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11.
A very long series of photographic observations of the comet Hale-Bopp has been made during January–April 1997 at the double
astrograph (400/2000) of the Main Astronomical Observatory (Kyiv, Ukraine). Some of the cometary photos were obtained with
two wide-band filter combinations. One of these combinations isolates C2 emission, another — the nearby dust continuum. The images were digitized by means of AMDPH-XY machine and then calibrated
following the standard procedure. After subtraction of the dust continuum the distribution of surface brightness in the C2 emission coma of comet Hale-Bopp was studied. We found an asymmetric brightness distribution both pre- and post-perihelion.
On 21.77 April 1997 a secondary brightness peak is found at the distance of 1.03 × 105 km from the nucleus. It is possible that this peak is related to the extended source of the C2 molecules.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
Pittichovâ J. Sekenina Z. Birkle K. Boehnhardt J. Engels D. Keller P. 《Earth, Moon, and Planets》1997,78(1-3):329-338
The Sekanina-Farrell particle fragmentation model for the striated tails of dust comets is successfully applied to two images
of comet Hale-Bopp to study the motions of 12 striae in a time span of March 12–15, 1997. There is evidence for recurring
outbursts with a periodicity of 11h21m, consistent with results based on analysis of dust jets. The ejecta in all the striae appear to have been released from one
source on the nucleus between the end of January and the second half of February 1997, some 60 to 40 days before perihelion.
The parent particles were subjected to a radiation pressure acceleration of βp ≃ 0.55 and their fragmentation lifetimes in 11 of the 12 striae were practically constant and equal to 13–15 days, when normalized
to 1 AU from the Sun. Brief analysis of Watanabe et al.'s measurements of striae on their images from March 5–9, 1997 shows
even shorter fragmentation lifetimes for the parent particles, mostly about 7–11 days at1 AU.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
Ch. Skokos G. Contopoulos C. Polymilis 《Celestial Mechanics and Dynamical Astronomy》1996,65(3):223-251
We numerically investigate the projections of non periodic orbits in a 4-dimensional (4-D) symplectic map composed of two coupled 2-dimensional (2-D) maps. We describe in detail the structures that are produced in different planes of projection and we find how the morphology of the 4-D orbits is influenced by the features of the 2-D maps as the coupling parameter increases. We give an empirical law that describes this influence. 相似文献
14.
C. Tadhunter K. Wills R. Morganti T. Oosterloo R. Dickson 《Monthly notices of the Royal Astronomical Society》2001,327(1):227-232
We present new spectroscopic observations of the southern radio galaxy . Despite the flat-spectrum character of the radio emission from this source, our optical spectra show no sign of the broad permitted lines and non-stellar continuum characteristic of quasar nuclei and broad-line radio galaxies. However, the high-ionization forbidden lines, including [O iii ] λλ 5007, 4959, are unusually broad for a narrow-line radio galaxy , and are blueshifted by 600 km s−1 relative to the low-ionization lines such as [O ii ] λλ 3726,3729. The [O ii ] lines are also considerably narrower than the [O iii ] lines, and have a redshift consistent with that of the recently detected H i 21-cm absorption-line system. Whereas the kinematics of the [O iii ] emission lines are consistent with outflow in an inner narrow-line region, the properties of the [O ii ] emission lines suggest that they are emitted by a more extended and quiescent gaseous component. We argue that, given the radio properties of the source, our line of sight is likely to be lying close to the direction of bulk outflow of the radio jets. In this case it is probable that the quasar nucleus is entirely obscured at optical wavelengths by the material responsible for the H i absorption-line system. The unusually broad [O iii ] emission lines suggest that the radio source is intrinsically compact. Overall, our data are consistent the idea that is a radio source in an early stage of evolution. 相似文献
15.
16.
L. K. Erastova 《Astrophysics》2004,47(4):547-554
Some features of a sample of galaxies from the Second Byurakan Survey are discussed. Most of them are small galaxies with star formation. It is shown that different types of galaxies are in the Survey, with high, medium, and low levels of excitation and continua ranging from blue to relatively red. Many of the galaxies have absorption lines in their spectra; their continua are formed by stars in later spectral classes. 相似文献
17.
Natural and agricultural wetlands are considered to be the major sources of global atmospheric methane (CH4). A one‐dimensional model was developed to simulate methane emission and used to examine the influence of various physical processes on the rate of methane emission. Three processes involved in the methane emission are implemented in the model: production, reoxidation and transport. Three transport pathways were considered: diffusion across water–air or soil–air interfaces, ebullition and diffusion through plants. These pathways are influenced by soil properties, plant growth, water‐table conditions, temperature and external inputs (e.g. fertilizer). The model was used to examine the seasonal variation of the methane emission at a rice field in Hunan, China, which was observed during a field experiment for consecutive (early and late) rice seasons in 1992. The observed seasonal variations of methane emission, and role of plants in transporting methane to the atmosphere, are captured by the model simulation. Further model applications were conducted to simulate effects of fertilizer and water‐level condition on the methane emission. The results indicate that unfermented organic fertilizer produces a higher methane emission rate than mineral fertilizer. The simulations with treatments of a deep‐water covering and constant moisture reduced the methane emission. The rice field study provides a framework for further development of the model towards simulations based on spatially distributed variables (e.g. water table, soil temperature and vegetation) at a regional scale. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
18.
Dr M. J. Wooller D. L. Swain K. J. Ficken A. D. Q. Agnew F. A. Street-Perrott G. Eglinton 《第四纪科学杂志》2003,18(1):3-15
Woody, subalpine shrubs and grasses currently surround Lake Rutundu, Mount Kenya. Multiple proxies, including carbon isotopes, pollen and grass cuticles, from a 755‐cm‐long core were used to reconstruct the vegetation over the past 38 300 calendar years. Stable carbon‐isotope ratios of total organic carbon and terrestrial biomarkers from the lake sediments imply that the proportion of terrestrial plants using the C4 photosynthetic pathway was greater during the Late Pleistocene than in the Holocene. Pollen data show that grasses were a major constituent of the vegetation throughout the Late Pleistocene and Holocene. The proportion of grass pollen relative to the pollen from other plants was greatest at the last glacial maximum (LGM). Grass cuticles confirm evidence that C4 grass taxa were present at the LGM and that the majority followed the cold‐tolerant NADP‐MEC4 subpathway. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
19.
R. K. Manchanda 《Journal of Astrophysics and Astronomy》2001,22(2-3):145-154
Spectral measurement of Mkn 421 were made in the hard X-ray energy band of 20–200 keV using a high sensitivity, large area
scintillation counter telescope on November 21, 2000 and these coincided with the onset of an active X-ray phase as seen in
the ASM counting rates on board RXTE. The observed spectrum can not be fitted to a single power law similar to the PDS data
of BeppoSAX. The data can be fitted both by a two component power-law function or a combination of an exponential function
with a power law component at the high energies above 80 keV. We identify these components with those arising from the synchrotron
self compton and the high energy power-law tail arising from the upgrading of the thermal photons due to multiple Compton
scattering a la Cyg X-1. A comparison with the earlier data clearly suggests a spectral variability in the hard X-ray spectrum
of the source. We propose a continuously flaring geometry for the source as the underlying mechanism for energy release. 相似文献
20.
Hari Om Vats M. R. Deshpande K. N. Iyer Tetsuro Kondo Takeshi Isobe 《Astrophysics and Space Science》1996,243(1):251-254
This article describes the observations of a type III radio burst observed at 103 MHz simultaneously by the two radio telescopes situated at Rajkot (22.3°N, 70.7°E) and Thaltej (23°N, 72.4°E). This event occurred on September 30, 1993 at about 0430 UT and lasted for only half a minute. The event consisted of several sharp spikes in a group. The rise and fall time of these are comparable, however the peaks of individual spikes varied by a factor of four. The comparison of these observations with the data of solar radio spectrograph HiRAS indicates that this was a metric radio burst giving highest emission at about 103 MHz. 相似文献