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Polarization Measurements of Post-Asymptotic Giant Branch Candidates and Related Stars
Parthasarathy, M.; Jain, S. K.; Sarkar, G.
We have obtained UBVRI polarization measurements of 26 post-asymptotic giant branch (post-AGB) candidates and related stars. The extremely metal-poor post-AGB star HR 4049 has been observed several times. In most cases we find the objects to be intrinsically polarized. The polarization measurements presented in this paper indicate asymmetric circu…
Fractal-Based Fuzzy Technique For Detection Of Active Regions From Solar Images
Revathy, K.; Lekshmi, S.; Nayar, S. R. Prabhakaran
Fractal concepts are used to describe the irregular structures and regions of interest of solar images. The most common and easiest way to extract regions of interest from an image is through segmentation. Segmentation techniques vary from conventional edge-detection mechanism to fuzzy c-means clustering. In this study, the pixelwise local fractal…
Properties of solar wind turbulence near the Sun as deduced from coronal radio sounding experiments
Plettemeier, D.; Bird, M. K.; Efimov, A. I. +2 more
The characteristics of plasma turbulence in the inner solar wind, as deduced from radio frequency fluctuation measurements recorded during solar conjunction, are reviewed. Special emphasis is placed on results from the radio occultation experiments performed with the Galileo and Ulysses spacecraft in the interval 1991-2000. Estimates of the power …
On the Ga II and Ga III Resonance Lines and the Implication for Chemical Stratification in HgMn Stars
Nielsen, K. E.; Leckrone, D. S.; Wahlgren, G. M. +2 more
The gallium abundance in HgMn stars has been reported to be different for analyses conducted from spectral lines in the optical versus those from the ultraviolet. We pursue this ultraviolet-optical discrepancy from a line-blending perspective by investigating the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) spectrum of …
Metastable hydrogen absorption in ejecta close to η Carinae
Gull, T. R.; Johansson, S.; Hartman, H. +1 more
Spectroscopy with the high spatial resolution of the Hubble Space Telescope (HST) reveals narrow absorption in the hydrogen Balmer lines in spectra of Eta Carinae and the nearby nebular-scattered starlight. While hydrogen Balmer absorption lines are seen in stellar photospheres and winds, we are not aware of such being seen in galactic nebulae. Th…
ISO observations and models of galaxies with hidden broad line regions
Siebenmorgen, R.; Efstathiou, A.
We present ISO mid-infrared spectrophotometry and far-infrared photometry of galaxies with Hidden Broad Line Regions (HBLR). We also present radiative transfer models of their spectral energy distributions which enable us to separate the contributions from the dusty disc of the AGN and the dusty starbursts. We find that the combination of tapered …
Structure of visible and dark matter components in spiral galaxies at redshifts z = 0.5{-0.9}
Tamm, A.; Tenjes, P.
We have constructed self-consistent light and mass distribution models for four disk galaxies at redshifts z=0.48, 0.58, 0.81 and 0.88, using the HST archive WFPC2 observations (HDF-S, MDS, Groth Strip survey) and rotation curves measured by Vogt et al. ([CITE]) and Rigopoulou et al. ([CITE]). The models consist of three components: a bulge, a dis…
Search for the elusive optical counterpart of PSR J0537-6910 with the HST Advanced Camera for Surveys
Pulone, L.; Mignani, R. P.; Iannicola, G. +3 more
We present the results of deep, high-resolution, multi-band optical observations of the field of the young (∼ 5000 yr) 16 ms X-ray pulsar PSR J0537-6910 performed with the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope (HST). Although a few new potential counterparts have been detected within or close to the revised Chandra X-…
Variability in Saturn's bow shock and magnetopause from Pioneer and Voyager: Probabilistic predictions and initial observations by Cassini
Russell, C. T.; Dougherty, M. K.; Neubauer, F. M. +2 more
Probability distributions for the location of the Saturnian bow shock and magnetopause have been derived by extrapolating observations of dynamic solar wind pressures to the position of Saturn's orbit. These observations are those made by the Pioneer 11, Voyager 1 and 2 spacecraft near Saturn's orbit and by the Ulysses spacecraft near its aphelion…
Hubble Space Telescope imaging polarimetry of Mars during the 2003 opposition
Kreslavsky, M.; Shkuratov, Yu.; Kaydash, V. +6 more
We report results of polarimetric imaging observations of Mars with the Hubble Space Telescope during the 2003 opposition. Through careful calibration, the observations with the ACS camera allow measurements of the polarization degree with an absolute accuracy better than 0.5% and detection of features with polarization degree contrast as small as…