6,177 research outputs found
The Statistical Analyses of the White-Light Flares: Two Main Results About Flare Behaviours
We present two main results, based on the models and the statistical analyses
of 1672 U-band flares. We also discuss the behaviours of the white-light
flares. In addition, the parameters of the flares detected from two years of
observations on CR Dra are presented. By comparing with the flare parameters
obtained from other UV Ceti type stars, we examine the behaviour of optical
flare processes along the spectral types. Moreover, we aimed, using large
white-light flare data,to analyse the flare time-scales in respect to some
results obtained from the X-ray observations. Using the SPSS V17.0 and the
GraphPad Prism V5.02 software, the flares detected from CR Dra were modelled
with the OPEA function and analysed with t-Test method to compare similar flare
events in other stars. In addition, using some regression calculations in order
to derive the best histograms, the time-scales of the white-light flares were
analysed. Firstly, CR Dra flares have revealed that the white-light flares
behave in a similar way as their counterparts observed in X-rays. As seen in
X-ray observations, the electron density seems to be a dominant parameter in
white-light flare process, too. Secondly, the distributions of the flare
time-scales demonstrate that the number of observed flares gets a maximum value
in some particular ratios, which are 0.5 or its multiples, and especially
positive integers. The thermal processes might be dominant for these
white-light flares, while non-thermal processes might be dominant in the
others. To reach better results for the behaviour of the white-light flare
process along the spectral types, much more stars in a wide spectral range,
from the spectral type dK5e to dM6e, must be observed in the white-light flare
patrols.Comment: 17 pages, 7 figures, 5 tabl
A Gamma Doradus Candidate In Eclipsing Binary BD And?
The BVR photometric light curves of the eclipsing binary BD And were obtained
in 2008 and 2009. We estimated the mass ratio of the system as 0.97 and the
photometric solutions were derived. The results show that BD And is a detached
binary system, whose components have a little temperature difference of about
40 K. By analyzing photometric available light minimum times, we also derived
an update ephemeris and found for the first time a possible periodic
oscillation with an amplitude of 0.011 days and a period of 9.6 years. The
results indicate that the periodic oscillation could be caused by a third
component physically attached to the eclipsing binary. After removing the light
variations due to the eclipses and proximity effects, the light-curve
distortions are further explained by the pulsation of the primary component
with a dominant period of 1 day. In accordance with the position of the primary
component on the Hertzsprung-Russell diagram and its pulsation period, the
primary component of BD And could be an excellent gamma Doradus candidate. It
is rarely phenomenon that a component of the eclipsing binary system is a gamma
Doradus variable.Comment: 34 pages, 8 figures. arXiv admin note: text overlap with
arXiv:1112.1916 by other authors without attributio
Rotation Modulations and Distributions of the Flare Occurrence Rates on the Surface of Five UV Ceti Type Stars
In this study, we considered stellar spots, stellar flares, and also the
relation between these two magnetic proccesses that take place on UV Cet stars.
In addition, the hypothesis about slow flares described by Gurzadyan (1986
Ap&SS, 125, 127) was investigated. All of these discussions were based on the
results of three years of observations of UV Cet-type stars: AD Leo, EV Lac,
V1005 Ori, EQ Peg, and V1054 Oph. First of all, the results show that stellar
spot activity occurs on the stellar surface of EV Lac, V1005 Ori, and EQ Peg,
while AD Leo does not show any short-term variability and V1054 Oph does not
exhibit any variability. We report on new ephemerides for EV Lac, V1005 Ori,
and EQ Peg, obtained from time-series analyses. The phases, computed at
intervals of 0.10 phase length, where the mean flare occurence rates to obtain
maximum amplitude; also, the phases of rotational modulation were compared in
order to investigate whether there is any longitudinal relation between stellar
flares and spots. Although the results show that flare events are related with
spotted areas on stellar surfaces during some of the observing seasons, we did
not find any clear correlation among them. Finally, it was tested whether slow
flares are fast flares occurring on the opposite side of the stars according to
the direction of the observers, as mentioned in a hypothesis developed by <A
>Gurzadyan (1986). The flare occurence rates reveal that both slow and fast
flares can occur in any rotational phases. The flare occurence rates of both
fast and slow flares vary in the same way along the longitudes for all program
stars. These results are not expected based on the case mentioned in the
hypothesis.Comment: 24 pages, 15 figures, 6 tabels, 2011PASJ...63..427
Absolute Properties of An Overcontact Binary HH Boo
We obtained multi-colour light curves of HH Boo. We analysed the orbital
period variation of the system. The analysis indicated that there is possible
mass transfer from the second component to the primary or mass loss with
-5.04x10-7 Msun per year. Re-analysing the available radial velocity curve, we
analysed the light curves. The inclination (i) of the system was found to be
69.71(0.16) deg, while the semi-major axis (a) was computed as 2.246(0.064)
Rsun. The mass of the primary component was found to be 0.92(0.08) Msun, while
it was obtained as 0.58(0.06) Msun for the secondary component. The radius of
the primary component was computed as 0.98(0.03) Rsun, while it was computed as
0.80(0.02) Rsun for the secondary component. We demonstrated that HH Boo should
be a member of the A-type subclass of W UMa binaries.Comment: 20 pages, 5 figures, 4 table
V1135 Herculis: a double-lined eclipsing binary with an Anomalous Cepheid
BVR light curves and radial velocities for the double-lined eclipsing binary
V1135\,Her were obtained. The brighter component of V1135\,Her is a Cepheid
variable with a pulsation period of 4.224330.00026 days. The orbital
period of the system is about 39.997820.00233 days, which is the shortest
value among the known Type\,II Cepheid binaries. The observed B, V, and R
magnitudes were cleaned for the intrinsic variations of the primary star. The
remaining light curves, consisting of eclipses and proximity effects, are
obtained. Our analyses of the multi-colour light curves and radial velocities
led to the determination of fundamental stellar properties of both components
of the interesting system V1135\,Her. The system consists of two evolved stars,
G1+K3 between giants and supergiants, with masses of M=1.4610.054
\Msun ~and M=0.5040.040 {\Msun} and radii of R=27.10.4
{\Rsun} and R=10.40.2 {\Rsun}. The pulsating star is almost filling
its corresponding Roche lobe which indicates the possibility of mass loss or
transfer having taken place. We find an average distance of d=7500450 pc
using the BVR magnitudes and also the V-band extinction. Location in the Galaxy
and the distance to the galactic plane with an amount of 1300 pc indicate that
it probably belongs to the thick-disk population. Most of the observed and
calculated parameters of the V1135\,Her and its location on the color-magnitude
and period-luminosity diagrams lead to a classification of an Anomalous
Cepheid.Comment: 25 pages, 9 Tables, 9 Figures, Accepted Revista Mexicana de
Astronom\'ia y Astrof\'isica. arXiv admin note: substantial text overlap with
arXiv:1211.120
On the Influence of Magnetic Fields on the Structure of Protostellar Jets
We here present the first results of fully three-dimensional (3-D) MHD
simulations of radiative cooling pulsed (time-variable) jets for a set of
parameters which are suitable for protostellar outflows. Considering different
initial magnetic field topologies in approximate with the
thermal gas, i.e., (i) a longitudinal, and (ii) a helical field, both of which
permeating the jet and the ambient medium; and (iii) a purely toroidal field
permeating only the jet, we find that the overall morphology of the pulsed jet
is not very much affected by the presence of the different magnetic field
geometries in comparison to a nonmagnetic calculation. Instead, the magnetic
fields tend to affect essentially the detailed structure and emission
properties behind the shocks at the head and at the pulse-induced internal
knots, particularly for the helical and toroidal geometries. In these cases, we
find, for example, that the emissivity behind the internal knots can
be about three to four times larger than that of the purely hydrodynamical jet.
We also find that some features, like the nose cones that often develop at the
jet head in 2-D calculations involving toroidal magnetic fields, are smoothed
out or absent in the 3-D calculations.Comment: 13 pages, 3 figures, Accepted by ApJ Letters after minor corrections
(for high resolution figures, see http://www.iagusp.usp.br/~adriano/h.tar
Detecting binary compact-object mergers with gravitational waves: Understanding and Improving the sensitivity of the PyCBC search
We present an improved search for binary compact-object mergers using a
network of ground-based gravitational-wave detectors. We model a volumetric,
isotropic source population and incorporate the resulting distribution over
signal amplitude, time delay, and coalescence phase into the ranking of
candidate events. We describe an improved modeling of the background
distribution, and demonstrate incorporating a prior model of the binary mass
distribution in the ranking of candidate events. We find a and
increase in detection volume for simulated binary neutron star and
neutron star--binary black hole systems, respectively, corresponding to a
reduction of the false alarm rates assigned to signals by between one and two
orders of magnitude.Comment: 7 pages, 3 figures, as accepted by Ap
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