ROMANIAN ASTRONOMICAL JOURNAL, VOL. 6, NO. 1, 1996

 

PRIMARY LIGHT MINIMA OF X TRIANGULI BETWEEN 1921-1995

GHEORGHE DORIN CHIS, ALEXANDRU POP, VLAD TURCU
Astronomical Institute of the Romanian AcademyAstronomical Observatory Cluj-NapocaStr. Ciresilor 19, 3400 Cluj-Napoca, Romania
E-mail: academy1@mail.soroscj.ro

Abstract. An extensive collection of primary light minima of X Tri is listed. The O-C diagram reveals a complex, but also an interesting structure, while the observations statistics shows an undesirable decrease of the observed minima number for this variable. This paper is intended to contribute to the revival of the interest for observing X Tri.

Key words:astrophysics - variable stars - eclipsing binary systems

 

 

NUMERICAL MODEL FOR THE STUDY OF WAVE-MEAN FLOW INTERACTIONS IN SOLAR MAGNETOHYDRODYNAMICS

MIHAI S. GHIZARU
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, 75212 Bucharest 28, Romania

MARCEL GOOSSENS
Center for Plasma Astrophysics, K.U., Leuven
Celestijnenlaan 200 B, B-3001 Leuven, Belgium

Abstract. A 2D MHD model in cylindrical geometry is developed for the study of the behaviour of MHD waves incident on critical layers in the presence of shearing in magnetic and velocity fields in the solar plasma The MHD code described in this paper is based on the resistive MHD equations written in (r,z) coordinates. The non-divergence constraint for the magnetic field is satisfied by using a vector potential. For the time advancing, an operator splitting procedure is performed when including the different physical effects, as well as for alternating direction in the advection terms. The rotating cone test is used for numerical experiments with different advenction schemes. The model equations are integrated on an Arakawa b grid, with Bø in the cell center and Aø in the velocity points. Second order schemes are used for the mass, momentum and energy advection with a monotonicity maintaining scheme applied periodically. Implicit methods, treated by gaussian elimination are used for the toroidal and poloidal magnetic field diffusion.

Key words: resistive MHD equations - numerical modeling - advection schemes

 

 

CCD PHOTOMETRY ON THE ASTEROID 2419 MOLDAVIA

MIREL BIRLAN

Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, 75212 Bucharest 28, Romania

Abstract.On September 26, 27 and October 2, 1995, observations were made at the Haute Provence Observatory on the asteroid 2419 Moldavia. The results show a fast rotator asteroid with the synodic period of 2.412  0.003 hours.

Key words: asteroids - CCD - photometry

 

 

ON THE GENERATORS OF THE NEW PERTURBATION METHODS

EUGENIU GREBENICOV
Institute for Supercomputers of the Russian Academy of Sciences
37, Vavilova St., Moscow 117312, Russia
E-mail: greben @ ext1.ccas.ru

Abstract. Some basic concepts (generator of the theory, generating equation) and ideas of the modern theory of perturbations are presented. Compared with the classical theory, the modern one has two essential advantages: the determination of the perturbation does not require the preliminary solution of the generating equation, and the choice of the new initial conditions is large. The algorithm of constructing the solution is presented.

Key words: celestial mechanics - theory of perturbations

 

FAMILY BOUNDARY CURVES IN ROTATING SYSTEMS

GEORGE BOZIS
Department of Theoretical Mechanics, University of ThessalonikiGR-540 06 Thessaloniki, GreeceE-mail: Bozis@ ccf.auth.gr

MIRA-CRISTIANA ANISIU
"T.Popoviciu" Institute of Numerical AnalysisP.O.Box 68, 3400 Cluj-Napoca, Romania
E-mail: anisiu @ math.ubbcluj.ro

Abstract. In the framework of the two-dimensional inverse problem of Dynamics with autonomous forces, we discuss the creation of the family boundary curves (FBC) with the aid of Dainelli's formulae. We then extend the notion of FBC to the case of rotating systems and we prove that these curves are loci either of points of equilibrium for the corresponding forces or points where the given family of orbits is "exterminated".

Key words: inverse problem - family boundary curves

 

 

ANALYTIC-NUMERICAL SOLUTIONS OF THE RESTRICTED THREE-BODY PROBLEM

YU. A. RYABOV
Moscow's Automobile and Highway Engineering University
Leningradsky pr. 64, 125829 Moscow, Russia

Abstract. The planar, circular, restricted three-body problem is being considered for the Sun-Jupiter-asteroid case. A classical algorithm with simple iterations and one consisting of iterations with rapid convergence are proposed for constructing quasi-periodic solutions in trigonometric form.

Key words: celestial mechanics - restricted three -body problem

NONLINEAR INSTABILITY OF SOME RELATIVE EQUILIBRIUM CONFIGURATIONS IN THE ( n + 1)-BODY PROBLEM

BADAOUI ELMABSOUT

Universite Paris 6, Unite de Formation et de Recherche de Mecanique, Laboratoire des Systemes Dynamiques
4, Place Jussieu, Tour 66, 75252 Paris cedex 05, France
E-mail: bae@ccr.jussieu.fr

Abstract. We study analytically the second order nonlinear stability of a degenerate configuration of relative equilibrium where n bodies having the same mass m are at the vertices of a regular polygon with n sides, while a body having a nonzero mass m0 is at the center of the polygon. It is shown that at this configuration of relative equilibrium the matrix of the second derivatives of the energy-momentum functional has always negative and positive eigenvalues, for any choice of n and of the ratio µ = m/m0. Consequently, the above configuration is nonlinearly unstable for any choice of n and µ, even if for n > 6 it is linearly stable for µ larger than some third degree polynomial of n, as we had shown in a previous paper.

Key words: celestial mechanics - (n + 1)-body problem - stability

 

 

LA METRIQUE DE MAUPERTUIS DANS L'ESPACE DES CONFIGURATIONS D'UN SYSTEME DYNAMIQUE CONSERVATIF

MIHAIL BARBOSU
Universite "Babes-Bolyai", Faculte de Mathematiques et Informatique1, rue Kogalniceanu, 3400 Cluj-Napoca, Roumanie
E-mail: mbarbosu@math.ubbcluj.ro

Resume. Le but de ce travail est de mettre au point et de justifier l'interet pour une methode qualitative (tres peu utilisee) d'etude de la stabilite des trajectoires d'un systeme dynamique conservatif. La methode est basee sur la liaison existante entre le signe des courbures riemanniennes (ou sectionnelles) et le comportement des geodesiques.

Key words: celestial mechanics - dynamical systems - differential geometry

 

 

A QUALITATIVE STUDY OF THE TWO-BODY PROBLEM IN MANEFF-TYPE FIELDS

CRISTINA STOICA

Institute for Gravitation and Space SciencesLaboratory for GravitationBd. Ana Ipatescu 21, 71111 Bucharest, Romania
E-mail: cstoica@math.uvic.ca

VASILE MIOC
Astronomical Institute of the Romanian AcademyAstronomical Observatory Cluj-Napoca
Str. Ciresilor 19, 3400 Cluj-Napoca, Romania
E-mail: vmioc@roastro.astro.ro

Abstract. The qualitative evolution of the relative motion in the two-body problem for Maneff-type potential laws (of the form A/r + B/r²) is being studied. Using the first integrals of angular momentum and energy, the trajectories in the phase plane are constructed for the whole allowed interplay among field parameters, angular momentum and total energy. All possible scenarios for the relative motion are found to be nine, illustrating four essential trends: path ending in collision, path leading to escape, trajectory tending to equilibrium, and quasiperiodic (or periodic) orbit. The cases of nonrectilinear motion are treated separately.

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

 

ORBITS AROUND STARS OF LINEARLY INCREASING MAGNITUDE

VASILE MIOC
Astronomical Observatory 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 particle around a star of linearly increasing magnitude (exponentially decreasing luminosity) is being studied using Delaunay-type canonical variables and a method due primarily to von Zeipel. The behaviour of every orbital element is determined. The solution of motion equations points out constancy of semilatus rectum and orbit plane positions, and first order mixed perturbations in semimajor axis and eccentricity (orbit deformation), argument of periastron (apsidal motion) and mean anomaly. The model is shown to belong to the two-body problem with changing equivalent gravitational parameter.

Key words: dynamical astronomy - perturbations

 

 

SOFTWARE PACKAGE FOR PREPARING AND PROCESSING OF AN ASTRONOMICAL OBSERVATION

OVIDIU VADUVESCU, MIREL BIRLAN
Astronomical Institute of the Romanian Academy,Str. Cutitul de Argint 5, 75212 Bucuresti 28, Romania

Abstract. This paper presents an astronomical software package which draws celestial charts. It was conceived taking into account the technical possibilities available for the Romanian astronomers and the actual trend of the observational astronomy. The software package, now to its third version, comes to decrease the time to prepare an observation and to perform accurate charts for searching and identification.

Key words: software - astrometry - star database - celestial maps

 


 

ROMANIAN ASTRONOMICAL JOURNAL, VOL. 6, NO. 2, 1996

 

 

COLOUR GRADIENTS IN CLUSTERS OF GALAXIES (1)

NEDELIA ANTONIA POPESCU, DORU MARIAN SURAN
Astronomical Institute of the Romanian Academy,Str. Cutitul de Argint 5, 75212 Bucharest 28, Romania
E-mail: delia@roastro.astro.ro, suran@roastro.astro.ro

Abstract. The analysis of the photometrical observations for galaxies with z > 0.2 is of great importance for both Extragalactic Astronomy and Cosmology. This reveals a large variety of phenimena and cosmological effects. We use the method of colour gradients in clusters of galaxies in order to study some of these evolutive effects. The results concerning the colour gradients in 15 clusters of galaxies with 0 < z < 0.81 and the implications in the morphology and evolution of the clusters are presented. The connexion between the colour gradient and the Butcher-Oemler effect, the problem of colour evolution of galaxies in clusters are also discussed.

Key words: cosmology - clusters evolution - colour gradients

 

 

STUDY OF THE ECLIPSING BINARY GO CYGNI BASED ON OBSERVATIONS OF BUCHAREST AND ATHENS OBSERVATORIES FROM 1985 TO 1994

 

G. OPRESCU (1), A. DUMITRESCU (1), M.D. SURAN (1), P.ROVITHIS (2), H. ROVITHIS-LIVANIOU (3)

(1) Astronomical Institute, Romanian Academy, Str. Cutitul de Argint No. 5,
75212 Bucharest 28, Romania
E-mail: goprescu@roastro.astro.ro, alex@roastro.astro.ro, suran@roastro.astro.ro

(2) Astronomical Institute, National Observatory of Athens, P.O. Box 20 048,GR-118 10 Athens, Greece

(3) Section of Astrophysics, Astronomy & Mechanics, Physics Dept.,
    University of Athens, GR- 157 84 Zografos, Greece

Abstract. The principal aim of this work is to study the eclipsing binary system GO Cygni for which a series of photoelectric observations have been carried out for ten years, 1985-1994, either at Athens or at the Bucharest Observatories. The unpublished data obtained from 1989 to 1992 are given and the corresponding light curves of the system are presented while a general discussion concerning some of their features is made. A shift of the order of 0.082 found in the V light curves of 1989-90 & 92 and those of 1993-94 can be due to the variability of the comparison star BD+35° 4197, which has to be checked; while some peculiar features of its light curves may be due to the activity of the system. Moreover, the observed variations in the period of GO Cygni are discussed.

Key words: stellar photometry - close binary systems

 

 

MULTIPERIODIC BEHAVIOUR OF RT PERSEI

ALEXANDRU POP (1), IOAN TODORAN (1) and FRANZ AGERER (2)

(1) Astronomical Institute of the Romanian Academy
Astronomical Observatory Cluj-Napoca
Str. Ciresilor 19, 3400 Cluj-Napoca, Romania

(2) Bundesdeutsche Arbeitsgemeinschaft fur Veranderliche Sterne e.V. (BAV),
Zweikirchen, Dorfstrasse 19, D-84184 Tiefenbach, Germany

Abstract. The period variation of RT Persei is resumed. A new, semi-empirical ephemeris, consisting in a polynomial term and a "multiperiodic" term, is established on the basis of 577 individual times of primary minimum light, covering 98 years. The frequencies detected in the amplitude spectrum of the O-C curve are believed to characterize the physical mechanisms occuring in the system.

Key words: variable stars - eclipsing binary systems - Algol binaries.

 

 

THE USE OF CHARACTERISTIC TIME TO THE STUDY OF PERIOD VARIABILITY PHENOMENA

ALEXANDRU POP
Astronomical Institute of the Romanian Academy
Astronomical Observatory Cluj-Napoca

Str. Ciresilor 19, 3400 Cluj-Napoca, RomaniaAbstract. The notion of characteristic time associated with a variable star with changing period is resumed. A possibility to use it in order to classify period variation phenomena is described. The practical aspects of the application in concrete observational situations are approached by taking into acccount an ephemeris for light time extrema with high degree of generality. The observation planning is also considered from the viewpoint of the characteristic time.

Key words: variable stars - stellar photometry - periodicity analysis - data analysis

 

 

GENERAL FORMULATION OF SOME PROBLEMS OF CELESTIAL MECHANICS FOR CONSTRUCTING SOLUTIONS USING COMPUTERS

EUGENIU GREBENICOV
Institute for Supercomputers of the Russian Academy of Sciences37, Vavilova ST., Moscow 117312, Russia
E-mail: greben@ext1.ccas.ru

ARPAD PAL
Babes-Bolyai University, Department of Mathematics and Computer Science
1, M. Kogalniceanu St., 3400 Cluj-Napoca, Romania
E-mail: apal@math.ubbcluj.ro
Abstract. Some problems of celestial mechanics are exposed in a modern way, the characteristic of the motion theory being not the order (power of a small parameter), but an a priori given accuracy (even if the theory accuracy depends implicitly on the small parameter). The mathematical formulation is given for six special problems, whose solutions can be obtained with the aid of the "Bogolyubov processor".

Key words: celestial mechanics - theory of motion - symbolic processors

 

 

MODIFIED LAGRANGE-BURMANN SERIES FOR REPRESENTING KEPLER'S EQUATION SOLUTION

EUGENIU GREBENICOV
Institute for Supercomputer Systems of the Russian Academy of Sciences,
37, Vavilova St., Moscow 117312, Russia
E-mail: greben @ ext1.ccas.ru

VLADIMIR V. MASYUKOV
State University, Tver, Russia

Abstract. New series representing the solution of Kepler's transcendent equation are being obtained. Their covergence domain is larger than the convergence domain of the well-known Lagrange series for the same solution.

Key words: celestial mechanics - Kepler's equation

 

ON THE SIMULTANEOUS TOTAL COLLISION FOR PARTICLE SYSTEMS
WITH QUASIHOMOGENEOUS POTENTIALS

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
21-25 Mendeleev St., Bucharest, Romania
E-mail: cstoica@math.uvic.ca

Abstract. The n-body problem in an attracting field featured by a quasihomogeneous potential is considered. Based on an equality concerning the moment of inertia and on the Lagrange-Jacobi relation transposed for this case, one proves the impossibility of the simultaneous total collision in infinite time.

Key words: celestial mechanics, n-body problem, quasihomogeneous potentials

 

 

SMALL STOCHASTIC PERTURBATIONS OF INTEGRABLE CANONICAL SYSTEMS

GHEORGHE STOICA
University of Bucharest, Mathematics Department
14, Academiei St., Bucharest, Romania

CRISTINA STOICA
Institute for Gravitation and Space Sciences
21-25 , Mendeleev St., Bucharest, Romania
E-mail: cstoica@math.uvic.ca

Abstract.We consider the integrable canonical systems perturbed by a Brownian motion and we present an asymptotic estimation (in probability and in uniform norm) of the difference between the coordinates, the momenta and their small stochastic perturbations. The typical examples of application of these estimates are the exactly harmonic systems.

Key words: canonical systems - Brownian perturbations - celestial mechanics

 

PERIOD CHANGES OF SATELLITE CIRCULAR MOTIN DUE TO ODD ZONAL HARMONICS OF GEOPOTENTIAL

STELIAN COJOCARU
Naval Academy, Str. Fulgerului 1-3, 8700 Constantza, RomaniaE-mail: cojocarus@yahoo.com

Abstract. The initially circular motion of an artificial satellite in the terrestrial gravitational field is being considered. The first order difference between the nodal period and the Keplerian one caused by all odd zonal harmonics of the geopotential is analytically determined. The effect of every such harmonic can be pointed out separately.

Key words: artificial satellites - terrestrial gravitational field

 

MEASUREMENT AND ASTROMETRIC REDUCTION OF CCD IMAGES IN BUCHAREST

GHEORGHE VASS, GABRIEL STEFANESCU, OVIDIU VADUVESCU
Astronomical Institute of the Romanian Academy,
Str. Cutitul de Argint 5, 75212, Bucuresti, Romania
E-mail: gvass@roastro.astro.ro, gsteph@roastro.astro.ro

Abstract. The paper presents the methods of measurement and astrometric reduction of the CCD images made at Bucharest Astronomical Observatory beginning with 1995. We present the programs for the automatic measurement and the astrometric reduction methods, as well as the accuracy of the astrometric positions obtained.

Key words: CCD - astrometry

 

TIME RECORDING IN CCD OBSERVATIONS

GABRIEL STEFANESCU
Astronomical Institute of the Romanian Academy,
Str. Cutitul de Argint 5, 75212 Bucharest 28, Romania
E-mail: gsteph@roastro.astro.ro

Abstract. This paper presents some methods improving the precision of time recording and time measurements in the image acquisition technique by CCD, using PCs equipped with chronographic cards. At the Astronomical Institute of the Romanian Academy a chronographic card designed by M. Dequin And F. Chollet, Paris Observatory, was used. The results show that the accuracy can come of the order of the commutation time of the CCD camera's shutter.

Key words: CCD - image acquisition - programming

 

REDUCTION OF ASTEROIDAL APPULSES. FIRST RESULTS IN BUCHAREST

OVIDIU VADUVESCU
Astronomical Institute of the Romanian Academy,
Cutitul de Argint Str. 5, 75212 Bucharest 28, Romania

Abstract. The method presented is applied to asteroidal approaches to catalogue stars ans ocultations, and derives the minimum separation at conjunction and the corresponding time of these ones. Three CCD observations, reported to the European Asteroidal Occultation Network, illustrate the method.

Key words: astrometry CCD - asteroidal occultation - appulse