2,732 research outputs found
Intermittency as a universal characteristic of the complete chromosome DNA sequences of eukaryotes: From protozoa to human genomes
Large-scale dynamical properties of complete chromosome DNA sequences of
eukaryotes are considered. By the proposed deterministic models with
intermittency and symbolic dynamics we describe a wide spectrum of large-scale
patterns inherent in these sequences, such as segmental duplications, tandem
repeats, and other complex sequence structures. It is shown that the recently
discovered gene number balance on the strands is not of random nature, and a
complete chromosome DNA sequence exhibits the properties of deterministic
chaos.Comment: 4 pages, 5 figure
X-ray and optical periodicities in X-ray binaries. I.A0535+26
A homogeneous set of UBV photometry (354 data points obtained between 1983
and 1998) for the Be/X-ray binary A0535+26 = V725Tau is analysed, aiming to
look for possible periodic component(s). After subtraction of the long-term
variation it was found that only a 103-day periodic component remains in the
power spectra in both the V and B colour bands. The probability of chance
occurrence of such a peak is less than 0.1%. There are no signs of optical
variability at the X-ray period (111 d). We discuss possible reasons for a
103-day modulation and suggest that it corresponds to a beat frequency of the
orbital period of the neutron star and the precession period (~1400 d) either
of an accretion disc around the neutron star or a warped decretion disc around
the Be star.Comment: LaTeX, 6 pages, 5 figures, uses psfig.st
Orbital, precessional and flaring variability of Cygnus X-1
We present the results of a 2.5-year multiwavelength monitoring programme of
Cygnus X-1, making use of hard and soft X-ray data, optical spectroscopy,
UBVJHK photometry and radio data. In particular we confirm that the 5.6-day
orbital period is apparent in all wavebands and note the existence of a
wavelength-dependence to the modulation, in the sense that higher energies
reach minimum first. We also find a strong modulation at a period of 142 +/- 7
days, which we suggest is due to precession and/or radiative warping of the
accretion disc. Strong modulation of the hard and soft X-ray flux at this long
period may not be compatible with simple models of an optically thin accretion
flow and corona in the low state. We present the basic components required for
more detailed future modelling of the system - including a partially optically
thick jet, quasi-continuous in the low state, the base of which acts as the
Comptonising corona. In addition, we find that there are a number of flares
which appear to be correlated in at least two wavebands and generally in more.
We choose two of these flares to study in further detail and find that the hard
and soft X-rays are well-correlated in the first and that the soft X-rays and
radio are correlated in the second. In general, the optical and infrared show
similar behaviour to each other but are not correlated with the X-rays or
radio.Comment: Accepted for publication in MNRAS, 2 figures in colou
Multi-waveband Emission Maps of Blazars
We are leading a comprehensive multi-waveband monitoring program of 34
gamma-ray bright blazars designed to locate the emission regions of blazars
from radio to gamma-ray frequencies. The "maps" are anchored by sequences of
images in both total and polarized intensity obtained with the VLBA at an
angular resolution of ~ 0.1 milliarcseconds. The time-variable linear
polarization at radio to optical wavelengths and radio to gamma-ray light
curves allow us to specify the locations of flares relative to bright
stationary features seen in the images and to infer the geometry of the
magnetic field in different regions of the jet. Our data reveal that some
flares occur simultaneously at different wavebands and others are only seen at
some of the frequencies. The flares are often triggered by a superluminal knot
passing through the stationary "core" on the VLBA images. Other flares occur
upstream or even parsecs downstream of the core.Comment: 5 pages, including 2 figures; to be published in Journal of
Astrophysics and Astronomy, as part of proceedings of the meeting
"Multiwavelength Variability of Blazars" held in Guangzhou, China, in
September 201
A long-lasting quiescence phase of the eruptive variable V1118 Ori
V1118 Ori is an eruptive variable belonging to the EXor class of Pre-Main
Sequence stars whose episodic outbursts are attributed to disk accretion
events. Since 2006, V1118 Ori is in the longest quiescence stage ever observed
between two subsequent outbursts of its recent history. We present
near-infrared photometry of V1118 Ori carried out during the last eight years,
along with a complete spectroscopic coverage from 0.35 to 2.5 um. A longterm
sampling of V1118 Ori in quiescence has never been done, hence we can benefit
from the current circumstance to determine the lowest values (i.e. the zeroes)
of the parameters to be used as a reference for evaluating the physical changes
typical of more active phases. A quiescence mass accretion rate between 1--3
10 M_{\sun} yr can be derived and the difference with
previous determinations is discussed. From line emission and IR colors analysis
a visual extinction of 1-2 mag is consistently derived, confirming that V1118
Ori (at least in quiescence) is a low-extinction T Tauri star with a bolometric
luminosity of about 2.1 L_{\sun}. An anti-correlation exists between the
equivalent width of the emission lines and the underlying continuum. We
searched the literature for evaluating whether or not such a behaviour is a
common feature of the whole class. The anti-correlation is clearly recognizable
for all the available EXors in the optical range (H and H
lines), while it is not as much evident in the infrared (Pa and
Br lines). The observed anti-correlation supports the accretion-driven
mechanism as the most likely to account for continuum variations.Comment: 6 figures, 5 tables, accepted on Ap
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