The variation of the magnetic field of the Ap star HD~50169 over its 29 year rotation period

Context. The Ap stars that rotate extremely slowly, with periods of decades to centuries, represent one of the keys to the understanding of the processes leading to the differentiation of stellar rotation. Aims. We characterise the variations of the magnetic field of the Ap star HD 50169 and derive constraints about its structure. Methods. We combine published measurements of the mean longitudinal field of HD 50169 with new determinations of this field moment from circular spectropolarimetry obtained at the 6-m telescope BTA of the Special Astrophysical Observatory of the Russian Academy of Sciences. For the mean magnetic field modulus , literature data are complemented by the analysis of ESO spectra, both newly acquired and from the archive. Radial velocities are also obtained from these spectra. Results. We present the first determination of the rotation period of HD 50169, Prot = (29.04+/-0.82) y. HD 50169 is currently the longest-period Ap star for which magnetic field measurements have been obtained over more than a full cycle. The variation curves of both and have a significant degree of anharmonicity, and there is a definite phase shift between their respective extrema. We confirm that HD 50169 is a wide spectroscopic binary, refine its orbital elements, and suggest that the secondary is probably a dwarf star of spectral type M. Conclusions. The shapes and mutual phase shifts of the derived magnetic variation curves unquestionably indicate that the magnetic field of HD 50169 is not symmetric about an axis passing through its centre. Overall, HD 50169 appears similar to the bulk of the long-period Ap stars.Comment: 10 pages, 3 figures, accepted for publication in A&

HD 965: An extremely peculiar A star with an extremely long rotation period

Context. One of the keys to understanding the origin of the Ap stars and their significance in the general context of stellar astrophysics is the consideration of the most extreme properties displayed by some of them. In that context, HD 965 is particularly interesting, as it combines some of the most pronounced chemical peculiarities with one of the longest rotation periods known. Aims. We characterise the variations of the magnetic field of the Ap star HD 965 and derive constraints about its structure. Methods. We combine published measurements of the mean longitudinal field of HD 965 with new determinations of this field moment from circular spectropolarimetry obtained at the 6-m telescope BTA of the Special Astrophysical Observatory of the Russian Academy of Sciences. For the mean magnetic field modulus , literature data are complemented by the analysis of ESO archive spectra. Results. We present the first determination of the rotation period of HD 965, P = (16.5+/-0.5) y. HD 965 is only the third Ap star with a period longer than 10 years for which magnetic field measurements have been obtained over more than a full cycle. The variation curve of is well approximated by a cosine wave. does not show any significant variation. The observed behaviour of these field moments is well represented by a simple model consisting of the superposition of collinear dipole, quadrupole and octupole. The distribution of neodymium over the surface of HD 965 is highly non-uniform. The element appears concentrated around the magnetic poles, especially the negative one. Conclusions. The shape of the longitudinal magnetic variation curve of HD 965 indicates that its magnetic field is essentially symmetric about an axis passing through the centre of the star. Overall, as far as its magnetic field is concerned, HD 965 appears similar to the bulk of the long-period Ap stars.Comment: 7 pages, 4 figures, accepted for publication in Astronomy & Astrophysics. arXiv admin note: text overlap with arXiv:1902.0586

HD 178892 - a cool Ap star with extremely strong magnetic field

We report a discovery of the Zeeman resolved spectral lines, corresponding to the extremely large magnetic field modulus =17.5 kG, in the cool Ap star HD 178892. The mean longitudinal field of this star reaches 7.5 kG, and its rotational modulation implies the strength of the dipolar magnetic component Bp>=23 kG. We have revised rotation period of the star using the All Sky Automated Survey photometry and determined P=8.2478 d. Rotation phases of the magnetic and photometric maxima of the star coincide with each other. We obtained Geneva photometric observation of HD 178892 and estimated Teff=7700+/-250 K using photometry and the hydrogen Balmer lines. Preliminary abundance analysis reveals abundance pattern typical of rapidly oscillating Ap stars.Comment: Accepted by Astronomy & Astrophysics; 4 pages, 4 figure

Comprehensive study of the magnetic stars HD 5797 and HD 40711 with large chromium and iron overabundances

We present the results of a comprehensive study of the chemically peculiar stars HD 5797 and HD 40711. The stars have the same effective temperature, Teff = 8900 K, and a similar chemical composition with large iron (+1.5 dex) and chromium (+3 dex) overabundances compared to the Sun. The overabundance of rare-earth elements typically reaches +3 dex. We have measured the magnetic field of HD 5797. The longitudinal field component Be has been found to vary sinusoidally between -100 and +1000 G with a period of 69 days. Our estimate of the evolutionary status of the stars suggests that HD 5797 and HD 40711, old objects with an age t \approx 5 \times 108 yr, are near the end of the core hydrogen burning phase.Comment: 26 pages, 5 Encapsulated Postscript figure

Study of chemically peculiar stars – I. High-resolution spectroscopy and K2 photometry of Am stars in the region of M44

ABSTRACT We present a study based on the high-resolution spectroscopy and K2 space photometry of five chemically peculiar stars in the region of the open cluster M44. The analysis of the high-precision photometric K2 data reveals that the light variations in HD 73045 and HD 76310 are rotational in nature and caused by spots or cloud-like co-rotating structures, which are non-stationary and short-lived. The time-resolved radial velocity measurements, in combination with the K2 photometry, confirm that HD 73045 does not show any periodic variability on time-scales shorter than 1.3 d, contrary to previous reports in the literature. In addition to these new rotational variables, we discovered a new heartbeat system, HD 73619, where no pulsational signatures are seen. The spectroscopic and spectropolarimetric analyses indicate that HD 73619 belongs to the peculiar Am class, with either a weak or no magnetic field, considering the 200-G detection limit of our study. The least-squares deconvolution profiles for HD 76310 indicate a complex structure in its spectra, suggesting that this star is either part of a binary system or surrounded by a cloud shell. When placed in the Hertzsprung–Russell diagram, all studied stars are evolved from the main sequence and situated in the δ Scuti instability strip. This work is relevant for further detailed studies of chemically peculiar stars, for example on inhomogeneities (including spots) in the absence of magnetic fields and the origin of the pulsational variability in heartbeat systems

Применение псевдослучайной последвательности на основе хаоса для создания широкополосных телекоммуникационных системы с улучшенными характеристиками

Проблематика. Телекомунікаційні системи з широкосмуговим сигналом мають безперечні переваги: підвищені завадостійкійкысть при вузькосмугових і широкосмугових перешкодах, конфіденційність передачі інформації, а також поліпшену електромагнітну сумісність з сусідніми радіоелектронними пристроями. Широкосмуговий сигнал формується як правило методом прямого розширення спектру з використанням відомих класичних псевдовипадкових послідовностей (ПВП) : m- послідовностей, послідовностей Касами, Голда,,Уолша, які в приймачі можна підібрати і прийняти сигнал. Мета досліджень. Створення ПВП на основі хаосу, які приймаючий абонент практично не зможе підібрати, і таким чином забезпечити підвищену конфіденційність прийому інформації. Методика реалізації. З використанням математичної моделі хаотичного логістичного відображення, яка, як показали попередні дослідження, забезпечує найкращі результати, а також звертаючись до біфуркаційної діаграми Фейгенбаума, визначаються параметри 3-х секретних ключів і створюються ПВП вибраної довжини. На основі застосування розробленого в системі МАТЛАБ графічного інтерфейсу користувача здійснюється кореляційний аналіз отриманих ПВП і визначаються ПВП з мінімальним рівнем бічних пелюсток автокореляційної функції. Результати досліджень. Шляхом емпіричного вибору 3 - х секретних ключів-динамического параметра діаграми Фейгенбаума, початкового значення послідовності і номера початкового імпульсу ПВП, а також дослідження автокореляційної функції отримані ПВП з прийнятним для практичного використання рівнем бічних пелюсток автокореляційної функції не більше 0,25. Висновки. Використання відомих псевдовипадкових последовательностей-Уолша, Касами, Голда при створенні систем з шумоподібним сигналом не забезпечує повну конфіденційність передачі інформації, оскільки їх можна підібрати в приймачі. Найбільш прийнятним за критерієм мінімуму бічної пелюстки автокореляційної функції -не гірше 0,25,є використання хаосу на основі логістичного відображення Фейгенбаума. При створенні псевдовипадкових послідовностей на основі хаосу найкращі результати дає вибір максимального значення динамічного параметра діаграми Фейгенбаума на рівні граничного значення, рівного 4, з точністю 0,05.Background. Telecommunication systems with a broadband signal have undoubted advantages: increased noise immunity with narrowband and wideband interference, confidentiality of information transmission, as well as improved electromagnetic compatibility with neighboring radio-electronic devices. A broadband signal is usually formed by direct spread spectrum using well-known classical pseudo-random sequences (PRS): m-sequences, Kasami, Gold, Walsh sequences, which can be decoded and received at the receiver. Objective. The aim of the paper is creating PRS on the basis of chaos, which the subscriber is practically unable to decode, and thus ensure increased confidentiality of information transmission. Methods. Using the mathematical model of chaotic logistic mapping, which, as shown by preliminary studies, provides the best results, as well as referring to the bifurcation diagram of Feigenbaum, the parameters of 3-secret keys are defined and the PRS of the selected length is created. Based on the application of the graphical user interface developed in the MATLAB system, a correlation analysis of the resulting PRS is performed and the PRS is determined with the minimum side lobes of the autocorrelation function. Results. By empirical decision of 3 secret keys of the dynamic parameter of the Feigenbaum diagram, the initial value of the sequence and the number of the initial pulse of the PRS, as well as the study of the autocorrelation function, we obtained a PRS with a side lobe level of the autocorrelation function acceptable for practical use of no more than 0.25. Conclusions. The use of well-known pseudo-random sequence: Walsh’s, Kasami’s, Gold’s, creating a system with a noise-like signal doesn’t ensure complete confidentiality of information transmission, since they can be decoded. The most acceptable by the criterion of the side lobe minimum of the autocorrelation function – no worse than 0.25 – is the use of chaos based on the Feigenbaum logistic map. When creating pseudo-random sequences based on chaos, the best results are obtained by choosing the maximum value of the dynamic parameter of the Feigenbaum diagram at the level of the boundary value equal to 4, with an accuracy of 0.05.Проблематика. Телекоммуникационные системы с широкополосным сигналом имеют несомненные преимущества: повышенные помехоустойчивости при узкополосных и широкополосных помехах, конфиденциальность передачи информации, а также улучшенную электромагнитную совместимость с соседними радиоэлектронными устройствами. Широкополосный сигнал формируется как правило методом прямого расширения спектра с использованием известных классических псевдослучайные последовательностей (ПСП): m-последовательностей, последовательностей Касами, Голда,,Уолша ,которые в приемнике можно подобрать и принять сигнал. Цель исследований. Создание ПСП на основе хаоса, которые принимающий абонент практически не сможет подобрать, и таким образом обеспечить повышенную конфиденциальность приема информации. Методика реализации. С использованием математической модели хаотического логистического отображения, которая, как показали предварительные исследования, обеспечивает наилучшие результаты, а также обращаясь к бифуркационной диаграмме Фейгенбаума определяются параметры 3-секретных ключей и создаются ПСП выбранной длины. На основе применения разработанного в системе МАТЛАБ графического интерфейса пользователя осуществляется корреляционный анализ полученных ПСП и определяются ПСП с минимальным уровнем боковых лепестков автокорреляционной функции. Результаты исследований. Путем эмпирического выбора 3- х секретных ключей-динамического параметра диаграммы Фейгенбаума, начального значения последовательности и номера начального импульса ПСП, а также исследования автокорреляционной функции получены ПСП с приемлемым для практического использования уровнем боковых лепестков автокорреляционной функции не более 0,25. Выводы. Использование известных псевдослучайных последовательностей-Уолша, Касами, Голда при создании систем с шумоподобным сигналом не обеспечивают полную конфиденциальность передачи информации, поскольку их можно подобрать в приемнике. Наиболее приемлемым по критерию минимума бокового лепестка автокорреляционной функции –не хуже 0,25 является использование хаоса на основе логистического отображения Фейгенбаума. При создании псевдослучайных последовательностей на основе хаоса наилучшие результаты дает выбор максимального значения динамического параметра диаграммы Фейгенбаума на уровне граничного значения, равного 4, с точностью 0,05

LARVAL STAGES OF TREMATODES IN FRESHWATER SNAILS OF THE CHORNOBYL ZONE OF RADIOACTIVE CONTAMINATION

In 1986, at the Chornobyl Nuclear Power Plant in the Exclusion Zone after an industrial accident, ecosystems began to have several features that distinguish them from the objects of the natural reserve fund. Parasitic systems are an informative indicator of the state of the ecosystem, which is now sporadically applied in the Exclusion Zone. Any change in the parasite population can lead to changes in the host population. The degree of imbalance in the “parasite-host” system depends on the strength and nature of the influence of external factors. At the same time, the presence of mutual adaptations of parasitic organisms and snails gives grounds to consider the “parasitehost” system comprehensively. Freshwater gastropod snails of various systematic groups, which can be intermediate and secondary hosts for trematode agents, were selected as an object of the study. In order to study freshwater gastropod snails for the presence of larval stages of helminths, snails were collected from such locations as Krasne Lake, Ilya River, Chernobyl Nuclear Power Plant cooling pond, bypass channel of the Chernobyl Nuclear Power Plant cooling pond, left bank of the Prypiat floodplain, Koshevka oxbow lake, Hrubchanskyi canal in the Meshevo village. Based on the results of the research, the presence of larval stages of trematode agents at different stages of their development (redia and metacercaria) parasitizing in the freshwater snails Lymnae stagnalis and Radix auricularia was establishe