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Item ULTRAVIOLET STELLAR SPECTRAL CLASSIFICATION USING A MULTILEVEL TREE NEURAL NETWORK(Elsevier Science Ltd, 1995-01-25) Gulati, R.K; Gupta, R; Gothoskar, P; et.alHere we present a pattern classification technique based on an Artificial Neural Network (ANN) in a multi-level tree configuration to classify ultraviolet stellar spectra from the IUE Low-Dispersion Spectra Reference Atlas. Preliminary results of this technique show that 94% of the spectra have been classified correctly with an accuracy of one sub-class. A conventional 9~2 minimization scheme has also been applied to the data to compare the classification obtained from these schemes with that of the IUE catalog classification.Item Star Formation Activity in the Galactic H ii Complex S255-S257(2011-06-09) Ojha, D.K.; Samal, M.R; Pandey, A.K.; et.alWe present results on the star-formation activity of an optically obscured region containing an embedded cluster (S255-IR) and molecular gas between two evolved H ii regions S255 and S257. We have studied the complex using optical, near-infrared (NIR) imaging, optical spectroscopy and radio continnum mapping at 15 GHz, along with Spitzer-IRAC results. It is found that the main exciting sources of the evolved H ii regions S255 and S257 and the compact H ii regions associated with S255-IR are of O9.5 - B3 V nature, consistent with previous observations. Our NIR observations reveal 109 likely young stellar object (YSO) candidates in an area of 40.9 40.9 centered on S255-IR, which include 69 new YSO candidates. To see the global star formation, we constructed the V I=V diagram for 51 optically identified IRAC YSOs in an area of 130 130 centered on S255-IR. We suggest that these YSOs have an approximate age between 0.1 - 4 Myr, indicating a non-coeval star formation. Using spectral energy distribution (SED) models, we constrained physical properties and evolutionary status of 31 and 16 YSO candidates outside and inside the gas ridge, respectively. The models suggest that the sources associated within the gas ridge are of younger population (mean age 1.2 Myr) than the sources outside the gas ridge (mean age 2.5 Myr). The positions of the young sources inside the gas ridge at the interface of the H ii regions S255 and S257, favor a site of induced star formationItem Galaxies(Observatory, 1961-02-10) Naralikar, J.V.Item Stellar and extragalactic radiation at the earth’s surface(IOP Publishing, 2006-03-27) Pecker, J. C.; Narlikar, J. V.Reviving a calculation made by Eddington in the 1920s, and using the most recent and comprehensive databases available on stars and galaxies, including more than 2,500,000 stars and around 20,000 galaxies we have computed their total radiation received at the Earth just outside its atmosphere. This radiation density, if thermalized, would be equivalent to a temperature of 4.212 K. The comparability of this temperature to that of the cosmic microwave background (2.723 K) may either be a pure coincidence or may hold a key to some as yet unknown, aspect of the universe.Item Dynamics of ejection from galaxies and the variable mass hypothesis(World Scientific Publishing Company, 2001-05-29) Narlikar, J. V.; Vishwakarma, R. G.; Banerjee, Shyamal K.Increasing numbers of active galaxies with signi cant alignments of quasars are being observed. It is the purpose of this paper to explore ejection dynamics of these quasars using the variable mass hypothesis (VMH) originally discussed by Narlikar and Das in 1980. According to the VMH quasars are ejected from parent galaxies initially with zero rest mass which grows through a Machian interaction. The intrinsic redshift of the quasar steadily decreases as its mass grows, but always remains in excess of the redshift of the galaxy. The ultimate aim of this hypothesis is to quantitatively relate the observed ordering of redshifts of ejected quasars, with separation from the galaxy, their intrinsic redshifts and the age of the evolutionary stage of the ejecta.Item Case against the big bang(Elsevier Science Publishers, 1999-04-14) Narlikar, J. V.This article takes a critical look at the Hot Big Bang Cosmology (HBBC). It shows that two of its strongest lines of evidence, viz the cosmic microwave background and the abundance of light nuclei are capable of being interpreted differently, and in a physically more realistic way the HBBC is shown to have shifted its ground frequently under observational constraints, changing its parameters like Ω0, Ωb, Ωλ and q0, reinterpreting inflation, bedging options on dark matter, etc. Many of its present deductions are seen to be based on untested physics and unobservable events of the very early Universe, while its beginning in a spacetime singularity indicates its incompleteness as a physical theory. The example of the quasi steady singularity indicates its incompleteness as a physical theory. The example of the quasi-steady state cosmology (QSSC) is given to demonstrate that an alternative cosmology relying more on the ongoing astrophysical properties of the Universe and directly observable events is possible. The case is therefore made that the HBBC does not hold the ‘monopoly’ to be THE model of the Universe.Item How universal is Hubble's law?(Indian Mathematical Society, 1995-05-18) Narlikar, J. V.Item Quasi-steady state cosmology : a note on criticisms by E.L. Wright(Wiley-Blackwell, 1995-08-11) Hoyle, F.; Burbidge, G.; Narlikar, J. V.We answer criticisms made by Wright of the quasi-steady-state cosmology (QSSC). It is shown that none of his criticisms is valid, and the QSSC remains a viable cosmologies theory.Item On the formation of elliptical galaxies(Royal Society, 1966-02-22) Hoyle, F.; Narlikar, J. V.Item Associations between quasi-stellar objects and galaxies(American Astronomical Society, 1990-11-12) Burbidge, G.; Hewitt, A.; Narlikar, J. V.; et al.