共查询到20条相似文献，搜索用时 15 毫秒
1.
The results of investigations of the Hα and Hβ lines in the spectrum of the star HD 206267 are presented. Observations were carried out in 2011–2014 at the Cassegrain focus of the 2-m telescope of the Tusi Shamakhy Astrophysical Observatory of the National Academy of Sciences of Azerbaijan using an echelle spectrometer. The following features have been revealed for the first time: the moving discrete absorption components in the core of the Hα line from the red side to the violet, the stable emission in the violet wing of the Hα line, the antiphase variation of the radial velocities and equivalent widths of the Hα line, and the independence of the changes of the equivalent widths of the Hβ line from the phase of the orbital period. No spectral features according to which this star could be considered as a source of X-ray radiation have been found. 相似文献
2.
Marco Tantardini Elena Fantino Yuan Ren Pierpaolo Pergola Gerard Gómez Josep J. Masdemont 《Celestial Mechanics and Dynamical Astronomy》2010,108(3):215-232
Of the three collinear libration points of the Sun–Earth Circular Restricted Three-Body Problem (CR3BP), L3 is that located opposite to the Earth with respect to the Sun and approximately at the same heliocentric distance. Whereas
several space missions have been launched to the other two collinear equilibrium points, i.e., L1 and L2, taking advantage of their dynamical and geometrical characteristics, the region around L3 is so far unexploited. This is essentially due to the severe communication limitations caused by the distant and permanent
opposition to the Earth, and by the gravitational perturbations mainly induced by Jupiter and the close passages of Venus,
whose effects are more important than those due to the Earth. However, the adoption of a suitable periodic orbit around L3 to ensure the necessary communication links with the Earth, or the connection with one or more relay satellites located at
L4 or L5, and the simultaneous design of an appropriate station keeping-strategy, would make it possible to perform valuable fundamental
physics and astrophysics investigations from this location. Such an opportunity leads to the need of studying the ways to
transfer a spacecraft (s/c) from the Earth’s vicinity to L3. In this contribution, we investigate several trajectory design methods to accomplish such a transfer, i.e., various types
of two-burn impulsive trajectories in a Sun-s/c two-body model, a patched conics strategy exploiting the gravity assist of
the nearby planets, an approach based on traveling on invariant manifolds of periodic orbits in the Sun–Earth CR3BP, and finally
a low-thrust transfer. We examine advantages and drawbacks, and we estimate the propellant budget and time of flight requirements
of each. 相似文献
3.
I. I. Romanyuk V. E. Panchuk N. E. Piskunov D. O. Kudryavtsev 《Astrophysical Bulletin》2007,62(1):26-35
The possibility of investigating the vertical structure of the magnetic field in chemically peculiar main-sequence stars is discussed. The nonuniform distribution of chemical elements over the surface complicates the problem substantially. The most efficient measurements are shown to be those of the longitudinal field components based on spectral lines with wavelengths longer and shorter than 3646 Å (shortward and longward of the Balmer jump), which form at different optical depths in the atmosphere. Various methodological problems are addressed that must be overcome in order to accomplish the task. The brightest magnetic star α 2 CVn is observed with the echelle spectrometer equipped with an Uppsala CCD chip. New observations corroborate our previous result: the longitudinal component of the magnetic field B e of the α 2 CVn star increases with depth by about 30% over the atmosphere thickness scale. 相似文献
4.
O. P. Zhelenkova N. S. Soboleva A. V. Temirova N. N. Bursov 《Astrophysical Bulletin》2017,72(2):150-164
We present a catalog of radio sources extending the RCR (RATAN Cold Refined) catalog to the right-ascension interval 2h ≤ RA < 7h. The list of objects was obtained in the process of a reprocessing of the observations of the “Cold” experiment conducted in 1980–1981 on RATAN-600 radio telescope at the declination of SS433, and the reduction of the 1987–1999 surveys of the same experiment.We report the right ascensions and integrated flux densities for 237 sources found at 7.6 cm (3.94 GHz) and their spectral exponents at 3.94 and 0.5 GHz. Twenty-nine sources of the list, which are mostly weaker than 30 mJy at 3.94 GHz, have available data only at two frequencies—1.4 and 3.94 Hz.We approximated the spectra of the sources using all catalogs available in the CATS and VizieR databases that meet the survey strip, and, in some cases, using the flux densities estimates from VLSSr,GLEAM, TGSS, and GB6 survey maps.We constructed the histograms of the spectral indices of the sources and verified the reliability of the identifications of sources found in the scans by comparing the coordinates and integrated flux densities with the corresponding parameters listed in the NVSS catalog. In the right ascension interval considered we found no objects at the 10–15 mJy level lacking in decimeter-wave catalogs. 相似文献
5.
S. Jejčič P. Heinzel N. Labrosse A. N. Zhukov A. Bemporad S. Fineschi S. Gunár 《Solar physics》2018,293(2):33
We determine the optimal width and shape of the narrow-band filter centered on the He?i D3 line for prominence and coronal mass ejection (CME) observations with the ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun) coronagraph onboard the PROBA-3 (Project for On-board Autonomy) satellite, to be launched in 2020. We analyze He?i D3 line intensities for three representative non-local thermal equilibrium prominence models at temperatures 8, 30, and 100 kK computed with a radiative transfer code and the prominence visible-light (VL) emission due to Thomson scattering on the prominence electrons. We compute various useful relations at prominence line-of-sight velocities of 0, 100, and 300 km?s?1 for 20 Å wide flat filter and three Gaussian filters with a full-width at half-maximum (FWHM) equal to 5, 10, and 20 Å to show the relative brightness contribution of the He?i D3 line and the prominence VL to the visibility in a given narrow-band filter. We also discuss possible signal contamination by Na?i D1 and D2 lines, which otherwise may be useful to detect comets. Our results mainly show that i) an optimal narrow-band filter should be flat or somewhere between flat and Gaussian with an FWHM of 20 Å in order to detect fast-moving prominence structures, ii) the maximum emission in the He?i D3 line is at 30 kK and the minimal at 100 kK, and iii) the ratio of emission in the He?i D3 line to the VL emission can provide a useful diagnostic for the temperature of prominence structures. This ratio is up to 10 for hot prominence structures, up to 100 for cool structures, and up to 1000 for warm structures. 相似文献
6.
Radosław Rek 《Solar physics》2010,261(2):337-351
The Maunder Minimum was the time during the second part of the 17th century, nominally from 1645 to 1717 AD, when unusually
low numbers of sunspots were observed. On the basis of numerous recorded observations of auroras in the early 18th century,
the end of the Minimum could be regarded as around 1700, but details of sunspot observations by Jan Heweliusz (Heweliusz,
Machina Coelestis, 1679), John Flamsteed and Philippe de La Hire in 1684 allow us to interpret the Maunder Minimum as the period without a significant
cessation of activity. This Minimum was also recognized in 14C data from trees which grew during the second part of 17th century.
The variation in the production rate of radioactive carbon isotope 14C is due to modulation of the cosmic ray flux producing it by the changing level of solar activity and solar magnetic flux.
Stronger magnetic fields in the solar wind make it more difficult for cosmic rays to reach the Earth, causing a drop in the
production rate of 14C. However, more detailed analyses of 14C data indicate that the highest isotope abundances do not occur at the time of sunspot minima, as would be expected on the
basis of modulation of the cosmic ray flux by the solar magnetic field, but two years after the sunspot number maximum. This
time difference (or phase delay) can be accounted for if in fact there are both solar and non-solar cosmic ray contributions.
Solar flares could also contribute high-energy particles and produce 14C and are generally not most frequent at the time of the highest sunspot numbers in the cycle. 相似文献
7.
New measurements of the longitudinal magnetic field of the Ap star γ Equ obtained with the MSS spectrograph of the 6-m telescope of the SAO RAS in 2002–2018 are present. Analyzing our results together with all the available literature data sources of 〈Bz〉 (441 measurements) we found the rotation period P = 89.1 ± 4.2 years (32 521 days). Fitting all the measurements with double sine-wave function resulted in two periods equal to 95.5 and 17.4 years (with the errors of 3.5 and 2 years correspondingly). According to our new estimate, the transition to positive values of 〈Bz〉, probably, will occur later than previously assumed, literally in 2031. 相似文献
8.
Ana I. Gómez de Castro Leire Beitia-Antero Sabina Ustamujic 《Experimental Astronomy》2018,45(2):147-163
Observations of the Earth’s exosphere have unveiled an extended envelope of hydrogen reaching further than 10 Earth radii composed of atoms orbiting around the Earth. This large envelope increases significantly the opacity of the Earth to Lyman α (Lyα) photons coming from the Sun, to the point of making feasible the detection of the Earth’s transit signature from 1.35 pc if pointing with an 8 meter primary mirror space telescope through a clean line of sight (N H <?1017 cm??2), as we show. In this work, we evaluate the potential detectability of Earth analogs orbiting around nearby M-type stars by monitoring the variability of the Lyα flux variability. We show that, in spite of the interstellar, heliospheric and astrospheric absorption, the transit signature in M5 V type stars would be detectable with a dedicated Lyα flux monitor implemented in a 4–8 m class space telescope. Such monitoring programs would enable measuring the robustness of planetary atmospheres under heavy space weather conditions like those produced by M-type stars. A 2-m class telescope, such as the World Space Observatory, would suffice to detect an Earth-like planet orbiting around Proxima Centauri, if there was such a planet or nearby M5 type stars. 相似文献
9.
We discuss the influence of nuclear masses and mass distributions of fission products on the formation of heavy elements at the final stages of the r-process recycled through fission on long duration timescales. The fission recycling is of great importance in an environment with a high density of free neutrons (e.g., in neutron star merger scenarios), when the r-process duration is long enough for most of the seed nuclei to be transformed into actinoids. The fission products of transuranium elements are again drawn into the r-process to produce the abundance curve beyond the iron peak. In this case, to explain the abundances of the A ～ 130 peak elements, not only the nuclear masses, fission barriers, and reaction rates, but also the fission product mass distribution must be predicted. Our r-process calculations using new nuclear masses and fission barriers and reaction rates based on them have shown that the simple two-fission-fragment model used previously in r-process calculations cannot describe adequately the position of the second peak in the observed abundance curve. We show that agreement between calculations and observations can be achieved only when we properly consider the mass distribution of fission products by taking into account the emission of instantaneous fission neutrons. 相似文献
10.
V. V. Klimenko S. A. Balashev A. V. Ivanchik D. A. Varshalovich 《Astronomy Letters》2016,42(3):137-162
An independent analysis of the molecular hydrogen absorption system at redshift z abs = 2.059 in the spectrum of the quasar J 2123?0050 is presented. The H2 system consists of two components (A and B) with column densities \(\log N_{{H_2}}^A = 17.94 \pm 0.01\) and \(N_{{H_2}}^B = 15.16 \pm 0.02\). The spectrum exhibits the lines of HDmolecules (logN HD A = 13.87±0.06) and the neutral speciesCI and Cl I associated with the H2 absorption system. For the molecular hydrogen lines near the quasar’s Lyβ and OVI emission lines, we detect a nonzero residual flux, ~3% of the total flux, caused by the effect of partial coverage of the quasar’s broad-line region by an H2 cloud. Due to the smallness of the residual flux, the effect does not affect the H2 column density being determined but increases the statistics of observations of the partial coverage effect to four cases. The uniqueness of the system being investigated is manifested in a high abundance of the neutral species H2 and CI at the lowest HI column density, logN HI = 19.18 ± 0.15, among the highredshift systems. The H2 and CI column densities in the system being investigated turn out to be higher than those in similar systems in our Galaxy and theMagellanic Clouds by two or three orders ofmagnitude. The \(N_{HD} /2N_{H_2 }\) ratio for component A has turned out to be also unusually high, (4.26 ± 0.60) × 10?5, which exceeds the deuterium abundance (D/H) for high-redshift systems by a factor of 1.5. Using the HI, H2, HD, and CI column densities as well as the populations of excited H2 and CI levels, we have investigated the physical conditions in components A and B. Component A represents the optically thick case; the gas has a low number density (~30 cm?3) and a temperature T ~ 140 K. In component B, the mediumis optically thin with n H ≤ 100 cm?3 and T ≥ 100 K. The ultraviolet (UV) background intensity in the clouds exceeds the mean intensity in our Galaxy by almost an order ofmagnitude. A high gas ionization fraction, \(n_{H^ + } /n_H \sim 10^{ - 2}\), which can be the result of partial shielding of the systemfrom hard UV radiation, is needed to describe the high HD and CI column densities. Using our simulations with the PDRMeudon code, we can reconstruct the observed column densities of the species within the model with a constant density (n H ~ 40 cm?3). A high H2 formation rate (higher than the mean Galactic value by a factor of 10?40) and high gas ionization fraction and UV background intensity are needed in this case. 相似文献
11.
The lateral distribution of cascade particles in extensive air showers from cosmic rays with energy E0 ? 1017 eV has been studied at the Yakutsk array by the ground scintillation detectors over the period of continuous observations 1977–2017. The experimental data are compared with those computed with various models for the development of extensive air showers from the CORSIKA software package. The best agreement between the theory and experiment is observed for the QGSjet-01-d model. In the energy range (1?20)× 1017 eV there is a change in the cosmic-raymass composition from 〈lnA〉 ≈ 2.5 to the proton one. 相似文献
12.
A runaway binary star escaping in runaway from the multiple system Θ1 Ori C is studied. The radial velocities of both components are measured and radial velocity curves are constructed and solved
for them. The physical parameters and chemical compositions of the stars are determined. 相似文献
13.
The data acquired by the Vega and Giotto spacecraft, while investigating comet 1Р/Halley in 1986, are compared to the results of the first phase of exploration of the nucleus of comet 67P/Churyumov–Gerasimenko performed with the Rosetta and Philae modules. The course of the Rosetta mission activity and the status of the modules after the Philae probe landing on the comet’s nucleus are overviewed. Since some elements of the touchdown equipment failed, a number of in-situ experiments on the comet’s nucleus were not carried out. 相似文献
14.
V. A. Simonenko D. A. Gryaznykh N. G. Karlykhanov V. A. Lykov A. N. Shushlebin 《Astronomy Letters》2007,33(2):80-92
We study the influence of turbulent mixing on the development of thermonuclear flashes in the surface layers of neutron stars. A simple K ε model that includes various physical processes is used to describe the turbulent processes. In contrast to the widespread mixing-length theory, the K ε model does not require using additional dimensional parameters, traces the development of turbulence in dynamics, describes the various turbulence development scenarios (gravitational and shear instabilities, convection, semiconvection, etc.) in a unified way, and can be used in multidimensional numerical simulations. Empirical constants of the model are chosen on the basis of experimental data and direct numerical simulations of typical processes. We have used the Era and Tigr-3T software packages to numerically simulate thermonuclear flashes in the accretion-renewable atmospheres of neutron stars. Turbulence is shown to accelerate significantly the transport of released energy to the stellar surface. Mixing equalizes the concentrations of matter components throughout the burning layer and increases the amount of matter involved in the thermonuclear burning during a flash. 相似文献
15.
Heinrich Eichhorn 《Astronomische Nachrichten》1971,293(3):127-130
It is shown that there is no intrinsic difference between the so-called “astrometric” and “photogrammetric” methods of reducing star plates, and that either, when applied by competent investigators, will yield equivalent results. 相似文献
16.
É. A. Vitrichenko 《Astronomy Letters》2002,28(12):843-846
We measured the radial velocity of the star θ1 Ori D from IUE spectra and used published observations. Based on these data, we determined the period of its radial-velocity variations, P=20.2675±0.0010 days, constructed the phase radial-velocity curve, and solved it by least squares. The spectroscopic orbital elements were found to be the following: the epoch of periastron passage Ep=JD 2430826.6±0.1, the system's center-of-mass velocity /Gg=32.4±1.0 km s?1, K=14.3±1.5 km s?1, Ω=3.3±0.1 rad, e=0.68±0.09, a1 sin i = 3 × 1010 km, and f1 = 0.0025M⊙. Twice the period, P=40.528±0.002 days, is also consistent with the observations. 相似文献
17.
We report an efficient method for analyzing the radial-velocity and line-profile variability. We show that a detailed analysis of the variations of line profiles and velocity field in the stellar atmosphere requires the radial velocities to be measured separately for the blue and red halves of the absorption lines at different levels of their residual intensity. We applied this method to 120 CCD spectra taken in 1998–99 with the coude echelle spectrograph attached to the 2-m telescope of Shemakha Astronomical Observatory of National Academy of Sciences of Azerbaijan and analyzed the variations of the radial velocities and profiles of ion and Hβ lines in the spectrum of α Cyg. In the case of ion lines both halves of the absorption profile exhibit synchronous radial-velocity variations at all levels of line intensity. In the case of the Hβ line, which forms in the layers where stellar wind originates, the pattern of radial-velocity variations differs for the blue and red halves of the absorption profile. The variability pattern is the same at all levels in the red half of the profile, the blue half of the profile exhibits different variability patterns at different levels of residual line intensity. Identification and analysis of such variations allows us to study the nature of stellar-wind variability in the region of wind formation.The spectrum of α Cyg showed no line-profile or radial-velocity variations for six days in both halves of the absorption contour at all levels of line intensity. The star was in the quiescent phase. 相似文献
18.
We discuss the evolution of the ratio in number of recombinations due to 2s two photon escape and due to the escape of Lyman-α photons from the resonance during the epoch of cosmological recombination, within the width of the last scattering surface and near its boundaries. We discuss how this ratio evolves in time, and how it defines the profile of the Lyman-α line in the spectrum of CMB. One of the key reasons for explaining its time dependence is the strong overpopulation of the 2p level relative to the 2s level at redshifts z ? 750. 相似文献
19.
Carlo di Lauro Franca Lattanzi Linda R. Brown Keeyoon Sung Jean Vander Auwera Arlan W. Mantz Mary Ann H. Smith 《Planetary and Space Science》2012,60(1):93-101
Building upon previous studies, we re-investigated the ethane spectrum between 1330 and 1610 cm?1 by combining unapodized spectra obtained at room temperature with a Bruker Fourier transform spectrometer (FTS) in Brussels and at 131 K with a Bruker FTS in Pasadena. The maximum optical path differences (MOPD) of the two datasets were 450 and 323.7 cm, corresponding to spectral resolutions of 0.0020 and 0.0028 cm?1, respectively. Of the 15,000 lines observed, over 4592 transitions were assigned to the ν6 (at 1379 cm?1), ν8 (at 1472 cm?1), ν4+ν12 (at 1481 cm?1) and 2ν4+ν9 (at 1388 cm?1) bands, and another 1044 transitions were located for the ν4+ν8?ν4 hot band (at 1472 cm?1). Our new analysis included an improved implementation of the Hamiltonian calculation needed to interpret the complex spectral structures caused by numerous interactions affecting these four modes of vibration. From these results, we created the first line-by-line database containing the molecular parameters for over 20,000 12C2H6 transitions at 7 μm. 相似文献
20.
Daniel Garcia-Castellanos Sierd Cloetingh Ronald Van Balen 《Global and Planetary Change》2000,27(1-4)
Middle Pleistocene uplift in the Eifel has been interpreted as the isostatic response of the lithosphere to a deep buoyant hot body. The spatial and temporal distribution of the uplift in the Ardennes–Rhenish Massif Region has recently been constrained by new data of river incision that have been compiled in this work. The uplift distribution can be reproduced using a thin elastic plate model and assuming that the uplift is created by a deep buoyant load, the distribution of which coincides with the weakening. Models incorporating a lithospheric weakening provide a better fit of the observed uplift than models with homogeneous flexural rigidity. These results are confirmed by numerical experiments using a depth-dependent elasto-plastic plate rheology, linking the flexural model with the thermo-mechanical structure of the lithosphere. 相似文献