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Schempp, W. V.

Publications and source records attributed to Schempp, W. V..

13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Digital array scanned interferometers for astronomy

Investigations are reported of digital array scanned interferometers (DASI) with silicon CCD array detectors to define the operational capabilities of a mapping (polarimetric) spectrometer for astronomical applications based on these instruments. For spectral mapping, spatially resolved spectra using a cylindrical lens to image in the interferometers's redundant coordinate are given. The signal-to-noise characteristics of the Fourier transformed data are demonstrated with regard to the effects of a rectangular sampling function, spectral multiplexing and the pixel-to-pixel variation of the CCD array. These data indicate that DASIs can offer simple, versatile (polarization) mapping spectrometers suitable for spectral mapping observations from the ultraviolet to the infrared of extended sources at variable spatial resolution, particularly where long term stable operation is essential, as for spacecraft instruments.

Smith, Wm. Hayden↗
NASA NTRS1989

O I concentration in Comet Halley

The present 200-mA spectral resolution and 1-inch spatial resolution long-slit spectra centered on Comet Halley's nucleus show an emission feature at the 5577 A wavelength of the green O I line whose spatial variation is very similar to that of the O I 6300-A line, but not the C2 bandhead nearby. On the assumption that the cometary O I 5577 A feature should share the cometary O I 6300-A line's spatial distribution, the 5577-A feature becomes at least partly attributable to oxygen; the ratio of the 6300-A line to the 5577-A line is then of the order of 10:1, which is consistent with the Festou and Feldman (1981) model in which water is the parent for the O I concentration features.

Smith, W. Hayden↗
NASA NTRS1989

The H2 4-0 S(0, 1, and 2) quadrupole features in Jupiter

In the wake of the detection of Jupiter's H2 S4(2) feature, low-temperature laboratory measurements of NH3 are used in a detailed analysis to ascertain an improved equivalent width for the H2 S4(0) line. Good agreement is obtained between equivalent widths computed from published models and the equivalent widths observed for this line. It is noted that the approximately 150 K effective formation line temperature at Jupiter's averaged disk center, which has been determined from the nominal S4(2)/S4(0) ratio, is in keeping with an H2 ortho-para ratio for Jovian equilibrium tropospheric H2.

Smith, Wm. Hayden↗
NASA NTRS1989

Limits on the diurnal variation of H2 quadrupole features in Neptune

Spectral profiles of the H2 S4(0) and S4(1) lines are presented for Neptune on three consecutive nights; no variation is detected in the equivalent widths of the H2 4-0 features to within an observational uncertainty of about 20 percent. Comparisons with previous H2 quadrupole observations indicate that no secular trends have been detected over about 15 yr. The equivalent-width error limits are interpreted in terms of the maximum variability of Neptunian tropospheric aerosols. Specifically, the error bars for the globally averaged equivalent widths of the two H2 quadrupole absorption features constrain the bottom of the visible atmosphere, as defined by a bright optically infinite isotropically scattering cloud, to be 2.9 + or - 0.6 bars, while the methane haze opacity is constrained to be 0.30 + or - 0.25.

Smith, Wm. Hayden↗
NASA NTRS1989

A search for K I in absorption in Comet Giacobini-Zinner

Spectra through the coma of P/Giacobini-Zinner toward the star SAO 035030 have been obtained during a close apulse. K I is searched for, and a 3-sigma upper limit of 3 x 10 to the 10th/cu cm at a distance of about 1500 km from the nucleus is found. This corresponds to a column abundance for Na I of less than 2 x 10 to the 11th/sq cm, assuming a solar abundance ratio for Na/K. The observations are not yet sufficiently sensitive to constrain either Na or K abundances, but a case is made from these data that such observations are feasible for the brighter periodic comets.

Schempp, W. V.↗
NASA NTRS1989

D/H for Uranus and Neptune

Searches for absorption features of HD near 6050 A are reported for Uranus and Neptune. The existence of blends of the HD features with weak features due to minor species in the atmosphere of Uranus is demonstrated. These blends make the unambiguous identification of the weak HD features exceedingly difficult. The data are analyzed with inhomogeneous scattering models to ascertain a D/H upper limit for Uranus and Neptune of 0.0001, a factor of 2 smaller than the upper limit reported from CH3D measurements.

Smith, Wm. Hayden↗
NASA NTRS1989

The D/H ratio for Jupiter

Observations of Jupiter's spectrum near the R5(0) HD line at 6063.88 A are reported. A feature with an equivalent width of 0.065 + or - 0.021 mA is coincident with the expected line. This feature is compared with HD profiles computed for inhomogeneous scattering models for Jupiter to yield a range for the Jovian D/H ratio of 1.0-2.9 x 10 to the -5th. This D/H ratio is in the lower range of previously reported D/H values for Jupiter and corresponds to an essentially solar D/H ratio for Jupiter. The detection of HD features in the presence of probable blends with spectral features of minor atmospheric hydrocarbon molecules is discussed. Such blends may make unambiguous identification of HD features difficult.

Smith, Wm. Hayden↗
NASA NTRS1987

Spectral imagery with an acousto-optic tunable filter

.A spectral imager for astronomy and aeronomy has been fabricated using collinear or non-collinear acoustooptic tunable filters (AOTFs). The AOTF provides high transparency, rapid tunability over a wide wavelength range, a capability of varying the bandwidth by more than an order of magnitude, high etendue, and linearly polarized output. Some typical observational applications of acoustooptic tunable filters used in several configurations at astronomical telescopes are demonstrated.

Smith, W. Hayden↗
NASA NTRS1985

On the detection of rubidium in diffuse interstellar clouds

A search for absorption from neutral rubidium at 7800 A was conducted. No evidence for absorption to a 3 sigma limit of less than 1.5 mA was seen in the diffuse interstellar gas toward the stars omicron Persei, zeta Persei, and zeta Ophiuchi. Present results do not confirm the detection by Jura and Smith (1981) toward zeta Oph. A possible reason for the discrepancy is presented. In light of the present measurements, the abundance of interstellar rubidium in reconsidered.

Federman, S. R.↗
NASA NTRS1984

A search for interstellar H2O(+) in diffuse clouds

Searches for H2O(+) toward HD 187982, Zeta Oph, O micron Per, and Zeta Per have yielded significant upper limits for H2O(+) when compared with existing models for similar lines of sight. Using available oscillator strength data, the column density for HD 187982, for example, cannot exceed 3 x 10 to the 12th per sq cm H2O(+) molecules. The most sensitive measurement for H2O(+) toward Zeta Oph is apparently limited by a blend with upper atmospheric H2O(+), which is also present in the HD 187982 spectrum.

Federman, S. R.↗
NASA NTRS1983

High-resolution observations of the 6815-A band of methane in the major planets

High-resolution (0.1-A) spectra of the 6815-A band of methane are presented for Jupiter, Saturn, Uranus, and Neptune. Spectra for Uranus, Neptune, and the equatorial region of Saturn were acquired with the SPIFI (Smith, Hicks, and Born (1978) at the 2.2-m telescope of the Mauna-Kea Observatory during May and June 1980. Additional spectra were obtained for Jupiter and the northern temperate and polar regions of Saturn in December 1980 and January 1981 from Kitt Peak National Obsevatory's McMath Solar Telescope. The spectra show a dichotomy in strength of methane absorption between Jupiter-Saturn and Uranus-Neptune. A simple model analysis, based on homogeneous scattering models, is unable to resolve whether this dichotomy is due to an actual increase in the methane mixing ratio with solar distance or to the temperature dependence of line strengths and absorption pathlengths in these atmospheres. If the rotational quantum number for the prominent 6818.9-A feature is J less than 4, then significant aerosol extinction must exist within the visibly accessible portion of Uranus' atmosphere for the methane mixing ratio to be greater than the solar value.

Baines, K. H.↗
NASA NTRS1979

Jovian sodium emission from Region C2

Observations of emission from sodium presumed to have been ejected from Io in the orbital plane of the Gallilean satellites and extending outward to at least 35 Jupiter radii are reported. Spectra of the sodium D line were observed to have an intensity of 20 to 30 R. Mechanisms for the escape of sodium from Io after sputtering from the surface are: (1) ejection from Io at velocities greater than Jupiter escape velocity, (2) ejection at velocities corresponding to orbits with apoapses of 35 Jupiter radii, and (3) ionization followed by magnetic field sweeping and recombination. The relative contributions of each mechanism are estimated and used to predict the sodium emission intensity at 35 Jupiter radii to be 7 to 8 R, a value considered to be in reasonable agreement with observations. Observations of emission line width and the correlation of intensity with the orbital phase of Io would provide further means of evaluating the proposed mechanisms of sodium ejection.

Pilcher, C. B.↗