ARPAD PAL
"Babes-Bolyai" University, Astronomical Observatory
Str. Ciresilor 19, 3400 Cluj-Napoca, Romania
E-mail: apal@math.ubbcluj.ro
Abstract. The present paper, dedicated to the 140th anniversary of the birthday of the Romanian mathematician, mechanicist, and astronomer Spiru Haret (1851-1912), is an attempt to state as a theorem his famous result concerning the well-known problem on the invariability of the major axes of planetary orbits, related to the stability of the solar-planetary system. "Spiru Haret's theorem" is to be naturally added to the logical succession of theorems with respect to this problem known as "Laplace-Lagrange theorem" and "Poisson's theorem". Using his own method to explain mathematically the phenomenon of secular acceleration of Moon's "mean motion", Spiru Haret gives a criterion for separating the higher order gravitational perturbations from every nongravitational perturbation in the motion of natural or artificial celestial bodies, criterion to which the author of the present paper intends to call the attention.
Key words: secular perturbations - problem of major axes invariability - motion of Moon and artificial satellites
THE MODEL OF TWO POINTS CORRELATION FUNCTIONS FOR THE DETERMINATION OF THE LARGE SCALE STRUCTURE OF THE UNIVERSE (I)
M. D. SURAN, NEDELIA POPESCU, GABRIELA OPRESCU
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, 75212 Bucharest, Romania
E-mail: suran@roastro.astro.ro, delia@roastro.astro.ro, goprescu@roastro.astro.ro
Abstract. In this paper the authors tried to raise a 2-D automatic theoretical catalogue of clusters of galaxies from a given catalogue of galaxies in order to apply the model of two points correlation for the determination of the Large Scale Structure of the Universe.
Key words: clusters of galaxies - Abell catalogue - automatic catalogues - large scale structure - continuous matter distribution in the Universe
CRISTINA CARMEN POPESCU
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, 75212 Bucharest 28, Romania
Abstract. In the present paper we have obtained the light geodesics, both in the stationary and in the non-stationary uniform model universe. We have found a peculiar exact solution of the differential equations system. In the non-stationary models we have worked with some categories of models in which it is possible to establish an analytic relation for the scale factor, R(1). The solution we have obtained allowed us to draw some fundamental conclusions in connection with the flowing speed of time on the geodesics.
Key words: light geodesics - models of the Universe - cosmology
IOAN TODORAN
Astronomical Observatory Cluj-Napoca, Romania
Abstract. The case of binary systems with pulsating components is considered and a new method of apsidal motion detection is proposed.
Key words: closed binary systems - apsidal motion
DORU MARIAN SURAN
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, 75212 Bucharest 28, Romania
E-mail: suran@roastro.astro.ro
Abstract. The paper deals with the estimate of physical, pulsational and dynamical properties for a Delta Scuti star of 2.3 solar masses. The model used is an original one, derived from a nonradial model without rotation and supplied with a 1pv (line profile variations) model for the determination of monochromatic parameters. The model was applied to the case of AB Cas and our NRP results are discussed with respect to Ando's results.
Key words: stellar pulsations - NRP pulsations - Delta Scuti stars.
VASILE URECHE
University of Cluj-Napoca
Str. M. Kogalniceanu 1, 3400 Cluj-Napoca, Romania
E-mail: vureche@math.ubbcluj.ro
Abstract. In the previous two papers (Ureche, 1988, 1989) a new class of barotropic stellar models, with an equation of state of type (1), was proposed. The basic equations of equilibrium and the power series solution for the Newtonian approximation were obtained. A numerical analysis of these equations was performed, and a stability criterion was given (Ureche and Oproiu, 1988, 1989). In this paper the basic equations for the relativistic approximation are given. With the equation of state in the non-dimensional form (7), the equations of hydrostatic equilibrium and the equations for the geometry of the space-time continuum are given (also in a non-dimensional form). The numerical results obtained for these equations will be given elsewhere.
Key words: relativistic stars - barotropic models
VASILE POP
University of Cluj-Napoca
Str. M. Kogalniceanu 1, 3400 Cluj-Napoca, Romania
E-mail: vpop@cs.ubbcluj.ro
Abstract. The radial velocities of Beta Cephei were determined from 4 high-dispersion spectrograms obtained with the coudé spectrograph of Ondrejov 2-m telescope.
Key words: Beta Cephei - radial velocities
FLARES ACTIVITY DURING SOLAR CYCLE 21
SIMONA DINULESCU, VASILE DINULESCU
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, 75212 Bucharest 28, Romania
Abstract. The present paper investigates the statistical behaviour of the solar flares through cycle 21 (1976 - 1986). The total number of solar flares and the number of flares of various importance are given. The year of maximum for all events was 1980 with 10132 flares. The subflares have had their maximum values in 1979 (9278 events) and in 1980 (9273 events) while, the other flares reached at maximum two-three years latterly. The asymmetry A for subflares and importance 1 flares favour the southern hemisphere (A = - 2.8 and - 0.9) but that of imp. > 2, the northern hemisphere (A = + 3.6). The maximum number of flares with importance > 2 (Fmax) in solar cycle 21 took place two years later than the maximum number of solar spots (Rmax), but Fmax in cycle 20 appeared one year before Rmax and for cycle 19 in the same year of Rmax.
Key words: the Sun – flares - activity cycles
QUASIBIENNIAL PERIODICITY OF SOLAR AND PLANETARY PHENOMENA
IRINA PREDEANU
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, 75212 Bucharest 28, Romania
Abstract. The quasibiennial oscillation (QBO) of various solar and geophysical parameters is anlysed, taking some planetary configurations as temporal reference points. The incidence of the QBO minima in the proximity of Sun-Mars oppositions is discussed. The increase of this effect when Mars is near the perihelion or Jupiter is conjunct to the Sun is pointed out.
Key words: solar and geophysical parameters - periodicity of solar and planetary phenomena
LUDMILA RUSU
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, 75212 Bucharest 28, Romania
Abstract. Using the data published in "Results of the International Latitude Service in a Homogeneous System (1899.9-1979.0)", the authoress determined the periodical components by statistical method and found the following values: 1.08 year; 0.963 year; 0.964 year; 0.768 year; 0.715 year; 1.74 year; 1.885 year; 6.54 year; 28.45 year and 19.5 year.
Key words: Earth's rotation - polar motion
MONICA CIOBANU
Institut Astronomique de l'Academie Roumaine
Str. Cutitul de Argint 5, 75212 Bucarest 28, Roumanie
Abstract. The possible consequences of the centrifugal potential on the Euler period in the case of the Earth are investigated.
Key words: Earth's rotation - Euler period
IERONIM MIHAILA
Universite de Bucarest, Faculte de Mathematiques
Str. Academiei 14, 70109 Bucarest, Roumanie
Abstract. A more accurate formula for the length of the tropical year is derived in terms of the coefficients of the polynomial expression of the Sun's mean longitude. The improved length of the tropical year is more short than the known length. The consequences regarding the definition of the second of ephemeris time and the calculation of the Besselian epoch corresponding to a Julian date are presented.
Key words: ephemeris time - tropical year - Besselian epoch
ARPAD PAL
"Babes-Boyai" University Cluj-Napoca
Str. M. Kogalniceanu 1, 3400 Cluj-Napoca, Romania
E-mail: apal@math.ubbcluj.ro
TIBERIU OPROIU
Astronomical Observatory Cluj-Napoca
Str. Ciresilor 19, 3400 Cluj-Napoca, Romania
E-mail: oproiu@roastro.astro.ro
Abstract. Starting from Rein's "semiaveraging" scheme of the elliptic restricted three-body problem (according to Mojseev's classification), there were determined the slopes of the "zero relative velocity" curves in the libration point L1 for different values of the eccentricity and of the mass ratio. The results are plotted in figures.
Key words: elliptic restricted three-body problem - averaging method
VASILE MIOC
Astronomical Observatory Cluj-Napoca
Str. Ciresilor 19, 3400 Cluj-Napoca, Romania
E-mail: vmioc@roastro.astro.ro
PAUL BLAGA
University of Cluj-Napoca
Str. M. Kogalniceanu 1, 3400 Cluj-Napoca, Romania
E-mail: cpblaga@math.ubbcluj.ro
Abstract. Adopting a post-Newtonian gravitational law with supplementary logarithmic term, and a perturbative treatment, the difference between the nodal and Keplerian periods, as well as the changes of the orbital elements over a nodal period are obtained. The first order approximation shows only a rotation of the orbit in its plane, while the second order approximation points out an orbit deformation, too.
Key words: post-Newtonian gravitational law - orbital motion
A. ALEXIU, G. BOCSA, M. STANESCU
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, 75212 Bucharest 28, Romania
E-mail: gbocsa@roastro.astro.ro
Abstract. In this paper, minor planets precise positions observed at Bucharest Observatory in the period 1982-1985 are presented. For performing the observations, a 380/6000 mm astrograph was used and the plates measurements were carried out at ASCORECORD machine.
Key words: photographical astrometry - minor planets
A. ALEXIU, G. BOCSA, M. STANESCU
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, 75212 Bucharest 28, Romania
E-mail: gbocsa@roastro.astro.ro
Abstract. In this paper the precise positions of minor planets observed at Buharest Observatory in 1982-1985 are presented. For performing the observations, a 380/6000 mm astrograph was used and the plates measurements were carried out with an ASCORECORD machine.
Key words: photographical astrometry - Halley comet