Solar granulation from photosphere to low chromosphere observed in BaII 4554 A line

The purpose of this paper is to characterize the statistical properties of solar granulation in the photosphere and low chromosphere up to 650 km. We use velocity and intensity variations obtained at different atmospheric heights from observations in BaII 4554 A. The observations were done during good seeing conditions at the VTT at the Observatorio del Teide on Tenerife. The line core forms rather high in the atmosphere and allows granulation properties to be studied at heights that have been not accessed before in similar studies. In addition, we analyze the synthetic profiles of the BaII 4554 A line by the same method computed taking NLTE effects into account in the 3D hydrodynamical model atmosphere. We suggest a 16-column model of solar granulation depending on the direction of motion and on the intensity contrast measured in the continuum and in the uppermost layer. We calculate the heights of intensity contrast sign reversal and velocity sign reversal. We show that both parameters depend strongly on the granulation velocity and intensity at the bottom photosphere. The larger the two parameters, the higher the reversal takes place in the atmosphere. On average, this happens at about 200-300 km. We suggest that this number also depends on the line depth of the spectral line used in observations. Despite the intensity and velocity reversal, about 40% of the column structure of granulation is preserved up to heights around 650 km.Comment: accepted by Astronomy and Astrophysic

Properties of convective motions in facular regions

In this paper, we study the properties of solar granulation in a facular region from the photosphere up to the lower chromosphere. Our aim is to investigate the dependence of granular structure on magnetic field strength. We use observations obtained at the German Vacuum Tower Telescope (Observatorio del Teide, Tenerife) using two different instruments: Triple Etalon SOlar Spectrometer (TESOS), in the BaII 4554 A line to measure velocity and intensity variations along the photosphere; and, simultaneously, Tenerife Infrared Polarimeter (TIP-II), in the FeI 1.56 $\mu$m lines to the measure Stokes parameters and the magnetic field strength at the lower photosphere. We obtain that the convective velocities of granules in the facular area decrease with magnetic field while the convective velocities of intergranular lanes increase with the field strength. Similar to the quiet areas, there is a contrast and velocity sign reversal taking place in the middle photosphere. The reversal heights depend on the magnetic field strength and are, on average, about 100 km higher than in the quiet regions. The correlation between convective velocity and intensity decreases with magnetic field at the bottom photosphere, but increases in the upper photosphere. The contrast of intergranular lanes observed close to the disc center is almost independent of the magnetic field strength. The strong magnetic field of facular area seems to stabilize the convection and to promote more effective energy transfer in the upper layers of the solar atmosphere, since the convective elements reach larger heights.Comment: accepted by Astronomy and Astrophysic

On the Absorption of X-rays in the Interstellar Medium

We present an improved model for the absorption of X-rays in the ISM intended for use with data from future X-ray missions with larger effective areas and increased energy resolution such as Chandra and XMM, in the energy range above 100eV. Compared to previous work, our formalism includes recent updates to the photoionization cross section and revised abundances of the interstellar medium, as well as a treatment of interstellar grains and the H2molecule. We review the theoretical and observational motivations behind these updates and provide a subroutine for the X-ray spectral analysis program XSPEC that incorporates our model.Comment: ApJ, in press, for associated software see http://astro.uni-tuebingen.de/nh

Surface temperature and synthetic spectral energy distributions for rotationally deformed stars

The spectral energy distribution (SED) of a non-spherical star could differ significantly from the SED of a spherical star with the same average temperature and luminosity. Calculation of the SED of a deformed star is often approximated as a composite of several spectra, each produced by a plane parallel model of given effective temperature and gravity. The weighting of these spectra over the stellar surface, and hence the inferred effective temperature and luminosity, will be dependent on the inclination of the rotation axis of the star with respect to the observer, as well as the temperature and gravity distribution on the stellar surface. Here we calculate the surface conditions of rapidly rotating stars with a 2D stellar structure and evolution code and compare the effective temperature distribution to that predicted by von Zeipel's law. We calculate the composite spectrum for a deformed star by interpolating within a grid of intensity spectra of plane parallel model atmospheres and integrating over the surface of the star. Using this method, we find that the deduced variation of effective temperature with inclination can be as much as 3000 K for an early B star, depending on the details of the underlying model.Comment: 38 pages, 9 figures (AAStex preprint format). Accepted for publication in the Ap

Numerical Simulations of Magnetoacoustic-Gravity Waves in the Solar Atmosphere

We investigate the excitation of magnetoacoustic-gravity waves generated from localized pulses in the gas pressure as well as in vertical component of velocity. These pulses are initially launched at the top of the solar photosphere that is permeated by a weak magnetic field. We investigate three different configurations of the background magnetic field lines: horizontal, vertical and oblique to the gravitational force. We numerically model magnetoacoustic-gravity waves by implementing a realistic (VAL-C) model of solar temperature. We solve two-dimensional ideal magnetohydrodynamic equations numerically with the use of the FLASH code to simulate the dynamics of the lower solar atmosphere. The initial pulses result in shocks at higher altitudes. Our numerical simulations reveal that a small-amplitude initial pulse can produce magnetoacoustic-gravity waves, which are later reflected from the transition region due to the large temperature gradient. The atmospheric cavities in the lower solar atmosphere are found to be the ideal places that may act as a resonator for various oscillations, including their trapping and leakage into the higher atmosphere. Our numerical simulations successfully model the excitation of such wave modes, their reflection and trapping, as well as the associated plasma dynamics

A NLTE line blanketed model of a solar type star

We present LTE and NLTE atmospheric models of a star with solar parameters, and study the effect of treating many thousands of Iron group lines out of LTE on the computed atmospheric structure, overall absolute flux distribution, and the moderately high resolution spectrum in the visible and near UV bands. Our NLTE modeling includes the first two or three ionization stages of 20 chemical elements, up to and including much of the Fe-group, and includes about 20000 Fe I and II lines. We investigate separately the effects of treating the light metals and the Fe-group elements in NLTE. Our main conclusions are that 1) NLTE line blanketed models with direct multi-level NLTE for many actual transitions gives qualitatively similar results as the more approximate treatment of Anderson (1989) for both the Fe statistical equilibrium and the atmospheric temperature structure, 2) models with many Fe lines in NLTE have a temperature structure that agrees more closely with LTE semi-empirical models based on center-to-limb variation and a wide variety of spectra lines, whereas LTE models agree more with semi-empirical models based only on an LTE calculation of the Fe I excitation equilibrium, 3) the NLTE effects of Fe-group elements on the model structure and flux distribution are much more important than the NLTE effects of all the light metals combined, and serve to substantially increases the violet and near UV flux level as a result of NLTE Fe over-ionization. These results suggest that there may still be important UV opacity missing from the models.Comment: Accepted for publication in The Astrophysical Journa

Исследование возобновляемого потенциала Республики Армении при реализации гибридной автономной системы энергоснабжения с использованием фотоэлектрических преобразователей солнечного света

Introduction. Solar energy is one of the leading renewable energy industries. Solar photovoltaic modules are most widely used to create hybrid autonomous electrification systems, since photovoltaics are not limited to specific limitations and can be applied almost everywhere.Aim. To determine the potential of meteorological and geographical features of the Republic of Armenia for the implementation of autonomous hybrid renewable energy sources systems (AHRESS) using solar photovoltaics (PV). To simulate operating conditions for various AHRESS configurations providing electric power to a cellular communication base station.Materials and methods. Climatic, geographical, social and economic features of the region of the Republic of Armenia are investigated. Regions are evaluated based on the key factors of AHRESS implementation potential and compared with studies performed by the Effergy-Irsolav. The simulations and technical and economic analysis were performed using the HOMER Pro software in Ttsovinar region.Results. The most efficient configuration is found to be B1, with an energy cost of 0.322 $/kW·h. The parameters of winning system: PV array with capacity of 4.5 kW, 12V battery with 100 A·h capacity, diesel generator with 3 kW capacity. The main efficiency criterion is the low economic costs for the implementation and operation of this AHRESS configuration. Ten additional variants of AHRESS were modeled in order to optimize the component base of the configuration.Conclusion. It was found that, depending on the consumer load, solar photovoltaic converters are limited and can only perform as supporting source of electricity. The use of the existing consumption load profile in the form of BSSS made it possible to cover the widest possible range of configurations of the component base, which indicates the high accuracy of the simulated results and, as a result, the technical and economic relevance of the study.Введение. Фотовольтаика является одной из лидирующих отраслей возобновляемой энергетики. Наибольшее распространение фотовольтаика получила в использовании фотоэлектрических преобразователей для создания гибридных автономных систем электрификации, поскольку фотовольтаика не привязана к конкретным факторам и может быть применена практически повсеместно.Цель работы. Определение потенциала метеорологических и географических особенностей Республики Армении для внедрения автономных гибридных систем возобновляемых источников энергии (АГСВИЭ) с использованием фотоэлектрических преобразователей солнечного света. Моделирование условий эксплуатации различных конфигураций АГСВИЭ для снабжения электроэнергией базовой станции сотовой связи (БССС). Оптимизация и анализ технико-экономических параметров оптимальных конфигураций.Материалы и методы. Исследуются климатические, географические, социальные и экономические особенности Республики Армении. Выполняется оценка регионов с высоким потенциалом для внедрения АГСВИЭ и сравнение результатов с исследованиями, проведенными комитетом энергоэффективности Effergy-irsolav. Осуществляется подбор компонентов на основе потребительской нагрузки БССС для моделирования системы автономного гибридного энергоснабжения и непосредственное моделирование условий эксплуатации АГСВИЭ при помощи программного обеспечения HOMER Pro для последующего анализа технической и экономической эффективности внедряемой АГСВИЭ в регионе рядом с населенным пунктом Тцовинар.Результаты. Были получены 10 основных разновидностей конфигураций АГСВИЭ. Наиболее эффективной является конфигурация В1, со стоимостью энергии 0.322$/кВт·ч, компонентами которой являются массив солнечных элементов общей мощностью 4.5 кВт, 12 В аккумуляторных батарей емкостью 100 А·ч, дизельная генераторная установка мощностью 3 кВт. Основными критериями эффективности являются низкие экономические затраты на реализацию и процесс эксплуатации данной конфигурации АГСВИЭ. Дополнительные варианты АГСВИЭ были смоделированы с целью оптимизации компонентной базы конфигурации АГСВИЭ.Заключение. В ходе проведенного исследования и моделирования условий эксплуатации было выявлено, что в зависимости от потребительской нагрузки солнечные фотопреобразователи ограничены и могут выступать как вспомогательный источник электроэнергии. Использование реального профиля потребительской нагрузки в виде БССС позволило охватить максимально широкий диапазон конфигураций компонентной базы, что свидетельствует о высокой точности результатов моделирования и, как следствие, технико-экономических результатов исследования

The impact of non-LTE effects and granulation inhomogeneities on the derived iron and oxygen abundances in metal-poor halo stars

This paper presents the results of a detailed theoretical investigation of the impact of non-LTE effects and of granulation inhomogeneities on the derived iron and oxygen abundances in the metal-poor halo subgiant HD140283. Our analysis is based on both the `classical' one-dimensional (1D) stellar atmosphere models and on the new generation of three-dimensional (3D) hydrodynamical models. We find that the non-LTE effects on the iron abundance derived from Fe {\sc i} lines are very important, amounting to ${\sim}0.9$ dex and to ${\sim}0.6$ dex in the 3D and 1D cases, respectively. On the other hand, we find that non-LTE and 3D effects have to be taken into account for a reliable determination of the iron abundance from weak Fe {\sc ii} lines, because the significant overexcitation of their upper levels in the granular regions tend to produce emission features. As a result such Fe {\sc ii} lines are weaker than in LTE and the abundance correction amounts to ${\sim}0.4$ dex for the 3D case. We derive also the oxygen-to-iron abundance ratio in the metal-poor star HD140283 by using the O {\sc i} triplet at 7772--5 \AA and the forbidden [O {\sc i}] line at 6300 \AA. Interestingly, when both non-LTE and 3D effects are taken into account there still remains significant discrepancies in the iron abundances derived from Fe {\sc i} and Fe {\sc ii} lines, as well as in the oxygen abundances inferred from the O {\sc i} and [O {\sc i}] lines. We conclude that the metalicity of this type of metal-poor stars could be significantly larger than previously thought, which may have far-reaching implications in stellar astrophysics.Comment: The Astrophysical Journal (in press). (35 pages, 5 figures and 4 tables

Permitted Oxygen Abundances and the Temperature Scale of Metal-Poor Turn-Off Stars

We use high quality VLT/UVES published data of the permitted OI triplet and FeII lines to determine oxygen and iron abundances in unevolved (dwarfs, turn-off, subgiants) metal-poor halo stars. The calculations have been performed both in LTE and NLTE, employing effective temperatures obtained with the new infrared flux method (IRFM) temperature scale by Ramirez & Melendez, and surface gravities from Hipparcos parallaxes and theoretical isochrones. A new list of accurate transition probabilities for FeII lines, tied to the absolute scale defined by laboratory measurements, has been used. We find a plateau in the oxygen-to-iron ratio over more than two orders of magnitude in iron abundance (-3.2 < [Fe/H] < -0.7), with a mean [O/Fe] = 0.5 dex (sigma = 0.1 dex), independent of metallicity, temperature and surface gravity. According to the new IRFM Teff scale, the temperatures of turn-off halo stars strongly depend on metallicity, a result that is in excellent qualitative and quantitative agreement with stellar evolution calculations, which predict that the Teff of the turn-off at [Fe/H] = -3 is about 600-700 K higher than that at [Fe/H] = -1.Comment: In press, Ap

Closed-form kinematic and dynamic models of an industrial-like RRR robot, in:

. Closed-form kinematic and dynamic models of an industrial-like RRR robot. In Proceedings of the 2002 IEEE International Conference on Robotics and Automation (ICRA &apos;02), May 11-15, 2002, Washington (pp. 1309-1314 Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher&apos;s website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the &quot;Taverne&quot; license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policy If you believe that this document breaches copyright please contact us at: [email protected] providing details and we will investigate your claim. Abstruct-This paper presents closed-form kinematic and dynamic models of a robot with three rotational degrees of freedom. The derivation of the models and estimation of their parameters are explained. Relevancy of the models is investigated with a writing task. Validation results, obtained by simulation and experiment, establish correctness of the models and illuminate their practical benefits