74 research outputs found
Integral group ring of the McLaughlin simple group
We consider the Zassenhaus conjecture for the normalized unit group of the integral group ring of the McLaughlin sporadic group McL. As a consequence, we confirm for this group the Kimmerle’s conjecture on prime graphs
Integral group ring of the first Mathieu simple group
We investigate the classical Zassenhaus conjecture for the normalized unit group
of the integral group ring of the simple Mathieu group M11. As a consequence, for
this group we confirm the conjecture by Kimmerle about prime graphs
Kimmerle conjecture for the Held and O'Nan sporadic simple groups
Using the Luthar--Passi method, we investigate the Zassenhaus and
Kimmerle conjectures for normalized unit groups of integral group rings of the
Held and O'Nan sporadic simple groups. We confirm the Kimmerle conjecture for
the Held simple group and also derive for both groups some extra information
relevant to the classical Zassenhaus conjecture
Covering theorems for Artinian rings
The covering properties of Artinian rings which depend on their additive structure only, are investigated
CoRoT-TESS eclipsing binaries with light-travel-time effect
Identifying long-period eclipsing binaries with space-based photometry is
still a challenge even in the century of space telescopes due to the relatively
short observation sequences and short lifetime of these missions. The
Transiting Exoplanet Survey Satellite (TESS) space telescope is an appropriate
tool to supplement previous space-based observations. In this paper we report
the first results of the eclipse timing variation (ETV) analyses of eclipsing
binaries (EBs) measured by CoRoT and TESS space telescopes. Among the 1428 EB
candidates we found 4 new potential triple candidates, for which ETV was
analysed and fitted by the well-known light-travel-time effect (LTTE). One of
them shows significant phase shift in its folded light curve which required
extra care. In this paper we also present some other systems showing
significant ETV signals that could be explained by mass transfer or apsidal
motion.Comment: 6 pages, 5 figures, accepted for publication in MNRAS. Table 3 is
available as online supplementary materia
The contact binary VW Cephei revisited: surface activity and period variation
Context. Despite the fact that VW Cephei is one of the well-studied contact
binaries in the literature, there is no fully consistent model available that
can explain every observed property of this system.
Aims. Our motivation is to obtain new spectra along with photometric
measurements, to analyze what kind of changes may have happened in the system
in the past two decades, and to propose new ideas for explaining them.
Methods. For the period analysis we determined 10 new times of minima from
our light curves, and constructed a new OC diagram of the system. Radial
velocities of the components were determined using the cross-correlation
technique. The light curves and radial velocities were modelled simultaneously
with the PHOEBE code. All observed spectra were compared to synthetic spectra
and equivalent widths of the H line were measured on their differences.
Results. We have re-determined the physical parameters of the system
according to our new light curve and spectral models. We confirm that the
primary component is more active than the secondary, and there is a correlation
between spottedness and the chromospheric activity. We propose that flip-flop
phenomenon occurring on the primary component could be a possible explanation
of the observed nature of the activity. To explain the period variation of VW
Cep, we test two previously suggested scenarios: presence of a fourth body in
the system, and the Applegate-mechanism caused by periodic magnetic activity.
We conclude that although none of these mechanisms can be ruled out entirely,
the available data suggest that mass transfer with a slowly decreasing rate
gives the most likely explanation for the period variation of VW Cep.Comment: 13 pages, 18 figures, 9 tables, accepted for publication in Astronomy
and Astrophysic
Genetic optimization of attosecond-pulse generation in light-field synthesizers
We demonstrate control over attosecond pulse generation and shaping by
numerically optimizing the synthesis of few-cycle to sub-cycle driver
waveforms. The optical waveform synthesis takes place in an ultrabroad spectral
band covering the ultraviolet-infrared domain. These optimized driver waves are
used for ultrashort single and double attosecond pulse production (with tunable
separation) revealing the potentials of the light wave synthesizer device
demonstrated by Wirth et al. [Science 334, 195 (2011)]. The results are also
analyzed with respect to attosecond pulse propagation phenomena
Variability of M giant stars based on Kepler photometry: general characteristics
M giants are among the longest-period pulsating stars which is why their
studies were traditionally restricted to analyses of low-precision visual
observations, and more recently, accurate ground-based data. Here we present an
overview of M giant variability on a wide range of time-scales (hours to
years), based on analysis of thirteen quarters of Kepler long-cadence
observations (one point per every 29.4 minutes), with a total time-span of over
1000 days. About two-thirds of the sample stars have been selected from the
ASAS-North survey of the Kepler field, with the rest supplemented from a
randomly chosen M giant control sample.
We first describe the correction of the light curves from different quarters,
which was found to be essential. We use Fourier analysis to calculate multiple
frequencies for all stars in the sample. Over 50 stars show a relatively strong
signal with a period equal to the Kepler-year and a characteristic phase
dependence across the whole field-of-view. We interpret this as a so far
unidentified systematic effect in the Kepler data. We discuss the presence of
regular patterns in the distribution of multiple periodicities and amplitudes.
In the period-amplitude plane we find that it is possible to distinguish
between solar-like oscillations and larger amplitude pulsations which are
characteristic for Mira/SR stars. This may indicate the region of the
transition between two types of oscillations as we move upward along the giant
branch.Comment: 12 pages, 13 figures, accepted for publication in MNRAS. The
normalized light curves are available upon reques
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