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Anantha Chanumolu Sivarani Thirupathi Damien Jones Sunetra Giridhar Deon Grobler Robert Jakobsson 《Experimental Astronomy》2017,43(1):39-58
As a continuation to the published work on model based calibration technique with HESP(Hanle Echelle Spectrograph) as a case study, in this paper we present the performance results of the technique. We also describe how the open parameters were chosen in the model for optimization, the glass data accuracy and handling the discrepancies. It is observed through simulations that the discrepancies in glass data can be identified but not quantifiable. So having an accurate glass data is important which is possible to obtain from the glass manufacturers. The model’s performance in various aspects is presented using the ThAr calibration frames from HESP during its pre-shipment tests. Accuracy of model predictions and its wave length calibration comparison with conventional empirical fitting, the behaviour of open parameters in optimization, model’s ability to track instrumental drifts in the spectrum and the double fibres performance were discussed. It is observed that the optimized model is able to predict to a high accuracy the drifts in the spectrum from environmental fluctuations. It is also observed that the pattern in the spectral drifts across the 2D spectrum which vary from image to image is predictable with the optimized model. We will also discuss the possible science cases where the model can contribute. 相似文献
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T. Sivarani 《Journal of Astrophysics and Astronomy》2013,34(1):5-17
We reviewed the recent progress in the field of stellar/galactic archeology, which is a study of the relics from the early galaxy. The oldest and most pristine objects that can be observed in the galaxy are the low mass metal poor stars of the Milky Way. They were formed during the early phases, when the ISM might have been polluted only by the Pop-III supernovae. With the recent large spectroscopic surveys (e.g. HK survey by Beers and collaborators, the Hamburg-ESO survey by Christlieb and collaborators and Sloan Digital Sky Survey) it has been possible to get clues on the nature of the first stars that has contributed to the heavy elements. Most of these metal-poor low mass stars also retain their signature of the early dynamical evolution of the galaxy, which can be studied through their orbits around the galaxy and spatial distribution. Here, we discuss the connection between the chemical and the kinematical properties of metal-poor stars in order to probe the early galaxy formation. We also discuss about the globular clusters, the satellite galaxies around the Milky Way and its possible contribution to the formation of the galaxy halo. 相似文献
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Smitha Subramanian Annapurni Subramaniam T. Sivarani Luc Simard G. C. Anupama Kim Gillies A. N. Ramaprakash B. Eswar Reddy 《Journal of Astrophysics and Astronomy》2016,37(3):24
The near-infrared instruments in the upcoming Thirty Meter Telescope (TMT) will be assisted by a multi conjugate Adaptive Optics (AO) system. For the efficient operation of the AO system, during observations, a near-infrared guide star catalog which goes as faint as 22 mag in JVega band is essential and such a catalog does not exist. A methodology, based on stellar atmospheric models, to compute the expected near-infrared magnitudes of stellar sources from their optical magnitudes is developed. The method is applied and validated in JHKs bands for a magnitude range of JVega 16–22 mag. The methodology is also applied and validated using the reference catalog of PAN STARRS. We verified that the properties of the final PAN STARRS optical catalog will satisfy the requirements of TMT IRGSC and will be one of the potential sources for the generation of the final catalog. In a broader context, this methodology is applicable for the generation of a guide star catalog for any existing/upcoming near-infrared telescopes. 相似文献
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Himadri Basu Kusum Prakash K. Mahendra Kumar P. V. Thirupathi A. Paul S. A. Pandit A. Chaki 《Journal of the Geological Society of India》2014,84(3):281-291
Uranium mineralization in Madyalabodu area, Cuddapah district, Andhra Pradesh, is spatially related to chloritized and brecciated quartzite of the Gulcheru Formation in the immediate vicinity of E-W to ESE-WNW trending basic dyke. Chloritization transgresses the lithological boundaries. Whole-rock geochemical data indicate enrichment of MgO and Al2O3 coupled with depletion of SiO2, Na2O, K2O, CaO and TiO2 in the chlorite-rich zone. Fe2O3 and FeO do not vary significantly in the altered and the unaltered zones. Electron Probe Microanalysis (EPMA) data reveal that the chlorites in contact with uranium minerals are enriched in MgO and depleted in FeO than in the others. Considering the petrological evidence, geochemical signature and structural constraints, it appears that chlorite acted more as an adsorbent rather than as a reductant in facilitating uranium mineralization. Uraninite crystallized later from the uranium originally adsorbed on chlorites. Chloritization might also have facilitated mineralization through the generation of nascent hydrogen, H2S and lowering pH of uranium-bearing solution. 相似文献
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D. John Devadas N. Subba Rao B. Thirupathi Rao K. V. Srinivasa Rao A. Subrahmanyam 《Environmental Geology》2007,52(7):1331-1342
Systematic hydrogeochemical survey has been carried out for understanding the sources of dissolved ions in the groundwaters
of the area occupied by Sarada river basin, Visakhapatnam district, Andhra Pradesh, India. Khondalites, charnockites and granite
gneisses and calc-granulites of Precambrians and alluvial deposits of Quaternaries underlie the study area. Groundwaters are
both fresh and brackish; the latter waters being a dominant. Most groundwaters are characterized by Na+:HCO3− facies due to chemical weathering of the rocks. Enrichment of Na+, K+, Cl−, SO42−, NO3− and F− in some groundwater samples is caused by seawater intrusion, locally accompanied by ion-exchange, and anthropogenic activities,
resulting in an increase of brackish in the groundwaters. Based on the results of this hydrogeochemical study, suitable management
measures are recommended to solve the water quality problems. 相似文献
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