Properties of dwarf stars in Cygnus OB2

We present the results of investigation of five stars, originally classified as dwarfs, belonging to Cyg OB2 association, their stellar and wind properties. Using both TLUSTY and CMFGEN codes we derived effective temperatures, surface gravities, chemical abundances, mass-loss rates and projected rotation velocities. Due to the fact that distance to the stars is well known, we were able to estimate their luminosities. Using evolutionary models we estimated the ages of these sample stars and find that lower mass ones - MT282 and MT343 - belong to older population of the association. Their ages are greater than 10 Myr. The ages of three other stars - MT317, MT299, MT259 - are between 4-6 Myr.Comment: 16 pages, 10 figures, accepted for publication in PAS

Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 parsecs: The Northern Sample I

We have embarked on a project, under the aegis of the Nearby Stars (NStars)/ Space Interferometry Mission Preparatory Science Program to obtain spectra, spectral types, and, where feasible, basic physical parameters for the 3600 dwarf and giant stars earlier than M0 within 40 parsecs of the sun. In this paper we report on the results of this project for the first 664 stars in the northern hemisphere. These results include precise, homogeneous spectral types, basic physical parameters (including the effective temperature, surface gravity and the overall metallicity, [M/H]) and measures of the chromospheric activity of our program stars. Observed and derived data presented in this paper are also available on the project's website at http://stellar.phys.appstate.edu/

Photometric and spectral variability of active star VY Arietis

Представлены квазиодновременные UBVRI фотометрические и H спектральные наблюдения хромосферно-активной двойной VY Ari. Ее фотометрическая переменность описывается зональной моделью запятненности, где пятна занимают до 32 % полной поверхности звезды. Пятна локализованы в низких и средних широтах, они холоднее спокойной фотосферы на 1 300 К. Спектральные наблюдения показывают в некоторые эпохи наличие в хромосфере звезды активных областей повышенной электронной плотности (факе- лов), сконцентрированных вблизи наиболее запятненных (активных) долгот. Отмечается цикличность в долговременных изменениях площади пятен и основных параметров чистой эмиссии H с характерным временем 9 10 лет.Quasi-simultaneous UBVRI photometric, and H spectroscopic observations of the chromospherically active binary star VY Ari are presented. The photometric variability of the star can be described by a zonal spottedness model. Spotted regions occupy up to 32 % of the total stellar surface. The temperature difference between the unspotted photosphere and starspots is about 1 300 K. Starspots are localized at middle-low latitudes. The spectroscopic observations show in some epochs the presence of chromospherically active regions with a higher electron density (plages), which concentrated near the mostly spotted stellar longitudes. There are the cyclic variations of the spot area and the H pure emission parameters with a typical time is about 9—10 years.Работа выполнена при частричной поддержке гранта РФФИ 16-02-00689, а также при финансовой поддержке Правительства Российской Федерации (постановление № 211, контракт 02.A03.21.0006)

Nonperturbative Analysis of the Electroweak Phase Transition in the Two Higgs Doublet Model

We perform a nonperturbative study of the electroweak phase transition (EWPT) in the two Higgs doublet model (2HDM) by deriving a dimensionally reduced high-temperature effective theory for the model, and matching to known results for the phase diagram of the effective theory. We find regions of the parameter space where the theory exhibits a first-order phase transition. In particular, our findings are consistent with previous perturbative results suggesting that the primary signature of a first-order EWPT in the 2HDM is m(A0) > m(H0) + m(Z).Peer reviewe

Development of Augmented Reality Mobile Application in Physics to Study the Electric Circuit

Проаналізовано використання віртуальних засобів навчання з технологією AR у різних сферах освіти, зокрема фізики. Проведено аналогію між фізичною та електронною моделями та обґрунтовано розробку мобільного додатку для дослідження простого електричного кола. Обґрунтовано доцільність створення технології мобільних додатків доповненої реальності. Окреслено віхи розвитку додатку доповненої реальності: розробка електронних моделей, встановлення ігрового движка Unity3D, розробка всіх програмних сцен, тестування та демонстрація роботи. Особливу увагу було приділено використанню сценаріїв для обертання та руху електронних моделей. Презентовано власно розроблений мобільний додаток доповненої реальності для мобільних пристроїв «Програма доповненої реальності для дослідження найпростішої електричної схеми». Створений мобільний додаток читає, розпізнає дизайнерський маркер і виводить на екран електронну модель товару. Встановлено, що розроблену колективом авторів програму доповненої реальності як програмне забезпечення для мобільного навчання можна використовувати для виконання завдань як для самостійної роботи студентів, так і для аудиторних занять у ВНЗ.Using the virtual teaching aids with AR technology in different spheres of education, including physics, has been analysed. The analogy between physical and electronic models has been drawn and the development of mobile app to study simple electric circuit has been substantiated. The reasonability of creating the technique f the augmented reality mobile apps has been given. The milestones in the development of the augmented reality app have been outlined: development of electronic models, installation of the game engine Unity3D, development of all program scenes, operation testing and demonstration. Using the scenarios for electronic models rotation and movement has been particularly focused on. Own developed augmented reality mobile app for mobile devices “Augmented reality program to study the simplest electric circuit” has been presented. The created mobile app reads, recognizes the designer marker and displays the product electronic model on the screen. It is established that the augmented reality program developed by the team of authors as the mobile teaching software can be used to do the tasks for the students’ individual work, as well as for the classroom studies at the universities

Tidal Venuses: Triggering a Climate Catastrophe via Tidal Heating

Traditionally stellar radiation has been the only heat source considered capable of determining global climate on long timescales. Here we show that terrestrial exoplanets orbiting low-mass stars may be tidally heated at high enough levels to induce a runaway greenhouse for a long enough duration for all the hydrogen to escape. Without hydrogen, the planet no longer has water and cannot support life. We call these planets "Tidal Venuses," and the phenomenon a "tidal greenhouse." Tidal effects also circularize the orbit, which decreases tidal heating. Hence, some planets may form with large eccentricity, with its accompanying large tidal heating, and lose their water, but eventually settle into nearly circular orbits (i.e. with negligible tidal heating) in the habitable zone (HZ). However, these planets are not habitable as past tidal heating desiccated them, and hence should not be ranked highly for detailed follow-up observations aimed at detecting biosignatures. Planets orbiting stars with masses <0.3 solar masses may be in danger of desiccation via tidal heating. We apply these concepts to Gl 667C c, a ~4.5 Earth-mass planet orbiting a 0.3 solar mass star at 0.12 AU. We find that it probably did not lose its water via tidal heating as orbital stability is unlikely for the high eccentricities required for the tidal greenhouse. As the inner edge of the HZ is defined by the onset of a runaway or moist greenhouse powered by radiation, our results represent a fundamental revision to the HZ for non-circular orbits. In the appendices we review a) the moist and runaway greenhouses, b) hydrogen escape, c) stellar mass-radius and mass-luminosity relations, d) terrestrial planet mass-radius relations, and e) linear tidal theories. [abridged]Comment: 59 pages, 11 figures, accepted to Astrobiology. New version includes an appendix on the water loss timescal