A rapidly evolving active region NOAA 8032 observed on April 15th, 1997     

Shibu K. Mathew  Ashok Ambastha 《Journal of Astrophysics and Astronomy》2000,21(3-4):233-236

The active region NOAA 8032 of April 15, 1997 was observed to evolve rapidly. The GOES X-ray data showed a number of sub-flares and two C-class flares during the 8–9 hours of its evolution. The magnetic evolution of this region is studied to ascertain its role in flare production. Large changes were observed in magnetic field configuration due to the emergence of new magnetic flux regions (EFR). Most of the new emergence occured very close to the existing magnetic regions, which resulted in strong magnetic field gradients in this region. EFR driven reconnection of the field lines and subsequent flux cancellation might be the reason for the continuous occurrence of sub-flares and other related activities.  相似文献   

Effects of rotation on the colours and line indices of stars 5. The ZRMS and the ZRZAMS     

Annamma Mathew  R. Rajamohan 《Journal of Astrophysics and Astronomy》1992,13(1):61-107

The observeduvby and H_α indices of member stars of the Hyades and Praesepe clusters have been analysed in detail for rotation effects. The Alpha Persei, Pleiades and the Centaurus subgroup of the Scorpio—Centaurus association have been reanalysed using the observed indices instead of the extinction-corrected indices used earlier. The observed rotation effects from the analysis of these cluster data are found to be in excellent agreement with the theoretical predictions of Collins & Sonneborn (1977). We have also analysed the α,c and (u − b) values of the member stars of NGC 1976, 2264, 2287, 2422, 4755,1C 2391, IC 2602 and IC 4665 for rotation effects. The results are found to be consistent with the theoretical predictions. The observed slopes of the rotation effects were used to determine the zero rotation main sequence values of the intermediate band photometric indices for selected clusters. We also corrected the observed indices for each star in each cluster using the theoretical predictions of Collins and Sonneborn and derived the ZRMS values for each cluster. The agreement between the two determinations is found to be good. The various ZRMS curves were utilised to derive the ZRZAMS values. A preliminary calibration of the absolute visual magnitudes as a function of α valid for ZRZAMS has also been derived. The ZRMS values of the intermediate band photometric indices for different clusters and the ZRZAMS values are listed as a function of α. on leave from Assumption College, Changanacherry, Kerala.  相似文献   

Effects of rotation on the colours and line indices of stars 1. The alpha Persei cluster     

R. Rajamohan  Annamma Mathew 《Journal of Astrophysics and Astronomy》1988,9(2):107-116

Analysis of the available observational data for the α-Persei cluster members shows that rotation effects on the intermediate-band indices c₁ and (u-b) are considerable. In c₁, rotation produces a reddening of 0.040 magnitudes per 100 km s^-1 In (u-b) the effect for B stars is found to be 0.06 magnitudes per 100 km s^-1 ofV sin i. The binaries and peculiar stars are found to behave differently in the colour excess (due to rotation) versusV sin i diagrams. These empirical effects can be utilised to recalibrate these colour indices and also to separate members that are either chemically peculiar or in binary systems.  相似文献   

Effects of rotation on the colours and line indices of stars 6. The reality of the blue straggler phenomenon     

Jacqueline D’Souza  Annamma Mathew  R. Rajamohan 《Journal of Astrophysics and Astronomy》1992,13(1):109-128

The effect of rotation on the observed colours of stars has been considered as a possible cause for the blue straggler phenomenon in clusters listed by Mermilliod (1982). It appears that this phenomenon is definitely not real in the case of the late B and early A spectral type blue stragglers that are intrinsic slow rotators. Among clusters containing the early B type blue stragglers it is found that the anomalous position of the stragglers in NGC 6633, NGC 6475 and NGC 2516 cannot be accounted for by rotation effects alone. on leave from Assumption College, Changanacherry, Kerala.  相似文献   

Development of Web Based Road Accident Data Management System in GIS Environment: a Case Study     

Ashish Dhamaniya  Mathew Sonu  M. Krishnanunni  Pynam Praveen  Austin Jaijin 《Journal of the Indian Society of Remote Sensing》2016,44(5):789-796

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A Computationally Efficient,Time-Dependent Model of the Solar Wind for Use as a Surrogate to Three-Dimensional Numerical Magnetohydrodynamic Simulations     

Owens  Mathew  Lang  Matthew  Barnard  Luke  Riley  Pete  Ben-Nun  Michal  Scott  Chris J.  Lockwood  Mike  Reiss  Martin A.  Arge  Charles N.  Gonzi  Siegfried 《Solar physics》2020,295(3):1-15

Solar radiation variability spans a wide range in time, ranging from seconds to decadal and longer. The nearly 40 years of measurements of solar irradiance from space established that the total solar irradiance varies by \(\approx 0.1\%\) in phase with the Sun’s magnetic cycle. Specific intervals of the solar spectrum, e.g., ultraviolet (UV), vary by orders of magnitude more. These variations can affect the Earth’s climate in a complex non-linear way. Specifically, some of the processes of interaction between solar UV radiation and the Earth’s atmosphere involve threshold processes and do not require a detailed reconstruction of the solar spectrum. For this reason a spectral UV index based on the (FUV-MUV) color has been recently introduced. This color is calculated using SORCE SOLSTICE integrated fluxes in the FUV and MUV bands. We present in this work the reconstructions of the solar (FUV-MUV) color and Ca ii K and Mg ii indices, from 1749–2015, using a semi-empirical approach based on the reconstruction of the area coverage of different solar magnetic features, i.e., sunspot, faculae and network. We remark that our results are in noteworthy agreement with latest solar UV proxy reconstructions that exploit more sophisticated techniques requiring historical full-disk observations. This makes us confident that our technique can represent an alternative approach which can complement classical solar reconstruction efforts. Moreover, this technique, based on broad-band observations, can be utilized to estimate the activity on Sun-like stars, that cannot be resolved spatially, hosting extra-solar planetary systems.

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Long-Term Variability of Nutrients and Chlorophyll in the Chesapeake Bay: A Retrospective Analysis, 1985–2008     

M. Bala Krishna Prasad  Mathew R. P. Sapiano  Clarissa R. Anderson  Wen Long  Raghu Murtugudde 《Estuaries and Coasts》2010,33(5):1128-1143

A retrospective analysis of freshwater discharge, riverine dissolved nutrient loads, dissolved nutrients, and chlorophyll in the Chesapeake Bay from 1985 to 2008 is presented. It is evident that each field displays an interannual variability averaged over the Bay. The N and P loads peaked in 1997 and have fluctuated with a decreasing trend since early 2004. Dissolved nutrient concentrations in the Bay appear to be largely controlled by riverine nutrient loads. The temporal variability of chlorophyll is positively correlated with nutrient loads and concentrations. Over the study period, N:P (DIN:DIP) molar ratios were consistently higher than the Redfield ratio (N:P?=?16:1) and strongly correlated with river discharge (R ²?=?0.68, p??16:1), and N is the limiting nutrient in summer and early autumn (N:P?4 from anoxic sediments. Long-term climate indices, such as El Niño Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO), appear to exert only a moderate control over the riverine discharge to the Bay or over the ecosystem response in terms of chlorophyll in the Bay. While not all related mechanisms can be inferred from available data, this analysis should help in determining future data needs for monitoring water quality and human and climate influence on the health of the Bay.  相似文献   

Noble gas components in planetary atmospheres and interiors in relation to solar wind and meteorites     

K. Marti  K. J. Mathew 《Journal of Earth System Science》1998,107(4):425-431

We discuss observed xenon isotopic signatures in solar system reservoirs and possible relationships. The predominant trapped xenon component in ordinary chondrites (OC) is OC-Xe and its isotopic signature differs from Xe in ureilites, in carbonaceous chondrites, in the atmospheres of Earth and Mars, and in the solar wind. Additional minor Xe components were identified in type 3 chondrites and in the metal phase of chondrites. The OC-Xe and ureilite signatures are both consistent with varying mixtures of HL-Xe and slightly mass fractionated solar-type Xe. Xenon in the Martian atmosphere is found to be strongly mass fractionated by 37.7‰ per amu, relative to solar Xe, favoring the heavy isotopes. Xenon in SNC’s from the Martian mantle show admixture of solar-type Xe, which belongs to an elementally strongly fractionated component. The origin of the isotopic signatures of Ne and Xe in the terrestrial atmosphere are discussed in the light of evidence that the Xe isotopic fractionations in the Martian and terrestrial atmospheres are consistent. However, in the terrestrial atmospheric Xe component excesses are observed for¹³²Xe and also for^129,131Xe, relative to fractionated solar Xe. The suggested chemically fractionated fission Xe component (CFF-Xe) seems to closely match the above excesses. We discuss models of origin for planetary volatiles and possible processes driving their evolution to present day compositions.  相似文献   

Solar Photospheric and Chromospheric Observations using a Lithium Niobate Fabry-Perot Etalon     

C. Debi Prasad  Shibu K. Mathew  Arvind Bhatnagar  Ashok Ambastha 《Experimental Astronomy》1998,8(2):125-133

We have made a narrow band tunable filter for solar observations using a Lithium Niobate Fabry-Perot etalon. The 60 mm aperture etalon with a free spectral range of 4.22 Å and finesse of 26 at = 6122 Å has been procured from CSIRO, Australia. The wavelength tuning is achieved by applying high voltage to the etalon substrate at the rate of 0.45 Å per 1000 Volts. The filter is being used for imaging the sun in H line and obtaining Doppler- and Magnetogram in CaI 6122 Å line. In this paper, we present some initial observations carried out with this filter at Udaipur Solar Observatory.  相似文献   

Photogeologic mapping north of Khairwara,Udaipur district,Rajasthan     

Arupkumar Mitra  Supriya Brahma 《Journal of the Indian Society of Remote Sensing》1988,16(2):27-31

Photogeologic mapping of a sample area defined by latitudes 24° O to 6′N and longitudes 73° 30′ to 45′ E from a part of the Aravalli orogen, illustrates the advantages, as well as limitations, of photo-interpretation (PI) in terrains comprsing, highly deformed ancient rock formations. Discrimination between psammitic and pelitic metasediments is easy, using micro-relief and drainage parameters as PI elements; but that between pelites, ultra-basic schists and impure marbles is difficult and less reliable. Trends of foliations, several sets of joints and faults are distinct on the aerial photographs, but complete reconstruction of the superposed fold geometry is not possible. Within the area studied, dominantly pelitic, psammitic and a little clacareous metasediments, intruded by ultra-basics, exhibit a prominent and persistent NNE trend defined by lithologic contacts, bedding and foliations, with steep northwesterly dips. In its central part, bands of psammites within the pelites exhibit a hook shaped fold interference pattern (type 3 of Ramsay, 1967) with the later upright (Fleuty, 1964) fold axial trace trending northwesterly.  相似文献