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91.
R. K. Das D. P. K. Banerjee N. M. Ashok 《Monthly notices of the Royal Astronomical Society》2009,398(1):375-384
We present near-infrared (1–2.5 μm) spectroscopic and photometric results of Nova V2615 Ophiuchi which was discovered in outburst in 2007 March. Our observations span a period of ∼80 d starting from 2007 March 28 when the nova was at its maximum light. The evolution of the spectra is shown from the initial P Cygni phase to an emission-line phase and finally to a dust formation stage. The characteristics of the JHK spectra are very similar to those observed in a nova outburst occurring on a carbon–oxygen white dwarf. We analyse an observed line at 2.088 μm and suggest that it could be due to Fe ii excited by Lyman α fluorescence. The highlight of the observations is the detection of the first overtone bands of carbon monoxide (CO) in the 2.29–2.40 μm region. The CO bands are modelled to estimate the temperature and mass of the emitting CO gas and also to place limits on the 12 C/13 C ratio. The CO bands are recorded over several epochs, thereby allowing a rare opportunity to study the evolution from a phase of constant strength through a stage when the CO is destroyed fairly rapidly. We compare the observed time-scales involved in the evolution of the CO emission and find a good agreement with model predictions that investigate the chemistry in a nova outflow during the early stages. 相似文献
92.
M. K. Das Pankaj Narang S. Mahajan M. Yuasa 《Journal of Astrophysics and Astronomy》2009,30(3-4):177-185
We have investigated the out of plane equilibrium points of a passive micron size particle and their stability in the field of radiating binary stellar systems Krüger-60, RW-Monocerotis within the framework of photo-gravitational circular restricted three-body problem. We find that the out of plane equilibrium points (L i , i = 6, 7, 8, 9) may exist for range of β 1 (ratio of radiation to gravitational force of the massive component) values for these binary systems in the presence of Poynting-Robertson drag (hereafter PR-drag). In the absence of PR-drag, we find that the motion of a particle near the equilibrium points L 6,7 is stable in both the binary systems for a specific range of β 1 values. The PR-drag is shown to cause instability of the various out of plane equilibrium points in these binary systems. 相似文献
93.
In high-Mg, Al metapelites, monophase sapphirine corona occur around spinel–corundum aggregates in monomineralic cordierite
layers, and bi-phase orthopyroxene–sillimanite aggregates replace locally warped sapphirine in polygonized cordierite aggregates.
P–T phase topologies computed (Perple_X software) using compositions of cordierite-rich layers that host the reaction textures
did not match the assemblages for the discontinuous reactions spinel + corundum + cordierite → sapphirine and sapphirine + cordierite → orthopyroxene + sillimanite.
Instead, the reaction assemblages were reproduced using P–T pseudosection analysis for micro-domain reaction volumes estimated from compositions of product phases in the volume proportion
they occur. The results are consistent with known phase relations deduced using Schreinmakers P–T grids. Apparently, the compositions of cordierite-rich layers that hosted the reaction textures were inadequate chemical
proxies for determining P–T–X relations of phase-boundary controlled reactions influenced by compositions of the nearest-neighbor minerals in the proportion
they react (effective composition), and not in the proportion they existed in the layer/bulk rock. In other words, P–T–X phase topologies and reconstructed P–T paths in dry and aluminous rocks may be best understood by thermodynamic modeling of reactions using effective reaction volume
compositions rather than the bulk composition of the rock or the mineralogical layer that host the reaction textures. 相似文献
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97.
X-ray emissions from Young Stellar Objects (YSO) are detected by many X-ray missions that are providing important information about their properties. However, their emission processes are not fully understood. In this research note, we propose a model for the generation of emissions from a YSO on the basis of a simple interaction between the YSO and its surrounding circumstellar accretion disc containing neutral gas and charged dust. It is assumed that the YSO has a weak dipole type magnetic field and its field lines are threaded into the circumstellar disc. Considering the motion of ions and charged dust particles in the presence of neutral gas, we show that the sheared dust-neutral gas velocities can lead to a current along the direction of ambient magnetic field. Magnitude of this current can become large and is capable of generating an electric field along the magnetic field lines. It is shown how the particles can gain energy up to MeV range and above, which can produce high-energy radiations from the YSO. 相似文献
98.
In this work, we consider the formation of electrostatic, dust-acoustic solitary structure in a unmagnetized plasma with Lorentzian electrons (kappa-distributed) and more than one species of thermal ions (Maxwellian). The work is inspired by results of different space-based observations of electrostatic solitary waves (ESW) in the near-earth and magnetospheric plasmas and recent experimental realization of existence of superthermal electron component in various space plasmas. We have, in this work, shown that existence of compressive potential structure is possible only with more than one species of thermal ions. Besides, formation of compressive double layers is also possible which depends on the amount of deviation of the electron thermal velocities from a Maxwellian distribution. We show that both dust-temperature and super-thermal electrons lead to a decrease in the soliton amplitude. 相似文献
99.
Santabrata Das Sandip K. Chakrabarti 《Monthly notices of the Royal Astronomical Society》2008,389(1):371-378
We study the dynamical structure of a cooling dominated rotating accretion flow around a spinning black hole. We show that non-linear phenomena such as shock waves can be studied in terms of only three flow parameters, namely the specific energy , the specific angular momentum (λ) and the accretion rate of the flow. We present all possible accretion solutions. We find that a significant region of the parameter space in the plane allows global accretion shock solutions. The effective area of the parameter space for which the Rankine–Hugoniot shocks are possible is maximum when the flow is dissipation-free. It decreases with the increase of cooling effects and finally disappears when the cooling is high enough. We show that shock forms further away when the black hole is rotating compared to the solution around a Schwarzschild black hole with identical flow parameters at a large distance. However, in a normalized sense, the flow parameters for which the shocks form around the rotating black holes are produced shocks closer to the black hole. The location of the shock is also dictated by the cooling efficiency in that higher the accretion rate , the closer is the shock location. We believe that some of the high-frequency quasi-periodic oscillations may be due to the flows with higher accretion rate around the rotating black holes. 相似文献
100.
Behera Rashmisikha Kar Abhipsa Das Manas Ranjan Panda Prachi Prava 《Natural Hazards》2019,96(2):731-751
Natural Hazards - The 485-km-long coastline of Odisha, a state in the northeastern part of the Indian peninsula, is potentially vulnerable to several disaster events that take place frequently. In... 相似文献