Engineering topics

Mink, D. J.

Publications and source records attributed to Mink, D. J..

14 records

NASA NTRS1992

SKYMAP: Exploring the Universe in software

SKYMAP is a computer program which produces maps of arbitrary portions of the sky in a variety of projections and coordinate systems. Over the past ten years it has been used to produce finder charts for occultations by planets, display scan and image data from the Spacelab 2 Infrared Telescope, and make maps of fields for astronomical observations at X-ray, optical, infrared, and radio wavelengths. It can display multiple source catalogs, including the HST Guide Star Catalog, as well as solar system objects with astrometric accuracy using the JPL DE-130 ephemeris or tabulated positions. SKYMAP can be tuned to a specific task using an ASCII parameter file which controls how information is displayed on any Tektronix-compatible graphics display. The program contains a variety of interactive graphic and image processing features and has been ported to a variety of computer systems. A recent project visually demonstrates source density variation in various commonly-used all-sky catalogs.

Mink, D. J.↗

NASA NTRS1986

JHK photometry of candidate stars for occultation by Neptune

Hubbard et al. (1985) have observed the occultation of a star by a ring-like arc of Neptune. The semitransparent, incomplete ring was located at a distance of about 67,000 km from Neptune. In connnection with the program for the Voyager 2 deep space probe to fly past Neptune in 1989 at this distance from the planet, it is urgent to determine the nature of this ring arc or arcs. The best approach to obtain the required information is related to an observation of occultations of stars by Neptune. In this context, a study has been conducted of six stars which will be occulted by Neptune during 1986 and 1987, taking into account their JHK photometry. The obtained data are presented in a table.

Vilas, F.↗

NASA NTRS1985

The 1983 June 15 occultation by Neptune. I - Limits on a possible ring system

Observations on 15 June 1983 of an occultation of a star by Neptune from Mauna Kea, Mount Stromlo, Siding Spring, and the Kuiper Airborne Observatory show no evidence for equatorial rings between 25,300 and 200,000 km (R/N/ = 25,269 km). Within most of this region, the upper limit on the optical depth along the line of sight, for rings broader than 6 km , is 0.04, which corresponds to a normal optical depth of 0.016. These results rule out a Neptunian ring system similar to that of Saturn or Uranus, but not a system of low optical depth similar to the Jovian rings. The data show no features that appear likely to have been caused by material in the equatorial plane of Neptune near the Roche limit.

Elliot, J. L.↗

NASA NTRS1985

Predicted occultations by Uranus, Neptune, and Pluto 1985-1990

Predictions are presented for 54 occultations by Uranus' ring system, 24 occultations by Uranus, 22 occultations by Neptune, and ten possible occultations by Pluto during the period 1985 through 1990. Notable occultations by Uranus occur 24 May 1985, 16 April 1987, 27 May 1990, 21 June 1990, and 7 August 1990. The best Neptune occultations are on 7 June 1985 and 25 May 1990. Of the Pluto events, there are six which are nominally observable somewhere on the earth, although uncertainties in Pluto's position combined with uncertainties in the star positions preclude prediction of a ground track until just before the events.

Mink, D. J.↗

NASA NTRS1983

The rings of Uranus - Occultation profiles from three observatories

Occultation profiles for the nine confirmed Uranian rings obtained from Las Campanas, the European Southern Observatory, and Cerro Tololo on 15-16 August 1980 are compared. The alpha ring shows a 'double-dip' structure; the eta ring shows a broad and narrow component (similar to Saturn's F ring); and the epsilon ring shows six features that appear in the data from all three observatories. Diffraction fringes appear at the edges of several of the occultation profiles.

Elias, J. H.↗

NASA NTRS1983

The structure of Neptune's upper atmosphere - The stellar occultation of 24 May 1981

Observations of the 24 May 1981 occulation of an uncatalogued star by Neptune made at the Cerro Tololo Inter-American Observatory have been analyzed to yield temperature profiles of Neptune's upper atmosphere for number densities near 5 x 10 to the 13th per cu cm. The mean temperatures at immersion (latitude - 56 deg) and emersion (latitude - 16 deg) obtained by numerical inversion were 140 + or - 10 K and 154 + or - 10 K, respectively. The immersion and emersion profiles are remarkably similar in overall shape, suggestive of global atmospheric layering. From the astrometry of the event, precise relative positions of Neptune and the occulted star were obtained.

French, R. G.↗

NASA NTRS1983

Occultations by possible rings in Saturn's outer magnetosphere - 1982-1985

The presence of particulate rings in the outer magnetosphere of Saturn is suggested by Pioneer and Voyager spacecraft low energy plasma ion data analyses. For each of the 14 stars near which Saturn passes, the table presented furnishes the date or dates on which the occultation would occur and the star's SAO catalog number. Of these 14 star occultations due to the hypothesized rings projected for the August 1982-December 1985 period, three stars are also occulted by Saturn and its known rings.

Mink, D. J.↗

NASA NTRS1982

Possible occulations by satellites of Uranus and Neptune - 1983-1985

Predictions are presented for 15 possible occulations by the satellites of Uranus and Neptune from 1983 through 1985. Umbriel, the third satellite of Uranus, might occult a 10.4-mag star (Hyd-20 deg 51699) on 25 March 1983 which will be occulted by Uranus 14 hr earlier. Uncertainties in star positions and ephemerides of planets and satellites are quite large in comparison to the size of these bodies, and these predictions are to be taken as possibilities only.

Mink, D. J.↗

NASA NTRS1981

No evidence of rings around Neptune

The results of two observations of stellar occultations of Neptune to determine if the planet has a ring system are reported. The sightings were made from Mt. Stromlo, Mauna Kea, and Cerro Tololo, noting that an equatorial ring would subtend only two arcsec of view. An upper accretion limit was defined to set the region around Neptune where rings, rather than satellites, could form. The intensities of the starlight from the two selected stars were recorded by photometers on magnetic tape during the occultation period. One of the stars did not occult, but passed through the entire region where a ring system might be present. No definitive evidence for rings was found, although an optical depth for a Neptunian ring was calculated at 0.07, with a width of more than 5 km and a radius of 31,400 km.

Elliot, J. L.↗

NASA NTRS1981

Orbits of nine Uranian rings

Observations of a stellar occultation by Uranus and its nine rings are presented and used to examine the structures and kinematics of the rings. The observations of the occultation of the K giant star KM 12 were obtained in the K band with the 4-m CTIO telescope at a signal-to-noise ratio higher than any previously obtained. Ring occultation profiles reveal the alpha ring to possibly have a double structure and less abrupt boundaries than the gamma ring, which exhibits diffraction fringes, while the eta ring is a broad ring with an unresolved narrow component at its inner edge. The present timing data, as well as previous occultation timings, are fit to a kinematic model in which all nine rings are treated as coplanar eclipses of zero inclination, precessing due to the zonal harmonics of the Uranian gravitational potential to obtain solutions for the ring orbits. Analysis of the residuals from the fitted orbits reveals that the proposed model is a good representation of ring kinematics. The reference system defined by the orbit solutions has also been used to obtain a value of 0.022 + or - 0.003 for the ellipticity of Uranus and a Uranian rotation period of 15.5 h.

Elliot, J. L.↗

NASA NTRS1981

The 20 March 1980 occultation by the Uranian rings

On March 20, 1980, observations of occultations by rings alpha, beta, gamma, delta, and epsilon were observed from Cerro Tololo and Sutherland. A model ring profile was fit to the data to obtain the midtimes of the occultations and the widths of the profiles. A 14-parameter kinematic model, including J sub 2, J sub 4, and some of the orbital elements for rings 4, alpha, beta, and epsilon as free parameters, was fit to these data and previous ring occultation timings. The results yield J sub 2 = (3.396 + or - 0.020) x 10 to the -3 and a 2 sigma upper limit, absolute value of J sub 4 less than 7 x 10 to the -5th. Uniform precession models for rings alpha, beta are established and the dispersion in the values of semimajor axes and eccentricities for rings alpha, beta, and epsilon have been obtained. If self-gravity is the cause of the uniform precession, the mass of the beta ring is estimated at approximately 4 x 10 to the 16th g; the mass of the alpha ring probably is also near this value.

Elliot, J. L.↗

NASA NTRS1981

Predicted occultations by Neptune - 1981-1984

Predictions are presented for eight occultations by and appulses to Neptune from 1981 through 1984. Of special interest are a near-central occultation of Hyd - 22 deg 58794 on June 15, 1983, and a July 22, 1984 occultation of SAO 186001.

Mink, D. J.↗

NASA NTRS1981

Predicted occultations by Uranus - 1981-1984

Predictions are presented for 11 occultations by and appulses to Uranus and its ring system for ten stars from 1981 through 1984. The brightest stars are occulted on April 26, 1981 (BD - 19 deg 4222) and on April 22, 1982 (Hyd - 20 deg 51699). The ring system occults the same star twice during March 1983 (Hyd - 21 deg 64352).

Klemola, A. R.↗

NASA NTRS1980

The radius and ellipticity of Uranus from its occultation of SAO 158687

From occultation timings obtained from the Kuiper Airborne Observatory and from Cape Town for Mar. 10, 1977 occultation of SAO 158687 by Uranus, the equatorial radius, Re, of the planet has been determined to be 26,228 + or - 30 km and its ellipticity epsilon = 1 - Rp/Re = 0.033 + or - 0.007. These values refer to the 1.0 x 10 to the 14th/cu cm number-density level, under the assumption that the upper atmosphere is composed of H2 and He with a mean molecular weight mu = 2.20. The dominant source of uncertainty is the position of the center of the ring system, which was used to define the center of Uranus in our analysis. A rotation rate of 12.8 + or - 1.7 hours for the planet is implied by our value for the ellipticity, under the assumption that Uranus is in hydrostatic equilibrium below the 1.0 x 10 to the 14th/cu cm number density level.

Elliot, J. L.↗