THE DETECTION AND DIAGNOSIS OF LOW-LEVEL STELLAR VARIABILITY THROUGH RESAMPLING METHODS
ALEXANDRU
POP1, CALIN
VAMOS2
1 Astronomical
Institute of the
Astronomical
Observatory Cluj-Napoca
Str.
Cireşilor
19, 400487 Cluj-Napoca, Romania
E-mail:
andi_pop@yahoo.com
2 “T. Popoviciu”
Institute of Numerical Analysis of the
P.O.
Box 68,
400110 Cluj-Napoca, Romania
E-mail:
cvamos@ictp.acad.ro
Abstract. Our previous
method (Pop 2005, 2007a) for detection and diagnosis
of stellar variability based on
observational noise Gaussianity is generalized by using
statistical tests
based on resampling methods with or without replacement. Its ability to
detect
low amplitude
periodic signals in the presence of Gaussian white noise and
correlated AR(1) noise is confirmed. The presence of a significant
amount of
noise may also be detected.
The investigated method may be useful for the
detection of new variable stars, for identification of the most stable
stars to
be used as comparison in differential
photometry, for detection of companions
signatures (maybe exoplanets) in noisy timing data on variable stars, etc.
Key words: stellar variability – data analysis.
SEARCH
FOR EVOLUTIONARY CHANGES IN PERIODS
AND RANDOM CYCLE-TO-CYCLE IN CLASSICAL
CEPHEIDS
mohamed abdel-sabour
National Research Institute of Astronomy and Geophysics (NRIAG)
11421-Helwan,
Cairo, Egypt
E-mail:
msabour@nriag.sci.eg
Abstract. Rate of period
changes for individual Cepheid variables are being
used to examine the parameters of stars as they cross the instability
strip.
O–C data
are used to establish the period change. Our studies so far have been
very successful in mapping the pulsation amplitude of Cepheids across
the
instability strip.
By using the formalism of Eddington and Plakidis (1929), we
found that the evolutionary period changes in classical Cepheids under
study
are not the result of
random cycle-to-cycle.
Key words: variable stars – Cepheids – period change.
FOUR CONTACT BINARIES AS SEEN BY HIPPARCOS
HELEN
ROVITHIS-LIVANIOU1,
SOTIRIOS TSANTILAS1, MARIAN DORU ŞURAN2,
ALEXANDRU DUMITRESCU2 PETROS
ROVITHIS3
1Section of
Astrophysics-Astronomy and
Mechanics, Department of Physics,
Panepistimiopolis,
Zografos, 157 84 Athens, Greece
E-mail:
elivan@phys.uoa.gr
2Astronomical
Institute of the
Str.
Cuţitul de
Argint 5, 040557 Bucharest, Romania
E-mail:
suran@aira.astro.ro
3Institute
of Astronomy and Astrophysics, National Observatory of
Abstract. In this paper the
photoelectric observations of four contact
binary systems discovered by Hipparcos mission are analyzed and
discussed.
The
analyzed systems are: Hip71107, (EF Boo);
Hip46005, (FN Cam); Hip76272, (FU Dra);
and Hip61237, (II UMa). The light
curve analysis was
made with the program PHOEBE, which is based on the Roche
model and it is a modification of the widely used W-D code.
Spectroscopic
studies have
been carried out for all four systems. And, as the first three
systems had been also analyzed earlier, when spectroscopic studies did
not
exist and their
analysis was based on q-search,
this offers a unique opportunity to compare the results based only on q-search with those derived when
the spectroscopic
mass ratio is known. As regards the fourth binary,
i.e., II UMa, this is its first
photometric solution appeared in a journal.
Key
words: eclipsing
binaries – light curves analysis – individual stars: EF Boo, FN Cam, FU
Dra, II
UMa.
ANALYSIS OF Y OPHIUCHI LIGHT CURVES OBSERVED BETWEEN 1948–2001
ALEXANDRU POP
Astronomical
Institute of the
Astronomical
Observatory Cluj-Napoca
Str.
Cireşilor
19, 400487 Cluj-Napoca, Romania
E-mail:
andi_pop@yahoo.com
Abstract. Twenty seven
photoelectric data sets (twenty six in Johnson V
filter and one in the Hp passband) on the
classical
Cepheid Y Ophiuchi,
covering a time base of about 52.8 years, were analyzed
through the Fourier decomposition method. The values of the Fourier
coefficients, Fourier
structural parameters, the full amplitude of each of the
27 light curves, as well as different types of light curve structural
parameters were determined.
For each data set we also determined a normal time
of maximum light using the fitted light curve.
Key words: variable stars – Cepheids – data analysis.
LASCO-C1 SPECTRAL
ANALYSIS OF FLOWS
MARILENA MIERLA1, RAINER SCHWENN2, LUCA TERIACA2,
GUILLERMO STENBORG3, BORUT PODLIPNIK2
1Astronomical
Institute of the
Str.Cutitul
de
Argint 5, RO-040557 Bucharest, Romania
E-mail:
marilena@aira.astro.ro
2Max Planck Institute for Solar System Research,
Max-Planck-Str.
2,
37191 Katlenburg-Lindau, Germany
E-mail:
schwenn@mps.mpg.de, teriaca@mps.mpg.de, podlipnick@mps.mpg.de
E-mail:
stenborg@kreutz.nascom.nasa.gov
Abstract. The purpose of this paper is to analyze flows in
the inner corona (region
between 1.1 and 1.6 Rs), by using the spectral data from
LASCO-C1. In
particular, we studied the emergence of the slow solar wind at activity
minimum
(August–October 1996) and during the
ascending phase of the solar cycle (March
1998). Series of images acquired at different wavelengths across the Fe
X 637.6
nm (red) and
Fe XIV 530.3 nm (green) coronal lines by LASCO-C1 allow us to
build radiance and velocity maps of the off-limb solar corona. From the
data in
1996 we deduce speeds in the range 9 to 15 km/s, at a distance of 1.3
solar
radii from the Sun center. In 1998 we could observe
flows inside the streamers
in the range 8 to 10 km/s. These values provide constraints for
theoretical
models of the source regions of the
slow solar wind.
Key words: Sun – green corona – dynamics – slow solar wind.