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1.
J. Koza 《Solar physics》2010,266(2):261-275
We examine the sensitivity of selected Ba?ii, Fe?i, Fe?ii, and Cr?i spectral lines to changes of the line-of-sight velocity by sharpness of their line profiles and response functions to line-of-sight velocity evaluated by the 1-D model of the quiet solar atmosphere in the LTE approximation. The set of selected lines includes the Ba?ii 4554 Å line, generally considered to be an excellent Doppler mapper. Our findings confirm earlier results showing that the sensitivity increases not only with wavelength, as anticipated from the Doppler relation, but mainly with the sharpness of line profiles given by the ratio of their depths and widths. The line Fe?i 5247 Å is the most sensitive in our set, whereas the Fe?i and Fe?ii infrared lines show very low sensitivity because of their large thermal widths. The line Ba?ii 4554 Å shows only moderate sensitivity due to its large width, given by a broad hyperfine structure and isotopic split. For the first time we identify a very promising and so far unknown Doppler mapper of the solar photosphere and low chromosphere, which is the line Ba?ii 6497 Å. Its sensitivity is comparable with the sensitivity of Fe?i 5247 Å and clearly surpasses the sensitivity of Ba?ii 4554 Å. The line Ba?ii 6497 Å offers many advantages, making it a highly recommendable choice for future studies of line-of-sight velocities in the photosphere and low chromosphere.  相似文献   

2.
It is well established that both total and spectral solar irradiance are modulated by variable magnetic activity on the solar surface. However, there is still disagreement about the contribution of individual solar features for changes in the solar output, in particular over decadal time scales. Ionized Ca ii K line spectroheliograms are one of the major resources for these long-term trend studies, mainly because such measurements have been available now for more than 100 years. In this paper we introduce a new Ca ii K plage and active network index time series derived from the digitization of almost 40 000 photographic solar images that were obtained at the 60-foot solar tower, between 1915 and 1985, as a part of the monitoring program of the Mount Wilson Observatory. We describe here the procedure we applied to calibrate the images and the properties of our new defined index, which is strongly correlated to the average fractional area of the visible solar disk occupied by plages and active network. We show that the long-term variation of this index is in an excellent agreement with the 11-year solar-cycle trend determined from the annual international sunspot numbers series. Our time series agrees also very well with similar indicators derived from a different reduction of the same data base and other Ca ii K spectroheliograms long-term synoptic programs, such as those at Kodaikanal Observatory (India), and at the National Solar Observatory at Sacramento Peak (USA). Finally, we show that using appropriate proxies it is possible to extend this time series up to date, making this data set one of the longest Ca ii K index series currently available.  相似文献   

3.
The hydrogen and helium lines are the most prominent lines in the solar prominences spectra. Observations with the SUMER spectrometer onboard SOHO showed that there are weak lines in the blue wings of the Lyman series which affect their profiles. They were all identified as He ii lines in the Lyman series wings, except for the Lα line whose profile was affected by the use of an attenuator. The He ii lines are the even Balmer lines of the He ii system, a set of lines that we complete with the odd ones. We characterize them by comparison with the blue wings of the Lyman series in order to improve the H Lyman series observations and modeling, on one hand and to provide He ii lines observations for further combined H – He i – He ii modeling, on the other hand.  相似文献   

4.
We study the radial-velocity and light curves of the two eclipsing binaries EE Aqr and Z Vul. Using the latest version of the Wilson and Van Hamme (Computing Binary Star Observables, 2003) model, absolute parameters for the systems are determined. We find that EE Aqr and Z Vul are near-contact and semi-detached systems, respectively. The primary component of EE Aqr fills about 96% of its ‘Roche lobe’, while its secondary one appears close to completely filling this limiting volume. In a similar way, we find fill-out proportions of about 72 and 100% of these volumes for the primary and secondary components of Z Vul respectively. We compare our results with those of previous authors.  相似文献   

5.
Spatially resolved studies of star-forming regions show that the assumption of spherical geometry is not realistic in most cases, with a major complication posed by the gas being ionised by multiple non-centrally located stars or star clusters. Geometrical effects including the spatial configuration of ionising sources affect the temperature and ionisation structure of these regions. We try to isolate the effects of multiple non-centrally located stars, via the construction of 3D photoionisation models using the 3D Monte Carlo photoionisation code mocassin with very simple gas density distributions, but various spatial configurations for the ionisation sources.Emission-line spectra from H?ii regions are often used to study the metallicity of star-forming regions, as well as for providing a constraint on temperatures and luminosities of the ionising sources. Empirical metallicity diagnostics must often be calibrated with the aid of photoionisation models. However, most studies so far have been carried out by assuming spherical or plane-parallel geometries, with major limitations on the allowed gas and dust density distributions and with the spatial distribution of multiple, non-centrally located ionising sources not being accounted for. We compare integrated emission-line spectra from our models and quantify any systematic errors caused by the simplifying assumption of a single, central location for all ionising sources. We find that the dependence of the metallicity indicators on the ionisation parameter causes a clear bias, due to the fact that models with a fully distributed configuration of stars always display lower ionisation parameters than their fully concentrated counterparts. The errors found imply that the geometrical distribution of ionisation sources may partly account for the large scatter in metallicities derived using model-calibrated empirical methods.  相似文献   

6.
Observations of the central intensity of the Ca ii K and 849.8 nm lines are used to derive the ratios of the oscillation power in the frequency ranges of the “five-minute” (W 5) and “three-minute” (W 3) oscillations. It is shown that at high significance level ratios, (W 5/W 3) >1 at coronal hole bases, and W 5/W 3 ≈1 in quiet chromospheric areas far from holes.  相似文献   

7.
We have obtained new constraints on the cosmological parameters Ω m and σ 8 from the peculiar velocities of flat edge-on spiral galaxies from the RFGC catalog. Based on these results presented graphically, we have found the quantitative condition (Ω m /0.3)0.37 σ 8 = 0.92 ± 0.05. The estimates of Ω m and σ 8, along with their combinations Ω m α σ 8 for various α, are compared with the estimates by other authors.  相似文献   

8.
In this work, we explore many cosmological implications of a four-dimensional cosmology dominated by quintessence with a static traversable wormhole, spatio-temporal varying G and by taking into account a decaying cosmological constant and a decaying graviton mass by means of an additional bimetric tensor in Einstein’s field equations proposed by Visser in 1998.  相似文献   

9.
We consider the circular planar restricted three-body problem with the mass parameter μ = 5 × 10?5. Two families of periodic solutions are calculated: family c, starting from the collinear fixed point L 1, and the initial part of familyi, which begins by direct circular orbits of an infinitely small radius around the body of bigger mass. The calculated families are very close to the generating ones, which we described earlier. In particular, the existence of the predicted zigzag structure of characteristics of family iis verified. New properties of the planar and vertical traces are discovered.  相似文献   

10.
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   

11.
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   

12.
We present the V light curves of δ Scuti type variable V350 Peg, obtained between August and October 2005 at the Ankara University Observatory (AUG) and the TüBíTAK National Observatory (TUG). By application of multiple-frequency analyses using Period04 to 7878 photometric V measurements (which are consist of our 747 V data and 7131 V data obtained at Monegrillo Observatory) of V350 Peg, a five-frequency solution was found to be fitted well to the data. In accordance with the computed Q values for V350 Peg, it was found that this star has probably radial mode with l=0 and g-mode oscillations.  相似文献   

13.
In this work, we first establish a simple procedure to obtain with 11-figure accuracy the values of Chandrasekhar’s H-function for isotropic scattering using a closed-form integral representation and the Gauss-Legendre quadrature. Based on the numerical values of the function produced by this method for various combinations of ? 0, the single scattering albedo, and μ, the cosine of the zenith angle θ of the direction of radiation emergent from or incident upon a semi-infinite scattering-absorbing medium, we propose a rational approximation formula with μ 1/4 and \(\sqrt{1-\varpi_{0}}\) as the independent variables. This allows us to reproduce the correct values of H(? 0,μ) within a relative error of 2.1×10?5 without recourse to any iterative procedure or root-finding process.  相似文献   

14.
We study variations of the lifetimes of high-ℓ solar p modes in the quiet and active Sun with the solar activity cycle. The lifetimes in the degree range ℓ=300 – 600 and ν=2.5 – 4.5 mHz were computed from SOHO/MDI data in an area including active regions and quiet Sun using the time – distance technique. We applied our analysis to the data in four different phases of solar activity: 1996 (at minimum), 1998 (rising phase), 2000 (at maximum), and 2003 (declining phase). The results from the area with active regions show that the lifetime decreases as activity increases. The maximal lifetime variations are between solar minimum in 1996 and maximum in 2000; the relative variation averaged over all ℓ values and frequencies is a decrease of about 13%. The lifetime reductions relative to 1996 are about 7% in 1998 and about 10% in 2003. The lifetime computed in the quiet region still decreases with solar activity, although the decrease is smaller. On average, relative to 1996, the lifetime decrease is about 4% in 1998, 10% in 2000, and 8% in 2003. Thus, measured lifetime increases when regions of high magnetic activity are avoided. Moreover, the lifetime computed in quiet regions also shows variations with the activity cycle.  相似文献   

15.
This paper describes design of the trajectory and analysis of the stability of collinear point L 2 in the Sun-Earth system. The modified restricted three body problem with additional gravitational potential from the belt is used as the model for the Sun-Earth system. The effect of radiation pressure of the Sun and oblate shape of the Earth are considered. The point L 2 is asymptotically stable up to a specific value of time t correspond to each set of values of parameters and initial conditions. The results obtained from this study would be applicable to locate a satellite, a telescope or a space station around the point L 2.  相似文献   

16.
We present the results of our analysis of the frequencies of galaxies with tidal tails and M51-type galaxies in several deep fields of the Hubble Space Telescope (HDF-N, HDF-S, HUDF, GOODS, GEMS). In total, we have found about seven hundred interacting galaxies at redshifts z ≤ 1.5 in these fields. At z ≤ 0.7, the observed space densities of galaxies with tidal structures and M51-type galaxies have been found to increase as ∝(1 + z) m , where m ≈ 2.6. According to our estimates, over the last 6–7 Gyr, i.e., at z ≤ 0.7, about a third of the galaxies with M(B) ≤ −18 m must have undergone strong gravitational perturbations and mergers and ∼1/10−1/5 of the galaxies have swallowed relatively low-mass nearby satellites typical of M51-type galaxies. The possible decrease in the time scale on which a distant galaxy appears peculiar with growing z can increase considerably the estimated rate of mergers.  相似文献   

17.
In this paper we have considered axially symmetric Bianchi-I, Kantowski Sachs and Bianchi-III space-time models with bulk viscosity, where the gravitational constant G and the cosmological term Λ vary with time. In Einstein equations this variation in G and Λ are taken in such a way as to preserve the energy momentum tensor. Solutions are obtained with the cosmological term varying inversely with square of time.  相似文献   

18.
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   

19.
We performed a detailed analysis of 27 slow coronal mass ejections (CMEs) whose heights were measured in at least 30 coronagraphic images and were characterized by a high quality index (≥4). Our primary aim was to study the radial evolution of these CMEs and their properties in the range 2 – 30 solar radii. The instantaneous speeds of CMEs were calculated by using successive height – time data pairs. The obtained speed – distance profiles [v(R)] are fitted by a power law v = a(R−b) c . The power-law indices are found to be in the ranges a=30 – 386, b=1.95 – 3.92, and c=0.03 – 0.79. The power-law exponent c is found to be larger for slower and narrower CMEs. With the exception of two events that had approximately constant velocity, all events were accelerating. The majority of accelerating events shows a v(R) profile very similar to the solar-wind profile deduced by Sheeley et al. (Astrophys. J. 484, 472, 1997). This indicates that the dynamics of most slow CMEs are dominated by the solar wind drag.  相似文献   

20.
We summarize results from deep spectroscopic observations of the HD 209458 planetary system, carried out with the Hubble Space Telescope—Cosmic Origins Spectrograph. Orbitally resolved observations are used to show that hot gas emission lines, arising only in the stellar atmosphere, are not variable, while lower ionizations species found in the upper atmosphere of the hot Jupiter HD 209458b absorb stellar photons during transit. For both C II and Si III, we find mean transit attenuation of ～8%. The firm detection of silicon is in direct conflict with previous low-resolution studies, which we attribute to long-term variability in the system. We also use these observations to search for auroral emission from the planet, detecting a statistically significant emission feature at 1582 Å that is consistent with H2 photoexcited by stellar O I photons.  相似文献   

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