Photometric and polarimetric studies of three W UMa-type binaries: FZ Ori,V407 Peg and LP UMa     

Vinod Prasad  J. C. Pandey  M. K. Patel  D. C. Srivastava 《Astrophysics and Space Science》2014,353(2):575-594

We present analyses of new optical photometric observations of three W UMa-type contact binaries FZ Ori, V407 Peg and LP UMa. Results from the first polarimetric observations of the FZ Ori and V407 Peg are also presented. The periods of FZ Ori, V407 Peg and LP UMa are derived to be 0.399986, 0.636884 and 0.309898 d, respectively. The O?C analyses indicate that the orbital periods of FZ Ori and LP UMa have increased with the rate of 2.28×10^?8 and 1.25×10^?6 d?yr^?1, respectively and which is explained by transfer of mass between the components. In addition to the secularly increasing rate of orbital period, it was found that the period of FZ Ori has varied in sinusoidal way with oscillation period of ～30.1 yr. The period of oscillations are most likely to be explained by the light-time effect due to the presence of a tertiary companion. Small asymmetries have been seen around the primary and secondary maxima of light curves of all three systems, which is probably due to the presence of cool/hot spots on the components. The light curves of all three systems are analysed by using Wilson-Devinney code (WD) and the fundamental parameters of these systems have been derived. The present analyses show that FZ Ori is a W-subtype, and V407 Peg and LP UMa are A-subtype of the W UMa-type contact binary systems. The polarimetric observations in B, V, R and I bands, yield average values of polarization to be 0.26±0.03, 0.22±0.02, 0.22±0.03 and 0.22±0.05 per cent for FZ Ori and 0.21±0.02, 0.29±0.03, 0.31±0.01 and 0.31±0.04 per cent for V407 Peg, respectively.  相似文献   

A search for the 53-MHz OH line near G48.4−1.4 using the National MST Radar Facility     

Srikumar M. Menon  D. Anish Roshi  T. Rajendra Prasad 《Monthly notices of the Royal Astronomical Society》2005,356(3):958-962

We present the results of a search for the ground-state hyperfine transition of the OH radical near 53 MHz using the National Mesosphere–Stratosphere–Troposphere (MST) Radar Facility at Gadanki, India. The observed position was G48.4−1.4 near the Galactic plane. The OH line is not detected. We place a 3σ upper limit for the line flux density at 39 Jy from our observations. We also did not detect recombination lines (RLs) of carbon, which were within the frequency range of our observations. The 3σ upper limit of 20 Jy obtained for the flux density of carbon RLs, along with observations at 34.5 and 327 MHz, are used to constrain the physical properties of the line-forming region. Our upper limit is consistent with the line emission expected from a partially ionized region with electron temperature, density and path lengths in the range 20–300 K, 0.03–0.3 cm⁻³ and 0.1–170 pc, respectively.  相似文献   

The problem of auroral NO+ concentration and the intensity of 1·27μ bands of O2     

S.S. Prasad  D.R. Furman  A.E.S. Green 《Planetary and Space Science》1975,23(9):1341-1343

The problem of the theoretical computation of the emission intensities and ion composition in a weak aurora which has been preceded by a stronger event is examined. For this purpose a model auroral precipitation consisting of biexponential primaries is considered. The softer of the two components is brighter, and begins to decay after remaining steady for ten to fifteen minutes. The other, harder component starts to build up at that instant. Our results suggest that at least a part of the high $\text{n(}\text{NO}{}^{\mathrm{+}}\text{)}\text{n(}\text{O}{}_2{}^{\mathrm{+}}\text{)}\text{or}\text{I}\text{(1·27 μ)}\text{I}\text{(3914}\text{A}\text{?}\text{)}$ ratios could be attributed to the retention, by the atmosphere, of the memory of previous auroral precipitations. Thus, the serious energy paradox in the context of 1·27 μ intensity need not arise, and, in the context of the large NO⁺ density, it may perhaps be unnecessary to invoke any major conversion of O₂ to NO thus avoiding the associated energy problem.  相似文献   

Observations of soft electron flux during SAR arc event     

J.S. Prasad  J.S. Kim  S. Okano 《Planetary and Space Science》1980,28(4):375-379

Attempts to test the validity of the soft electron flux hypothesis for the excitation of SAR arcs have heretofore met with no apparent success. However, observations of other emissions during the times of some SAR arcs repeatedly favour the presence of the soft electron flux in the topside ionosphere.Although no new cases of coincident measurements of SAR arc intensities and the corresponding soft electron flux values are available, an instance has been analyzed in which an SAR arc was examined shortly after an OGO 6 measurement of the soft electron flux. The SAR arc observations were then interrupted by the weather, but in view of the behaviour of the electron flux during the arc development it is believed that this event lends strong observational support to the hypothesis that soft electrons can be an excitation source for SAR arcs.In the case considered, the precipitation of soft electron flux peaks at about the same location and time of occurrence as the SAR arc. The peak value is found to be 5.2 × 10⁸ cm^?2 sec^?1, which is more than adequate to excite the observed arc.  相似文献   

Exposure and its effects,reciprocity law failure and hypersensitizing     

Shanti Prasad Mamgain 《Journal of the Indian Society of Remote Sensing》1981,9(1):21-28

Exposure and its response to photographic emulsion is discussed. The paper further describes exposure, its contents, intensity and time (i and t), effects of low and high i and t, Reciprocity law Failure (R. L. F.), intermittent exposures, solarisation, Clayden and Herschel effect, and hypersensitizing through neutral density filter and long time development. Through these processes mentioned already, print of low contrast and high definition as compared with the normal print from the same negative has been achieved.  相似文献   

Nonlinear Time Series Analysis of Sunspot Data     

Vinita Suyal  Awadhesh Prasad  Harinder P. Singh 《Solar physics》2009,260(2):441-449

This article deals with the analysis of sunspot number time series using the Hurst exponent. We use the rescaled range (R/S) analysis to estimate the Hurst exponent for 259-year and 11 360-year sunspot data. The results show a varying degree of persistence over shorter and longer time scales corresponding to distinct values of the Hurst exponent. We explain the presence of these multiple Hurst exponents by their resemblance to the deterministic chaotic attractors having multiple centers of rotation.  相似文献   

‘Corrigendum to “Uniform and graded bed-load sediment transport in a degrading channel with non-equilibrium conditions” [International Journal of Sediment Research 35 (2020) 115–124/04-258]’     

Khabat Khosravi  Amir H.N. Chegini  James R. Cooper  Prasad Daggupati  Andrew Binns  Luca Mao 《国际泥沙研究》2021,36(1):163

  相似文献   

Intensity and Magnetic Field Distribution of Sunspots     

Trevor Leonard  Debi Prasad Choudhary 《Solar physics》2008,252(1):33-41

We study the relationship between the brightness (I) and magnetic field (B) distributions of sunspots using 272 samples observed at the San Fernando Observatory and the National Solar Observatory, Kitt Peak, whose characteristics varied widely. We find that the I – B relationship has a quadratic form for the spots with magnetic field less than about 2000 G. The slope of the linear part of the I – B curve varies by about a factor of three for different types of spots. In general the slope increases as the spot approaches disk center. The I – B slope does not have a clear dependency on the spot size but the lower limit appears to increase as a function of the ratio of umbra and penumbra area. The I – B slope changes as a function of age of the sunspots. We discuss various sunspot models using these results.  相似文献   

Damping of slow magnetoacoustic waves in an inhomogeneous coronal plasma     

Nagendra Kumar  Pradeep Kumar  Shiv Singh  Anil Kumar 《Journal of Astrophysics and Astronomy》2008,29(1-2):243-248

We study the propagation and dissipation of slow magnetoacoustic waves in an inhomogeneous viscous coronal loop plasma permeated by uniform magnetic field. Only viscosity and thermal conductivity are taken into account as dissipative processes in the coronal loop. The damping length of slow-mode waves exhibit varying behaviour depending upon the physical parameters of the loop in an active region AR8270 observed by TRACE. The wave energy flux associated with slow magnetoacoustic waves turns out to be of the order of 10⁶ erg cm^?2 s^?1 which is high enough to replace the energy lost through optically thin coronal emission and the thermal conduction below to the transition region. It is also found that only those slow-mode waves which have periods more than 240s provide the required heating rate to balance the energy losses in the solar corona. Our calculated wave periods for slow-mode waves nearly match with the oscillation periods of loop observed by TRACE.  相似文献   

Seismic loss estimation tool as rapid survey for prioritizing buildings for disaster preparedness: case study to hospital buildings     

Nanda  Radhikesh Prasad  Paul  Nilendu Krishna  Chanu  Ningthoujam Monika 《Natural Hazards》2019,95(3):769-781

Natural Hazards - Hospital buildings must be fully operational after the earthquake to protect the lives of patients as well as to provide emergency care and medical treatment to the victims....  相似文献