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991.
992.
993.
We have investigated the fine structure of the object 1803+784 at a wavelength of 18 cm with an angular resolution of ~0.5 mas. The structure consists of a core (injector) and a jet. The angle of the relativistic plasma outflow is equal to the angle of a conical diverging helix—the trajectory of compact components, suggesting a similar shape of the jet. The helical structure and the curvature of the jet axis are assumed to be determined by rapid and long-period precession of the rotation axis. The core radio emission at 18 cm is attenuated by absorption in the ambient ionized medium (cocoon wall) by >25 db. The bright compact component is the nearby part of the jet extending outside the dense part of the screen. Ionization variations in the medium cause low-frequency radio variability. Screen parameters are estimated. 相似文献
994.
995.
Donald G. York Pushpa Khare Daniel Vanden Berk Varsha P. Kulkarni Arlin P. S. Crotts James T. Lauroesch Gordon T. Richards Donald P. Schneider Daniel E. Welty Yusra Alsayyad Abhishek Kumar Britt Lundgren Natela Shanidze Tristan Smith Johnny Vanlandingham Britt Baugher Patrick B. Hall Edward B. Jenkins Brice Menard Sandhya Rao Jason Tumlinson David Turnshek Ching-Wa Yip Jon Brinkmann 《Monthly notices of the Royal Astronomical Society》2006,367(3):945-978
996.
S. Frank M. C. Bentz K. Z. Stanek S. Mathur M. Dietrich B. M. Peterson D. W. Atlee 《Astrophysics and Space Science》2007,312(3-4):325-330
We examine the recent report by Prochter et al. that gamma-ray burst (GRB) sight lines have a much higher incidence of strong
Mg II absorption than quasar sight lines. We propose that the discrepancy is due to the different beam sizes of GRBs and quasars,
and that the intervening Mg II systems are clumpy with the dense part of each cloudlet of a similar size as the quasars, i.e.
≲1016 cm, but bigger than GRBs. We also discuss observational predictions of our proposed model. Most notably, in some cases the
intervening Mg II absorbers in GRB spectra should be seen varying, and quasars with smaller sizes should show an increased
rate of strong Mg II absorbers. In fact, our prediction of variable Mg II lines in the GRB spectra has been now confirmed
by Hao et al., who observed intervening Fe II and Mg II lines at z=1.48 to be strongly variable in the multi-epoch spectra of z=4.05 GRB 060206. 相似文献
997.
998.
Joseph D. Meiring James T. Lauroesch Varsha P. Kulkarni Celine Péroux Pushpa Khare Donald G. York Arlin P. S. Crotts 《Monthly notices of the Royal Astronomical Society》2007,376(2):557-572
We present chemical abundance measurements from high-resolution observations of seven subdamped Lyα (sub-DLA) absorbers and one DLA system at z < 1.5 . Three of these objects have high metallicity, with near or supersolar Zn abundance. Grids of cloudy models for each system were constructed to look for possible ionization effects in these systems. For the systems in which we could constrain the ionization parameter, we find that the ionization corrections as predicted by the cloudy models are generally small and within the typical error bars (∼0.15 dex), in general agreement with previous studies. The Al iii to Al ii ratio for these and other absorbers from the literature are compared, and we find that while the sub-DLAs have a larger scatter in the Al iii to Al ii ratios than the DLAs, there appears to be little correlation between the ratio and N H i . The relationship between the metallicity and the velocity width of the profile for these systems is investigated. We show that the sub-DLAs that have been observed to date follow a similar trend as DLA absorbers, with the more metal rich systems exhibiting large velocity widths. We also find that the systems at the upper edge of this relationship with high metallicities and large velocity widths are more likely to be sub-DLAs than DLA absorbers, perhaps implying that the sub-DLA absorbers are more representative of massive galaxies. 相似文献
999.
1000.
Samuel Boissier 《Astrophysics and Space Science》2002,281(1-2):457-460
We model the chemical and spectrophotometric evolution of the Milky Way, spiral galaxies and Low Surface Brightness Galaxies
in a consistent way. Some consequences with respect to the nature of Damped Lyman-α systems (DLAs) are investigated.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献