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81.
bdAbstract The open cluster NGC 2818 containing a planetary nebula has been observed inVRI bands using the CCD system at prime focus of the 2.3-metre Vainu Bappu Telescope. The study extending to starsV ∼ 21 magnitude establishes the distance modulus as(m-M) 0 = 12.9 ±0.1 for the cluster. Based on the fitting of theoretical isochrones computed for solar metallicity, an age of 5(±1) × 108 years has been assigned to the cluster. Association of the planetary nebula with the cluster indicates that the progenitor mass of the planetary nebula on the main sequence is ≥2.5M Based on observations obtained with the Vainu Bappu Telescope.  相似文献   
82.
A new procedure to separate the instrumental and atmospheric components of stray light is presented. It is based on the dependence of the aureole's atmospheric component on the air mass and is applied to measurements taken with the Vacuum Newton Telescope (VNT) at the Observatorio del Teide (Tenerife). The resulting instrumental part is independent of the air mass.The variation of both components with wavelength is also studied. The instrumental component shows no dependence on wavelength, in contrast to the atmospheric one which is greater in the blue than in the red.It is concluded that observations with air masses larger than two will probably be strongly affected by stray light.  相似文献   
83.
84.
Photopolarimetric observations of comet Austin with the IAU/IHW filter system were obtained on the 2.34 m Vainu Bappu Telescope (VBT) of the Indian Institute of Astrophysics, at Kavalur, India, during pre-perihelion phase on February 20,1990 and on the 1.2 m telescope of the Physical Research Laboratory at Gurusikhar, Mount Abu during postperihelion phase on May 2 and 4, 1990. The comet appeared bluer than a solar analog during post-perihelion phase on May 2 and 4. The percent polarization shows a sharp increase towards the red on May 2 and 4. The dominant sizes of the dust particles appear to lie in a narrow range of 0.1 to 0.5 Μm. Regarding the molecular band emission, CN and C2 bands are quite strong; C3 emission was also found to be strong though the observations on May 2 and 4 show significant variation as compared to C2 emission. Molecular band polarization for CN, C3, C2 and H2 O+ have been calculated. It has been found that emission polarization in CN, C2 and C3 is between 1–7% (phase angle between 107.4–109 degrees). For CN and C2 the polarization values are close to the theoretically predicted values, but for C3 the polarization value falls much below the theoretically predicted value. A similar result was found for comet Halley.  相似文献   
85.
Two spectrophotometric scans of comet Levy (1990c) have been analysed to estimate Haser model column densities and production rates of CN andC 2 molecules.  相似文献   
86.
87.
An updated Lagrangian finite-element formulation has been developed for time-dependent problems of soil consolidation involving finite deformations. Large plastic strains as well as rotations occur in such problems and nominal stress measures are introduced in the formulation to redefine stresses. This leads to corrective terms for equilibrium and yield violations in addition to geometric stiffening terms in the governing integral equations. The soil is considered to be either a linear elastic or an elastoplastic, critical-state material. Some simple numerical examples are studied to validate the formulation, followed by a detailed analysis of the problem of penetration of a pile into soil. The results of this problem are viewed with emphasis on the physical interpretation and practical significance.  相似文献   
88.
89.
SHRIMP dating of xenotime overgrowths on detrital zircon grains can constrain maximum durations since diagenesis and therefore provide minimum dates of sediment deposition. Thus, xenotime dating has significant economic application to Precambrian sediment-hosted ore deposits, such as Witwatersrand Au–U, for which there are no precise depositional ages. The growth history of xenotime in the Witwatersrand Supergroup is texturally complex, with several phases evident. The oldest authigenic xenotime 207Pb/206Pb age obtained in sandstone underlying the Vaal Reef is 2764 ± 5 Myr (1 σ), and most likely represents a mixture of diagenetic and hydrothermal growth. Nevertheless, this represents the oldest authigenic mineral age yet recorded in the sequence and provides a minimum age of deposition. Other xenotime data record a spread of ages that correspond to numerous post-diagenetic thermotectonic events (including a Ventersdorp event at ≈ 2720 Ma) up to the ≈2020 Ma Vredefort event.  相似文献   
90.
We report intermediate resolution H spectroscopy of the black hole candidate Nova Muscae 1991 during quiescence. We classify the companion star as a K3-K4V which contributes 85±6 percent to the total flux from the binary. The photospheric absorption lines are broadened by 106±13 kms−1 with respect to template field stars, leading to a system mass ratio of q =M1/M2 = 7.8−2.0+3.4. Doppler imaging of the H line shows strong emission coming from the secondary star (EW=3.1±0.6Å) which we associate with chromospheric activity. However, the hot-spot is not detected and this may indicate a lower mass transfer rate than in other X-ray transients of comparable orbital periods. The surface brightness distribution of the accretion disk in H follows a relation I∝R−1.1, less steep than typically observed in cataclysmic variables. Updated system parameters are also presented.  相似文献   
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