BV PHOTOMETRY OF THE ACTIVE BINARY

BV PHOTOMETRY OF THE ACTIVE BINARY YY CORONAE BOREALIS

ALEXANDRU DUMITRESCU
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, RO-75212 Bucharest, Romania
E-mail: alex@aira.astro.ro

Abstract. The paper presents the ground-based photoelectric observations of the newly discovered eclipsing binary YY Coronae Borealis. The observations were carried out with an EMI 9502 B type photomultiplier attached to the 50-cm Cassegrain reflector of the Bucharest Observatory. The light curves in B and V colors are presented.

Key words: photoelectric photometry – eclipsing binaries – YY CrB.

SYMMETRIC CIRCULAR CONFIGURATIONS AS RELATIVE EQUILIBRIA

BADAOUI ELMABSOUT ¹, VASILE MIOC ²
¹ Université Paris VI, Laboratoire de Modélisation en Mécanique
8, rue du Capitaine Scott, F-75007 Paris, France
E-mail: bae@ccr.jussieu.fr
² Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, RO-75212 Bucharest, Romania
E-mail: vmioc@aira.astro.ro

Abstract. We consider the n-body problem with , , all bodies being situated on a circle such that and have the same mass and determine a diameter of the circle for all . We state the conjecture that such a configuration is a relative equilibrium if and only if the polygon formed by these bodies is regular and all masses are equal. We prove the conjecture in the case and verify it for .

Key words: celestial mechanics – n-body problem – relative equilibria.

THE SCHWARZSCHILD - DE SITTER PROBLEM (II): SYMMETRIES

VASILE MIOC
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, RO-75212 Bucharest, Romania
E-mail: vmioc@aira.astro.ro

Abstract. The two-body problem in the Schwarzschild - de Sitter gravitational field is resumed from a single point of view: symmetries. The motion equations exhibit remarkable symmetries in both initial polar coordinates and collision-blow-up and infinity-blow-up coordinates. These symmetries form isomorphic commutative groups endowed with a Boolean structure. A larger group, with the same structure, is formed by the symmetries that characterize the equations of motion written in Levi-Civita regularizing coordinates.

Key words: celestial mechanics – Schwarzschild - de Sitter two-body problem – McGehee transformations – Levi-Civita transformations – symmetries.

FAMILIES OF STRAIGHT LINES IN ROTATING FRAMES

GEORGE BOZIS ^1, MIRA-CRISTIANA ANISIU ²
^{1 Department of Physics,}
^{University of Thessaloniki, GR-54006, Greece}
^{E-mail: gbozis@ccf.auth.gr}
^{2 "T. Popoviciu" Institute of Numerical Analysis}
^{Romanian Academy, P.O. Box 68, 3400 Cluj-Napoca, Romania}
^{E-mail: mira@math.ubbcluj.ro}

^{Abstract. In the light of the inverse problem of Dynamics, we
establish families of straight lines, possibly traced by a material
point in a uniformly rotating plane Oxy in the presence of a ''potential
function'' W = W (x,y). It is shown that not any W allows for the
creation of such families, but only those which satisfy a certain differential
condition. For some particular cases (parallel and concurrent straight
lines) classes of solutions for W are found analytically. For each compatible
pair of potential and family, the Jacobian constant is calculated.}

^{Key words: inverse problem - rotating frames.}

INFINITY MANIFOLD IN POPOVICI'S PHOTOGRAVITATIONAL TWO-BODY PROBLEM

VASILE MIOC
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, RO-75212 Bucharest, Romania
E-mail: vmioc@aira.astro.ro

Abstract. The two-body problem associated to the modified photogravitational law proposed by the Romanian astronomer Constantin Popovici is being resumed. After studying the equilibria and the collision manifold (Mioc and Blaga 2001) via the powerful tools of the qualitative analysis, here we tackle the escape/capture orbits. We start from the equations of motion established in the quoted paper, then we apply a mixed sequence of McGehee-type transformations of the first and second kind, obtaining new regular motion equations. In this way the infinity singularity is replaced by the infinity manifold, pasted on the phase space. The flow on this manifold is entirely described, pointing out special features.

Key words: celestial mechanics – qualitative analysis – McGehee-type transformations – photogravitational model.

A BI-PARAMETRIC LIE-HORI-TYPE TRANSFORMATION

CATALIN CUCU-DUMITRESCU
Institute for Space Science
Str. Mendeleev 21-25, RO-70168 Bucharest, Romania

Abstract. The classical Lie-Hori transformation is extended to a class of canonical systems whose Hamiltonian depends on two small parameters. The compatibility of the transformation with the averaging-type methods is proved.

Key words: celestial mechanics – Hamiltonian systems – averaging methods.

SYMMETRIES IN FOCK'S TWO-BODY PROBLEM

VASILE MIOC
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, RO-75212 Bucharest, Romania
E-mail: vmioc@aira.astro.ro

Abstract. The two-body problem associated to a potential that corresponds, in classical mechanics, to Fock's relativistic field is being considered. The equations of motion are regularized via a set of McGehee-type collision-blow-up transformations. The resulting vector field has symmetries, which form a commutative group endowed with a Boolean structure. Then, starting from the regularized equations of motion, we apply a set of McGehee-type infinity-blow-up transformations. The vector field we obtain also benefits of symmetries, which form a group with the same properties as the previous one.

Key words: celestial mechanics – Fock's field – symmetries.

INTERMEDIATE STARS IN EXTRAGALACTIC RADIOSOURCE FIELDS

GHEORGHE BOCSA ¹, MIREL BÎRLAN ^1,2
² Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, RO-75212 Bucharest, Romania
E-mail: gbocsa@aira.astro.ro
² Observatoire de Paris-Meudon, DESPA
5, Place Jules Janssen, F-92195 Meudon, France
E-mail: Mirel.Birlan@obspm.fr

Abstract. The present paper joins the astrometric efforts to determine the connection between the optical reference frame and the radio one. The final product of this survey will be the astrometric catalogue of the intermediate stars in the neighbourhood of extragalactic radiosources. The statistic analysis of the O–C for the RRS2 standard stars for 188 extragalactic radiosource fields situated between –20? and +70? declination are presented. These results were performed in Bucharest Observatory.

Key words: astrometry – reference frames – radiosources.

HEPITES AND THE ROMANIAN ASTRONOMY

MAGDA STAVINSCHI
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, RO-75212 Bucharest, Romania
E-mail: magda@aira.astro.ro

Abstract. Stefan Hepites (1851–1922) was the founder of the Romanian meteorology, metrology and seismology. At the same time he was one of the promoters of the national astronomy. The paper presents the beginnings of the astronomical research in Romania and the role ?tefan Hepites played in its development.

Key words: history of astronomy – Observatory of Bucharest.