IGR J17445-2747—Yet another X-ray burster in the galactic bulge     

I.?A.?MereminskiyEmail author  S.?A.?Grebenev  R.?A.?Sunyaev 《Astronomy Letters》2017,43(10):656-663

The discovery of a type I X-ray burst from the faint unidentified transient source IGR J17445-2747 in the Galactic bulge by the JEM-X telescope onboard the INTEGRAL observatory is reported. Type I bursts are believed to be associated with thermonuclear explosions of accreted matter on the surface of a neutron star with a weak magnetic field in a low-mass X-ray binary. Thus, this observation allows the nature of this source to be established.  相似文献   

Estimates of abundance of the short-baseline (1-3 meters) slopes for different Venusian terrains using terrestrial analogues     

M.?A.?IvanovEmail author  L.?V.?Zasova  L.?M.?Zeleny  M.?V.?Gerasimov  N.?I.?Ignatiev  O.?I.?Korablev  M.?Ya.?Marov 《Solar System Research》2017,51(2):87-103

The interplanetary mission, Venera-D, which is currently being planned, includes a lander. For a successful landing, it is necessary to estimate the frequency distributions of slopes of the Venusian surface at baselines that are comparable with the horizontal dimensions of lander (1–3 m). The available data on the topographic variations on Venus preclude estimates of the frequency of the short-wavelength slopes. In our study, we applied high-resolution digital terrain models (DTM) for specific areas in Iceland to estimate the slopes on Venus. The Iceland DTMs have 0.5 m spatial and 0.1 m vertical resolution. From the set of these DTMs, we have selected those that morphologically resemble typical landscapes on Venus such as tessera, shield, regional, lobate, and smooth plains. The mode of the frequency distribution of slopes on the model tessera terrain is within a 30°–40° range and a fraction of the surface has slopes <7°, which is considered as the upper safety limit. This is the primary interest. The frequency distribution of slopes on the model tessera is not changed significantly as the baseline is changed from 1 m to 3 m. The terrestrial surfaces that model shield and regional plains on Venus have a prominent slope distribution mode between 8°–20° and the fraction of the surfaces with slopes <7° is less than 30% on both 1 m and 3 m baselines. A narrow, left-shifted histogram characterizes the model smooth plains surfaces. The fraction of surfaces with slopes <7° is about 65–75% for the shorter baseline (1 m). At the longer baseline, the fraction of the shallow-sloped surfaces is increased and fraction of the steep slopes is decreased significantly. The fraction of surfaces with slopes <7° for the 3-m baseline is about 75–88% for the terrains that model both lobate and smooth plains.  相似文献   

EUV and Magnetic Activities Associated with Type-I Solar Radio Bursts   总被引：1，自引：0，他引：1  

C. Y. Li  Y. Chen  B. Wang  G. P. Ruan  S. W. Feng  G. H. Du  X. L. Kong 《Solar physics》2017,292(6):82

Type-I bursts (i.e. noise storms) are the earliest-known type of solar radio emission at the meter wavelength. They are believed to be excited by non-thermal energetic electrons accelerated in the corona. The underlying dynamic process and exact emission mechanism still remain unresolved. Here, with a combined analysis of extreme ultraviolet (EUV), radio and photospheric magnetic field data of unprecedented quality recorded during a type-I storm on 30 July 2011, we identify a good correlation between the radio bursts and the co-spatial EUV and magnetic activities. The EUV activities manifest themselves as three major brightening stripes above a region adjacent to a compact sunspot, while the magnetic field there presents multiple moving magnetic features (MMFs) with persistent coalescence or cancelation and a morphologically similar three-part distribution. We find that the type-I intensities are correlated with those of the EUV emissions at various wavelengths with a correlation coefficient of 0.7?–?0.8. In addition, in the region between the brightening EUV stripes and the radio sources there appear consistent dynamic motions with a series of bi-directional flows, suggesting ongoing small-scale reconnection there. Mainly based on the induced connection between the magnetic motion at the photosphere and the EUV and radio activities in the corona, we suggest that the observed type-I noise storms and the EUV brightening activities are the consequence of small-scale magnetic reconnection driven by MMFs. This is in support of the original proposal made by Bentley et al. (Solar Phys. 193, 227, 2000).  相似文献   

Spectroscopic Variability of Supergiant Star HD14134, B3Ia     

Y. M. Maharramov 《Journal of Astrophysics and Astronomy》2017,38(2):20

Profile variations in the \(\hbox {H}\alpha \) and \(\hbox {H}\beta \) lines in the spectra of the star HD14134 are investigated using observations carried out in 2013–2014 and 2016 with the 2-m telescope at the Shamakhy Astrophysical Observatory. The absorption and emission components of the \(\hbox {H}\alpha \) line are found to disappear on some observational days, and two of the spectrograms exhibit inverse P-Cyg profile of \(\hbox {H}\alpha \). It was revealed that when the \(\hbox {H}\alpha \) line disappeared or an inversion of the P-Cyg-type profile is observed in the spectra, the \(\hbox {H}\beta \) line is displaced to the longer wavelengths, but no synchronous variabilities were observed in other spectral lines (CII \( \lambda \) 6578.05 Å, \( \lambda \) 6582.88 Å  and HeI \( \lambda \) 5875.72 Å) formed in deeper layers of the stellar atmosphere. In addition, the profiles of the \(\hbox {H}\alpha \) and \(\hbox {H}\beta \) lines have been analysed, as well as their relations with possible expansion, contraction and mixed conditions of the atmosphere of HD14134. We suggest that the observational evidence for the non-stationary atmosphere of HD14134 can be associated in part with the non-spherical stellar wind.  相似文献   

A model of possible variations of the galactic cosmic ray intensity over the recent billion years     

V.?A.?AlexeevEmail author 《Solar System Research》2017,51(3):196-203

Based on the analysis of published data on exposure ages of iron meteorites determined with the ⁴⁰K/K method (T _K) and ages calculated using short-lived cosmogenic radionuclides (with the half-life T _1/2 < 1 Myr) in combination with stable cosmogenic isotopes of noble gases (T_RS), the following results have been obtained. (1) The distribution of T _RS ages (106 values) has an exponential shape, similar to that for ordinary chondrites, but different from the distribution of T _K ages (80 values). The difference is most likely due to small amounts of data for meteorites with low T _K ages (less than ~200–300 Myr). The latter can be ascribed to the difficulty of measurement of small concentrations of cosmogenic potassium isotopes. This circumstance makes the selection of meteorites with ⁴⁰K/K ages nonrepresentative and casts doubt on the correctness of conclusions about the variations of the intensity of galactic cosmic rays (GCR) based on the analysis of distribution of these ages. (2) The magnitude of the known effect (systematic overestimation of T _K ages in comparison with T _RS ages) has been refined. The value k = T _K/T _RS = 1.51 ± 0.03 is acquired for the whole population of data. We have shown the inefficiency of the explanation of this effect on account of an exponential change in the GCR intensity (I _T ) with time (T) according to the relation I _T = I ₀exp(–γT) over the whole range of ages of iron meteorites. (3) In order to explain the overestimation of T _K ages in comparison with T _RS ages, a model has been proposed, according to which the GCR intensity has exponentially increased in the interval of 0–1500 Myr governed by the relation: I _T = I _{T = 1500} (1 + αexp(–βT)). For one of the variants of this model, the GCR intensity has exponentially increased by a factor of two only over the recent ~300 Myr, remaining approximately constant for the rest of the time. The data acquired with the use of this model indicate that the measured T _K ages are close to the actual time that the meteorites existed in space; the data are in agreement with the observed exponential distribution of T _RS ages.  相似文献   

The nature of terrains of different types on the surface of Venus and selection of potential landing sites for a descent probe of the <Emphasis Type="Italic">Venera-D</Emphasis> Mission     

M.?A.?IvanovEmail author  L.?V.?Zasova  M.?V.?Gerasimov  O.?I.?Korablev  M.?Ya.?Marov  L.?M.?Zelenyi  N.?I.?Ignat’ev  A.?G.?Tuchin 《Solar System Research》2017,51(1):1-19

We discuss a change in the resurfacing regimes of Venus and probable ways of forming the terrain types that make up the surface of the planet. The interpretation of the nature of the terrain types and their morphologic features allows us to characterize their scientific priority and the risk of landing on their surface to be estimated. From the scientific point of view, two terrain types are of special interest and represent easily achievable targets: the lower unit of regional plains and the smooth plains associated with impact craters. Regional plains are probably a melting from the upper fertile mantle. The material of smooth plains of impact origin is a well-mixed and representative sample of the Venusian crust. The lower unit of regional plains is the most widespread one on the surface of Venus, and it occurs within the boundaries of all of the precalculated approach trajectories of the lander. Smooth plains of impact origin are crossed by the approach trajectories precalculated for 2018 and 2026.  相似文献   

Method for Validation of the Onboard Attitude Control System Software of the <Emphasis Type="Italic">Auriga</Emphasis> Earth Remote Sensing Small Spacecraft     

P.?E.?RozinEmail author 《Solar System Research》2017,51(7):646-653

The paper considers a digital modeling complex for the attitude control system of the Auriga Earth remote sensing small spacecraft. Mathematical models of measuring and executive devices are described. The results of spacecraft orbital attitude tests are presented.  相似文献   

Long term evolution of distant retrograde orbits in the Earth-Moon system   总被引：1，自引：0，他引：1  

Collin?BezroukEmail authorView author&#;s OrcID profile  Jeffrey?S.?Parker 《Astrophysics and Space Science》2017,362(9):176

This work studies the evolution of several Distant Retrograde Orbits (DROs) of varying size in the Earth-Moon system over durations up to tens of millennia. This analysis is relevant for missions requiring a completely hands off, long duration quarantine orbit, such as a Mars Sample Return mission or the Asteroid Redirect Mission. Four DROs are selected from four stable size regions and are propagated for up to 30,000 years with an integrator that uses extended precision arithmetic techniques and a high fidelity dynamical model. The evolution of the orbit’s size, shape, orientation, period, out-of-plane amplitude, and Jacobi constant are tracked. It has been found that small DROs, with minor axis amplitudes of approximately 45,000 km or less decay in size and period largely due to the Moon’s solid tides. Larger DROs (62,000 km and up) are more influenced by the gravity of bodies external to the Earth-Moon system, and remain bound to the Moon for significantly less time.  相似文献   

Scientific prospects for spectroscopy of the gamma-ray burst prompt emission with SVOM     

M. G. Bernardini  F. Xie  P. Sizun  F. Piron  Y. Dong  J.-L. Atteia  S. Antier  F. Daigne  O. Godet  B. Cordier  J. Wei 《Experimental Astronomy》2017,44(1):113-127

SVOM (Space-based multi-band astronomical Variable Objects Monitor) is a Sino-French space mission dedicated to the study of Gamma-Ray Bursts (GRBs) in the next decade, capable to detect and localise the GRB emission, and to follow its evolution in the high-energy and X-ray domains, and in the visible and NIR bands. The satellite carries two wide-field high-energy instruments: a coded-mask gamma-ray imager (ECLAIRs; 4–150 keV), and a gamma-ray spectrometer (GRM; 15–5500 keV) that, together, will characterise the GRB prompt emission spectrum over a wide energy range. In this paper we describe the performances of the ECLAIRs and GRM system with different populations of GRBs from existing catalogues, from the classical ones to those with a possible thermal component superimposed to their non-thermal emission. The combination of ECLAIRs and the GRM will provide new insights also on other GRB properties, as for example the spectral characterisation of the subclass of short GRBs showing an extended emission after the initial spike.  相似文献   

Cloning and phylogenetic analysis of a fatty acid elongase gene from Nannochloropsis oculata CS179     

Kehou Pan  Xiaolei Ma  Jianzhong Yu  Baohua Zhu  Guanpin Yang 《中国海洋大学学报(英文版)》2009,8(4):392-398

Nannochloropsis oculata CS179, a unicellular marine microalga, is rich in long-chain polyunsaturated fatty acids (LCPUFAs). Elongase and desaturase play a key role in the biosynthesis of PUFAs. A new elongase gene, which encodes 322 amino acids, was identified via RT-PCR and 5′ and 3′ RACE. The sequence of the elongase gene was blast-searched in the NCBI GenBank and showed a similarity to those of the cryptosporidium. But the NJ-tree revealed that the N. oculata CS179 elongase clustered with those of the microalgae Phaeodactylum tricornutum, Ostreococcus tauri and Thalassiosira pseudonana.  相似文献