Engineering topics

Carleton, N. P.

Publications and source records attributed to Carleton, N. P..

At least 19 records

NASA NTRS1990

Spectral dispersion and fringe detection in IOTA

Pupil plane beam combination, spectral dispersion, detection, and fringe tracking are discussed for the IOTA interferometer. A new spectrometer design is presented in which the angular dispersion with respect to wavenumber is nearly constant. The dispersing element is a type of grism, a series combination of grating and prism, in which the constant parts of the dispersion add, but the slopes cancel. This grism is optimized for the display of channelled spectra. The dispersed fringes can be tracked by a matched-filter photon-counting correlator algorithm. This algorithm requires very few arithmetic operations per detected photon, making it well-suited for real-time fringe tracking. The algorithm is able to adapt to different stellar spectral types, intensity levels, and atmospheric time constants. The results of numerical experiments are reported.

Traub, W. A.↗

NASA NTRS1987

The continuum of type 1 Seyfert galaxies. I - A single form modified by the effects of dust

Broad-band measurements from 1 to 20 microns of 26 emission-line active galactic nuclei (AGNs), mainly Seyfert 1 galaxies, have been made. These data have been combined with previous optical and infrared photometry and IRAS 12, 25, 60 and 100 micron fluxes, giving a total sample of 37 AGNs, all of which have hard X-ray measurements. The sample includes all the emission-line AGNs identified in the Piccinotti et al. (1982) survey. When corrected for stellar contributions in the near-infrared, the continuum energy distributions can be classified observationally into three types: (1) bare, minimally reddened AGNs; (2) reddened AGNs; and (3) AGNs for which the far-infrared emission is contaminated by the host galaxy. These classifications reflect a range of luminosities and different environments rather than intrinsic differences in the primary continuum of the AGNs. The data are consistent with a single underlying form of active galaxy continuum modified by the presence of dust and of the host galaxy.

Ward, Martin↗

NASA NTRS1985

Seyfert galaxy narrow-line regions. I - Observations of forbidden O III lambda 5007

High-resolution (23 km/s) spectra of the forbidden O III emission line at 500.7 nm from the nuclear regions of 32 Seyfert galaxies and low-redshift QSOs have been obtained at the Smithsonian Institution/University of Arizona Multiple Mirror Telescope. The properties of the data are summarized by a group of measures which efficiently describe the entire line profiles, are stable in the presence of noise, and have easily visualized geometric meaning. The distributions of line profile measures are shown. In particular, typical forbidden O III FWHM values of 200-520 km/s (mean + or - 1 sigma) and a highly significant tendency for the lines to fall off more slowly on the blue than on the red side of the peak have been found, in agreement with previous work. Using galaxian system velocities obtained from absorption-line measurements, the distribution of differences between forbidden O III emission-line velocities and galaxian system velocities has been determined; in disagreement with previous work, this distribution has been found to be consistent with symmetry about zero difference velocity.

Vrtilek, J. M.↗

NASA NTRS1985

Observations from 1 to 20 microns of low-luminosity active galaxies

The 1-20 micron photometry of Liners (Low Ionization Nuclear Emission-line Regions), star burst nuclei, and high-excitation (mostly Seyfert 2) nuclei are presented and discussed. Liners have strong, flattish 10-20 micron excesses but are dominated by a stellar population through 1-5 micron. By contrast, most type 2 Seyfert galaxies and all star-burst nuclei have flux distributions that are flat through 1-5 microns, and steeply rising through 10-20 microns. The 1-5 micron flux distributions of type 2 Seyfert galaxies and starburst nuclei can be explained by mixtures of stellar emission, recombination radiation, and hot dust, although a nonthermal component is likely in a few objects. One Liner, NGC 3079, was found to be extended to 10 microns. A map which shows the 10-micron and optical maxima to differ by 6 arcsec is presented.

Lawrence, A.↗

NASA NTRS1985

COSMIC: A high resolution, large collecting area telescope

The spaceborne Coherent Optical System of Modular Imaging Collectors (COSMIC) is presented. It has high angular resolution and can produce images of complex, low-surface-brightness objects such as distant galaxies. If configured as a 36 m filled linear array, COSMIC can have 15 times better angular resolution and 10 times greater collecting area than the Space Telescope. Alternatively, if the collecting area is spread out to create an unfilled two-dimensional array, there is the additional advantage of not needing to rotate the array in order to build up a reconstructed image. Considerations which led to the design concept, scientific goals, and the potentially useful role of a space station for assembly are discussed.

Traub, W. A.↗

NASA NTRS1984

1-20 micron infrared photometry of 3CR radio galaxies

Seven emission-line radio galaxies in the wavelength range from 1 to 20 microns were observed in February 1983. Three broad emission-line galaxies (BLRGs 3C 109, 3C 234, and 3C 445), and four narrow emission-line radio galaxies (NLRGs 3C 98, 3C 198, 3C 223, and 3C 293) were found. The BLRGs showed strong infrared fluxes beyond 3.5 microns, with steep infrared slopes similar to optical slopes. In a comparison with earlier observational data it was found that two of the BLRGs are variable in the JHK filter range without a change of slope. The NLRGs showed strong excess at 10 microns and normal elliptical galaxy colors at JHK and L. Simple predictions based on type-2 Seyfert galaxies show that strong infrared excesses are absent.

Elvis, M.↗

NASA NTRS1983

Methane on Triton and Pluto - New CCD spectra

Spectra of Triton and of Pluto from 4553-9558 A at 25 A resolution are presented. Both spectra show the methane absorption near 8900 A; its equivalent width was 16 times greater on Pluto than on Triton at the time of the observations. This is the first published observation of the 8900 A feature in Triton's spectrum. The previously reported 27 m-amagat abundance of the Pluto atmosphere ignored contributions due to methane ice and should therefore be regarded as an upper limit. The observations of the Pluto spectrum discussed here show sharp structure in the 8900 and 8600 A bands; the case for an atmosphere on Pluto may turn on whether new laboratory measurements show that such structure is present in methane ice.

Apt, J.↗

NASA NTRS1982

Use of a Fourier transform spectrometer on a balloon-borne telescope and at the multiple mirror telescope (MMT)

The design and use of an infrared Fourier transform spectrometer which has been used for observations of laboratory, stratospheric, and astronomical spectra are described. The spectrometer has a spectral resolution of 0.032/cm and has operated in the mid-infrared (12 to 13 microns) as well as the far-infrared (40 to 140 microns), using both bolometer and photoconductor cryogenic detectors. The spectrometer is optically sized to accept an f/9 beam from the multi-mirror telescope (MMT). The optical and electronic design are discussed, including remote operation of the spectrometer on a balloon-borne 102-cm telescope. The performance of the laser-controlled, screw-driven moving cat's-eye mirror is discussed. Segments of typical far-infrared balloon flight spectra, lab spectra, and mid-infrared MMT spectra are presented. Data reduction, interferogram processing, artifact removal, wavelength calibration, and intensity calibration methods are discussed. Future use of the spectrometer is outlined.

Traub, W. A.↗

NASA NTRS1979

O2/1 Delta/ emission in the day and night airglow of Venus

An intense airglow from O2(1 Delta) at 1.27 microns on both the light and the dark sides of Venus has been detected by using a ground-based high-resolution Fourier-transform spectrometer. Both dayglow and nightglow are roughly 1,000 times brighter than the visible O2 nightglow found by Veneras 9 and 10 in 1975. The column emission rate of O2(1 Delta) from Venus is close to the rate at which fresh O atoms are produced from photolysis of CO2 on the day side. Formation of O2(1 Delta) is thus a major step in the removal of O atoms from the atmosphere, and dynamical processes must carry these atoms to the night side fast enough to yield a maximum density near 90 km, which is almost constant over the planet.

Connes, P.↗

NASA NTRS1979

The latitude variation of O2 dayglow and O3 abundance on Mars

Spectroscopic observations of the Martian O2 dayglow near 1.27 microns directly show that the parent molecule, O3, has a strong latitude variation. These measurements give actual data on the equatorial concentrations, where Mariner gave only upper limits. The data also agree with a recent photochemical model, and the derived atmospheric temperature is in good agreement with this model.

Traub, W. A.↗

NASA NTRS1979

Retrograde winds on Venus - Possible periodic variations

Spectroscopic observations of the differential Doppler shift in a CO2 absorption line on Venus show that the upper atmospheric wind near the equator appears to have both a retrograde motion of about -85 + or - 10 m/s (confirming previous results) and, in addition, a periodically varying component, with an amplitude of about 40 + or - 14 m/s and a period of 4.3 + or - 0.2 days.

Traub, W. A.↗

NASA NTRS1976

Detection of O2 dayglow emission from Mars and the Martian ozone abundance

High-resolution spectroscopy of Mars in the vicinity of 1.27 microns has revealed the presence of emission lines of O2 which are interpreted as the result of production of O2(1 delta g) in the ultraviolet photolysis of Martian ozone. In the equatorial region of Mars, the dayglow intensity implies an ozone abundance near 0.2 microatm, which seems consistent with theoretical models which utilize the measured water-vapor abundance. A much larger ozone abundance exists in the atmosphere at high winter latitude, in agreement with direct measurement of ozone absorption performed by the Mariner spacecraft.

Noxon, J. F.↗

NASA NTRS1975

Spectroscopic observations of winds on Venus

Measurements of the differential Doppler shift between various points on Venus using a high-resolution PEPSIOS interferometer. Using both a CO2 line and a Fraunhofer line a mean zonal-wind velocity of about -83 m/s is found near the equator; the velocity appears to vary from about -2 to -125 m/s with a time scale of greater than one week. Meridional velocities are measured to be weak. The equatorial zonal velocity appears to be smaller in the 'morning' than in the 'afternoon'. A comparison with reported velocities of the ultraviolet dark markings reveals general agreement in that both find the motion to be retrograde, variable, and accelerated during the day. A new potential source of systematic error in all spectroscopic determinations of the differential Doppler shift of nonuniformly illuminated objects is pointed out.

Traub, W. A.↗

NASA NTRS1974

A search for H2O and CH4 in Comet Kohoutek

A spectroscopic search for H2O and CH4 in Comet Kohoutek (1973f) was made using a Pepsios interferometer. No evidence was found for either molecule, allowing to set an upper limit on their production rates (on about Jan. 21, 1974) of Q(H2O) less than 6.2 times 10 to the 28th power per sec and Q(CH4) less than 20 times 10 to the 30th power per sec.

Traub, W. A.↗

NASA NTRS1974

Cosmic background radiation at 1.32 millimeters

The R(2) line of the 3874 A band of interstellar CN toward zeta Oph was measured. An equivalent width of 0.120 mA implying an R(2)-R(1) rotational temperature of about 3.1 K was observed. Taking into account also earlier observations, it is found that the R(2) equivalent width is about 0.089 mA. The results imply a temperature of about 2.9 K for the cosmic background radiation at 1.32 mm.

Hegyi, D. J.↗

NASA NTRS1974

Search for deuterium in Orion and detection of high-velocity features

Results of a search for D alpha emission near the bright H alpha line in Orion. The observations revealed a high-velocity H alpha feature near -60 km/sec, whose intensity varied across the nebula, ranging from 0.005 to 0.005 relative to H alpha; another much weaker feature, possibly also H alpha, was observed at about -100 km/sec. Because these high-velocity H alpha features partially overlap the expected position of D alpha, only an upper limit D/H less than .00013 for the number ratio in Orion can be derived.

Traub, W. A.↗

NASA NTRS1973

Observation of HD on Jupiter and the D/H ratio.

The measurement of the HD (7467 A) 4-0 P(1) absorption line on Jupiter was carried out during integration times on an off-axis PEPSIOS spectrometer with a resolution exceeding 100,000. A nearly model-independent number ratio D/H was determined for the Jovian atmosphere by comparing the results with the H2 (6367 A) 4-0 S(1) line.

Trauger, J. T.↗

NASA NTRS1972

Detection of molecular oxygen on Mars.

Molecular oxygen was detected in Martian spectra near 7635 A and its abundance was measured both during and after the 1971 dust storm. Its column abundance in the clear Martian atmosphere is about 10.4 plus or minus 1.0 cm/amagat, giving a mixing ratio of molecular oxygen to carbon dioxide 0.0013. The mixing ratio of molecular oxygen to carbon monoxide (1.4 plus or minus 0.3) is quite different from the value of 0.5 that would result from the photolysis of a pure carbon dioxide atmosphere, which indicates that there is or was a net source of oxygen relative to carbon (probably water) in the Martian atmosphere.

Carleton, N. P.↗