Apsidal motion and light a curve solution for eighteen SMC eccentric eclipsing binaries

Aims: The Danish 1.54-meter telescope at the La Silla observatory was used for photometric monitoring of selected eccentric eclipsing binaries located in the Small Magellanic Cloud. The new times of minima were derived for these systems, which are needed for accurate determination of the apsidal motion. Moreover, many new times of minima were derived from the photometric databases OGLE and MACHO. Eighteen early-type eccentric-orbit eclipsing binaries were studied. Methods: Their (O-C) diagrams of minima timings were analysed and the parameters of the apsidal motion were obtained. The light curves of these eighteen binaries were analysed using the program PHOEBE, giving the light curve parameters. For several systems the additional third light also was detected. Results: We derived for the first time and significantly improved the relatively short periods of apsidal motion from 19 to 142 years for these systems. The relativistic effects are weak, up to 10% of the total apsidal motion rate. For one system (OGLE-SMC-ECL-0888), the third-body hypothesis was also presented, which agrees with high value of the third light for this system detected during the light curve solution.Comment: 8 pages, 5 figures, 4 tables, plus the appendix data tables with times of minima. Published in 2014A&A...572A..71

New inclination changing eclipsing binaries in the Magellanic Clouds

Context: Multiple stellar systems are unique laboratories for astrophysics. Analysis of their orbital dynamics may reveal invaluable information about the physical properties of the participating stars. Unfortunately, there are only a few known and well described multiple systems, this is even more so for systems located outside the Milky Way galaxy. A particularly interesting situation occurs when the inner binary in a compact triple system is eclipsing. This is because the stellar interaction, typically resulting in precession of orbital planes, may be observable as a variation of depth of the eclipses on a long timescale. Aims: We aim to present a novel method to determine compact triples using publicly available photometric data from large surveys. Here we apply it to eclipsing binaries (EBs) in Magellanic Clouds from OGLE III database. Methods: We analyzed light curves (LCs) of 26121 LMC and 6138 SMC EBs with the goal to identify those for which the orbital inclination varies in time. Archival LCs of the selected systems, when complemented by our own observations with Danish 1.54m telescope, were thoroughly analyzed using the PHOEBE program. Time dependence of the EB's inclination was described using the theory of orbital-plane precession. By observing the parameter-dependence of the precession rate, we were able to constrain the third companion mass and its orbital period around EB. Results: We identified 58 candidates of new compact triples in Magellanic Clouds. This is the largest published sample of such systems so far. Eight of them were analyzed thoroughly and physical parameters of inner binary were determined together with an estimation of basic characteristics of the third star. These data may provide important clues about stellar formation mechanisms for objects with different metalicity than found in our galactic neighborhood.Comment: Accepted for publication in Astronomy and Astrophysic

First apsidal motion and light curve analysis of 162 eccentric eclipsing binaries from LMC

We present an extensive study of 162 early-type binary systems located in the LMC galaxy that show apsidal motion and have never been studied before. For the ample systems, we performed light curve and apsidal motion modelling for the first time. These systems have a median orbital period of 2.2 days and typical periods of the apsidal motion were derived to be of the order of decades. We identified two record-breaking systems. The first, OGLE LMC-ECL-22613, shows the shortest known apsidal motion period among systems with main sequence components (6.6 years); it contains a third component with an orbital period of 23 years. The second, OGLE LMC-ECL-17226, is an eccentric system with the shortest known orbital period (0.9879 days) and with quite fast apsidal motion period (11 years). Among the studied systems, 36 new triple-star candidates were identified based on the additional period variations. This represents more than 20% of all studied systems, which is in agreement with the statistics of multiples in our Galaxy. However, the fraction should only be considered as a lower limit of these early-type stars in the LMC because of our method of detection, data coverage, and limited precision of individual times of eclipses.Comment: 24 pages, 18 figures, 5 tables, published in 2020A&A...640A..33

Regression towards the mean in studies of arterial blood pressure

Regresja w kierunku wartości średniej (RTM, regression towards the mean) jest zjawiskiem statystycznym, które występuje w badaniach ciśnienia tętniczego niezależnie od analizowanego problemu badawczego, wieku badanych, metody pomiaru lub czasu prowadzonej obserwacji. Problem ten pojawia się zawsze, gdy dobór uczestników do grupy badanej nie jest randomizowany. Regresja w kierunku wartości średniej jest tym większa, im słabsza jest korelacja między ocenianymi zmiennymi. Spostrzeżenie to ma istotne implikacje w badaniach populacyjnych wykorzystujących pomiar przygodnego ciśnienia tętniczego, gdyż w największym stopniu może skutkować błędną interpretacją otrzymanych rezultatów. Wartość RTM stanowi problem zwłaszcza w ocenie skuteczności terapii hipotensyjnej oraz w ocenie rozpowszechnienia nadciśnienia tętniczego. Mimo że eliminacja efektu RTM nie jest często możliwa, warto uwzględnić ten problem w metodologii i odnieść się do niego w dyskusji uzyskanych wyników.Regression towards the mean (RTM) is a statistical phemonenon that occurs in blood pressure studies independently of the problem or duration of the research, age of the studied population, or the method being used. RTM is observed whenever the study group is not randomized. It is assumed that the less correlated the two variables are the greater the RTM is. The infuence of RTM should be considered mostly in casual blood pressure measurements because of imprecise assessment of the results. Consequently, RTM may be mistakenly attributed to a treatment effect and the prevalence of hypertension. Despite the entire elimination of RTM can be impossible, it is suggested to remind this problem to the reader either in the section of „materials and methods” or „discussion”

The record-breaking rotational braking of the He strong CP star HD 37776

We study the long-term light and spectral variations in the He-strong magnetic chemically peculiar star HD 37776 (V901 Ori) to search for changes of its 1.5387 d period in 1976-2007. We analyze all published photometric observations and spectrophotometry in the HeI 4026 A line. The data were supplmented with 506 new (U)VB observations obtained during the last 2 observing seasons, 66 estimates of HeI equivalent widths on 23 CFHT spectrograms and 35 of the 6-m Zeeman spectrograms. All the 1895 particular observations heve been processed simultaneously. We confirm the previously suspected increase of the period in HD 37776 which is a record-breaking among CP stars. The mean rate of the period increase during the last 31 years is 0.541+-0.020 s per year. We interpret this ongoing period increase as the slowing down of the star's surface rotation due to momentum loss through events and processes in its magnetosphere.Comment: 3 pages, 1 figure, Proceedings of the "CP#AP Workshop", Vienna, 10.-14.Sept.2007, eds.J.Ziznovsky, J.Zverko, E.Paunzen, M.Netopil, will be published in Contrib. Astron. Obs. Skalnate Ples

ASSOCIATION OF FAMILIAL AND ENVIRONMENTAL FACTORS WITH ASTHMA AND ALLERGIC DISEASES IN UKRAINIAN CHILDREN POPULATION

Background. Asthma and other allergic diseases as influenced by environmental and familial factors might be targeted using preventive measures. These diseases are a matter of some urgency in Ukraine because of the clinical, social and economic importance of childhood.Objective. The aim of this study was to investigate the relationship between prevalence of asthma, spastic bronchitis, allergic rhinitis, atopic eczema, unspecified hypersensitization and some selected environmental and familial factors in a population sample of 6 to14-yrs old Western Ukraine schoolchildren.Methods. The data set of the study was collected using a questionnaire-based survey, containing the data of 4871 urban and rural children aged 6 to 14 years. Correlation of asthma and allergic disease with familial and environmental factors was examined by means of multivariate logistic regression.Results. Increased risk of asthma (1.7 %) was associated with the urban residence (OR=1.8; p=0.04) and high parental education (OR=1.8; p=0.02); spastic bronchitis (6.2%) – with parental allergy (OR=1.3; p=0.03); atopic eczema (6.2 %) – with younger age (OR=1.3; p=0.03), high parental education (OR=1.3; p=0.03), parental allergy (OR=1.4; p=0.02), tobacco smoke at home (OR=0.7; p=0.01) and household density (OR=0.6; p=0.001); diagnosis of unspecified allergic sensitization (11.8 %) was related to high parental education (OR=1.2; p=0.03),parental employment (OR=0.8; p=0.02) and pets at home (OR=1.2; p=0.06).Conclusions. This study identifies that lifestyle and building factors are associated with an altered prevalence of common childhood allergic disease. Prevention may need to address the minimization of potential risk-factorsKEY WORDS: asthma, environmental factors, children

Surprising variations in the rotation of the chemically peculiar stars CU Virginis and V901 Orionis

CU Vir and V901 Ori belong among these few magnetic chemically peculiar stars whose rotation periods vary on timescales of decades. We aim to study the stability of the periods in CU Vir and V901 Ori using all accessible observational data containing phase information. We collected all available relevant archived observations supplemented with our new measurements of these stars and analysed the period variations of the stars using a novel method that allows for the combination of data of diverse sorts. We found that the shapes of their phase curves were constant, while the periods were changing. Both stars exhibit alternating intervals of rotational braking and acceleration. The rotation period of CU Vir was gradually shortening until the year 1968, when it reached its local minimum of 0.52067198 d. The period then started increasing, reaching its local maximum of 0.5207163 d in the year 2005. Since that time the rotation has begun to accelerate again. We also found much smaller period changes in CU Vir on a timescale of several years. The rotation period of V901 Ori was increasing for the past quarter-century, reaching a maximum of 1.538771 d in the year 2003, when the rotation period began to decrease. A theoretically unexpected alternating variability of rotation periods in these stars would remove the spin-down time paradox and brings a new insight into structure and evolution of magnetic upper-main-sequence stars.Comment: 5 pages, 3 figure