HT Cas - eclipsing dwarf nova during its superoutburst in 2010

We present results of a world-wide observing campaign of the eclipsing dwarf nova - HT Cas during its superoutburst in November 2010. Using collected data we were able to conduct analysis of the light curves and we calculated $O-C$ diagrams. The CCD photometric observations enabled us to derive the superhump period and with the timings of eclipses the orbital period was calculated. Based on superhump and orbital period estimations the period excess and mass ratio of the system were obtained

IX Draconis - a curious ER UMa-type dwarf nova

We report results of an extensive world-wide observing campaign devoted to a very active dwarf nova star - IX Draconis. We investigated photometric behaviour of the system to derive its basic outburst properties and understand peculiarities of IX Dra as well as other active cataclysmic variables, in particular dwarf novae of the ER Uma-type. In order to measure fundamental parameters of the system, we carried out analyses of the light curve, O-C diagram, and power spectra. During over two months of observations we detected two superoutbursts and several normal outbursts. The V magnitude of the star varied in the range 14.6 - 18.2 mag. Superoutbursts occur regularly with the supercycle length of 58.5+/-0.5 d. When analysing data over the past 20 years, we found that the supercycle length is increasing at a rate of P_dot = 1.8 * 10^{-3}. Normal outbursts appear to be irregular, with typical occurrence times in the range 3.1 - 4.1 d. We detected a double-peaked structure of superhumps during superoutburst, with the secondary maximum becoming dominant near the end of the superoutburst. The mean superhump period observed during superoutbursts equals 0.066982(36) d, which is constant over the last two decades of observations. Based on the power spectrum analysis, the evaluation of the orbital period was problematic. We found two possible values: the first one, 0.06641(3) d, which is in agreement with previous studies and our O-C analysis (0.06646(2) d), and the second one, 0.06482(3) d, which is less likely. The evolutionary status of the object depends dramatically on the choice between these two values. A spectroscopic determination of the orbital period is needed. We updated available information on ER UMa-type stars and present a new set of their basic statistics. Thereby, we provide evidence that this class of stars is not uniform.Comment: Accepted for publication in MNRAS; 15 pages, 15 figures, 6 tables; typo correcte

Fourier decomposition and frequency analysis of the pulsating stars with P<1 d in the OGLE database. I. Monoperiodic Delta Scuti, RRc and RRab variables. Separation criteria and particularities

The OGLE database is revisited to investigate in more detail the properties of the Fourier parameters. Methodological improvements led us to identify a clear separation among High-Amplitude Delta Scuti (HADS), RRc and RRab stars. The bimodal distribution of the R21 parameter in HADS stars is explained as a contamination effect from RRc stars: there is evidence that all stars with 0.20<P<0.25 d are RRc variables. The previously claimed existence of a subclass of unusual HADS is demonstrated to be a spurious result. Candidate overtone pulsators are found among HADS and RRc variables. The properties of the Fourier parameters are discussed as a function of the physical conditions in the stars involved. Among the field RRab stars we detected different light-curve groups producing distinct "tails" in the Fourier plots for P>0.55 d; evolutionary phases or the combination of different physical conditions (not only metallicity) are suggested to explain this separation, observed also in the cluster RRab stars. The stellar parameters of RRc stars in a given globular cluster show different tendencies than those of RRc stars from different clusters.Comment: 12 pages (in A&A style), 14 eps figures. Accepted for A&A Main Journal. Table 3, 4 and 5 are also included as ascii files. The atlas of the light curves and least-squares fits can be requested from the autho

On approximate solutions of semilinear evolution equations

A general framework is presented to discuss the approximate solutions of an evolution equation in a Banach space, with a linear part generating a semigroup and a sufficiently smooth nonlinear part. A theorem is presented, allowing to infer from an approximate solution the existence of an exact solution. According to this theorem, the interval of existence of the exact solution and the distance of the latter from the approximate solution can be evaluated solving a one-dimensional "control" integral equation, where the unknown gives a bound on the previous distance as a function of time. For example, the control equation can be applied to the approximation methods based on the reduction of the evolution equation to finite-dimensional manifolds: among them, the Galerkin method is discussed in detail. To illustrate this framework, the nonlinear heat equation is considered. In this case the control equation is used to evaluate the error of the Galerkin approximation; depending on the initial datum, this approach either grants global existence of the solution or gives fairly accurate bounds on the blow up time.Comment: 33 pages, 10 figures. To appear in Rev. Math. Phys. (Shortened version; the proof of Prop. 3.4. has been simplified

Fourier decomposition and frequency analysis of the pulsating stars with P < 1day in the OGLE database. II. Multiperiodic RR Lyrae variables in the Galactic Bulge

We present the results of a systematic search for multiperiodic pulsators among the Galactic Bulge RR Lyrae stars of the OGLE-1 sample. We identify one "canonical" double-mode variable (RRd star) pulsating in two radial modes. In 38 stars we detect secondary periodicities very close to the primary pulsation frequency. This type of multiperiodic variables constitute ~23% of RRab and ~5% of RRc population of the Bulge. With the observed period ratios of 0.95-1.02 the secondary periods must correspond to nonradial modes of oscillation. Their beating with the primary (radial) pulsation leads to a long-term amplitude and phase modulation, known as the Blazhko effect. The Blazhko RRab variables occur more frequently in the Galactic Bulge than in the LMC. The opposite tendency is seen in case of the RRd stars. The differences of incidence rates are most likely caused by different metallicity of the two populations. We discuss pulsation properties of the OGLE-1 Blazhko stars and compare them with predictions of theoretical models. We argue, that the oblique magnetic pulsator model of Shibahashi (2000) cannot account for the observations and should be ruled out.Comment: 11 pages, 8 figures, accepted for publication in Astronomy & Astrophysic

MN Draconis - peculiar, active dwarf nova in the period gap

Context: We present results of an extensive world-wide observing campaign of MN Draconis. Aims: MN Draconis is a poorly known active dwarf nova in the period gap and is one of the only two known cases of period gap SU UMa objects showing the negative superhumps. Photometric behaviour of MN Draconis poses a challenge for existing models of the superhump and superoutburst mechanisms. Therefore, thorough investigation of peculiar systems, such as MN Draconis, is crucial for our understanding of evolution of the close binary stars. Methods: To measure fundamental parameters of the system, we collected photometric data in October 2009, June-September 2013 and June-December 2015. Analysis of the light curves, $O-C$ diagrams and power spectra was carried out. Results: During our three observational seasons we detected four superoutburts and several normal outbursts. Based on the two consecutive superoutbursts detected in 2015, the supercycle length was derived P_sc = 74 +/- 0.5 days and it has been increasing with a rate of P_dot = 3.3 x 10^(-3) during last twelve years. Based on the positive and negative superhumps we calculated the period excess epsilon = 5.6% +/- 0.1%, the period deficit epsilon_ = 2.5% +/- 0.6%, and in result, the orbital period P_orb = 0.0994(1) days (143.126 +/- 0.144 min). We updated the basic light curve parameters of MN Draconis. Conclusions: MN Draconis is the first discovered SU UMa system in the period gap with increasing supercycle length.Comment: 14 pages, 20 figures, 8 tables, accepted for publication in Astronomy and Astrophysic

Variable Stars in the Globular Cluster M5. Application of the Image Subtraction Method

We present $V$-band light curves of 61 variables from the core of the globular cluster M5 obtained using a newly developed image subtraction method (ISM). Four of these variables were previously unknown. Only 26 variables were found in the same field using photometry obtained with DoPHOT software. Fourier parameters of the ISM light curves have relative errors up to 20 times smaller than parameters measured from DoPHOT photometry. We conclude that the new method is very promising for searching for variable stars in the cores of the globular clusters and gives very accurate relative photometry with quality comparable to photometry obtained by HST. We also show that the variable V104 is not an eclipsing star as has been suggested, but is an RRc star showing non-radial pulsations.Comment: submitted to MNRAS, 9 pages, 4 figure

TLC determination of flavonoids from different cultivars of Allium cepa and Allium ascalonicum

This study comprises the optimization and validation of a new TLC method for determination of flavonols in the bulbs of seven cultivars of onions and shallots. Separation was performed on RP-18 plates with the solvent mixture tetrahydrofuran/water/formic acid (40+60+6, V/V/V) as a mobile phase. The method was validated for precision, linearity, LOD, LOQ, accuracy and robustness. Chromatographic analysis of the extracts revealed the presence of three main flavonols, quercetin, quercetin-4’-O-glucoside and quercetin-3,4’-O-diglucoside in the majority of analyzed cultivars. The content of flavonols in the analyzed extracts of onion bulbs varied from 123 (‘Exihibition’) to 1079 mg kg–1 fresh mass (fm) (‘Hybing’) in edible parts, and from 1727 (‘Hyline’) to 28949 mg kg–1 fm (‘Red Baron’) in outer scales. The bulbs of two shallot cultivars contained 209 (‘Ambition’) and 523 mg kg–1 fm (‘Matador’) of flavonols in edible parts and 5426 and 8916 mg kg–1 fm in outer scales, respectively

Identification of a molecular defect in a stillborn fetus with perinatal lethal hypophosphatasia using a disease-associated genome sequencing approach

Lethal skeletal disorders represent a heterogeneous and clinically variable group of genetic conditions, usually difficult to diagnose without post-mortem radiological assessment. Here we report on a stillborn patient delivered at 22 weeks of gestation who presented with severe skeletal symptoms comprising limb shortening and intrauterine fractures detected upon prenatal ultrasound and autopsy examination. Since post-mortem X-ray was refused and no phenotypic diagnosis could be attempted, we performed next-generation sequencing (NGS) of 2741 genes associated with all known Mendelian disorders. With this strategy, we were able to demonstrate the diagnosis at a molecular level, which turned out to be perinatal lethal hypophosphatasia (HPP). This severe form of HPP represents an inborn defect of ossification often resulting in stillbirth or postnatal death. The NGS panel revealed compound heterozygous ALPL missense mutations: c.1283G>C(p.Arg428Pro) and c.1363G>A(p.Gly455Ser). Mutations detected in our case, although previously described in other patients, have not been reported to co-occur in a single individual. The diagnosis established in our index using the NGS-based approach could have been successfully reached by standard radiography. Thus, our report points to the importance of X-ray examination in stillborn cases and highlights the emerging role of NGS strategies in the diagnostic process of prenatally manifesting skeletal disorders