Thermodynamic models and fine structure of prominences

Observed H brightness versus size of emission substructures of quiescent prominences are compared with values predicted from thermodynamical models. The measured size of an emission element of a given brightness is substantially less than the theoretical value.Two possible causes for the discrepancy are suggested: (1) The partial filling of a recording aperture, due to the prominence fine structure, may affect the measurements seriously. Caution is therefore urged against using face values of observed brightness vs ratios in model calculations in cases of partly optically thick lines. (2) Changes of individual fine structure elements on a time scale of a few minutes implies that the prominence plasma may be in a non-stationary radiative state.     

Systematic reductions of 19th century planetary observations

Systematic reductions of nineteenth century observations to the system of the FK4 are discussed. Reductions made on a nightly basis are described and compared with the results obtained through the use of conventional tables. The series of observations made at the Paris Observatory from 1837 to 1881 was used to compare the two methods, and a combined system of 24 000 FK4, FK4 Sup and AGK 3R positions and proper motions provided the reference stars. The results show that for Uranus the mean error of a single observation in right ascension is ±1..33 when tables are used for the reductions, and ±1.12 when nightly reductions are made, while in declination the corresponding mean errors are ±0.88 and ±0.80. The observations of Neptune show an even greater difference between the two methods; the mean errors for the tabular and nightly reductions are ±1.57 and ±1.09 in right ascension and ±0.88 and ±0.75 in declination. Secular rates in the (0–C)'s of Uranus of –0.029/year in right ascension and ±0.030/year in declination are present when the observations are reduced with tables. These rates are reduced to –0.007/year and +0.015/year, respectively, when nightly reductions are made.Presented at the Symposium Star Catalogues, Positional Astronomy and Celestial Mechanics, held in honor of Paul Herget at the U.S. Naval Observatory, Washington, November 30, 1978.     

Frequency domain light curve analysis of partially eclipsing binary systems: With an application to β Persei (Algol)

Kopal's new iterative method for analysing partially eclipsing binary light curves in the frequency domain has been put into a form suitable for applications, and explicit forms for basic expressions developed. To facilitate the computations in practice, the required newS _m -functions, which are expressed in terms ofJ _, ⁰ -integrals, have been extensively tabulated by making use of hypergeometric series. The automated method has been tested successfully on the light curves of Persei (Algol). Short information on the system and the revised sets of elements including a new determination of the limb-darkening coefficient in the ultraviolet have been presented.     

Energetic properties of interplanetary plasma at the earth's orbit following the August 4, 1972 flare

Solar wind and interplanetary magnetic field data were obtained by the PROGNOZ 1 and PROGNOZ 2 satellites during the period following the August 4, 1972 (0621 UT) solar flare. A thermalized plasma was recorded one hour after the shock followed two hours later by the plasma piston with a bulk velocity higher than 1700 km s^-1. The comparison between the PROGNOZ and PIONEER 9 solar wind data shows an attenuation of the plasma properties with the deflection from the flare's meridian.     

The equations of motion of an artificial satellite in nonsingular variables

The equations of motion of an artificial satellite are given in nonsingular variables. Any term in the geopotential is considered as well as luni-solar perturbations up to an arbitrary power ofr/r, r being the geocentric distance of the disturbing body. Resonances with tesseral harmonics and with the Moon or Sun are also considered. By neglecting the shadow effect, the disturbing function for solar radiation is also developed in nonsingular variables for the long periodic perturbations. Formulas are developed for implementation of the theory in actual computations.     

On the nature of polar cap magnetic activity during undisturbed periods

The correlation between the polar cap geomagnetic variations (H-traces) and the changes of the azimuthal (Y_SE) and vertical (Z_SE) components of the interplanetary magnetic field (IMF) during undisturbed periods is examined. It is shown that peak-to-peak correlation between Y_SE and geomagnetic horizontal component variations may be generally observed in the daytime cusp region, independently of the magnitude and polarity of the Z_SE. The existence of the DP₃ disturbances associated with the northward component Z_SE > 0 is confirmed. It is shown that the disturbances due to the vertical component of the IMF dominate in the region near the pole. In so far as the southward component of the IMF generates both polar cap disturbances and geomagnetic substorms, the disturbances in the region near the pole, associated with Z_SE < 0, may be regarded as a precursor of a substorm. On this basis a new index of the polar cap magnetic activity PC_L, characterizing the changeability of the magnetic field is proposed. It is shown that the increase of the PC_L index is followed in 1–2 hr by a substorm in 70% of events considered.