CCD photometry inVRI bands of the galactic cluster NGC 2818     

R. Surendiranath  N. Kameswara Rao  Ram Sagar  J. S. Nathan  K. K. Ghosh 《Journal of Astrophysics and Astronomy》1990,11(2):151-166

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   

Prediction of Stellar Atmospheric Parameters using Instance-Based Machine Learning and Genetic Algorithms   总被引：1，自引：0，他引：1  

J. Federico Ramírez  Olac Fuentes  Ravi K. Gulati 《Experimental Astronomy》2001,12(3):163-178

In this article we present a method for the automated prediction of stellar atmospheric parameters from spectral indices. This method uses a genetic algorithm (GA) for the selection of relevant spectral indices and prototypical stars and predicts their properties, using the k-nearest neighbors method (KNN). We have applied the method to predict the effective temperature, surface gravity, metallicity, luminosity class and spectral class of stars from spectral indices. Our experimental results show that the feature selection performed by the genetic algorithm reduces the running time of KNN up to 92%, and the predictive accuracy error up to 35%. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

On the highly reddened members in six young galactic star clusters – a multiwavelength study     

Brijesh Kumar  Ram Sagar  B. B. Sanwal  M. S. Bessell 《Monthly notices of the Royal Astronomical Society》2004,353(3):991-1014

  相似文献   

UBV RI CCD photometric study of the open clusters Basel 4 and NGC 7067     

R. K. S. Yadav  Ram Sagar 《Monthly notices of the Royal Astronomical Society》2004,349(4):1481-1492

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Geo-effectiveness of solar wind extremes     

Hari Om Vats 《Journal of Astrophysics and Astronomy》2006,27(2-3):227-235

Examples of extreme events of solar wind and their effect on geomagnetic conditions are discussed here. It is found that there are two regimes of high speed solar wind streams with a threshold of ∼ 850 km s^-1. Geomagnetic activity enhancement rate (GAER) is defined as an average increase in Ap value per unit average increase in the peak solar wind velocity (Vp) during the stream. GAER was found to be different in the two regimes of high speed streams with +ve and-ve IMF. GAER is 0.73 and 0.53 for solar wind streams with +ve and -ve IMF respectively for the extremely high speed streams (< 850 km s^-1). This indicates that streams above the threshold speed with +ve IMF are 1.4 times more effective in enhancing geomagnetic activity than those with -ve IMF. However, the high speed streams below the threshold with -ve IMF are 1.1 times more effective in enhancing geomagnetic activity than those with +ve IMF. The violent solar activity period (October–November 2003) of cycle 23 presents a very special case during which many severe and strong effects were seen in the environment of the Earth and other planets; however, the z-component of IMF (Bz) is mostly positive during this period. The most severe geomagnetic storm of this cycle occurred when Bz was positive.  相似文献   

Solar radio burst (type III)     

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   

Axially-symmetric quasi-neutral charged dust distributions in general relativity     

Ram  Shri 《Astrophysics and Space Science》1985,114(2):329-333

A solution of Einstein-Maxwell equations representing a distribution of equal and opposite charges moving in circles in opposite directions around thez-axis is obtained. In a particular case the solution reduces to the special case of Levi-Civita metric for a line-mass placed along thez-axis. The asymptotic behaviour of the solution is also discussed.  相似文献   

Strain localization in sandstone during embryonic stages of shear-zone evolution     

Yoram Katz  Ram Weinberger 《地学学报》2005,17(4):311-316

Geometric analysis of nested Riedel structures was used to identify and quantify strain localization processes within faulted Navajo sandstone. The analysis shows systematic deviation from the basic Riedel geometry complying with the Mohr–Coulomb criterion. Using cross-cutting relations amongst deformation bands within the Riedel structures, and comparing the orientations of the deformation bands to theoretical strain calculations, we identify two coupling deformation mechanisms involved in the early stages of shear-zone evolution, namely, granular flow and discrete faulting. Both mechanisms localize during strain accumulation, and the granular flow facilitates considerable change in the initial geometry of the Riedel structures. The analysis demonstrates a systematic sequence, by which new Riedel structures form after a constant amount of shear strain takes place in the sandstone. Analysis further indicates that granular flow is the major deformation mechanism during early stages of shear-zone evolution and discrete faulting is the dominant mechanism during later deformation stages.  相似文献   

Indians in England: why did they emigrate?     

Ram S 《Population geography : a journal of the Association of Population Geographers of India》1987,9(1-2):37-44

The period of highest migration from India to England was 1955-1975. In 1981, the Bradford metropolitan district had about 13,000 Indians. 46% were Punjabis and 43.3% were from Gujarat. Using a 10% sample of Indian households in the Bradford district in 1984 and secondary information, this study examines the impact of the following reasons on decision to migrate: 1) push factors in the area of origin, 2) the 1947 partition of India, 3) strong economic attraction of the destination, and 4) "cultural ethos" and "status competition" among the migrant communities in the areas of emigration. Findings show that 1) Punjab and Gujarat do not have high poverty levels nor very high population densities; 2) the partition of India did not influence migration decisions; 3) the economic well-being of returning migrants and the high conversion rate of English currency did attract migrants to England (39% of surveyed migrants emigrated to England for purely economic reasons); and 4) 60% of the Punjabis and over 50% of the Gujaratis state that local status competition had a significant influence on their decisions to migrate. Thus, the economic attraction of England and the status competition among local families and the community were the dominant factors in migration decision making.  相似文献   

A spatial perspective on the distribution of the Indians in the United Kingdom, 1981     

Ram S 《Population geography : a journal of the Association of Population Geographers of India》1986,8(1-2):17-26

The author analyzes the spatial distribution of Indians living in Great Britain in 1981. The impact of factors such as demand for labor, location of manufacturing industries, and the attraction of urban areas is examined.  相似文献