Engineering topics

Rahe, J.

Publications and source records attributed to Rahe, J..

At least 37 records · Page 2

NASA NTRS1982

The International Halley Watch

The International Halley Watch (IHW) is a program designed to promote cooperation, standardization, and archival documentation in all phases of study of Comet Halley during its 1985-86 apparition. Discipline Specialists have been selected to create cooperative nets of ground-based observers encompassing seven different technical areas and to coordinate the observations and publication of results in each. The IHW will promote cooperation among ground-based and space studies of Comet Halley wherever reasonable and feasible. More specifically, the IHW will make ephemerides from the astrometric net available to any country flying a deep space mission. It will coordinate special Halley Watch Days with the arrival dates of space probes or periods of observation from earth orbit. And the IHW will provide a permanent archive in published form of all scientific observations of Comet Halley.

Rahe, J.↗

NASA NTRS1981

Modern Observational Techniques for Comets

Techniques are discussed in the following areas: astrometry, photometry, infrared observations, radio observations, spectroscopy, imaging of coma and tail, image processing of observation. The determination of the chemical composition and physical structure of comets is highlighted.

Brandt, J. C.↗

NASA NTRS1981

Observing facilities at the European Southern Observatory (ESO) in Chile for cometary observations

The (ESO) is located on the mountain La Silla (geographical coordinates: 4h42m55s10 west, -29 deg 15' 25".8 south, 2400 m elevation. The size of the telescopes ranges from a 40 cm Astrograph to the 3.6 m Richey-Chretien telescope. Future telescopes are discussed: a 2.2 m RC-Telescope which will be identical with the German 2.2 m telescope on Calor Alto in SE-Spain, and a 3.5 m telescope, the New Technology Telescope. In addition to these telescopes, a great number of auxiliary instrumentation are operational. Because ESO has to serve all requests of the visiting astronomers these instruments are designed for very different applications. The telescopes and auxiliary instruments that are especially suited for cometary observations are discussed. The dicussion is divided into three parts: photography, photometry-polarimetry and spectroscopy.

Schnur, G. F. O.↗

NASA NTRS1981

Existing cometary data and future needs

To assist scientists studying comets and their interaction with the interplanetary medium, compilations of existing cometary observations and data plans for additional publication are reported. The works cited include updates and/or supplements to: (1) the Catalogue of Cometary Orbits, (2) Physical Characteristics of Comets, (3) the Atlas of Representative Cometary Spectra, (4) the Atlas Cometas-Viento Solar, (5) the Isophotometrischer Atlas der Kometen, and (6) the Atlas of Cometary Forms. An Atlas of Cometary Spectra and an Atlas of Comet Halley 1910 (II) photographs and spectra are in preparation.

Rahe, J.↗

NASA NTRS1981

Plans for Comet Halley

The configuration, trajectories, and payloads of a spinning Earth-orbiting satellite designed by ESA for a post-perihelion flythrough (Giotto mission) of Comet Halley are described. Experiments approved for use on two identical three-axis stabilized Venera spacecraft destined to encounter the comet after releasing probes to Venus are listed as well as the instruments to be carried on Japan's Planet-A flyby mission. The main features launch windows are given for each spacecraft.

Rahe, J.↗

NASA NTRS1981

The ultraviolet spectrum of UW Canis Majoris

High resolution spectra of the eclipsing binary UW CMa have been obtained in the wavelength range 950 to 3200 A with the Copernicus (OAO-3) and IUE satellites. UW CMa is an interacting system, consisting of an 07f Ia primary and an O-B secondary. The spectra have been used to compile a list of stellar and interstellar lines. Identifications together with position and laboratory wavelengths are given. The spectra are dominated by envelope (P Cygni) lines. Numerous, but less conspicuous photospheric absorption lines from the 07f component are present. In addition, a wealth of interstellar lines appear.

Drechsel, H.↗

NASA NTRS1981

Structure and origin of cometary nuclei

There is strong evidence that a comet nucleus consists of a single object whose basic structure is Whipple's icy conglomerate. A number of cometary phenomena indicate that the nucleus is a low density, fragile object with a large degree of radial uniformity in structure and composition. Details of the ice-dust pattern are more uncertain. A working model is proposed which is based on theories of accumulation of larger objects from grains. This nucleus is a distorted spherical aggregate of a hierarchy of ice-dust cometesimals. These cometesimals retain some separate identity which lead to comet fragmentation when larger components break off. The outer layers of new comets were modified by cosmic ray irradiation in the Oort Cloud. The evidence for meteorite-comet association is steill controversial. Current dynamical studies do not seem to require a cometary source of meteorites.

Donn, B.↗

NASA NTRS1981

H I and dust in Kutner's cloud

A map in the 1.420 GHz line of H I, with an angular resolution of 9.1 arcmin, is made toward Kutner's Cloud and the region between Kutner's Cloud and Heiles' Cloud. It is assumed that the cold H I in the clouds is located only in front of, and absorbs the H I background; the column density of cold H I, N(H I), is obtained from this absorption. The visual extinction for this region is determined from star counts on red and blue POSS prints. It is noted that most of the gas in the cloud is in the form of H2. The column density of H2 is obtained from the visual extinction and the extinction-to-gas ratio given by Bohlin et al. (1978).

Batrla, W.↗

NASA NTRS1981

Phase-correlated P Cygni profile variations of the C III multiplet in UW Canis Majoris

The interacting close binary system UW CMa has been observed, in the wavelength range from 1161 to 1188 A, continuously during a complete orbital cycle in 1979 with the Copernicus (OAO-3) U2 spectrometer. The C III multiplet at 1175 A, observed as a P Cygni feature, exhbits a clear dependence on the orbital phase of the binary; the radial velocity variation of this feature lags behind that of the O7 primary component by 0.1 orbital phase, which agrees with the anticipations in an earlier study by the same authors. The radiation-driven matter, flowing out of the binary, originates in the primary component.

Drechsel, H.↗

NASA NTRS1981

Analysis of IUE observations of CS in Comet Bradfield (1979 l)

The high resolution rotational band profiles were fitted with theoretical band profiles which are derived using a Boltzmann temperature of 70 K. A very rapid variation with heliocentric distance for the CS brightness was found. The implications of these results for models of the coma along with the origin of the CS species are discussed.

Rahe, J.↗

NASA NTRS1980

Abundances and excitation of interstellar methyl formate

The detection of methyl formate (HCOOCH3) in four transitions toward Orion KL, in two transitions toward Sagitarrius B2, and in one transition toward W51 is reported. The column densities of HCOOCH3 are found to be surprisingly large (2-5 x 10 to the 14th per sq cm) in all three clouds. Stimulated emission in the 18 cm K doublet of HCOOCH3 toward Sagittarius B2 is clearly demonstrated. The relatively large column densities of HCOOCH3 in clouds outside the galactic-center region probably imply that this molecule is widely distributed in the galaxy, but the negative results in other clouds require lower column densities than in Orion by a factor of 0.5 or less. Two unidentified lines were detected in Orion, at approx. 91 and 99 GHz.

Churchwell, E.↗

NASA NTRS1980

Detection of periodic light variations in the old nova V 603 Aquilae /1918/

Periodic visible light variations of the old nova V 603 Aql (1918) were detected with the Fine Error Sensor Instrument (FES) aboard the IUE satellite. Continuous observations were carried out during more than two complete cycles. The light curve shows a broad maximum and a pronounced minimum which was covered three times, and is tentatively interpreted as an eclipse of the accretion disk around the white dwarf by the late main sequence component.

Rahe, J.↗

NASA NTRS1980

IUE observations of the UV spectrum of Comet Bradfield

Comet Bradfield (1979), discovered shortly after perihelion on Christmas day 1979, is characterized by a retrograde orbit of period approximately equal to 250 yr. This orbit was very favorable for observation by the IUE satellite, and the first observations, the preliminary results of which are reported here, were made on 10 and 11 January 1980. Previously, comprehensive vacuum UV cometary spectra were available only for Comet West (1976VI) from rocket observations and Comet Seargent (1978m) with IUE, hence three comets have now been observed in the wavelength region where most of the major constituents are detectable spectroscopically. The UV spectra of these comets are remarkably similar, despite large differences between them in the gas-to-dust ratio and the different heliocentric distances at which the observations were made, and although the statistical basis is still very small, the implication for cosmogony is that nearly all comets have the same primary composition and origin.

Feldman, P. D.↗

NASA NTRS1980

Ultraviolet spectroscopy of comets

The UV spectra of a comet, Comet Seargent 1978m, were obtained two weeks after the comet's discovery before any ground-based spectroscopic observations were made. The second comet observed with IUE was Comet Bradfield 1979e. It was first observed on January 10 and 11, 1980, and subsequently on several occasions until the beginning of March of 1980. The comets were observed at various heliocentric distances in the low and high dispersion mode. In the long wavelength region, emission bands of OH, CS, CO2(+), NH and CO(+) were identified, and the rotational structures of the (0, 0) and (1, 0) bands of OH were resolved. In the short wavelength region, emission lines of H(L alpha), O I, C I, C II, and C 1 and the CO fourth positive bands appeared. The results of these observations are the detection of S I; indications that CS exists as "Parent Molecules" in the cometary ice; the resolution of the (0, 0) and (1, 0) bands of OH; the determination of the spatial variations of various emissions; the determination of the variation of the production rates of various species, especially of H and OH, with heliocentric distance.

Rahe, J.↗

NASA NTRS1980

Mass loss from UW Canis Majoris

The present analysis is an application of the theory described by Lucy (1971) for the calculation of P Cygni resonance line profiles formed by isotropic and coherent scattering in spherically symmetric expanding circumstellar envelopes. Copernicus satellite measurements of resonance features in the FUV spectrum of the O 7 supergiant UW Canis Majoris (= HD 57060) are compared with theoretical P Cygni profiles. Grids of line profiles are computed using four free parameters which contain information about the velocity law, ionization equilibrium, temperature, and envelope density. Thus, with the assumption of a spherically symmetric steady flow, and of solar element abundances, the stellar mass loss rate and the electron temperature of the expanding shell can be derived. The mass flow is treated in a fully transonic way, i.e., the Sobolev approximation is applied.

Drechsel, H.↗

NASA NTRS1980

Mass flow analysis of the ultraviolet spectrum of UW Canis Majoris

The ultraviolet spectrum of the close binary UW CMa, obtained with the Copernicus (OAO-3) and IUE satellites in the wavelength region from 1010 to 1510 A and from 1200 to 3000 A, respectively, is analyzed. The observed P Cygni line profiles are compared with theoretically predicted profiles formed by isotropic and coherent scattering in a spherically symmetric expanding circumstellar envelope. Tables illustrate the identified stellar lines, laboratory wavelengths, and line strengths in terms of peak height for emission or central depth for absorption components, normalized to the local stellar continuum.

Drechsel, H.↗

NASA NTRS1979

The ultraviolet spectrum of Comet Seargent 1978m

UV spectrograms of Comet Seargent (1978m) have been obtained with the IUE satellite in the low- (1.8-nm) and high- (0.1-nm) dispersion modes. In the long-wavelength region (189-340 nm) emission bands of OH, CS, CO2(+), NH, and CO(+) can be identified, and the rotational structure of OH could clearly be resolved. In the short-wavelength region (119-192 nm) emission lines of H(Lyman-alpha), O I, C I, and S I appear. These observations demonstrate that the IUE observatory can effectively be used to obtain high-quality spectra of comets as faint as ninth magnitude.

Jackson, M. W.↗

NASA NTRS1979

Mass flow in close binaries - Results of optical and ultraviolet observations

Observational data provide information regarding mass flow in close binaries. Data about origin, condition, and development of circumstellar matter can also be obtained. The investigations are based on an evaluation and correlation of photometric observations and simultaneously made photoelectric and spectrographic observations in the visible spectral range and, in addition, also on satellite observations in the ultraviolet range. Supplementary information concerning the mass flow in close binaries is obtained on the basis of observations related to the X-ray, infrared, and radio range. Suitable theoretical models are employed to interpret the observational data.

Rahe, J.↗