Engineering topics

Wyckoff, S.

Publications and source records attributed to Wyckoff, S..

16 records

NASA NTRS1989

Spectrophotometric observations of comet P/Giacobini-Zinner

Spectroscopic observations of the Giacobini-Zinner comet were performed on March 20, June 20 and 21, September 11, and October 19, 1985. The September observations were performed at perihelion, exactly at the time of the International Cometary Explorer (ICE) encounter with the comet. The March and June observations were obtained with an intensified image dissector scanner (IIDS) on the 2.1-meter Kitt Peak telescope and the September and the October observations were obtained with a charge-coupled device (CCD) on the 4-meter Kitt Peak telescope. The nucleus spectra from these observations are presented.

Konno, I.↗

NASA NTRS1987

The spectral behavior of P/Halley at large heliocentric distance in light of the Giotto/Vega results

This paper presents the results of the preperihelion spectroscopic observations of the P/Halley comet, conducted with the Mayall 4 m telescope/CRYOCAM combination on Kitt Peak when the comet was between 8.8 and 5.6 AU from the sun. The V magnitudes and the (g - r) and (V - R) color indices, derived from the five spectra obtained between October 10, 1983, and February 4, 1984, showed a trend to increasing redness with decreasing heliocentric distance. However, the (V - R) color of the comet while near 8 AU was anomalous in that it was significantly bluer than the sun. Tentative interpretation of this phenomenon is presented.

Belton, M. J. S.↗

NASA NTRS1986

New molecular ions in spectra of comet P/Halley

Spectroscopic observations (4000 to 7000 A) were obtained of comet P/Halley near the time of the spacecraft encounters in March 1986. Molecular ion emission features were observed in the long-slit CCD spectra. Additional spectroscopic observations obtained in April 1986 confirm the presence of many new ion features in the plasma tail. It is proposed that CO2(+) be identified with the new features in the 4000 to 4350 A region. The other unidentified ion features may be attributable to a single ion species.

Wyckoff, S.↗

NASA NTRS1986

Spectra of the plasma tail of Comet P/Giacobini-Zinner at the time of the ICE counter

Ground-based CCD spectra of comet P/Giacobini-Zinner were obtained at the time of the ICE encounter. A spectral extraction gives the spectrum of the comet at the position and time of the spacecraft at midencounter. Column densities are given for neutral and ion molecules observed. The surface brightness profile for H2O(+) from 1000 km sunward to 34,600 km tailward obtained at the time of the encounter is also presented.

Wyckoff, S.↗

NASA NTRS1986

Comet P/Halley 1910, 1986: An objective-prism study

V. M. Slipher of the Lowell Obs. collected a large amount of spectroscopic data during the 1910 apparition of Halley's comet. Three of his post perihelion objective-prism plates were selected, digitized, and subjected to modern digital data reduction procedures. Some of the important steps in the analysis where: (1) Density to intensity conversion for which was used 1910 slit spectra of Fe-arc lamp on similar plates (Sigma) and derived an average characteristic curve; (2) Flux calibration using the fact that during the period June 2 to 7 1910 P/Halley was very close (angular distance) to the bright star Alpha Sex (A0III, V-4.49), and the spectra of both star and comet were recorded on the same plates. The flux distribution of Alpha Sex was assumed to be similar to that of the standard star 58 Aql and derived a sensitivity curve for the system; (3) Atmospheric extinction using the standard curve for the Lowell Obs.; (4) Solar continuum subtraction using the standard solar spectrum binned to the spectral resolution. An example of a flux-calibrated spectrum of the coma (integrated over 87,000km) before the subtraction of solar continuum is presented.

Carsenty, U.↗

NASA NTRS1986

Spectroscopy of comets

Comets constitute the most accessible samples of the outer solar system in its most primitive state. The physical and chemical properties of comet nuclei were determined to infer the conditions and processes related to the origin and evolution of the outer solar system. The procedure is to acquire and analyze digital spectra of a sample of comets covering a large range in heliocentric distance. During 1984 to 1986 the emphasis has been on Comet P/Halley (1982i). Large ground-based telescopes and state-of-the-art detectors were used to observe Comet P/Halley pre- and post-perihelion, covering a heliocentric distance range, 0.9 to 6.1 AU.

Wyckoff, S.↗

NASA NTRS1986

International Halley Watch: Discipline specialists for spectroscopy and spectrophotometry

Spectroscopic observations of Comets P/Crommelin, P/Giacobini-Zinner and P/Halley are coordinated, preliminary results are delivered to the astronomical community and the data collected from observers throughout the world are archived. The ASU IHW Center has the additional responsibility of maintaining the IHW Electronic Bulletin Board which reports real-time information on the status of Comet P/Halley. Access to this electronic bulletin board via telephone modem connection is available to any astronomer upon request.

Wyckoff, S.↗

NASA NTRS1986

Detection of CN emission in Comet P/Halley

The first detection of the CN 3883 A band in emission in Comet P/Halley (1982) in February 1985 is reported. The detection technique, which is described, used blind offsets from secondary reference stars to the comet's predicted position, and involved plotting the comet's track on an enlargement of an appropriate section of the Palomar Sky Survey E plates. The strong solar continuum in the resulting cometary spectrum demonstrates the dominance of the dust reflection spectrum and the reflection from the nucleus. The 3883 A feature is identified with the v = 0 band sequence of the blue system of CN; no other significant features were identified in the spectrum.

Wyckoff, S.↗

NASA NTRS1986

Kitt Peak spectroscopy of P/Halley: October 1983-March 1985

Four low-resolution optical spectra of P/Halley obtained at heliocentric distances between 8.78 ad 4.83 AU using the cryogenic camera and R-C spectrograph on the 4 m Mayall reflector of Kitt Peak National Observatory are discussed. The resulting spectrogram shows a lack of the emission bands commonly seen in nearby cometary spectra. The optical color of Halley indicates that the comet is redder than the sun at less than 6000 A and slightly bluer above 6500 A. The substantial extent of the Halley dust coma is discussed, and an oxygen production rate of 3 x 10 to the 26th atoms/s at r = 4.83 AU is derived. These results are compared with those for other comets and those found for Halley by other authors.

Spinrad, H.↗

NASA NTRS1985

Strong Lyman-alpha emission in three distant radio galaxies

Very strong, narrow Lyman alpha emission (equivalent width approximately 1000 angstroms) has been discovered in the redshifted ultraviolet spectra of three radio galaxies having z between 1.62 and 1.82. The three are 3C 256, 3C 239, and 3C 241. It is noted that Lyman alpha will probably be a very useful redshift and classification determinant in future spectroscopic surveys of active galaxies at still greater distances.

Spinrad, H.↗

NASA NTRS1985

Onset of sublimation in comet P/Halley (1982i)

The first direct evidence for the onset of sublimation of a comet nucleus is reported. Emission due to CN observed in spectra of the comet P/Halley provides evidence for the development of the gas coma. Broad-band photometric observations of the comet indicate that the dust coma developed near a preperihelion heliocentric distance r of about 6 AU. Rates of gas production and brightening for the comet have been derived at r of 4-6 AU. The mean preperihelion nuclear magnitude derived for the comet was used to calculate an effective radius of the nucleus, which for plausible values of the geometric albedo lies in the range 1-4 km.

Wyckoff, S.↗

NASA NTRS1985

Ultraviolet spectral evolution and heavy element abundances in Nova Austrinae 1981

Nova CrA 1981, a moderately fast galactic nova, was systematically observed over a period of seven months with the IUE satellite. The initial evolution of the UV spectrum was similar to that of previously observed novae; however, several months after maximum, weak emission due to very high ionizating forbidden lines of Na, Mg, Al, and Si appeared, eventually decreasing in strength over the next two months. The spectral development of the lines is consistent with the photoionization of an expanding shell; a high-temperature 'coronal' origin is ruled out. Abundances deduced from the spectra show that most of the observed heavy elements in the ejected material are enhanced with respect to helium, with neon the most abundant of these. In addition, there are substantial deviations of the Na/Mg/Al/Si abundance ratios from solar values. This is interpreted as evidence for the mixing of core material with the accreted envelope on a massive O-Ne-Mg (as opposed to a C-O) white dwarf. Furthermore, the proportion of core material in the ejecta implies that the mass of the white dwarf decreased as a consequence of the outburst.

Williams, R. E.↗

NASA NTRS1982

A new intermediate Seyfert galaxy - X-ray, optical, and radio properties

It is shown that the X-ray source X0459 + 034 is a Seyfert galaxy of intermediate type, and optical spectroscopy and radio observations were performed to study the nature of the object. The object appears almost stellar and slightly diffuse on Palomar Sky Survey prints. The source is identified as a Type 1.5 Seyfert with broad and narrow line components of redshift 0.016 + or - 0.001, according to H-Beta line profile. In addition, the broad line component H-Beta equivalent width is larger than that of the narrow line component by a factor of three. Finally, it is shown that this is a weak radio source with a steep nonthermal spectrum and an angular extent of approximately 3 in., and the composite radio-to-X-ray spectrum suggests that in different spectral regions, different relativistic electron populations or emission mechanisms are contributing factors.

Ghigo, F. D.↗

NASA NTRS1982

IUE observations of the 1981 outburst of nova Cr A

Low dispersion spectrum observations are analyzed. The light curve of nova Cr A, indicating a moderately fast nova, is presented. Flux calibrated, merged spectrum graphs of April 21, 1981 and September 13, 1981 are presented, demonstrating very strong lines of Al and Si. Additional strong C, Ni, O, and Ne emission lines were identified. Emission lines due to highly ionized species such as Mg VII and Al Vl were observed for short times in May and June 1981. Preliminary analysis of spectra obtained 200 days after maximum indicate that the nebula is still in transition and has not yet reached the nebula state. An over abundance of N and Ne are suggested.

Sparks, W. M.↗

NASA NTRS1981

Ground-based cometary spectroscopy

The observational problems presented by bright comets near perihelion are discussed. High and low resolution spectra (3100-800A) of the bright comets Kohoutek, Kobayashi-Berger-Milon, West and d'Arrest are presented. Digital reduction of calibrated photographic spectra to relative intensity versus wavelength, can provide useful information. The reduction of comet spectra to absolute intensities involves, however, large uncertainties and should be interpreted cautiously. Data on recent comets lead to the following results: tentative identification of a new ion in the tail of comets, namely, NH(+); spectroscopic resolution of the fragmented nucleus of comet West; and an accurate monochromatic intensity profile of the Co+ emission (4020A) in comet West.

Wyckoff, S.↗

NASA NTRS1976

H2O(+) ions in comets: Comet Kohoutek (1973f) and comet Bradfield (1974b)

The image tube Cassegrain slit spectra of comet Kohoutek and Bradfield calibrated and reduced to relative intensities are discussed. Monochromatic changes in the surface brightness for various neutral and ionized molecules are determined. The intensities of C2 and CN decreased approximately four times faster than the intensity change for the H2O(+) features. It is shown that the excitation mechanism for the observed H2O(+) bands is by fluorescent scattering of the incident solar radiation. The effects of solar activity on the photoionization rate of H2O in a comet are discussed. Observations of another bright comet at the time of maximum solar activity are needed to determine changes in band intensities of comet tail ions due to solar activity.

Wehinger, P.↗