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A set of restrictions upon the magnetic field and visible angular size of a canonical nonthermal source (one whose emission is incoherent electron synchrotron) has been obtained in another paper. The degree of electron anisotropy and magnetic field disordering were left as free parameters. In the present paper these restrictions are applied to the variable compact radio sources 3C 84, 3C 120, 3C 273, 3C 279, 3C 454.3, CTA 102, 3C 446, PKS 2134 + 004, VRO 42.22.01, and OJ 287. The theoretically derived angular sizes for these sources are in reasonable agreement with published VLBI sizes, provided that the characteristic pitch angles are not extremely small. The magnetic field strengths determined from the degree of circular polarization are generally compatible with field strengths derived from the self-absorption and synchrotron self-Compton conditions, again provided that the pitch angles are not too small. It is argued that the self-absorption optical depth cannot be much less than unity near the low-frequency turnovers; otherwise, serious discrepancies with observation result.

In a previous paper, the PPN (parametrized post-Newtonian) formalism was used to analyze relativistic influences on stellar stability in nearly all metric theories of gravity. That analysis omitted all preferred-frame terms. In this paper, possible preferred-frame effects on stellar stability are examined and no new instabilities are found. Although terms linear in the preferred-frame velocity w (time-odd terms, analogous to viscosity and energy generation) change the shapes of the normal modes, their symmetry properties prevent them from changing the characteristic frequencies. Thus, no new vibrational or secular instabilities can occur. Terms quadratic in w do not change either the shapes of the normal modes or the characteristic frequencies for radial pulsations (except for the effects due to the renormalization of the gravitation constant which does not affect stability). Thus, they have no influence on radial stability. Terms quadratic in w do change both the normal modes and the characteristic frequencies of nonradial pulsations; but in the limit of a neutral mode these changes vanish.

Dicke has recently contested our statement in an earlier paper that faculae could account for a large part, if not all, of the solar oblateness signal measured by Dicke and Goldenberg in 1966. Using the facular oblateness signal published in our earlier paper and some hitherto unpublished data from his 1966 observations, he concludes that faculae account for only a small part (11%) of the observed excess oblateness. His analysis considers data only from a restricted 48-day sample and is based on the assumption that only the observed oblateness signal is subject to error. Our analysis considers data from all 64 days on which observations were made, and is based on the assumption that both the observed oblateness signal and the facular signal are subject to error. We find that faculae account for at least one-third to one-half of the observed excess oblateness, depending on whether 48 days or 64 days are used in the analysis.

This paper argues that the bridges and tails seen in some multiple galaxies are just tidal relics of close encounters. These consequences of the brief but violent tidal forces are here studied in a deliberately simple-minded fashion. Each encounter is considered to involve only two galaxies and to be roughly parabolic; each galaxy is idealized as just a disk of noninteracting test particles which initially orbit a central mass point. As shown here, the two-sided distortions provoked by gravity alone in such circumstances can indeed evolve kinematically into some remarkably narrow and elongated features. Besides extensive pictorial survey of tidal damage, this paper offers reconstructions of the orbits and outer shapes of four specific interacting pairs: Arp 295, M51 + NGC 5195, NGC 4676, and NGC 4038/9.

The long-period V/R emission variations in three Be stars, HD 20336, 25 Ori, and beta-one Mon have been studied according to the mathematical formulation of the eccentric rotating model presented in a previous paper. The predictions of the theory fit satisfactorily the general trend of observed data. Periods, eccentricities, and sizes of the emitting ring with respect to the stellar radius are thereby derived and found to be consistent with results of the previous investigation of 105 Tauri.

This paper presents the observational results of a high spatial-resolution mapping and photometric study in the wavelength range from 1.65 to 20 microns of four H II regions and seven OH sources. Infrared emission indicative of the presence of heated dust was found from the compact H II condensations in W51, DR21, and NGC7538. Infrared emission was also found from the positions of maser sources in NGC 7538, W75(N) W75(S) and Sharpless 269, but not from that in W51. An extended infrared source was found coincident with the peculiar OH source OH 0739-14.

Infrared excess based on the disk model proposed in a previous paper was computed. It was found that the disk alone will emit infrared radiation below the margin of detection. However, if individual condensations are present, the combined result of the disk proper and the condensations yields results of infrared excesses that are consistent with observations. The presence of condensations also makes the secondary light variation understandable. An elementary theory is developed that analyzes such light variations. The result of the analysis yields the size of the orbit of the condensation around the secondary component.

Discussion of some limitations on synchrotron models for optical pulsars and compact extragalactic objects. Using the results of a previous paper, it is shown that several existing models for the pulsar NP 0532 are inconsistent with the measured time variations and polarization of the optical emission. The possibility that the low-frequency falloffs in some extragalactic objects (PKS 2134 + 004, OQ 208, and NGC 1068) could be due to emission from particles with small pitch angles, absorption by a thermal plasma, or synchrotron self-absorption is also considered. It is found that radiation by particles with small pitch angles could explain the radio emission from PKS 2134 + 004 and OQ 208, but this process is inconsistent with the observations of NGC 1068. The absorption interpretations cannot account for the turnover in the spectrum of PKS 2134 + 004.

This paper discusses what can happen to clouds as they move from arm regions to interarm regions, through a density-wave shock, and back to arm regions again. Shu et al. (1972) have taken the viewpoint that interstellar clouds will survive the trip between arms. Biermann et al. (1972) have taken the viewpoint that they will not. We shall point out that cloud-cloud collisions and other processes may lead to the destruction of interstellar clouds in less time than the 100 m.y. it takes clouds to travel across arms. A possible observational test is suggested to distinguish between the two possibilities.

The seventh Orbiting Solar Observatory, OSO-7, carries an X-ray detector for measuring the positions, spectra, and time variations of X-ray sources in the energy range from 1 to 60 keV. The instrument has operated successfully since the launch on 1971 September 29. The purpose of this paper is to describe the instrument and to report a measurement of the spectrum of Tau X-1 based on data covering the widest energy range that has so far been observed in a single experiment.

For solar system bodies with little or no atmosphere, a linear relation exists between the depth of the negative polarization branch and the reciprocal of the geometric albedo. Considered in this fashion, the polarization data for Iapetus imply an albedo difference by about a factor of 6 between its leading and trailing hemispheres, and are consistent with the amplitude of the light curve for Iapetus. The brightness of the satellite at any particular maximum or minimum is unpredictable by a certain factor because of inadequately understood variations in solar phase angle and rotation. Although other measurements of the Iapetus albedos give results different from those in the presented paper, it is still clear that the two hemispheres have very different albedos.