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Landau, R.

Publications and source records attributed to Landau, R..

6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Mercury - Wavelength and longitude dependence of polarization

The polarization-time variations noted in the present linear polarization observations of the integrated Mercury disk, with filters covering the 0.3-1.0 micron bandpass and between 53-130 deg of phase angle, may be accounted for in terms of longitude dependence through the variation of brightness or other properties over the surface. Kepler's equation for the eccentric anomaly was solved for each observation, and the true anomaly was used to find the subsolar longitude. The difference found in the polarization-albedo relations of Mercury and the moon indicates a difference in surface texture and/or composition.

Gehrels, T.↗
NASA NTRS1986

Active extragalactic sources - Nearly simultaneous observations from 20 centimeters to 1400 A

IRAS, IUE, and ground-based optical, NIR, mm and submm, and radio observations obtained mainly on Apr. 9-23, 1983, are reported for 19 active extragalactic sources and eight control sources. The overall spectra of the compact active sources are shown to be well represented by continuous-curvature functions such as parabolas. The spectra are found to be consistent with models involving continuous particle injection (with synchrotron losses) or first-order Fermi acceleration (with escape and synchrotron losses), but not with models using relativistic Maxwellian electron distributions.

Landau, R.↗
NASA NTRS1984

Data compression techniques for astronomy

The photometric and astrometric accuracy of the Minnesota automated dual-plate scanner is summarized. The relation between magnitude and isophotometric image diameter is linear on Schmidt plates over a large useful range. Results of a study of centroid measurement accuracy and image classification ability of parameters derived from both densitometric and isophotometric scanning techniques are presented. The data analyzed for this purpose are synthesized ideal star and galaxy brightness distributions with appropriate random noise added to simulate plate grain and sky background effects. A preliminary study of image classification using real plates and single isophote data finds that a parameter describing the raggedness of the isophote may be useful in distinguising stars from galaxies.

Landau, R.↗
NASA NTRS1984

Techniques of isophotometry

The expected performance of the Minnesota automated dual-plate scanner (APS) is discussed with regard to photometry, position measurement accuracy, and ability to classify images. In addition, a fast algorithm for calculating image parameters is described.

Ghigo, F. D.↗
NASA NTRS1983

Extragalactic 1 millimeter sources - Simultaneous observations at centimeter, millimeter, and visual wavelengths

Observations simultaneously made at visual (B, V, and R) wavelengths, at 1, 1.4, and 3.4 mm and at 1.3, 2, 6, and 20 cm of 9 QSOs and BL Lac objects are reported. The range of the millimeter-visual spectral index alpha sub mv was only 0.65-0.82, typical of optically thin synchrotron emission. This may indicate that the electrons radiating synchrotron emission in this portion of the spectrum are not subjected to large radiation losses, and therefore relativistic bulk motion with Doppler factors of about 10 are required. The visual spectral index is much more broadly distributed and typically larger than alpha sub mv. The spectral energy distributions have not changed much in the last two to five years except for 2251+15 and perhaps 0235+164. Only 1749+09 shows a sharp spectral break shortward of 1 mm. Sixteen other sources were observed at 1 mm, of which seven were detected.

Landau, R.↗