W. V. Schempp

Digital array scanned interferometers for astronomy

We report investigations 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, we demonstrate spatially resolved spectra using a cylindrical lens to image in the interferometers redundant coordinate. We demonstrate enhanced spectral resolution with a band limiting filter and standard aliasing techniques. 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 spaceraft instruments.

The D/H ratio for Jupiter

Observations of Jupiters 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. 26 references.

A search for interstellar H2O(+) in diffuse clouds

Searches for H/sub 2/O/sup +/ toward HD 187982, zeta Oph, o Per, and zeta Per have yielded significant upper limits for H/sub 2/O/sup +/ when compared with existing models for similar lines of sight. Using available oscillator strength data, the column density for HD 18792, for example, cannot exceed 3 x 10/sup 12/ cm/sup -2/ H/sub 2/O/sup +/ molecules. Our most senstive measurement for H/sub 2/O/sup +/ toward zeta Oph is apparently limited by a blend with upper atmosphere H/sub 2/O/sup +/, which is also present in the HD 187982 spectrum.

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. 21 references.

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

Abstract We have detected the H 2 S 4 (2) feature in Jupiter. Using new low-temperature laboratory measurements for NH 3 , we have conducted a detailed analysis to determine an improved equivalent width for the Jovian H 2 S 4 (0) line. We have found good agreement of the equivalent widths computed from published models with the observed H 2 4−0 line equivalent widths for Jupiter. The effective line formation temperature of ∼150°K at the averaged disk center of Jupiter found from the nominal S 4 (2)/ S 4 (0) ratio is consistent with an H 2 ortho-para ration for equilibrium tropospheric H 2 in Jupiter.

Spectral imagery with an acousto-optic tunable filter

The authors have fabricated a spectral imager for astronomy and aeronomy using collinear or non-collinear acousto-optic 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. They demonstrate some typical observational applications of acousto-optic tunable filters used in several configurations at astronomical telescopes.

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. 20 references.

[OI] in Comet Halley

Abstract Long slit spectra centered on the nucleus of Comet Halley were obtained on 5 April 1986 at 200 mA spectral resolution with a spatial resolution of 1″ along the 70″ long slit. The spectra show an emission feature at 5577 A, the wavelength of the green [OI] line. This feature at 5577 A has a spatial variation closely similar to the [OI]6300-A line, but not the nearby C 2 bandhead. If it is assumed that the cometary [OI] feature at 5577 A should have the same spatial distribution as the cometary [OI] 6300-A line, then the 5577-A feature is at least partly due to oxygen. The data, then, indicate that the ratio of the [OI] 6300-A line to the [OI] 5577-A line is at least 10:1 which is not inconsistent with the M. C. Festou and P. D. Feldman (1981, Astron. Astrophys. 103, 154–159) model for H 2 O as the parent for the [OI] features.

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. 43 refs.

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.