Spectroscopic monitoring of SS 433: A search for long-term variations of kinematic model parameters     

V. V. Davydov  V. F. Esipov  A. M. Cherepashchuk 《Astronomy Reports》2008,52(6):487-506

Between 1994 and 2006, we obtained uniform spectroscopic observations of SS 433 in the region of Hα. We determined Doppler shifts of the moving emission lines, Hα ₊ and Hα _?, and studied various irregularities in the profiles for the moving emission lines. The total number of Doppler shifts measured in these 13 years is 488 for Hα _? and 389 for Hα ₊. We have also used published data to study possible long-term variations of the SS 433 system, based on 755 Doppler shifts for Hα _? and 630 for Hα ₊ obtained over 28 years. We have derived improved kinematic model parameters for the precessing relativistic jets of S S 433 using five-and eight-parameter models. On average, the precession period was stable during the 28 years of observations (60 precession cycles), at 162.250^d ± 0.003^d. Phase jumps of the precession period and random variations of its length with amplitudes of ≈6% and ≈1%, respectively, were observed, but no secular changes in the precession period were detected. The nutation period, P _nut = 6.2876^d ± 0.00035^d, and its phase were stable during 28 years (more than 1600 nutation cycles). We find no secular variations of the nutation cycle. The ejection speed of the relativistic jets, v, was, on average, constant during the 28 years, β = v/c = 0.2561 ± 0.0157. No secular variation of β is detected. In general, S S 433 demonstrates remarkably stable long-term characteristics of its precession and nutation, as well as of the central “engine” near the relativistic object that collimates the plasma in the jets and accelerates it to v = 0.2561c. Our results support a model with a “slaved” accretion disk in S S 433, which follows the precession of the optical star’s rotation axis.  相似文献   

The Seyfert 1 galaxy Ark 120. Spectral variability in 1992–2005     

V. T. Doroshenko  S. G. Sergeev  V. I. Pronik 《Astronomy Reports》2008,52(6):442-462

We have studied the variability of the Hβ line and the adjacent continuum in the spectrum of the Seyfert galaxy Ark 120, based on spectral observations of the galaxy’s nucleus obtained in the Crimea in 1992–2005, supplemented by published data for 1988–1996. Irregular variability on various timescales (years to days) can be accompanied by periodic brightness variations in both the continuum and the Hβ line, with a period of P ～ 430 days and an amplitude of Δm ～ 0.2 ^m in the continuum, which were traced for more than 13 cycles. In total, in 1988–2005, the flux variations in the line lag those in the continuum by 55 ± 9 days if calculated from the peak of the cross correlation function, or by 72 ± 7 days, if calculated from the centroid of the CCF. The delay is correlated with the continuum brightness, increasing when the continuum flux increases. The Hβ line profiles indicate both a high degree of diversity and the presence of features that recur after various extended time intervals. Analysis of the evolution of the differences between each individual normalized line profile and the mean normalized profile indicates systematic motion of excesses relative to the average profile from negative to positive radial velocities. In contrast, parts of the Hβ line with low radiation relative to the mean normalized profile evolve in the opposite direction (from the red to the blue Hβ wing). This pattern is also typical for the rotating broad-line region, if this region has the form of a disk. The rotation period exceeds 9000–10000 days, or 25–27 years. The size of the broad-line region calculated form this period corresponds to a reverberation time of no fewer than 30 days, consistent with the results of cross-correlation analysis.  相似文献   

Non-uniform model for the synchrotron radiation of Sgr A* and other low-luminosity galactic nuclei     

V. I. Slysh 《Astronomy Reports》2008,52(5):343-351

A model for non-uniform source of synchrotron radiation with a power-law radial distribution of the magnetic field and relativistic-electron density along one-or two-sided jets is described. Non-relativistic jets with both constant cross sections (collimated jets) and cross sections that are proportional to distance (conical jets) are considered. Formulas that can be used to determine source parameters from the spectral index, source size, and index of the relativistic-electron energy spectrum based on multi-frequency observations are obtained. In the case of a conical jet, these formulas coincide with the analogous formulas for a spherical source obtained by A.P. Marscher. Relations that can be used to estimate the magnetic-field strength from the brightness temperature in the self-absorbed region are also obtained. As examples, the inhomogeneous-source model is applied to the compact radio sources at the centers of the Milky Way, Sgr A*, and the low-luminosity galactic nuclei M81* and M87*, which are associated with supermassive black holes. The inner radius of the radiation region is determined. For Sgr A*, this distance turns out to be comparable to the gravitational radius, smaller than the radius of the last stable orbit for a non-rotating black hole, and consistent with the radius of the last stable orbit expected for a rotating black hole. The inner radii in M81* and M87* are ～15 R _S , an order of magnitude larger than for Sgr A*. Estimates of the magnetic field at the inner radius are 400 G for M81*, 0.65–5.3 kG for Sgr A*, and 20–100 kG for M87*. These magnetic fields and the Blandford-Znajek model for the radiation of a rotating black hole are used to estimate the rotational speed of the black holes, which are in agreement with the characteristic variability time scales for these three objects. However, the accuracy of these estimates is modest, and is limited primarily by the accuracy of interferometric measurements at millimeter wavelengths.  相似文献   

Timescales for mechanisms for the dynamical evolution of open star clusters     

V. M. Danilov  L. V. Dorogavtseva 《Astronomy Reports》2008,52(6):467-478

We have obtained the stellar velocity dispersion in three mutually perpendicular directions in the halos and cores of clusters as a function of time for several non-stationary open-cluster models. During the dynamical evolution of the open-cluster models, the velocity dispersions undergo oscillations that do not decay during 5–10 violent-relaxation timescales, τ _vr . We estimated the time for synchronization of the rotation of the open-cluster models and their motion around the center of the Galaxy, t _s , which, depending on the model parameters, is t _s ? (5–27)τ _vr . Synchronization mechanisms for the models are discussed. The disruption of the systems in the force field of the Galaxy is strongly affected by tidal friction. We have also estimated the time for the formation of a spherical stellar-velocity distribution in the cluster models, t _σ ? (6 ? 25)τ _vr . The impact of instability in the stellar motions in a cluster on the formation of a spherical velocity distribution in the open-cluster models is discussed. We have noted a tendency for a weakening of the dependence of the coarse phase density of the cluster on small initial perturbations of the stellar phase coordinates in the model cluster cores for times about five times longer than the violent-relaxation time.  相似文献   

Mirdita Zone ophiolites and associated sediments in Albania reveal Neotethys Ocean origin   总被引：1，自引：1，他引：0  

Hans-Jürgen Gawlick  Wolfgang Frisch  Lirim Hoxha  Paulian Dumitrica  Leopold Krystyn  Richard Lein  Sigrid Missoni  Felix Schlagintweit 《International Journal of Earth Sciences》2008,97(4):865-881

The Mirdita Ophiolite Zone in Albania is associated with widespread mélanges containing components of up to nappe-size. We dated matrix and components of the mélange by radiolarians, conodonts, and other taxa. The components consist of radiolarites, pelagic limestones and shallow-water limestones, all of Triassic age, as well as ophiolites. Triassic radiolarite as a primary cover of ophiolite material proves Middle Triassic onset of Mirdita ocean-floor formation. The mélange contains a turbiditic radiolarite-rich matrix (“radiolaritic flysch”), dated as Late Bajocian to Early Oxfordian. It formed as a synorogenic sediment during west-directed thrusting of ophiolite and sediment-cover nappes representing ocean floor and underplated fragments of the western continental margin. The tectonic structures formed during these orogenic events (“Younger Kimmeridian or Eohellenic Orogeny”) are sealed by Late Jurassic platform carbonates. The geological history conforms with that of the Inner Dinarides and adjoining areas; we therefore correlate the Mirdita-Pindos Ophiolite Zone with the Vardar Zone and explain its present position by far-distance west-directed thrusting.  相似文献   

Surface complexation modeling of Cu(II) adsorption on mixtures of hydrous ferric oxide and kaolinite     

Tracy J Lund  Carla M Koretsky  Christopher J Landry  Melinda S Schaller  Soumya Das 《Geochemical transactions》2008,9(1):9

Background  

The application of surface complexation models (SCMs) to natural sediments and soils is hindered by a lack of consistent models and data for large suites of metals and minerals of interest. Furthermore, the surface complexation approach has mostly been developed and tested for single solid systems. Few studies have extended the SCM approach to systems containing multiple solids.  相似文献   

Oxidation and metal-insertion in molybdenite surfaces: evaluation of charge-transfer mechanisms and dynamics     

CV Ramana  U Becker  V Shutthanandan  CM Julien 《Geochemical transactions》2008,9(1):8

Molybdenum disulfide (MoS₂), a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS₂ is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia.  相似文献   

Spatiotemporal Patterns of Subtidal Benthic Microalgal Biomass and Community Composition in Galveston Bay,Texas, USA     

James L. Pinckney  Alyce R. Lee 《Estuaries and Coasts》2008,31(2):444-454

Many Gulf of Mexico estuaries have low ratios of water volume to bottom surface area, and benthic processes in these systems likely have a major influence on system structure and function. The purpose of this study was to determine the spatiotemporal distribution of biomass and community composition of subtidal benthic microalgal (BMA) communities in Galveston Bay, TX, USA, compare BMA community composition and biomass to phytoplankton in overlying waters, and estimate the potential contribution of BMA to the trophodynamics in this shallow, turbid, subtropical estuary. The estimates of BMA biomass (mean = 4.21 mg Chl a m⁻²) for Galveston Bay were within the range of the reported values for similar Gulf of Mexico estuaries. BMA biomass in the central part of the bay was essentially homogeneous, whereas biomass at the seaward and upper bay ends of the transect were significantly lower. Peridinin, fucoxanthin, and alloxanthin were the three carotenoids with the highest concentrations, with fucoxanthin having the highest mean concentration (1.82 mg m⁻²). The seaward and landward ends of the transect differed from the central region of the bay with respect to the relative abundances of chlorophytes, cyanobacteria, and photosynthetic bacteria. Benthic microalgal community composition also showed a gradual shift over time due to changes in the relative abundances of photosynthetic bacteria, cryptophytes, dinoflagellates, and cyanobacteria. Major changes in community composition occurred in the spring months (March to April). On an areal basis, BMA biomass in Galveston Bay occurred at minor concentrations (16.5%) relative to phytoplankton. Furthermore, the concentrations of carotenoid pigments for phytoplankton and BMA (fucoxanthin, alloxanthin, and zeaxanthin) were correlated (r = 0.48 to 0.61), suggesting a close linkage between microalgae in the water column and sediments. The contribution of BMA to the primary productivity of the deeper waters (>2 m) of Galveston Bay is probably very small in comparison to shallower waters along the bay margins. The significant similarities in the community composition of phytoplankton and BMA illustrate the potential importance of deposition and resuspension processes in this turbid, shallow estuary.  相似文献   

Tidal and Meteorological Forcing of Suspended Sediment Flux in a Muddy Mesotidal Estuary     

J. R. French  H. Burningham  T. Benson 《Estuaries and Coasts》2008,31(5):843-859

Although the supply and fate of suspended sediment is of fundamental importance to the functioning and morphological evolution of muddy estuaries, reliable sediment budgets have been established in only a few cases. Especially for smaller estuaries, inadequate bathymetric surveys and a lack of intertidal sedimentation data often preclude estimation of the sediment budget from morphological change, while instrument-derived residual fluxes typically lie well within the errors associated with measurement of much larger gross tidal transports. Given suitably long-term records of continuously monitored suspended sediment concentration (SSC), however, analysis of the major scales of variation in sediment transport and their relation to hydrodynamic and meteorological forcing permits qualitative testing of hypotheses suggested by directly measured residual fluxes. This paper analyzes data from a 1-year acoustic Doppler profiler deployment in the Blyth estuary, a muddy mesotidal barrier-enclosed system on the UK east coast. Flux calculations indicate a small sediment import equivalent to just 1.5% of the gross flood tide transport. Little confidence can be assigned to either the magnitude or direction of such a small residual when considered in isolation. However, the inference that the sediment regime is finely balanced is qualitatively supported by the close similarity between flood-tide and ebb-tide SSC values. Singular spectrum analysis of the SSC time series shows the expectedly large contributions to the variance in SSC at intratidal and subtidal (semimonthly and monthly) scales but also picks out intermittent variability that is initially attributed to a combination of non-tidal surge and wind stress forcing. Closer examination of the data through cross-correlograms and event-scale analysis indicates that local meteorological forcing is the major factor. Acting through the resuspension of intertidal mudflat sediments at times of strong westerlies, meteorological forcing is directly implicated in episodic sediment export from the estuary. Thresholding of tide-averaged fluxes using a range of critical wind stress values further indicates that ‘tide-dominated’ (i.e., low wind stress) and ‘wave-dominated’ (high wind stress) conditions are associated with sediment import and export. Sediment balance is potentially sensitive to the frequency of high wind stress events, since the associated sediment exports are several times larger than the average import under calm conditions. Intermittent meteorological forcing may thus exert an important control on the sedimentary balance of otherwise tidally dominated muddy estuarine systems, and the role of wind climate should not be overlooked in studies of estuary response to environmental change.  相似文献   

Macrofaunal Spatial Patterns in Relationship to Environmental Variables in the Richibucto Estuary,New Brunswick,Canada   总被引：1，自引：0，他引：1  

Lin Lu  Jon Grant  Jeffrey Barrell 《Estuaries and Coasts》2008,31(5):994-1005

Estuarine macrobenthos respond to a variety of environmental gradients such as sediment type and salinity, and organic enrichment. A relatively new influence, organic loading from suspended bivalve culture, has the potential to alter this response. A study on soft-bottom macrobenthic communities was carried out in the Richibucto estuary (46°40′N, 64°50′W), New Brunswick, Canada, with samples collected from 18 stations in late September and early October 2006. The site consisted of a large tidal channel originating upstream in a small river. The channel was punctuated by bag culture of oysters along its length. A total of 88 species were recorded. The mean values of abundance, species richness, and diversity (H′) of macrofauna were 11,199 ind. m⁻² (ranged from 4,371 to 19,930 ind. m⁻²), 23.4 species grab⁻¹ and 3.29 grab⁻¹, respectively. In general species richness and H′ increased from the upper estuary to the estuarine mouth. Multivariate analyses clearly exhibited the spatial distribution in community structure, which coincided with the locations along the estuary (the upper, the lower and the mouth), as well as inside and outside the channel. Species richness and diversity H′ showed strong positive correlations with salinity (21.2–25.2 ppt), and abundance was positively correlated with water depth (1.0–4.5 m). Abundance and species richness were negatively correlated with both of silt–clay fraction (3.3–24.8%) and sorting (σ_I). Species richness was also negatively correlated with organic content (1.9–12.7%). The BIO-ENV analyses identified silt–clay fraction, σ_I and salinity as the major environmental variable combination influencing the macrofaunal patterns, and silt–clay fraction as the single best-correlated variable.  相似文献