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**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

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**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

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**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.

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**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

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**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

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**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

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**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

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**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

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**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.

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

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**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.

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**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

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**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

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**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.

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**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

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**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

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**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

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** **

**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

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**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

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**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.

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**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

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**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

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