ROMANIAN ASTRONOMICAL JOURNAL
Vol. 20, No. 1, 2010
C O N T E N T S
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Vasile URECHE,
Rodica ROMAN,
Mean Densities of Neutron Stars
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3–8
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Alexandru
POP, Rodica ROMAN,
Long-Term Orbital Period Variation of RT Andromedae
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9–15
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Emil POPESCU,
Nedelia Antonia POPESCU,
Modeling Fluctuations of
Solar Wind Parameters with Heavy-Tailed Distributions
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17–25
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Liliana
DUMITRU, Cristiana DUMITRACHE,
Active Region 9612 Evolution ……………...............................................................
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27–33
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Cristiana
DUMITRACHE, Diana CONSTANTIN,
Kink Instabilities Triggering a Filament
Eruption …………………………………..
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35–44
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Suresh CHANDRA,
Lalan PRASAD,
Oblique Propagation and Dissipation
of Alfvén Waves in Coronal Holes Reinvestigated
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45–48
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Iharka SZÜCS-CSILLIK,
The Lie Integrator and the Hénon-Heiles System
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49–66
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Adrian DRǍGUŞAN,
Quantitative and Qualitative
Analysis of Geostationary Satellite Dynamics ……...
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67–72
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Alin NEDELCU,
Petre POPESCU, Octavian BǍDESCU, Petre PARASCHIV,
DCRF–ICRF Connection and Asteroid Differential
Astrometry ………………….
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73–78
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Octavian
BǍDESCU, Marin PLOPEANU, Alin NEDELCU, Petre POPESCU, Petre PARASCHIV,
A Project for Modern Astrogeodetic Geoid Determination
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79–84
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Doina IONESCU,
125 Years since the Birth of the
Astronomer Gheorghe Demetrescu (1885–1969)…
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85–90
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MISCELLANEA
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The International Workshop “Recent
Insights into our Universe”, Bucharest, Romania, 28–29 October 2009 (Vasile
Mioc, Nedelia Antonia Popescu, Cristiana Dumitrache) ……………...
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91–93
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MEAN DENSITIES OF NEUTRON STARS
VASILE URECHE
1, RODICA ROMAN
2
1 Babeş-Bolyai University of Cluj-Napoca
Str. M. Kogãlniceanu 1, 400084 Cluj-Napoca, Romania
E-mail: vureche@math.ubbcluj.ro
2 Astronomical Institute of the
Romanian Academy
Astronomical Observatory Cluj-Napoca
Str. Cireşilor 19, 400487 Cluj-Napoca, Romania
E-mail: rdcroman@yahoo.com
Abstract. For a spherical neutron star the proper (relativistic)
volume is computed. Then, by using Douchin-Haensel
equation of state, the mean densities of neutron stars were obtained.
So, different characteristics of neutron stars can
be represented as functions of mean density, instead of central density.
The concentration of matter towards the center
of star is a decreasing function of central density or, alternatively,
a decreasing function of dimensionless central pressure,
for stable configurations. This means that the most compact neutron stars
tend to become closer to homogeneous objects.
Key
words: stellar structure – neutron stars.
LONG-TERM ORBITAL PERIOD
VARIATION
OF RT ANDROMEDAE
ALEXANDRU POP, RODICA ROMAN
Astronomical Institute of the Romanian Academy
Astronomical Observatory Cluj-Napoca
Str. Cireşilor 19, 400487 Cluj-Napoca, Romania
E-mail: andi_pop@yahoo.com,
rdcroman@yahoo.com
Abstract. Different authors approached the problem of orbital period
variation of the active eclipsing binary
RT Andromedae on long time scales. Some of them suggested the presence
of a periodicity longer than 100 years.
Such a conclusion encounters an important difficulty: the inferred periodicity
is longer than the time base of the
available data. We tackled this problem using visual, photographic, and
photoelectric times of minimum light.
Key words: variable stars – eclipsing binary systems – data analysis.
MODELING FLUCTUATIONS
OF SOLAR
WIND PARAMETERS
WITH HEAVY-TAILED DISTRIBUTIONS
EMIL POPESCU 1,2, NEDELIA ANTONIA POPESCU 1
1 Astronomical Institute of the
Romanian Academy
Str. Cuţitul de Argint 5, 040557 Bucharest, Romania
E-mail: nedelia@aira.astro.ro
2 Technical University of Civil
Engineering
Bd. Lacul Tei
124, 020396 Bucharest, Romania
E-mail: epopescu@utcb.ro
Abstract. Recent approaches for heavy-tail time series models
are applied to the study of the statistical properties
in solar wind turbulence. We investigate the probability distribution
functions (PDFs) of fluctuations for solar wind
plasma parameters and interplanetary magnetic field, for in-situ data
recorded by Ulysses during 2001. The scale
dependence of the observed PDFs for velocity, and magnetic field intensity
fluctuations are well fitted for different
time lags using multi-scale statistical methods. Analysis of the magnetic
field strength shows that these fluctuations
are less intermittent at larger scales than at small scales, their behavior
at different scales being quantitatively described
by the PDFs.
Key
words: solar wind turbulence – solar wind plasma parameters – interplanetary
magnetic field – probability distribution function – intermittent behavior.
ACTIVE REGION 9612 EVOLUTION
LILIANA DUMITRU, CRISTIANA DUMITRACHE
Astronomical Institute
of the Romanian Academy
Str. Cuţitul de Argint 5, 040557 Bucharest, Romania
E-mail: lyly@aira.astro.ro,
crisd@aira.astro.ro
Abstract. The active region 9612 was observed between 6 and
17 September 2001. Situated in the Northern
hemisphere of the Sun, this region is closely linked to a filament evolution,
forming together an interesting magnetic
topology. We analyze the evolution of this active region and the explosive
events that occurred during this period:
the flares on 13 and 16 September, and a CME on 15 September 2001. We
use ground-based observations and
data from space (SOHO, Yohkoh).
Key
words: Sun – active regions – filaments – magnetic fields – CMEs.
KINK INSTABILITIES TRIGGERING
A FILAMENT ERUPTION
CRISTIANA DUMITRACHE, DIANA CONSTANTIN
Astronomical Institute
of the Romanian Academy
Str. Cuţitul de
Argint 5, 040557 Bucharest, Romania
E-mail: crisd@aira.astro.ro,
diana@aira.astro.ro
Abstract. A huge complex filament was observed between 28 December
2000 and 7 January 2001. We analyze
its dynamics and its sudden disappearance. We analyze the 3D coronal
magnetic field extrapolated from the MDI
photospheric magnetograms and compare with filament coronal images. The
filament erupted in a CME after a mild
helical upward movement of plasma on 7 January. We attempt to explain
this CME event onset by kink instabilities.
An approach to estimate the filament helicity and magnetic flux injection
explain the filament destabilization.
Key
words: Sun – prominences – CMEs – instability.
OBLIQUE PROPAGATION AND
DISSIPATION
OF ALFVÉN WAVES IN CORONAL HOLES REINVESTIGATED
SURESH CHANDRA 1, LALAN PRASAD 2
1 School of Physics, Shri Mata Vaishno
Devi University
Katra 182 320 (J&K), India
E-mail: suresh492000@yahoo.co.in
2 Department of Physics, M.B. Govt.
P.G. College
Haldwani 263 241, India
Abstract. We have reinvestigated the work on oblique propagation
and dissipation of Alfvén waves in coronal
holes. Srivastava and Dwivedi (2007) derived a dispersion relation for
oblique propagation of Alfvén waves.
This relation seems to be erroneous. Consequently, the conclusions formulated
by them are not reliable.
Key
words: solar physics – coronal holes – Alfvén waves.
THE LIE-INTEGRATOR
AND THE HÉNON-HEILES SYSTEM
IHARKA SZÜCS-CSILLIK
Astronomical Institute
of the Romanian Academy
Astronomical Observatory Cluj-Napoca
Str. Cireşilor 19, 400487 Cluj-Napoca, Romania
E-mail: iharka@gmail.com
Abstract. There are several integration schemes intended to solve
the equations of motion in problems of
celestial mechanics. The Lie-integration method is based on the idea to
tackle systems of ODE via Lie series.
It is applied to solve Hamiltonian systems by giving recurrence formulae
for the calculation of the Lie-terms.
Here we present these recurrence formulae, which considerably simplify
the linearized equations of motion.
To exemplify, we choose the famous chaotic Hénon-Heiles system. Then the
Lie-integrator is compared with
the well-known Runge-Kutta method and the symplectic integrator for the
Hénon-Heiles system. The convergence
of the Lie-integrator can be regarded as a kind of a symplectic integrator,
which conserves the integrals of motion.
The Lie-integrator method is found to be very well suited for a long-time
integration of orbits in celestial mechanics.
Key
words: celestial mechanics – numerical methods – Lie series – Hénon-Heiles’ model.
QUANTITATIVE AND QUALITATIVE
ANALYSIS
OF GEOSTATIONARY SATELLITE DYNAMICS
ADRIAN DRǍGUŞAN
Naval Academy
“Mircea cel Bătrân”, Constanţa, Romania
Abstract. This paper presents a quantitative and qualitative
analysis of geostationary satellite motion. This analysis
is included in the doctoral thesis of the author, sustained in September
2009. The numerical results are well known
and they are found in many scientific works. We use an original method,
based on Runge-Kutta 4th order, in order
to obtain the separate effect of each perturbation on the orbit of the
geostationary satellite. The satellite will be
launched soon by South Korea at 128 degrees longitude. The qualitative
approach is first time used to analyze the
orbital motion of the geostationary satellite.
Key
words: geostationary satellites – qualitative analysis.
DCRF-ICRF CONNECTION
AND ASTEROID DIFFERENTIAL ASTROMETRY
ALIN NEDELCU 1, PETRE POPESCU 1, Octavian bǍdescu 1,2,
PETRE PARASCHIV 1
1 Astronomical Institute of the
Romanian Academy
Str. Cuțitul de Argint 5, 040557 Bucharest, Romania
E-mails: [nedelcu,
petre, octavian, paras]@aira.astro.ro
2 Technical University of Civil
Engineering, Faculty of Geodesy
Bd. Lacul Tei
124, 020396 Bucharest, Romania
Abstract. One of the methods used to obtain an accurate tie
between the different reference frames is the
simultaneous observation of an object referred to both frames. In our
case, in which we investigate the link
between dynamical reference frame and ICRF, this method will require CCD
imaging of an asteroid and of
an angular nearby quasar. The direct comparison of the asteroid position
obtained from a dynamical model
of the Solar System with the quasar optical position in an optimally
calibrated astrometric field will yield the
local, instantaneous orientation of the dynamical celestial reference
frame (DCRF) with respect to a quasi-inertial,
extragalactic reference frame. We present a database of apparent close
approaches between asteroids and
quasars, events that could be used to investigate the DRF-ICRF link.
Key
words: astrometry – reference frames – asteroids.
A PROJECT FOR MODERN
ASTROGEODETIC
GEOID DETERMINATION
Octavian bǍdescu 1,2, marin Plopeanu 2, ALIN NEDELCU 1,
PETRE POPESCU 1, PETRE PARASCHIV 1
1 Astronomical Institute of the
Romanian Academy
Str. Cuțitul de
Argint 5, 040557, Bucharest, Romania
E-mails: [octavian,
nedelcu, petre,paras]@aira.astro.ro
2 Technical University of Civil
Engineering
Bd. Lacul Tei
124, 020396, Bucharest, Romania
E-mail: mplopeanu@geodezie.utcb.ro
Abstract. Nowadays, astrogeodetic methods for geoid determination
are often considered obsolete.
We present in this paper a new project for geoid determination by astrogeodetic
vertical deviation,
based on state-of-the-art geodetic and astronomical technologies. Our
proposal tracks the accuracy
and efficient real time determination of the vertical deviations, in sufficient
number points, which will
serve to the geoid determination. This project is designed as collaboration
between the Bucharest
Technical University of Civil Engineering, Faculty of Geodesy, and the
Astronomical Institute of the
Romanian Academy, Fundamental Astronomy Department.
Key
words: astrogeodesy – geoid – vertical deviation.
125 YEARS SINCE THE BIRTH OF THE ASTRONOMER
GHEORGHE DEMETRESCU (1885–1969)
DOINA IONESCU
Astronomical Institute
of the Romanian Academy
Str. Cuţitul de
Argint 5, 040557 Bucharest, Romania
E-mail: doinaionescu36@clicknet.ro
Abstract. We survey the life and work of Academician Gheorghe
Demetrescu, renowned Romanian
astronomer, at the 125th anniversary of his birth. We point out especially
his activity as a professor and
as the Director of the Bucharest Astronomical Observatory.
Key
words: history of astronomy – Bucharest Astronomical Observatory.