Showing papers in "The Astronomical Journal in 1974"
TL;DR: In this article, the authors consider the problem of determining the distribution of proper motions in a line-of-sight line of sight (LoSOS) image from a given number count.
Abstract: J q,•.=I:Pi,Vt;, i-I f \"'(~)d~=1 and \"'W~O of the variation of star density along a line-of-sight from the distribution of proper motions in that direction; (2) the determination of the space distribution of radio sources from number counts; (3) the determination of the radial variation of star density in a globular cluster from star counts; (4) the correction of radioastronomical and spectrographic observations for the effect of the instrumental profile; and (5) the determination of the temperature stratification in the solar atmosphere from limb-darkening data. These examples suffice to show that the problem under consideration arises in many branches of astronomy and that its solution is vital to the process of extracting useful information from observations.
3,670 citations
169 citations
TL;DR: In this paper, the authors studied the evolution of the spin axis of the Earth's spin axis in terms of generalized Cassini's laws using the Hamiltonian approach, and three stable positions (Cassini states) were discerned.
Abstract: Possible evolutionary paths of the spin axis of Mercury are studied theoretically in terms of generalized Cassini's laws using the Hamiltonian approach. Three stable positions (Cassini states) of the spin axis are discerned. The Cassini states in which the spin axis remains fixed in the frame rotating with the orbit precession are extremes in the tide-free Hamiltonian under the condition of constant angular momentum. The stability of the 3/2 spin resonance for Mercury as a function of obliquity is discussed, and it is shown how control of the resonance is passed from one to another term in the averaged potential as the obliquity is increased with a corresponding loss of stability at each transfer. A sampling technique is used to infer the evolution due to tidal interaction. Two tidal models are used - one with a constant value of the specific dissipation function Q and the other with Q inversely proportional to frequency. An approximate analytic solution for precession trajectories very close to a Cassini state is developed.
102 citations
TL;DR: The O-B5 stars, supergiants, young clusters, and associations within 1 kpc of the sun populate two flat systems inclined to each other by 19 to 22 degrees as mentioned in this paper.
Abstract: The O-B5 stars, supergiants, young clusters, and associations within 1 kpc of the sun populate two flat systems inclined to each other by 19 to 22 deg. The historical background, statistical significance, composition, spatial arrangement of the contents, and interstellar extinction in the two belts are discussed. A more or less random distribution in space and in age characterizes the O-B5 stars of the 'galactic belt', which is aligned nearly along the Milky Way. The 'Gould belt' is inclined to the Milky Way (north in Sco-Oph and south in Orion), and exhibits a projected distribution of O-B5 stars in its mean plane that resembles a 'dragonfly', with five major features defining it. A crude 'diameter' of the system is 750 to 1000 pc, and the sun's position is eccentric, lying toward Ophiuchus. The nuclear age of the system, while not unique, may be characterized as 30 m.y. from the spectral type of the broad main-sequence turnup near B2-5. Most of the O-B2 stars and youngest stellar groups near the sun belong to the Gould belt, but both belts have approximately equal space densities of B3-B5 stars and similar average values of interstellar extinction.-
86 citations
TL;DR: Bolometric magnitudes for a large number of M type dwarf stars, obtained by broadband infrared photometry at 1.65, 2.2, and 3.5 microns, are reviewed in this paper.
Abstract: Bolometric magnitudes for a large number of M type dwarf stars, obtained by broadband infrared photometry at 1.65, 2.2, and 3.5 microns, are reviewed. The data obtained indicate that one parameter is sufficient to describe the blanketing in all of the UBVRI bands for all types of M dwarfs. In general, late M dwarfs seem to have lower effective temperatures than are predicted by theoretical models.
84 citations
73 citations
TL;DR: Polarimetric observations of 43 asteroids were presented in this article, where the empirical slope-albedo law for diffusely reflecting solid surfaces was reexamined and used to compute polarimetric albedos and diameters for 30 asteroids.
Abstract: Polarimetric observations of 43 asteroids are presented. All objects show a well-developed negative polarization branch as an indicator of unconsolidated surface regoliths. The empirical slope-albedo law for diffusely reflecting solid surfaces is reexamined and used to compute polarimetric albedos and diameters for 30 asteroids. In many cases the results are in good agreement with infrared-radiometric diameters; the older visual diameter measurements were systematically too small. Radiometric albedos below 5%, however, are not confirmed by the polarimetry. Bimodal frequency distributions are noted for asteroid color, albedo, and the depth of the negative polarization branch. Correlations between B - V color and polarimetric parameters suggest that most of the asteroid population can be divided into silicaceous and carbonaceous opacity classes.
71 citations
64 citations
64 citations
TL;DR: In this article, the authors used combined photometric and radiometric observations to determine the albedos and radii of airless solar-system objects such as asteroids and most satellites.
Abstract: Combined photometric and radiometric observations can be used to determine the albedos and radii of airless solar-system objects such as asteroids and most satellites. We use recent observations of the Galilean satellites to derive a new calibration of this method and use these results to calculate the radii and albedos of eight bright asteroids. Possible errors in the method are also discussed.
59 citations
TL;DR: In this article, the light curves of beta Scorpii AB and C were recorded during occultation by Jupiter with a time resolution of 0.01 sec. The spikes on the curves, correlated with flashes observed through the eyepiece, were shown to be due to density fluctuations in Jupiter's atmosphere.
Abstract: The light curves of beta Scorpii AB and C were recorded during occultation by Jupiter with a time resolution of 0.01 sec. The spikes on the curves, correlated with flashes observed through the eyepiece, are shown to be due to density fluctuations in Jupiter's atmosphere. Using the delays in spike arrival times, the ratio of the refractivities at 3934 and 6201 A is found to be 0.9713 + or - 0.0015. Temperature profiles for three different assumed atmospheric compositions are generated from the light curves. Assuming the terrestrial value for the eddy diffusion coefficient, the turbopause is calculated to occur at the 10 to the 13th power per cu cm level, below which a positive temperature gradient of about 1 K/km is indicated.
TL;DR: In this article, the color-phase and polarization-phase relations of Geographos were analyzed and the largest amplitude of 2.03 mag is the largest observed on asteroids to date.
Abstract: Analysis of the light curves and color-phase and polarization-phase relations of Geographos according to observations over an eight-month period in 1969. The light curves are relatively smooth with two distinct maxima and minima. The largest amplitude of 2.03 mag is the largest observed on asteroids to date. The average B-V is 0.87 and the average U-B is 0.50. A laboratory model that best reproduced Geographos' light curves was a cylinder having hemispherical ends with a length to width ratio of 2.7; on the basis of this model and a relation of Bowell and Zellner (1973), Geographos was calculated to be approximately 1.50 km wide and 4.0 km long.
TL;DR: Periodic orbits about the triangular equilibrium points were found for the planar restricted three-body problem using the earth-sun system in this article, where the maximum semimajor axis for tadpole orbits ranges from the infinitesimal orbit at 1000 AU to the near-limiting orbit at 100285 AU Horseshoe orbits for 10029 to 10080 AU, larger horseshoes being unstable because of close approaches to the earth.
Abstract: Periodic orbits about the triangular equilibrium points are found for the planar restricted three-body problem using the earth-sun system The maximum semimajor axis for tadpole orbits ranges from the infinitesimal orbit at 1000 AU to the near-limiting orbit at 100285 AU Horseshoe orbits are found for 10029 to 10080 AU, larger horseshoes being unstable because of close approaches to the earth Using stability tests devised by Rabe (1961, 1962), the limit of stability for nonperiodic orbits is found to occur for maximum semimajor axes near 10020 AU In addition, near-periodic tadpole orbits appear to be stable against perturbations by Jupiter and Venus for periods of at least 10,000 yr The possibility that minor planets actually exist in such orbits is considered
TL;DR: A high-resolution study of the surface of Mercury with a 2.388 GHz radar reveals the existence of hills and valleys with heights (depths) of about 1 km as discussed by the authors.
Abstract: A high-resolution study of the surface of Mercury with a 2.388 GHz radar reveals the existence of hills and valleys with heights (depths) of about 1 km. There is also evidence supporting the existence of craters with diameters of about 50 km and depths of about 700 m.
TL;DR: In this article, a survey of the galactic background radiation at 3.93 and 6.55 MHz is presented for the region between declinations of -60 and +60 deg. The results are consistent with the findings of high-resolution ground-based surveys at low frequencies and provide a first step in extending such observations over the whole sky.
Abstract: A survey of the galactic background radiation at 3.93 and 6.55 MHz is presented for the region between declinations of -60 and +60 deg. The observations were obtained with the 229-m traveling-wave V-antenna on the Radio Astronomy Explorer-1 satellite with an angular resolution of the order of one steradian. The results are consistent with the findings of high-resolution ground-based surveys at low frequencies and provide a first step in extending such observations over the whole sky.