Analysis of HST ultraviolet spectra for T Tauri stars: DR Tau     

A. S. Kravtsova  S. A. Lamzin 《Astronomy Letters》2002,28(10):676-690

We analyze the spectra of DR Tau in the wavelength range 1200 to 3100 Å obtained with the GHRS and STIS spectrographs from the Hubble Space Telescope. The profiles for the C IV 1550 and He II 1640 emission lines and for the absorption features of some lines indicate that matter falls to the star at a velocity ～300 km s^?1. At the same time, absorption features were detected in the blue wings of the N I, Mg I, Fe II, Mg II, C II, and Si II lines, suggesting mass outflow at a velocity up to 400 km s^?1. The C II, Si II, and Al II intercombination lines exhibit symmetric profiles whose peaks have the same radial velocity as the star. This is also true for the emission features of the Fe II and H₂ lines. We believe that stellar activity is attributable to disk accretion of circumstellar matter, with matter reaching the star mainly through the disk and the boundary layer. At the time of observations, the accretion luminosity was L_ac ? 2L_⊙ at an accretion rate ?10^?7M_⊙ yr^?1. Concurrently, a small (<10%) fraction of matter falls to the star along magnetospheric magnetic field lines from a height ～R_*. Within a region of size ?3.5R_*, the disk atmosphere has a thickness ～0.1R_* and a temperature ?1.5 × 10⁴ K. We assume that disk rotation in this region significantly differs from Keplerian rotation. The molecular hydrogen lines are formed in the disk at a distance <1.4 AU from the star. Accretion is accompanied by mass outflow from the accretion-disk surface. In a region of size <10R_*, the wind gas has a temperature ～7000 K, but at the same time, almost all iron is singly ionized by H I L _α photons from inner disk regions. Where the warm-wind velocity reaches ?400 km s^?1, the gas moves at an angle of no less than 30° to the disk plane. We found no evidence of regions with a temperature above 10⁴ K in the wind and leave open the question of whether there is outflow in the H₂ line formation region. According to our estimate, the star has the following set of parameters: M_* ? 0.9M_⊙, R_* ? 1.8R_⊙, L_* ? 0.9L_⊙, and \(A_V \simeq 0\mathop .\limits^m 9\). The inclination i of the disk axis to the line of sight cannot be very small; however, i≤60°.  相似文献   

Nonautonomous nanophase on a hydrothermal pyrite surface and its geochemical significance     

V. L. Tauson  D. N. Babkin  S. V. Lipko  R. G. Kravtsova  V. I. Grebenshchikova  E. E. Lustenberg 《Doklady Earth Sciences》2008,423(2):1501-1506

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Late Weichselian sea level changes at Sotra, Hordaland, western Norway   总被引：1，自引：0，他引：1  

KNUT KRZYWINSKl  BJØRG STABELL 《Boreas: An International Journal of Quaternary Research》1984,13(2):159-202

Sediments from twenty-eight basins were surveyed; ten of these basins with a representative lithostrati-gfaphy wee studied to determine their isolation from the sea during Late Weichselian. Diatom analysis was used to determine salinity changes, which were dated by pollen analysis and the radiocarbon method. The area was deglaciated in the early Boiling, and a regression of about 5 m followed. A transgression of more than 10 m started in late Boiling and terminated in middle Younger Dryas, with a transgression maximum between 38.2 and 40 m above present sea level. All the investigated basins were finally isolated in late Younger Dryas/early Preboreal, during a rapid regression. Repeated cycles of chinophilous/ chinophobous plant communities in the area reflect climatic changes in the period. No evidence of an Older Dryas ice readvance was found.  相似文献   

The Physical Parameters of V680 Mon—Eclipsing Star with the Highest Known Eccentricity     

Volkov  I. M.  Kravtsova  A. S.  Chochol  D. 《Astronomy Reports》2021,65(3):184-202

Astronomy Reports - We present the first high accuracy UBVRI(RI)c CCD light curves of the poorly investigated eclipsing system V680 Mon = GSC 7428 218 (P = 8.54d, V = 10.02m). They were used to...  相似文献   

BU CMi as a Quadruple Doubly Eclipsing System     

Volkov  I. M.  Kravtsova  A. S.  Chochol  D. 《Astronomy Reports》2021,65(9):826-838

Astronomy Reports - We found that the known spectroscopic binary and variable BU CMi = HD65241 ( $$V = 6.4{-} {{6.7}^{{\text{m}}}}$$ , A0 V) is a quadruple doubly eclipsing 2+2 system. Both...  相似文献   

Hydrological-morphological and landscape features of the Niger River delta     

V. I. Kravtsova  V. N. Mikhailov  A. S. Kozyukhina 《Water Resources》2008,35(2):121-136

The Niger River delta, one of the largest deltas of the world, is characterized in this article. The geographic features, including the delta hydrographic system, natural and territorial complexes, hydrological regime, and the dynamics of the coastline, are discussed. Special emphasis is given to the assessment of the impact of the following factors on the delta structure and regime: river flow regulation, tides, the ocean level rise, sea waves, natural and human-induced land subsidence.  相似文献   

Long-Term Variations of Danube Delta Coastline     

Mikhailova  M. V.  Kravtsova  V. I.  Morozov  V. N. 《Water Resources》2019,46(5):659-669

Water Resources - Ground (expedition) and remote (space-based) methods have been used to carry out detail studies of variations of Danube delta coastline (DC). The displacements of the DC (the...  相似文献   

Galaxies with rows     

A. D. Chernin  A. S. Kravtsova  A. V. Zasov  V. P. Arkhipova 《Astronomy Reports》2001,45(11):841-853

The results of a search for galaxies with straight structural elements, usually spiral-arm rows (“rows” in the terminology of Vorontsov-Vel'yaminov), are reported. The list of galaxies that possess (or probably possess) such rows includes about 200 objects, of which about 70% are brighter than 14^m. On the whole, galaxies with rows make up 6–8% of all spiral galaxies with well-developed spiral patterns. Most galaxies with rows are gas-rich Sbc-Scd spirals. The fraction of interacting galaxies among them is appreciably higher than among galaxies without rows. Earlier conclusions that, as a rule, the lengths of rows are similar to their galactocentric distances and that the angles between adjacent rows are concentrated near 120° are confirmed. It is concluded that the rows must be transient hydrodynamic structures that develop in normal galaxies.  相似文献   

THE POTENTIAL FOR VISUAL AND AUTOMATED INTERPRETATION OF FOREST VEGETATION WITH SCANNER IMAGERY     

V. I. Kravtsova  Ye. M. Lapteva  I. K. Lur'ye 《地理信息系统科学与遥感》2013,50(1):41-50

Feature classification maps derived from visual and automated methods of interpreting band-specific and composite imagery from the “Fragment” multispectral scanning system are compared in the study of vegetation and related features along the Gulf of Riga. The automated method, featuring a two-stage unsupervised/supervised classification algorithm developed at Moscow University (see MSRS, 1984, No. 3, pp. 255-261) provided for enhanced discrimination of wetland areas, farm land, and settlements, as well as for the elimination of extraneous components (especially the above) visually classified as deciduous forest. Translated from: Vestnilk Moskovskogo Universiteta, geografiya, 1988, No. 3, pp. 49-57 by Jay K. Mitchell, PlanEcon, Inc., Washington, DC 20005.  相似文献   

A first-order analysis of the potential rôle of CO₂ fertilization to affect the global carbon budget: a comparison of four terrestrial biosphere models     

DAVID W. KICKLIGHTER  MICHELE BRUNO  SILKE DÖNGES  GERD ESSER  MARTIN HEIMANN  JOHN HELFRICH  FRANK IFT  FORTUNAT JOOS  JÖRG KADUK  GUNDOLF H. KOHLMAIER  A. DAVID McGUIRE  JERRY M. MELILLO  ROBERT MEYER  BERRIEN MOORE III  REAS NADLER  I. COLIN PRENTICE  WALTER SAUF  ANNETTE L. SCHLOSS  STEPHEN SITCH  UWE WITTENBERG  GUDRUN WÜRTH 《Tellus. Series B, Chemical and physical meteorology》1999,51(2):343-366

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