect of cometary physical decay is also considered, and a strong observational bias against the detection of small active comets is found. The following three factors are involved: (1) small comets must pass closer to the earth than large comets in order to be detected, (2) the resulting higher angular velocity for nearby comets leads to a decrease in the time available to discover a small comet, and (3) small comets physically decay and vanish faster than do large comets.

Zook, H. A.↗
NASA NTRS1986

Two Cepheid variables in the Fornax dwarf galaxy

Two fields surrounding globular clusters 2 and 3 in the Fornax dwarf spheroidal galaxy have been searched for short-period variable stars that are brighter than the horizontal branch. This survey confirmed as variable the two suspected suprahorizontal-branch variables discovered by Buonanno et al. (1985) in their photometry of the clusters. The observations show that the star in cluster 2 is a W Virginis variable of 14.4 day period. It is the first W Vir variable to be found in a dwarf spheroidal galaxy, and its proximity to the center of cluster 2 suggests that it is a cluster member. The other star appears to be an anomalous Cephpeid of 0.78 day period. It lies outside or very near the boundary of cluster 3, and is therefore probably a member of the field population of Fornax. Although no other suprahorizontal-branch variables were discovered in the survey, it did confirm as variable two of the RR Lyrae candidates of Buonanno et al., which appeared at the survey limit. The implications of these observations for the understanding of the stellar content at Fornax are discussed.

Light, R. M.↗
NASA NTRS1986

Research in planetary astronomy and operation of the 2.2-meter telescope

The turn-around in the secular change in brightness of Pluto was detected, the planet is now beginning to brighten. The spectral signature was found of an ammonia bearing compound in the surface ices of Europa. Specific Io volcanic hotspots were detected from infrared photometry of the mutual events of the Jovian satellites. The polarized emission from the volcanic hotspots on Io was discovered and the locations of those hotspots were determined. The orbit of Charon was refined from speckle observations of the Pluto-Charon system. The spectral properties of liquid nitrogen-methane mixtures with reference to the infrared spectrum of Triton were studied. Major progress was made in modeling asteroid lightcurves from a modern theory of photometric properties of the asteroid surfaces. Several additional olivine-rich asteroids from near-infrared spectrophotometry were discovered. Important photometric, spectroscopic, narrow-band imaging data on Comet P/Halley was acquired, along with Schmidt photographs of Comet P/Halley and its tail.

Hall, D. N. B.↗
NASA NTRS1986

Studies of extended planetary atmospheres

Telescopic observations were made of gases and plasmas in the Jupiter system, and related phenomena such as the recently-discovered sodium atmosphere of Mercury. Sodium absorption in Io's atmosphere was observed to distances as large as 5 Io radii during the mutual-eclipse season of the Jovian satellites. Analysis of Jovian disk spectra has proceeded, as planned, from an emphasis on the H2 ortho-para ratio to analysis of methane absorptions and determination of cloud structure. Several 2-channel photometers were constructed in 1978 for the Uranus event at which the rings were discovered and a smaller, single-channel unit was built more recently. Although the photometers themselves are still fully usable, the data-acquisition systems have major deficiencies.

Hunten, D. M.↗
NASA NTRS1986

The molecular gas in the supernova remnant IC443

Although a few highly perturbed regions characterized by gas motions with velocities larger than 20 km/s have been discovered during the last several years in the supernova remnant (SNR) IC 443, the nature of these perturbed clumps and their relationship to the quiescent molecular gas near the SNR remains unknown. In part, this is due to a lack of large-scale, high angular resolution observations. Therefore, a systematic survey of this SNR in the CO (J=1 yields 0) line has been conducted, covering a roughly 50' x 50' region spaced by 2'. The observations were made with the 14 m telescope of the Five College Radio Astronomy Observatory (FCRAO), which has a resolution of 45" and a single sideband receiver temperature of 200 K at 2.6 mm wavelength. Five new clumps were discovered, bringing the total number of known perturbed regions to eight. To study the physical structure of these clumps in more detail, more complete maps of the clumps have been made in both the CO(J=1 yields 0) and (J=2 yields 1) transitions with the FCRAO telescope. These maps show that the extent of perturbed gas in a typical clump is several arcmin, or a few pc at a distance of 1.5 kpc.

Huang, Y. L.↗
NASA NTRS1986

A study of large, medium and small scale structures in the topside ionosphere

Alouette and ISIS data were studied for large, medium, and small scale structures in the ionosphere. Correlation was also sought with measurements by other satellites, such as the Atmosphere Explorer C and E and the Dynamic Explorer 2 satellites, of both neutrals and ionization, and with measurements by ground facilities, such as the incoherent scatter radars. Large scale coherent wavelike structures were found from ISIS 2 electron density contours from above the F peak to nearly the satellite altitude. Such structures were also found to correlate with the observation by AE-C below the F peak during a conjunction of the two satellites. Vertical wavefronts found in the upper F region suggest the dominance of diffusion along field lines as well. Also discovered were multiple, evenly spaced field-aligned ducts in the F region that, at low latitudes, extended to the other hemisphere and were in the form of field-aligned sheets in the east-west direction. Low latitude heating events were discovered that could serve as sources for waves in the ionosphere.

Gross, Stanley H.↗
NASA NTRS1987

Observations on the magnitude-frequency distribution of Earth-crossing asteroids

During the past decade, discovery of Earth-crossing asteroids has continued at the pace of several per year; the total number of known Earth crossers reached 70 as of September, 1986. The sample of discovered Earth crossers has become large enough to provide a fairly strong statistical basis for calculations of mean probabilities of asteroid collision with the Earth, the Moon, and Venus. It is also now large enough to begin to address the more difficult question of the magnitude-frequency distribution and size distribution of the Earth-crossing asteroids. Absolute V magnitude, H, was derived from reported magnitudes for each Earth crosser on the basis of a standard algorithm that utilizes a physically realistic phase function. The derived values of H range from 12.88 for (1627) Ivar to 21.6 for the Palomar-Leiden object 6344, which is the faintest and smallest asteroid discovered.

Shoemaker, Eugene M.↗
NASA NTRS1987

Planetary nomenclature

In fiscal 1986, names were chosen for prominent features on the five previously known Uranian satellites and for features on the largest of the 10 satellites discovered by Voyager 2. The names of the five large satellites are taken mostly from Shakespeare, and most are spirits; therefore, Shakespearean and spirit themes were used to choose names for topographic features on the satellites. Crater names and most other feature names on Miranda, Oberon, and Titania are from Shakespeare; features on Ariel are named for bright spirits and those on Umbriel for dark, all taken from universal mythology. Preliminary coordinates for these features are derived from shaded relief maps of the satellites to be published in 1987. Orbital elements have been established for the 10 new satellites, and a paper describing this work is in progress; satellite positions are under review by Commission 16 of the IAU. The moon 1985 U1 is informally designated Puck. The nine small satellites discovered in 1986 are to be named for Shakespearean heroines; these names are to be listed in the 1987 edition of the Annual Gazetteer of Planetary Nomenclature.

Strobell, M. E.↗
NASA NTRS1986

International collaboration leads to new Aten asteroid discovery, 1984 QA

A new earth-crossing asteroid of the Aten type (orbit smaller than earth's) was discovered on August 30, 1984 at Palomar. The asteroid, designated 1984 QA, is the fourth known member of the Aten type and the first discovered since 1978. The discovery of this object was the highlight of a collaboration between the JPL Asteroid Search Team and an ESA scientist, and demonstrates one aspect of an ongoing joint search effort with other Schmidt observers.

Helin, E. F.↗
NASA NTRS1986

Spectroscopy of six X-ray-selected BL Lacertae candidates

Results of a continuing program aimed at extending the small list of X-ray-selected BL Lac objects are reported. High-quality spectra have been obtained of six faint blue objects that lie within the positional error boxes of X-ray sources discovered serendipitously by the Einstein Observatory. Three of the objects are found to be previously uncataloged low-red-shift quasi-stellar objects, including one formerly suggested as BL Lac candidate. Two are faint galactic stars, while the final object has a featureless spectrum, and thus remains a candidate. Although X-ray selection may ultimately be an effective means of discovering faint BL Lac objects, such sources are evidently rare at the X-ray flux levels attainable by the Einstein Observatory.

Margon, Bruce↗
NASA NTRS1987

Observation of the HH 1 and 2 region with IRAS

Infrared Astronomical Satellite (IRAS) observations of the region in Orion containing HH 1 and 2 reveal for the first time the large-scale distribution of newly formed stars. New infrared sources discovered in these observations are discussed, and attempts are made to untangle the complex infrared morphology of this field. A major finding of this study is that HH 1 is near the peak of an intense and broad plateau of 60 and 100 micron emission that spatially corresponds well with the boundaries of a previously detected molecular cloud. Other findings include the detection of an emitting circum-HH object dust complex around HH 2, 25 micron emission associated with the putative HH 1 and 2 exciting source discovered with the VLA, a new luminous far-infrared source, and numerous infrared source complexes, some in blank optical fields and others in fields containing optical emission-line stars.

Pravdo, Steven H.↗
NASA NTRS1987

Search for low-mass objects. II

The IR (K and L) magnitudes of 20 white dwarfs have been measured with a view to discovering brown dwarf companions, as previously discussed by Kumar (1985). The white dwarf mass was taken to be 0.7 solar masses, with progenitor and brown dwarf masses being 2.1 and 0.05, respectively; a brown dwarf companion with this mass, an age of less than 5 Gyr, and a distance 1-20 AU from the white dwarf's progenitor would have been detected. However, none was discovered.

Krishna Kumar, C.↗
NASA NTRS1986

Exploring the Uranian satellites

Data on the Uranian satellites from the January 25, 1986 flyby of Voyager 2 are presented. Ten new satellites were discovered by Voyager 2; the features and orbits of these ten satellites are examined. The main geological characteristics for Oberon, Umbriel, Titania, Ariel, and Miranda discovered in the Voyager 2 images are described. Possible relationships between the Uranian satellites and Jovian and Saturnian satellites are being researched.

Brown, Robert Hamilton↗
NASA NTRS1987

Monocrystalline silicon gradiometer for gravity experiments in space

A very important research effort has been made in the last decade in the field of high precision measurement with laser instrumentation. The development of a space borne gradiometer operating at a high sensitivity level using laser measurement of the distance between proof mass over a short base line of order one meter is discussed. Two aspects of laser technology make it a promising tool for gradiometry measurements: quantum limited accuracy and absolute distance measurements. The quantum limit associated with laser instrumentation was formulated. The relevant quantum and classical sources of errors in laser measurements were reviewed and corresponding laser performance requirements for gradient measurements were evaluated. Some mechanical quality factor measurements were made on simple resonant monocrystalline silicon suspensions. It was discovered that the use of zero derivative restoring forces to position the gradiometer test masses will dramatically reduce the gradiometer temperature control requirements. A laser beam side injection scheme was discovered which permits rejection of common mode accelerations. These concepts are briefly discussed.

Richard, Jean-Paul↗
NASA NTRS1988

4C 40.36 - A radio galaxy at a redshift of 2.3

Long-slit spectroscopy of a faint extended optical object identified with the radio source 4C 40.36 is presented. Three emission lines are detected. Their wavelengths match those of C IV 1549 A, He II 1640 A, and semiforbidden C III 1909 A to within 0.5 percent for a redshift of z = 2.269. The extended continuum emission (20 kpc) together with the large equivalent widths (about 100 A) and narrow profiles (1500 km/s) of the emission lines, all show that 4C 40.36 is a galaxy with properties similar to those of other distant radio galaxies. The redshift of 4C 40.36, however, considerably exceeds that of the most distant radio galaxy (3C 326.1 at z = 1.825) known to date. 4C 40.36 is of additional interest as an excellent example of the recently discovered phenomenon of alignment between the optical and radio axes of powerful distant radio galaxies. The object was investigated as part of a survey of ultra-steep spectrum radio sources, and it is shown that the selection criteria used to discover 4C 40.36 result in a sample of objects having a relatively low dispersion of monochromatic radio luminosities.

Chambers, K. C.↗
NASA NTRS1988

Astrometric observations of comets and asteroids and subsequent orbital investigations

The 155-cm reflector was used for observations of comets and minor planets on 28 nights during April-October. Twenty-two of the observations refer to comets, 62 to numbered minor planets (numbered, that is, by the end of the semester: only nine of them refer to minor planets already numbered at the time of the last report), and the remainer to unnumbered minor planets. Observations were made of four new comets discovered during the semester and a fifth discovered in January. Observations of Wilson (19861), P/Tempel 2 and two other returning short-period comets are also continuing. Among the odd numbered minor planets observed were the earth-approaching objects (1685) Toro and (1980) Tezcatlipoca. The Earth approacher 1980 PA was numbered (3908).

Mccroskey, Richard E.↗
NASA NTRS1988

Planetary astronomy P. I. research summary

A systematic survey for near-Earth and planet-crossing asteriods is being conducted with the 0.46 m Schmidt at Palomar to increase the number of known asteroids and establish improved estimates of their populations and size distribution. Access to a limited number of PSS11 plates from the 1.2 m Schmidt are used also to search for unusual objects. Field pairs from the 0.46 m are photographed and inspected with a stereomicroscope; new objects are detected and followed to establich definitive orbits. When near-Earth asteroids are discovered, other astronomers are informed so that physical observations can be obtained. With remote sensing results, possible generic relationships are suggested. Population refinements can be accomplished by increasing the number of known asteroids under well-established conditions of search. From 13 observing runs made at Palomar, 215 new asteroids were discovered and reported with good orbits determined for 90. Significant discoveries are Apollo 1988 EG, Amor 1987 QB, and an unusual high inclination asteroid, 1988 EO. Other discoveries of importance include 12 Mars-crossers, 6 Hungaries, and 13 Phocaeas. The discovery of short-period comet Helin, 1988w, which makes a close approach to Saturn, is also notable.

Helin, Eleanor F.↗
NASA NTRS1989

Antarctic Meteorite Location Map Series

Antarctica has been a prolific source of meteorites since meteorite concentrations were discovered in 1969. The Antarctic Search For Meteorites (ANSMET) project has been active over much of the Trans-Antarctic Mountain Range. The first ANSMET expedition (a joint U.S.-Japanese effort) discovered what turned out to be a significant concentration of meteorites at the Allan Hills in Victoria Land. Later reconnaissance in this region resulted in the discovery of meteorite concentrations on icefields to the west of the Allan Hills, at Reckling Moraine, and Elephant Moraine. Antarctic meteorite location maps (reduced versions) of the Allan Hills main, near western, middle western, and far western icefields and the Elephant Moraine icefield are presented. Other Antarctic meteorite location maps for the specimens found by the ANSMET project are being prepared.

Schutt, John↗