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R. Vasundhara J. C. Bhattacharyya R. Rajamohan H. S. Mahra 《Earth, Moon, and Planets》1983,29(1):79-82
The results of photometric observations of the occultation of BD-19° 4222 by Uranus on April 26, 1981 from two stations in India conform with the model proposed by Elliotet al. (1981). 相似文献
2.
R. Vasundhara 《Journal of Astrophysics and Astronomy》1989,10(1):85-88
Results of a search for occultations of stars in the SAO catalogue by Saturn’s outer magnetosphere during 1989-1990 are presented.
A total of nine events are predicted to occur during this period. The most favourable event will be the occultation of 28
Sgr (SAO 187255) during July 2–3, 1989. Occultations of SAO 187036, SAO 188348 and SAO 188120 occur near opposition and therefore
can be observed over a wide longitude range 相似文献
3.
R. Vasundhara 《Icarus》2009,204(1):194-208
The pre-Deep Impact images of Comet Tempel-1 obtained at the Indian Astronomical Observatory are used to investigate the morphology of the dust coma of the comet. We show that the trajectory of a cometary grain under the influence of solar radiation pressure is a reliable diagnostic to estimate its initial velocity. Four main active regions at mean latitudes +45° ± 5°(D), 0° ± 5° (E),−30° ± 5°(A) and−60° ± 5°(F) are found to explain the morphology of the dust coma in the ground-based and published images obtained by the High Resolution Instrument(HRI) cameras aboard the Deep Impact flyby spacecraft. From a χ2 fit of the intensity distribution in the observed and the simulated images, we derive the fraction of the productivity of the active vents to the total dust emission of the comet to be 27%. Of this the southern source alone accounts for 19.8%. The grains are found to be ejected with a velocity distribution with an upper limit of 70 ± 7 m s−1. However, the broad region ‘A’ appears to eject slower grains with an upper limit of 24 ± 2.5 m s−1. This source, that is active throughout the cycle is likely to be driven by CO2 sublimation. We compute the dependence of the percentage contribution of the southern source on the heliocentric distance and show that this ratio varies over the apparition and reaches a maximum at around 260 days before perihelion. The published images of the nucleus of Comet Tempel-1 show significant departure from sphericity. Therefore, the torque exerted by the enhanced activity of the southern region may be significant enough to produce changes in the rotational state of the nucleus before each perihelion passage. 相似文献
4.
R. Vasundhara 《Journal of Astrophysics and Astronomy》1988,9(1):63-65
Results of a search for occultations of stars in the SAO catalogue by Saturn’s outer magnetosphere during 1988 are presented. 相似文献
5.
Fabrication of an optical dual-beam spectropolarimeter as an add-on facility to an existing astronomical spectrograph at the Vainu Bappu Telescope is described. The polarimetric optics consists of a superachromatic Pancharatnam design half-wave plate and a modified Glan-Taylor polarizing beam splitter. Instrumental response, calibration and characterization of the system are presented. Performance of the spectropolarimeter has been assessed based on the results of observations of polarized and unpolarized standard stars. The attainable accuracy of the instrument is found to be dependent on the S/N of the data. The present data set yields an accuracy of ±0.5% at 4000 Å and ±0.3% at 7500 Å, at a spectral resolution of 7.2 Å. Analysis of spectropolarimetric data is systematically covered for removal of instrumental errors. The spectropolarimetric reduction software (SPRS), extremely versatile, user friendly and compatible with the IRAF image processing package, was developed for reducing spectropolarimetric data. The empirical relation by Serkowski (IAU Symposium 52, Interstellar Dust and Related Topics, J. M. Greenberg and H. C. van de Hulst (eds.), Dordrecht, Reidel, 1975, p. 145) for wavelength dependence of polarization due to interstellar medium has been fitted to the data for the star HD 43384 (9 Gem). Our result shows a polarization larger by 0.49% from Hsu and Berger (ApJ 262, 1982, 732). We attribute this difference to the long term variation in P for this star. 相似文献
6.
R. Vasundhara 《Journal of Astrophysics and Astronomy》1991,12(1):69-87
Results of the observations of mutual eclipses of Galilean satellites observed from the Vainu Bappu Observatory during 1985
are presented. Theoretical models assuming a uniform disc, Lambert’s law and Lommel-Seeliger’s law describing the scattering
characteristics of the surface of the eclipsed satellite were used to fit the observations. Light curves of the 1E2 event
on 1985 September 24 and the 3E1 event on 1985 October 24 observed from VBO and published light curves of the 1E2 event on
1985 September 14, the 3E1 event on 1985 September 26 and the 2E1 event on 1985 October 28 (Arlotet al 1989) were fitted with theoretical light curves using Marquardt’s algorithm. The best fitting was obtained using Lommel-Seeliger’s
law to describe the scattering over the surface of Io and Europa. During the fitting, a parameterδxshift which shifts the theoretical light curve along the direction of relative motion of the eclipsed satellite with respect
to the shadow centre, on the sky plane (as seen from the Sun) was determined along with the impact parameter. In absence of
other sources like prominent surface features or non perfect sky conditions which could lead to asymmetric light curves,δxshift would be a measure of the phase correction (Aksnes, Franklin & Magnusson 1986) with an accuracy as that of the midtime.
Heliocentric Δα cos (δ) and gDδ at mid times derived from fitted impact parameters are reported 相似文献
7.
R. Vasundhara 《Planetary and Space Science》2008,56(14):1791-1796
Salient features of the analysis of the mutual event light curves of planetary satellites are presented. The need to carefully evaluate the flux contribution of the occulting/eclipsing satellite to the total flux is illustrated. Albedo variations on the satellites will produce signatures on the mutual event light curves. The partial events of the upcoming mutual event series of the uranian satellites can be modeled taking into account the albedo variations inferred from the maps of the southern regions imaged by Voyager 2 when only these regions are occulted/eclipsed. This will enable a robust determination of the astrometric parameters. The shape and asymmetry of the mutual event light curves along with the rotational light curves of the satellites obtained simultaneously during the planet's equinox crossing period can be utilized to obtain a coarse albedo map of the northern hemisphere of the satellites. These studies will also help in investigating possible changes in the known southern regions since the 1986 encounter of Voyager 2. 相似文献
8.
Vasundhara R. Chakraborty Pavan Hänel Andreas Heiser Erwin 《Earth, Moon, and Planets》1997,78(1-3):321-328
Persistent jet and shell structures from comet Hale-Bopp showing gradual changes in the shapes and orientations with aspect
angle and solar illumination geometry indicate long lived active sources. A model to simulate the dust features has been applied
to the series of observations from September 1996 to May 1997. Most of the structures can be explained as arising due to ejections
from persistent active regions at comet-o-centric latitudes near +65°, +55°, −5° to −15°, −35° and −65°. The best fitting
pole positions vary between 255° ±10° and 275° ± 10° in right ascension and −45° ± 10° to −75° ± 10° in declination. Lower
limits on the dust and gas production rates at various epochs are presented.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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