Near infrared photometry of some RS CVn systems and candidates     

R. P. Verma  S. K. Ghosh  K. V. K. Iyengar  T. N. Rengarajan  S. N. Tandon  R. R. Daniel  N. B. Sanwal 《Astrophysics and Space Science》1983,97(1):161-169

Infrared observations in the J, H, and K bands were made on eleven RS CVn systems. Infrared (IR) excess 0.3 mag in the J, H, and K bands was observed from the three systems UX Ari, HR 1099 and CrB. Similar observations were also made on the RS CVn candidates HD 26354, 39937, 42449, 51268, and 86005.The IR excess in the RS CVn systems for which near infrared photometric data are available is found to be correlated with the maximum of optical wave amplitude of these systems.The observed excess cannot be explained on the basis of a single process such as: (i) emission from cool spots on the photosphere; (ii) free-free emission from an optically thin circumstellar plasma; or (iii) dust grain emission from circumstellar material.On leave from TIFR, Bombay, India.  相似文献   

Stalagmite growth perturbations from the Kumaun Himalaya as potential earthquake recorders     

C. P. Rajendran  Jaishri Sanwal  Kristin D. Morell  Mike Sandiford  B. S. Kotlia  John Hellstrom  Kusala Rajendran 《Journal of Seismology》2016,20(2):579-594

The central part of the Himalaya (Kumaun and Garhwal Provinces of India) is noted for its prolonged seismic quiescence, and therefore, developing a longer-term time series of past earthquakes to understand their recurrence pattern in this segment assumes importance. In addition to direct observations of offsets in stratigraphic exposures or other proxies like paleoliquefaction, deformation preserved within stalagmites (speleothems) in karst system can be analyzed to obtain continuous millennial scale time series of earthquakes. The Central Indian Himalaya hosts natural caves between major active thrusts forming potential storehouses for paleoseismological records. Here, we present results from the limestone caves in the Kumaun Himalaya and discuss the implications of growth perturbations identified in the stalagmites as possible earthquake recorders. This article focuses on three stalagmites from the Dharamjali Cave located in the eastern Kumaun Himalaya, although two other caves, one of them located in the foothills, were also examined for their suitability. The growth anomalies in stalagmites include abrupt tilting or rotation of growth axes, growth termination, and breakage followed by regrowth. The U-Th age data from three specimens allow us to constrain the intervals of growth anomalies, and these were dated at 4273?±?410 years BP (2673–1853 BC), 2782?±?79 years BP (851–693 BC), 2498?±?117 years BP (605–371 BC), 1503?±?245 years BP (262–752 AD), 1346?±?101 years BP (563–765 AD), and 687?±?147 years BP (1176–1470 AD). The dates may correspond to the timings of major/great earthquakes in the region and the youngest event (1176–1470 AD) shows chronological correspondence with either one of the great medieval earthquakes (1050–1250 and 1259–1433 AD) evident from trench excavations across the Himalayan Frontal Thrust.  相似文献   

Serpentinization and the inorganic synthesis of H₂ in planetary surfaces     

Christopher Oze  Mukul Sharma 《Icarus》2007,186(2):557-561

The near-surface inorganic synthesis of molecular hydrogen (H₂) is a fundamental process relevant to the origins and to the sustenance of early life on Earth and potentially other planets. Hydrogen production through the decomposition of water is thought to be a principal reaction that occurs during hydrothermal alteration of olivine, an iron-magnesium silicate abundant near planetary surfaces. We demonstrate that copious amounts of H₂ are produced only when the olivine undergoing alteration (serpentinization) contains 1 to 50 mol% iron over a variety of planetary surface P-T conditions. This suggests that extrasolar Earth-like planets that are hosted by a star with iron contents up to two times the solar value could support life provided they are hydrothermally active and fall within the habitable zone around the star.  相似文献   

Erratum to: Enhancing Hydrologic Modelling in the Coupled Weather Research and Forecasting–Urban Modelling System     

Jiachuan Yang  Zhi-Hua Wang  Fei Chen  Shiguang Miao  Mukul Tewari  James A. Voogt  Soe Myint 《Boundary-Layer Meteorology》2015,155(2):369-369

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The effect of groundwater interaction in North American regional climate simulations with WRF/Noah-MP     

Michael Barlage  Mukul Tewari  Fei Chen  Gonzalo Miguez-Macho  Zong-Liang Yang  Guo-Yue Niu 《Climatic change》2015,129(3-4):485-498

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On heating and cooling in some active region loops     

Udit Narain  Mukul Kumar 《Solar physics》1985,99(1-2):111-118

It is shown that the neglect of radiative losses by Antiochos and Sturrock (1976) in investigating conduction cooling is not justified. It is further shown that the anomalous current dissipation leads to substantial amount of heating contrary to remarks made by Ionson (1982).  相似文献   

Coronal transients in radio and X-rays     

Mukul R. Kundu 《Astrophysics and Space Science》1996,243(1):15-22

We present a summary of several studies of transient coronal phenomena based upon high spatial resolution radio imaging data along with Yohkoh SXT and HXT observations. In addition to normal flares the studies also involve such exotic events as active region transient brightenings (ARTB) and coronal jets and bright points. We provide evidence of nonthermal processes in flaring X-ray bright points from spatially resolved meter-wave data, existence and propagation of type II burst emitting electrons in coronal jets, radio signatures of ARTB's, and beaming of electrons producing microwave and hard X-rays. The implications of these observations are discussed.  相似文献   

Spatial Distribution and Temporal Evolution of Coronal Bright Points     

Zhang  Jie  Kundu  Mukul R.  White  Stephen M. 《Solar physics》2001,198(2):347-365

Solar Physics - We present a statistical study of the spatial distribution and temporal evolution of coronal bright points (BPs) by analyzing a continuous set of observations of a quiet-Sun region...  相似文献   

Search for the proverbial mantle osmium sources to the oceans: Hydrothermal alteration of mid-ocean ridge basalt     

Mukul Sharma  Erin J. Rosenberg  David A. Butterfield 《Geochimica et cosmochimica acta》2007,71(19):4655-4667

We present Os and Sr isotopes and Mg, Os, and Sr concentrations for ridge-crest high-temperature and diffuse hydrothermal fluids, plume fluids and ridge-flank warm spring fluids from the Juan de Fuca Ridge. The data are used to evaluate the extent to which (1) the high- and low-temperature hydrothermal alteration of mid-ocean ridge basalts (MORBs) provides Os to the deep oceans, and (2) hydrothermal contributions of non-radiogenic Os and Sr to the oceans are coupled. The Os and Sr isotopic ratios of the high-temperature fluids (265-353 °C) are dominated by basalts (¹⁸⁷Os/¹⁸⁸Os = 0.2; ⁸⁷Sr/⁸⁶Sr = 0.704) but the concentrations of these elements are buffered approximately at their seawater values. The ¹⁸⁷Os/¹⁸⁸Os of the hydrothermal plume fluids collected ∼1 m above the orifice of Hulk vent is close to the seawater value (=1.05). The low-temperature diffuse fluids (10-40 °C) associated with ridge-crest high-temperature hydrothermal systems on average have [Os] = 31 fmol kg⁻¹, ¹⁸⁷Os/¹⁸⁸Os = 0.9 and [Sr] = 86 μmol kg⁻¹, ⁸⁷Sr/⁸⁶Sr = 0.709. They appear to result from mixing of a high-temperature fluid and a seawater component. The ridge-flank warm spring fluids (10-62 °C) on average yield [Os] = 22 fmol kg⁻¹, ¹⁸⁷Os/¹⁸⁸Os = 0.8 and [Sr] = 115 μmol kg⁻¹, ⁸⁷Sr/⁸⁶Sr = 0.708. The data are consistent with isotopic exchange of Os and Sr between basalt and circulating seawater during low-temperature hydrothermal alteration. The average Sr concentration in these fluids appears to be similar to seawater and consistent with previous studies. In comparison, the average Os concentration is less than seawater by more than a factor of two. If these data are representative they indicate that low-temperature alteration of MORB does not provide adequate non-radiogenic Os and that another source of mantle Os to the oceans must be investigated. At present, the magnitude of non-radiogenic Sr contribution via low-temperature seawater alteration is not well constrained. If non-radiogenic Sr to the oceans is predominantly from the alteration of MORB, our data suggest that there must be a different source of non-radiogenic Os and that the Os and Sr isotope systems in the oceans are decoupled.  相似文献   

BV 690, a new bright Type II Cepheid     

N. B. Sanwal  M. B. K. Sarma 《Journal of Astrophysics and Astronomy》1991,12(2):119-131

B andV observations of the suspected variable BV 690 = NSV 04298 are reported. The star shows light variations with a period of l^d.2400 and with amplitudes of 0^m.27, 0^m.36 and 0^m.11 inV, B, andB-V respectively. The light curves show steeper rise than decline, and there is evidence for the presence of a bump in the descending branch around the phase of 0.35. From considerations of the period, spectral type, presence of the bump and high tangential velocity we conclude that BV 690 belongs to the BL Herculis class of Typen Cepheids  相似文献