Abstract: We have detected a pulsar with a pulsation period that varies systematically between 0.058967 and 0.059045 sec over a cycle of 0.3230 d. Approximately 200 independent observations over 5-minute intervals have yielded a well-sampled velocity curve which implies a binary orbit with projected semimajor axis sin i = 1.0 solar radius, eccentricity e = 0.615, and mass function f(m) = 0.13 solar mass. No eclipses are observed. We infer that the unseen companion is a compact object with mass comparable to that of the pulsar. In addition to the obvious potential for determining the masses of the pulsar and its companion, this discovery makes feasible a number of studies involving the physics of compact objects, the astrophysics of close binary systems, and special- and general-relativistic effects.

Abstract: We examine what mass spectrum of primordial black holes should result if the early universe consisted of small density fluctuations superposed on a Friedmann background. It is shown that only a certain type of fluctuation favors the formation of primordial black holes and that, consequently, their spectrum should always have a particular form. Since both the fluctuations which arise naturally and the fluctuations which are often invoked to explain galaxy formation are of the required type, primordial black holes could have had an important effect on the evolution of the universe. In particular, although primordial black holes are unlikely to have a critical density, big one could have been sufficiently numerous to act as condensation nuclei for galaxies. Observational limits on the spectrum of primordial black holes place strong constraints on the magnitude of density fluctuations in the early universe and support the assumption that the early universe was nearly Friedmann rather than chaotic. Any model in which the early universe has a soft equation of state for a prolonged period is shown to be suspsect, since primordial black holes probably form too prolifically in such a situation to be consistent with observation. (AIP)

Abstract: The spectrum of X-rays produced by an accretion disk around a black hole is influenced markedly by Doppler shifts, gravitational redshifts, and the gravitational lens effect. These influences can be described by a ''transfer function,'' which one folds into any assumed spectrum emitted on the disk's surface to get the spectrum observed at various locations far from the disk. This paper formulates such a transfer function and tabulates it for Kerr black holes of a/M=0 and 0.9981. The transfer function depends strongly on the polar angle of the observer: An observer near the plane of the disk sees radiation from its hot inner regions to be less reshifted and to subtend a greater solid angle than does an observer near the disk's polar axis. Consequently, the equatorial observer sees a much harder spectrum at high energies than does the polar observer. This effect is more pronounced for black holes of larger angular momentum. (AIP)

Abstract: It appears to be very unlikely that primordial binaries in globular clusters have evolved to produce high-luminosity X-ray sources like the four variable sources detected by the Uhuru and OSO-7 satellites. It is suggested that the cluster X-ray sources are binaries formed by capture from the remnants of massive single stars that exploded with sufficient isotropy to remain bound in the cluster. These remnants have lurked near the centers of the clusters where the high stellar densities have favored their capture of field stars which eventually turn the remnants on as X-ray sources when the captives enter the post-main-sequence expansion phase of their evolution. A case is made for the conclusion that there is approximately one potential binary X-ray source near the center of each of the globular clusters.

Abstract: Dynamo waves, as solutions of the dynamo equations governing the solar cycle, propagate along isorotation surfaces inside the Sun. This theorem, universal in most dynamo models of the solar cycle, is proven analytically, and the nature of the propagation is analyzed. The effects of meridional circulation and the diffusion process on the propagation nature of the dynamo waves are estimated. The importance of this theorem is stressed for understanding the solar cycle and for inferring the rotational law of the interior of the Sun. (AIP)

Abstract: Isolated giant galaxies may accrete their dwarf companions, and those in clusters their neighbors, by the process of dynamical friction. The computed effect is of the opposite sign and similar magnitude to the luminosity change caused by normal stellar evolution. The process, which would cause an increase in $delta$M$sub 12$ (the magnitude difference between first and second brightest cluster galaxies) with time, may be visible in the tabulated data of Sandage and Hardy (1973). Cosmological investigations could compensate for the postulated effect, if fainter galaxies were used as well as first brightest cluster galaxies in the magnitude-redshift test. (AIP)

Abstract: An empirical relation between interstellar X-ray absorption and optical extinction is derived from the correlation of measurements made on objects of large intrinsic diameter. The result is Av = 4.5 times 10 to the -22nd power N(H) mag, with the principal error being largely systematic in origin, where N(H) represents the column density of interstellar matter in the Brown and Gould model for the X-ray absorption coefficient. Applying this ratio to optically identified compact sources, it is concluded that sources in binary systems showing pronounced X-ray occultations have an intrinsic absorption equivalent to about 10 to the 22-nd power atoms per sq cm of interstellar matter and that there are a few compact sources where the absorption seems to be primarily interstellar in origin. The interstellar absorption expected in Cyg X-1 from the extinction of its optical counterpart is much greater than that suggested by X-ray spectra, which may be due to a soft X-ray component greater than that predicted by the power law fitted to higher energy data.

Abstract: The rotation curve, up to 0/sup prime/.6 from the center, has been derived from Ca ii H and K lines for the elliptical galaxy NGC 4697. A maximum seems to be reached at 15'' with 65 km s$sup -1$. The same galaxy has been investigated by means of photographic photometry in the B system. The luminosity profile follows the r$sup 1$/$sup 4$ law, and the mean ellipticity is 0.4. The total apparent magnitude is B=10.30 mag, and the corresponding absolute magnitude reaches M/subB/=20.5 magn assuming a distance of 14.8 Mpc. The spatial velocity curve and the light density profile are derived. Mass and angular momentum have been computed on the hypothesis that the mass-to-light ratio is constant through the galaxy, leaving it as a free parameter. Under several assumptions it is found that the angular momentum of the elliptical NGC 4697 is lower than that of a spiral of comparable mass by a factor 5 to a factor 30, when the mass-to-light ratio varies from 5 to 50. (AIP)

Abstract: The general problem of a supernova explosion in a binary star system is studied. We show that to a good approximation the effect of the impinging blast wave which strips and ablates mass from the companion can be expressed in terms of a single parameter. The eccentricity imparted to the system and the ratio of final to initial semimajor axes depend on two to six parameters, depending on the level of approximation. Results for calculations of the eccentricity imparted to an initially circular system are presented by means of graphs, tables, and simple fitting formulae for two basis types of models; one in which the companion is a ''normal'' star (polytrope, n=3) and one in which the companion is in a ''red- giant'' phase.

Abstract: The equation of radiative transfer in the comoving frame makes possible an economical solution of the line formation problem in spherical atmospheres expanding with arbitrarily large velocities A stable differencing scheme and a frequency-by-frequency elimination procedure have been developed to solve the partial differential equations that describe the radiation field in the comoving frame Numerical results were obtained for a large number of illustrative models involving line formation by two-level atoms, electron scattering, and continuous absorption Selected results that simulate situations in the stellar winds of hot stars and similar objects are discussed In addition to P Cygni and other very broad profiles, extreme center-to-limb variations are obtained that show both limb darkening and limb brightening For very high velocity flows with very weak or nonexistent continuum and electron-scattering opacities, the flux profiles are very nearly symmetric about the laboratory wavelength and have shapes reminiscent of those observed in the nuclei of Seyfert galaxies Comparisons are presented between the results of Sobolev-type escape probability calculations and those obtained here The force of radiation on the gas is examined in a number of situations; the mechanism mentioned by Noerdlinger and Rybicki for the disruption of radiatively driven envelopes in planar geometriesmore » is shown to become inoperative for even slightly extended spherical systems« less

Abstract: The solar chromosphere at the limb seen in D3 is an irregular bright band 1000 km thick with a dark band 1000 km thick beneath. The D3 chromosphere disappears in coronal holes. It is shown that the D3 emission, as well as the other He I and He II lines, can be explained quantitatively by photoionization by coronal back-radiation. A Chapman layer with N(He)H = 5 times 10 to the 17th power is formed near tau = 1 in the He I and He II continua. The chromospheric He emission or absorption is weak in coronal holes because there is no coronal back-radiation. Based on this model, the soft X-ray flux from stars with He 10830-A absorption lines is estimated as proportional to the 10830-A equivalent width and the apparent area.

Abstract: A method is described for the numerical calculation of the hydrodynamic evolution of a self-gravitating configuration in two space dimensions with assumed axial symmetry. The calculation is formulated in cylindrical coordinates with respect to a moving Eulerian grid and is solved using explicit hydrodynamics combined with implicit radiative transfer. The physics included is appropriate for calculation of the collapse of a rotating protostellar cloud. The gravitational field is obtained by means of an alternating-direction iterative technique. Numerical tests to demonstrate the correctness of the method are presented for special cases.

Abstract: The Markov approximation to the propagation of waves in an extended, irregular medium is discussed in an astrophysical context. A new derivation is presented which is simple and which shows that the assumption of Gaussian statistics used by previous authors is irrelevant. We discuss the relevance of the approximation and show that it may apply in many situations of interest, including interstellar scintillations of pulsar signals. The approximation does not require the assumption of weak scattering or Gaussian correlation functions. The Markov equation for the angular spectrum is particularly simple, and solutions are discussed for typical turbulence spectra. It is found that the equation for the angular spectrum is very nearly that used by previous authors, and the present discussion shows that these results are much more general than previously thought. A possible observational test for distinguishing between Gaussian and power-law interstellar density spectra is discussed.

Abstract: We calculate neutron star models using four realistic high-density models of the equation of state. We conclude that the maximum mass of a neutron star is unlikely to exceed 2 M/sub sun/. All of the realistic models are consistent with current estimates of the moment of inertia of the Crab pulsar.

Abstract: An experiment to determine the relative bending of microwave radiation from three radio sources (0116+08, 0119+11, and 0111+02) as they passed near the Sun was performed with a radio interferometer of baseline 35 km in 1974 March and April. The measured bending in terms of that at the solar limb is 1/sup double- prime/./sub /775plus-or-minus0/sup double-prime/./sub /019 (standard error), or 1.015plus-or-minus0.011 times the Einstein prediction of general relativity. The result is not consistent with the scalar-tensor formulation of general relativity with a scalar-coupling constant $omega$<23.