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31.
Spiral galaxies show axial symmetry and an intrinsic 2D-chirality. Environmental effects can influence the chirality of originally
isolated stellar systems and a progressive loss of chirality can be recognized in the Hubble sequence. We point out a preferential
modality for genetic galaxies as in microscopic systems like aminoacids, sugars or neutrinos. This feature could be the remnant
of a primordial symmetry breaking characterizing systems at all scales. 相似文献
32.
This study uses the adding-doubling radiative transfer method in which we take into account the curvature effect of the planetary atmosphere in order to test the sensitivity of the jovian Ly-α emission line in relation to H column density, eddy diffusion coefficient, frequency redistribution function for photon scattering, temperature vertical profile, and an added hot atomic H layer on the top of the atmosphere. We also focus here on developing new diagnostic tools that will help us to obtain more confidently the underlying thermospheric structure of Jupiter. First, using the brightness distribution for specific wavelength bands as proposed by Ben Jaffel et al. [Ben Jaffel, L., Magnan, C., Vidal-Madjar, A., 1988. Astron. Astrophys. 204, 319-326], we show that the spatial thickness of the atomic H layer above the homopause level can be measured directly as the separation between the vertical positions of respectively the line core and line wing optical limbs. This thickness also constrains the [H] column and the value KH of the eddy diffusion coefficient at the homopause level at the disc location under consideration. We also propose to refine the value of KH and [H], respectively, at a specific planetary latitude, using the Q ratio of the limb peak brightness to the intensity from other regions over the planetary disc. Finally, the relationship between the disc brightness distribution from specific wavelength bands of the emission line and the temperature gradient in the thermosphere is demonstrated, thus providing an accurate tool to access this key information from high resolution observations. Quick, preliminary comparisons with some existing HTS/STIS data show the H layer thickness at auroral latitudes (∼1700 km) is much smaller than at equatorial latitudes (∼3900 km). These results strongly support the existence of a gradient in both H density and KH versus latitude, with higher values of KH at high latitudes and higher values of the H density at the equatorial regions. Such a small H layer thickness at auroral latitudes is consistent with a high mixing in the atmosphere that brings the hydrocarbons upwards, reducing consequently the column of hydrogen that scatters photons. These preliminary results show the strength of the proposed approach and open new horizons to use strong resonant emission lines at high resolution as a diagnostic for the state and structure of planetary upper atmospheres. 相似文献
33.
A. D. Chernin I. D. Karachentsev O. G. Kashibadze D. I. Makarov P. Teerikorpi M. J. Valtonen V. P. Dolgachev L. M. Domozhilova 《Astrophysics》2007,50(4):405-415
The Hubble Space Telescope observations of the nearby galaxy group M81/M82 and its vicinity indicate that the dynamics of
the expansion outflow around the group is dominated by the antigravity of the dark energy background. The local density of
dark energy in the area is estimated to be near the global dark energy density or perhaps exactly equal to it. This conclusion
agrees well with our previous results for the Local Group vicinity and the vicinity of the Cen A/M83 group.
Published in Astrofizika, Vol. 50, No. 4, pp. 493–505 (November 2007). 相似文献
34.
We present an analysis of the chiral property of 667 spiral and barred spiral galaxies in the Local Supercluster (radial velocity
<3 000 km s−1). The arms of a galaxy (spiral or barred spiral) can be distinguished according to their orientation (leading or trailing)
relative to the direction of the rotation. We use environment of each galaxy as a subsample in order to study the chiral property
of galaxies. In addition, equatorial position angle distributions of leading and trailing arm galaxies are studied. We classify
our database according as their morphology, diameters, radial velocities, axial ratios and magnitudes. The distribution of
trailing and leading arm galaxies in the Local Supercluster is found homogeneous. A significant dominance of either trailing
or leading structures is noticed within the Virgo cluster region, suggesting that the aggregation of these structures might
have already started there. The rotation axes of the galaxies in the Virgo cluster is found to lie in the equatorial plane.
Chirality of galaxies is found strong for the subsamples that showed a random alignment in the equatorial position angle distribution.
Possible explanations of the results will be presented. 相似文献
35.
We acquired high spectral and spatial resolution hyperspectral imaging spectrometer observations of Mars from near-UV to near-IR wavelengths (∼300 to 1020 nm) using the STIS instrument on the Hubble Space Telescope during the 1999, 2001, and 2003 oppositions. The data sets have been calibrated to radiance factor (I/F) and map-projected for comparison to each other and to other Mars remote sensing measurements. We searched for and (where detected) mapped a variety of iron-bearing mineral signatures within the data. The strong and smooth increase in I/F from the near-UV to the visible that gives Mars its distinctive reddish color indicates that poorly crystalline ferric oxides dominate the spectral properties of the high albedo regions (as well as many intermediate and low albedo regions), a result consistent with previous remote sensing studies of Mars at these wavelengths. In the near-IR, low albedo regions with a negative spectral slope and/or a distinctive ∼900 nm absorption feature are consistent with, but not unique indicators of, the presence of high-Ca pyroxene or possibly olivine. Mixed ferric-ferrous minerals could also be responsible for the ∼900 nm feature, especially in higher albedo regions with a stronger visible spectral slope. We searched for the presence of several known diagnostic absorption features from the hydrated ferric sulfate mineral jarosite, but did not find any unique evidence for its occurrence at the spatial scale of our observations. We identified a UV contrast reversal in some dark region spectra: at wavelengths shorter than about 340 nm these regions are actually brighter than classical bright regions. This contrast reversal may be indicative of extremely “clean” low albedo surfaces having very little ferric dust contamination. Ratios between the same regions observed during the planet-encircling dust storm of 2001 and during much clearer atmospheric conditions in 2003 provide a good direct estimate of the UV to visible spectral characteristics of airborne dust aerosols. These HST observations can help support the calibration of current and future Mars orbital UV to near-IR spectrometers, and they also provide a dramatic demonstration that even at the highest spatial resolution possible to achieve from the Earth, spectral variations on Mars at these wavelengths are subtle at best. 相似文献