NEUTRON STAR MODELS WITH THE SPLINE - FITTED EQUATION OF STATE

VASILE POP, CRACIUN IANCU

University of Cluj-Napoca

Faculty of Mathematics and Computer Science

Str. M. Kogalniceanu 1, 3400 Cluj-Napoca, Romania

E-mail: vpop@cs.ubbcluj.ro, ciancu@math.ubbcluj.ro

TIBERIU OPROIU

Astronomical Institute of the Romanian Academy

Astronomical Observatory Cluj-Napoca

Str. Ciresilor 19, 3400 Cluj-Napoca, Romania

E-mail: oproiu@roastro.astro.ro

Abstract.In order to integrate the differential equation system which describes the structure of a neutron star, the equation of state has been fitted by spline functions. The integration yields M (mass) = 1.36 solar masses, R (radius) = 6.8 km, and k (gravitational packing coefficient) = 0.48, these results being in agreement with the corresponding values determined observationally for radiopulsars belonging to binary systems.

Key words: astrophysics – stellar structure – neutron stars – spline functions

RELATIONSHIP BETWEEN PHOTOSPHERIC AND CHROMOSPHERIC ACTIVITY IN THE MCMath REGIONS 14789, 14801, 14815 AND 14822

SIMONA DINULESCU, ALEXANDRA DIMITRIU, GEORGETA MARIS

Astronomical Institute of the Romanian Academy

Str. Cutitul de Argint 5, 75212 Bucharest 28, Romania

E-mail: gmaris@roastro.astro.ro

Abstract. The work presents the analysis of four solar active regions appeared in the period June - July, 1977. The evolution of the sunspot areas and the eruptive activity depending on the magnetic polarity of each group of sunspot areas and the eruptive activity depending on the magnetic polarity of each group of sunspots have been studied. The results show that the maximum areas of the sunspots and the maximum index of flares correspond to the days in which the groups analysed had magnetic polarity of ?-configuration. The variations in time of the structures of the sunspot groups and the associated chromospheric phenomena registered at Bucharest Solar Station are also analysed.

Key words: solar activity – solar magnetic field – sunspot – flare and filament

THE SOLAR FLARES AND THEIR SUDDEN IONOSPHERIC EFFECTS

SIMONA DINULESCU and VASILE DINULESCU

Astronomical Institute of the Romanian Academy

Str. Cutitul de Argint 5, 75212 Bucharest 28, Romania

Abstract. The paper analyses the relation between the moment of starting times of the sudden ionospheric disturbance (SID) and the starting times of the flare in H-alpha, in the case of phenomena brought forth during solar activity cycle 21 (1976-1986). Out of the total of 6180 SID-flare H-alpha associated events, 1711 (27.7 %) have ?T negative, 1126 (18.2 %) have ?T = 0 and for 3343 (54.1%) ?T is positive. This emphasizes the fact that the ionizing radiation (EUV, X) is emitted in one of the three basic phases of the development of a chromospheric flare set off by observations. A growth of the electron density of the six up to seven times against the normal value has been determined.

Key words: solar flares, sudden ionospheric effects.

FORMAL CONSTRUCTION OF THE GENERALIZED KRYLOV-BOGOLYUBOV EQUATIONS

ARPAD PAL, BAZIL PARV

University "Babes - Bolyai"

Faculty of Mathematics and Computer Science

Str. M. Kogalniceanu 1, 3400 Cluj-Napoca, Romania

E-mail: apal@math.ubbcluj.ro, bparv@math.ubbcluj.ro

Abstract. One presents the general averaging scheme for systems of differential equations with slow and fast variables. By using the Maple Computer Algebra System, the partial differential equations (so-called generalized Krylov-Bogolyubov equations) which define the transition between standard and averaged variables are deduced. The proposed procedure is general; one can obtain these equations for an arbitrary approximation order. The generalized Krylov-Bogolyubov equations are important for at least two reasons: first, these equations define the transition between the space of standard variables and the space of averaged ones, and, second, by means of them one can obtain the right-hand-side terms of the averaged equations for higher orders of approximation.

Key words: celestial mechanics - averaging method - computer algebra

ELLIPTIC-TYPE MOTION IN A SPHERICAL POST-NEWTONIAN GRAVITATIONAL FIELD

VASILE MIOC, EUGENIA RADU

Astronomical Institute of the Romanian Academy,

Astronomical Observatory Cluj-Napoca,

Str. Ciresilor 19, 3400 Cluj-Napoca, Romania

E-mail: vmioc@roastro.astro.ro

Abstract. The elliptic-type motion of a test particle in a spherical post-Newtonian gravitational field is being studied by means of the classic perturbation theory. The relativistic perturbations of five independent orbital parameters over one nodal period, as well as those of the nodal period itself, are analytically estimated with an accuracy of first order in a small parameter featuring the field, and of the second order in eccentricity. Different particular cases (initial position in ascending node or in pericentre, quasi-circular or circular orbit) are taken into account. The nodal period behaviour in the spherical Einstein post-Newtonian field is discussed for three values of the gauge parameter.

Key words: celestial mechanics - post-Newtonian fields - perturbation theory

ON THE PHOTOGRAVITATIONAL MODEL OF C. POPOVICI

MIRA-CRISTIANA ANISIU

Institute of Mathematics, Cluj-Napoca

Str. Republicii 37, P.O. Box 68, 3400 Cluj-Napoca, Romania

Abstract. For the system governed by a central force depending on distance and radial velocity considered by C. Popovici, one studies the existence and linear stability of the equlibrium points.

Key words: radiation pressure - equilibrium points

LIE GROUPS METHOD IN FRIEDMAN-ROBERTSON-WALKER COSMOLOGY

C. DARIESCU, MARINA-AURA DARIESCU

"Al. I. Cuza" University Iasi, Department of Theoretical Physics,

Bd. Copou 11, 6600 Iasi, Romania

M. AGOP

"G. Asachi" Technical University Iasi, Department of Physics,

Splai Bahlui 67, 6600 Iasi, Romania

Abstract. The major goal of this paper is to revise the Friedman-Robertson-Walker (FRW) cosmological models with constant and positive spatial curvature, by using the group theoretical methods which exploit the high symmetry of S³ spacelike hypersurface. A special interest has been given to FRW universe with isotropic thermal background radiation and also to the actual FRW spacetime with baryonic matter content (incoherent dust).

Key words: Lie groups - Friedman-Robertson-Walker cosmology - S³ x R topology - Cartan formalism - Einstein field equations

ELECTROMAGNETIC FIELD IN S³ x R UNIVERSE

MARINA-AURA DARIESCU, C. DARIESCU

"Al. I. Cuza" University Iasi, Department of Theoretical Physics

Bd. Copou 11, 6600 Iasi, Romania

Abstract. The electromagnetic Lagrangian and the field equations with respect to the algebraically invariant right-handed tetrad are derived, pointing out major differences as against the Minkowskian case. Two particular solutions are obtained.

Key words: Lie groups - S³ x R spacetime - Maxwell equations

FROM "ASTRONOMICAL CONCEPTS" TO AN "ASTRONOMICAL POINT OF VIEW" CONCERNING THE SCIENTIFIC CONCEPTUALIZATION

GHEORGHE VASS

Astronomical Institute of the Romanian Academy

Str. Cutitul de Argint 5, 75212 Bucharest 28, Romania

Abstract. The proper place of astronomical concepts in science education can be derived only from the epistemological statute of astronomy.But astronomy has a fundamental epistemological statute, because astronomy (and nothing else) created the mathematical modelling. This fact has complex implications in the pedagogy of mathematics and exact sciences, most of which are still ignored or insufficiently evaluated. The paper presents an operational definition of concepts and, on this basis, analyses the way of constructing scientific concepts (particularly, astronomical concepts). The resulting main idea is that the most proper way to integrate astronomy in education is to use the astronomical concepts as a natural model and background for general scientific conceptualization.

Key words: teaching of astronomy - genetic epistemology - mathematical modelling - science education - teaching of exact sciences.

ROMANIAN ASTRONOMICAL JOURNAL, VOL. 5, NO. 2, 1995

CATACLYSMIC VARIABLE TT ARIETIS OBSERVED AT BUCHAREST OBSERVATORY DURING 1994

GABRIELA OPRESCU, ALEXANDRU DUMITRESCU

Astronomical Institute of the Romanian Academy

Str. Cutitul de Argint 5, 75212 Bucharest 28, Romania

E-mail: g@oprescuroastro.astro.ro, alex@roastro.astro.ro

Abstract. New photoelectric observations of the cataclysmic variable TT Arietis obtained in 1994's observational season are presented. The observations were performed in Filter B only, using a 50 cm Cassegrain telescope of the Bucharest Observatory.

Key words: stellar photometry, cataclysmic variables.

DIFFERENTIAL PHOTOMETRY OF NSV5798

JOSE F. LAHULLA, JOSE PENSADO

Observatorio Astronomico Nacional,

Alfonso XII, 3, 28014 Madrid, Spain

Abstract. Blue and yellow photometric observations of the eclipsing binary system NSV5798 were made on 21 nights during 1984 to 1992. A listing of all the observations and the corresponding light curve and ephemeris are given.

Key words: variable stars - W UMa system - photometry

TOTAL SOLAR IRRADIANCE IN THE MAXIMUM PHASE OF THE ELEVEN YEARS SOLAR CYCLE

GEORGETA MARIS, SIMONA DINULESCU

Astronomical Institute of the Romanian Academy

Str. Cutitul de Argint 5, 75212 Bucuresti 28, Romania

E-mail: gmaris@roastro.astro.ro

Abstract. The authors set out to study the link between IR (registering performed on ERB/NIMBUS 7) and certain solar activity indices, in the maximum phase for solar cycles 21 (1979-1980) and 22 (1989-1990). From among the solar activity indices we have used : the daily sunspot relative number (R), the radio flux on 10.7 cm (F), the coronal index in green line (Ic), the daily flare index (If), the daily scaled flare number (SFN), the daily weighted flare index (IfP) and the daily flare total area index (IfA).The results presented proof of the existence of real correlatons between the total irradiance variation and the manifestations of the solar activity in the active regions (sunspots, flares, radio emission).

Key words: total solar irradiance - activity of the Sun

BLACK HOLES AS ELECTRIC CONDENSERS

ALEX B. GAINA

Institute for gravitation and Space Sciences

Laboratory for Gravitation

21, Ana Ipatescu Blvd., 71111 Bucharest, Romania

Abstract. A nonrotating (Schwarzschild) black hole of mass greater than  g is being considered. It is shown that thermal and quantum effects led to the electric charging of the black hole in a plasma containing particles with different masses. The notion of electric capacitance for a black hole is introduced.

Key words: astrophysics - black holes.

AN INVERSE PROBLEM FOR ISOLATED ORBITS

GEORGE BOZIS

Department of Theoretical Mechanics,

University of Thessaloniki

Thessaloniki GR-540 06 Greece

E-mail: bozis@ccf.auth.gr

CRISTINA BLAGA

Astronomical Institute of the Romanian Academy

Astronomical Observatory Cluj-Napoca

Ciresilor St., 19, 3400 Cluj-Napoca, Romania

Abstract. We examine the question of finding al potentials V(x,y) which can produce a specific isolated planar orbit f(x,y) = 0, given in advance and traced by a material point for adequate initial conditions. We study in some detail an example to clarify the difference of this version of the problem from the usual version dealing with a monoparametric family of orbits f(x,y) = constant.

Key words: celestial mechanics - inverse problem of dynamics

FREE-FALL COLLAPSE OF A HOMOGENEOUS SPHERE IN MANEFF'S GRAVITATIONAL FIELD

VASILE URECHE

Babes-Bolyai University of Cluj-Napoca

Faculty of Mathematics and Computer Science

1, M. Kogalniceanu St., 3400 Cluj-Napoca, Romania

Abstract. The free-fall collapse of a homogeneous spherical cloud in Maneff's gravitational field is analysed. The exact analytic solution of the collapse is obtained. The free-fall time is determined and compared with Newtonian free-fall time. For an interstellar cloud the effect of the supplementary term in Maneff's potential is negligible, but this is important for the collapse of a compact object. In Maneff's field the collapse is accelerated.

Key words: astrophysics - stellar evolution - gravitational collapse - Maneff's field

ON THE INVERSE PROBLEM OF DYNAMICS FOR GENERALIZED LAGRANGIAN SYSTEMS

MIRA-CRISTIANA ANISIU

Mathematical Institute

P.O.Box 68, 3400 Cluj, Romania

Abstract. A system of partial differential equations for the force function U (hence for the potential function -U) is given when one knows a family of orbits for a generalized Lagrangian system; this is a generalization not only of the results of Szbehely for 2-dimensional conservative systems but also of those of Dramba for the planar circular restricted three-body probem.

Key words: generalized Lagrangian systems - potential function - inverse problem

BOUNDED NONCOLLISIONAL ORBITS IN GENERALIZED MANEFF-TYPE FIELDS

CRISTINA STOICA

Institute for Gravitation and Space Sciences

Laboratory for Gravitation

21, Blvd. Ana Ipatescu, 71111, Bucharest, Romania

E-mail: cstoica@math.uvic.ca

Abstract. The motion of a particle under the influence of a generalized Maneff-type potential field is considered. Using reduction at one degree of freedom and the graphic of the effective potential energy, possible orbits are given. In the case of bounded noncollisional orbits complete integration is made.

Key words: celestial mechanics - Maneff's generalized law

SOLUTION OF REGULARIZED EQUATIONS FOR THE TWO-BODY PROBLEM IN MANEFF-TYPE FIELDS

VASILE MIOC

Astronomical Institute of the Romanian Academy

Astronomical Observatory Cluj-Napoca

Str. Ciresilor 19, 3400 Cluj-Napoca, Romania

E-mail: vmioc@roastro.astro.ro

CRISTINA STOICA

Institute for Gravitation and Space Sciences

Laboratory for Gravitation

Bd. Ana Ipatescu 21, 71111 Bucharest, Romania

E-mail: cstoica@math.uvic.ca

Abstract. The two-body problem governed by a Maneff-type interaction law (combination of an inverse square law and an inverse cubic law) is being considered. The equations of motion and the integral of energy are regularized. The problem is completely solved for the whole allowed interplay between the parameters of the field and the initial conditions.

Key words: celestial mechanics - two-body problem - Maneff-type fields - regularization

CONSIDERATIONS CONCERNING THE DEPENDENCE OF THE ORBITAL ENERGY OF AN ARTIFICIAL SATELLITE ON THE SOLAR AND GEOMAGNETIC ACTIVITY

MAGDALENA CARSMARU, TIBERIU OPROIU

Astronomical Institute of the Romanian Academy

5, Cutitul de Argint St., 75212 Bucharest 28, Romania

E-mail: carsmaru@roastro.astro.ro, oproiu@roastro.astro.ro

Abstract. A numerical method for the determination of the orbital energy variation ?E = ?E (F10.7, Kp) for a given orbit is proposed and tested by means of the TD88 and C atmospheric models; a quasilinear variation with both F10.7 and Kp is found for a theoretical (ideal) orbit similar to Intercosmos 19 rocket's orbit. Numerical examples are given.

Key words: artificial satellites - orbital energy.

ANALYSIS OF DOUBLE STARS CATALOGUES OBSERVED IN BELGRADE AND BUCHAREST

PETRE POPESCU, MIHELA LICULESCU

Astronomical Institute of the Romanian Academy

5, Cutitul de Argint St., 75212 Bucharest 28, Romania

E-mail: petre@roastro.astro.ro

Abstract. The analysis of the systematic errors in right ascension and declination was made by comparing stars positions from Double Stars Catalogues observed in Belgrade and Bucharest.

Key words: double stars catalogues - systematic errors

OBSERVATIONS OF MINOR PLANETS IN 1991-1994 AT THE BUCHAREST ASTRONOMICAL OBSERVATORY

MIREL BIRLAN, GHEORGHE BOCSA

Astronomical Institute of the Romanian Academy

5, Cutitul de Argint St., 75212 Bucharest 28, Romania

E-mail: gbocsa@roastro.astro.ro

Abstract. The precise positions of asteroids observed at Bucharest Observatory in 1991-1994 period are presented.

Key words: astrometry - minor planets