Influence of Inelastic Collisions with Hydrogen Atoms on Non-LTE Oxygen Abundance Determinations     

T. M. Sitnova  L. I. Mashonkina 《Astronomy Letters》2018,44(6):411-419

We present the results of our modeling of the O I line formation under non-LTE conditions in the atmospheres of FG stars. The statistical equilibrium of O I has been calculated using Barklem’s quantum-mechanical rates of inelastic collisions with hydrogen atoms. We have determined the non-LTE oxygen abundance from atomic O I lines for the Sun and 46 FG stars in a wide metallicity range, ?2.6 < [Fe/H] < 0.2. The application of accurate atomic data has led to an increase in the departures from LTE and a decrease in the oxygen abundance compared to the use of Drawin’s theoretical approximation. The change in the non-LTE abundance from the infrared O I 7771-5 Å triplet lines is 0.11 dex for solar atmospheric parameters and diminishes in absolute value with decreasing metallicity. We have revised the [O/Fe]–[Fe/H] relationship derived by us previously. The change in [O/Fe] is small in the [Fe/H] range from ?1.5 to 0.2. For stars with [Fe/H] < ?1 the [O/Fe] ratio has increased so that [O/Fe] = 0.60 at [Fe/H] = ?0.8 and rises to [O/Fe] = 0.75 at [Fe/H] = ?2.6.  相似文献   

Antenna design and implementation for the future space Ultra-Long wavelength radio telescope     

Linjie Chen  Amin Aminaei  Leonid I. Gurvits  Marc Klein Wolt  Hamid Reza Pourshaghaghi  Yihua Yan  Heino Falcke 《Experimental Astronomy》2018,45(2):231-253

In radio astronomy, the Ultra-Long Wavelengths (ULW) regime of longer than 10 m (frequencies below 30 MHz), remains the last virtually unexplored window of the celestial electromagnetic spectrum. The strength of the science case for extending radio astronomy into the ULW window is growing. However, the opaqueness of the Earth’s ionosphere makes ULW observations by ground-based facilities practically impossible. Furthermore, the ULW spectrum is full of anthropogenic radio frequency interference (RFI). The only radical solution for both problems is in placing an ULW astronomy facility in space. We present a concept of a key element of a space-borne ULW array facility, an antenna that addresses radio astronomical specifications. A tripole–type antenna and amplifier are analysed as a solution for ULW implementation. A receiver system with a low power dissipation is discussed as well. The active antenna is optimized to operate at the noise level defined by the celestial emission in the frequency band 1 ? 30 MHz. Field experiments with a prototype tripole antenna enabled estimates of the system noise temperature. They indicated that the proposed concept meets the requirements of a space-borne ULW array facility.  相似文献   

Phase Shift between Changes in Global Temperature and Atmospheric CO2 Content under External Emissions of Greenhouse Gases into the Atmosphere     

Muryshev  K. E.  Eliseev  A. V.  Denisov  S. N.  Mokhov  I. I.  Arzhanov  M. M.  Timazhev  A. V. 《Izvestiya Atmospheric and Oceanic Physics》2019,55(3):235-241

Izvestiya, Atmospheric and Oceanic Physics - The phase shift between changes in the global surface temperature Tg and atmospheric CO2 content $${{q}_{{{\text{C}}{{{\text{O}}}_{2}}}}}$$ has been...  相似文献   

Design Experience of a Demonstrator Descent Vehicle Introducing Aeroelastic Deployable Structural Elements to Space Engineering     

O. M. Alifanov  A. L. Medvedskiy  V. V. Terentyev  D. V. Lyskov 《Solar System Research》2018,52(7):590-596

The development project of a prototype demonstrator for a descent vehicle and the possibilities of descent from orbit using aero-elastic braking devices deployable in space and in the atmosphere is considered. The project was carried out jointly by the Lavochkin Scientific Production Association and the Moscow Aviation Institute teams in 2013–2015. The results are evaluated for both the project itself and the cooperation of the two organizations.  相似文献   

Simulating the Propagation of Infrasonic Waves and Estimating the Energy of the Chelyabinsk Meteoroid Explosion Observed on February 15, 2013     

S.?N.?KulichkovEmail author  O.?Ye.?Popov  K.?V.?Avilov  I.?P.?Chunchuzov  O.?G.?Chkhetiani  A.?A.?Smirnov  V.?I.?Dubrovin  A.?A.?Mishenin 《Izvestiya Atmospheric and Oceanic Physics》2018,54(3):293-303

Results obtained from simulating the propagation of infrasonic waves from the Chelyabinsk meteoroid explosion observed on February 15, 2013, are given. The pseudodifferential parabolic equation (PDPE) method has been used for calculations. Data on infrasonic waves recorded at the IS31 station (Aktyubinsk, Kazakhstan), located 542.7 km from the likely location of the explosion, have been analyzed. Six infrasonic arrivals (isolated clearly defined pulse signals) were recorded. It is shown that the first “fast” arrival (F) corresponds to the propagation of infrasound in a surface acoustic waveguide. The rest of the arrivals (T1–T5) are thermospheric. The agreement between the results of calculations based on the PDPE method and experimental data is satisfactory. The energy E of the explosion has been estimated using two methods. One of these methods is based on the law of conservation of the acoustic pulse I, which is a product of the wave profile area S/2 of the signal under analysis and the distance to its source E _I [kt] = 1.38 × 10^–10 (I [kg/s])^1.482. The other method is based on the relation between the energy of explosion and the dominant period T of recorded signal E _T [kt] = 1.02 × (T [s]²/σ)^3/2, where σ is the dimensionless distance determining the degree of nonlinear effects during the propagation of sound along ray trajectories. According to the data, the explosion energy E _I,T ranges from 1.87 to 32 kt TNT.  相似文献   

The isotopic signature of monsoon conditions,cloud modes,and rainfall type          下载免费PDF全文

Costijn Zwart  Niels C. Munksgaard  Alain Protat  Naoyuki Kurita  Dionisia Lambrinidis  Michael I. Bird 《水文研究》2018,32(15):2296-2303

This work provides a comprehensive physically based framework for the interpretation of the north Australian rainfall stable isotope record (δ¹⁸O and δ²H). Until now, interpretations mainly relied on statistical relationships between rainfall amount and isotopic values on monthly timescales. Here, we use multiseason daily rainfall stable isotope and high resolution (10 min) ground‐based C‐band polarimetric radar data and show that the five weather types (monsoon regimes) that constitute the Australian wet season each have a characteristic isotope ratio. The data suggest that this is not only due to changes in regional rainfall amount during these regimes but, more importantly, is due to different rain and cloud types that are associated with the large scale circulation regimes. Negative (positive) isotope anomalies occurred when stratiform rainfall fractions were large (small) and the horizontal extent of raining areas were largest (smallest). Intense, yet isolated, convective conditions were associated with enriched isotope values whereas more depleted isotope values were observed when convection was widespread but less intense. This means that isotopic proxy records may record the frequency of which these typical wet season regimes occur. Positive anomalies in paleoclimatic records are most likely associated with periods where continental convection dominates and convection is sea‐breeze forced. Negative anomalies may be interpreted as periods when the monsoon trough is active, convection is of the oceanic type, less electric, and stratiform areas are wide spread. This connection between variability of rainfall isotope anomalies and the intrinsic properties of convection and its large‐scale environment has important implications for all fields of research that use rainfall stable isotopes.  相似文献   

Earliest Musa banana from the late Quaternary sequence at Fahien Rock Shelter in Sri Lanka          下载免费PDF全文

Rathnasiri Premathilake  Chris O. Hunt 《第四纪科学杂志》2018,33(6):624-638

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Geometric Aspects and Testing of the Galactic Center Distance Determination from Spiral Arm Segments     

I. I. Nikiforov  A. V. Veselova 《Astronomy Letters》2018,44(2):81-102

We consider the problem of determining the geometric parameters of a Galactic spiral arm from its segment by including the distance to the spiral pole, i.e., the distance to the Galactic center (R₀). The question about the number of points belonging to one turn of a logarithmic spiral and defining this spiral as a geometric figure has been investigated numerically and analytically by assuming the direction to the spiral pole (to the Galactic center) to be known. Based on the results obtained, in an effort to test the new approach, we have constructed a simplified method of solving the problem that consists in finding the median of the values for each parameter from all possible triplets of objects in the spiral arm segment satisfying the condition for the angular distance between objects. Applying the method to the data on the spatial distribution of masers in the Perseus and Scutum arms (the catalogue by Reid et al. (2014)) has led to an estimate of R₀ = 8.8 ± 0.5 kpc. The parameters of five spiral arm segments have been determined from masers of the same catalogue. We have confirmed the difference between the spiral arms in pitch angle. The pitch angles of the arms revealed by masers are shown to generally correlate with R₀ in the sense that an increase in R₀ leads to a growth in the absolute values of the pitch angles.  相似文献   

Influence of periodic orbits on the formation of giant planetary systems     

Anne-Sophie Libert  Sotiris Sotiriadis  Kyriaki I. Antoniadou 《Celestial Mechanics and Dynamical Astronomy》2018,130(2):19

The late-stage formation of giant planetary systems is rich in interesting dynamical mechanisms. Previous simulations of three giant planets initially on quasi-circular and quasi-coplanar orbits in the gas disc have shown that highly mutually inclined configurations can be formed, despite the strong eccentricity and inclination damping exerted by the disc. Much attention has been directed to inclination-type resonance, asking for large eccentricities to be acquired during the migration of the planets. Here we show that inclination excitation is also present at small to moderate eccentricities in two-planet systems that have previously experienced an ejection or a merging and are close to resonant commensurabilities at the end of the gas phase. We perform a dynamical analysis of these planetary systems, guided by the computation of planar families of periodic orbits and the bifurcation of families of spatial periodic orbits. We show that inclination excitation at small to moderate eccentricities can be produced by (temporary) capture in inclination-type resonance and the possible proximity of the non-coplanar systems to spatial periodic orbits contributes to maintaining their mutual inclination over long periods of time.  相似文献   

Determination of Supermassive Black Hole Spins Based on the Standard Shakura–Sunyaev Accretion Disk Model and Polarimetric Observations     

V.?L.?Afanasiev  Yu.N.?GnedinEmail author  M.Yu.?Piotrovich  S.?D.?Buliga  T.?M.?Natsvlishvili 《Astronomy Letters》2018,44(6):362-369

Based on spectropolarimetry for 47 type 1 active galactic nuclei observed with the 6-m BTA telescope, we have estimated the spins of the supermassive black holes at the centers of these galaxies. We have determined the spins based on the standard Shakura–Sunyaev accretion disk model. About 70% of the investigated active galactic nuclei are shown to have Kerr supermassive black holes with a dimensionless spin greater than 0.9.  相似文献