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141.
M. Stupar M. D. Filipović Q. A. Parker G. L. White T. G. Pannuti P. A. Jones 《Astrophysics and Space Science》2007,307(4):423-435
The Parkes–MIT–NRAO (PMN) radio survey has been used to generate a quasi all-sky study of Galactic Supernova Remnants (SNRs)
at a common frequency of 4.85 GHz (λ=6 cm). We present flux densities estimated for the sample of 110 Southern Galactic SNRs (up to δ=−65°) observed with the Parkes 64-m radio telescope and an additional sample of 54 from the Northern PMN (up to δ=+64°) survey undertaken with the Green Bank 43-m (20 SNRs) and 91-m (34 SNRs) radio telescopes. Out of this total sample
of 164 selected SNRs (representing 71% of the currently 231 known SNRs in the Green catalogue) we consider 138 to provide
reliable estimates of flux density and surface brightness distribution. This sub-sample represents those SNRs which fall within
carefully chosen selection criteria which minimises the effects of the known problems in establishing reliable fluxes from
the PMN survey data. Our selection criteria are based on a judicious restriction of source angular size and telescope beam
together with careful evaluation of fluxes on a case by case basis. Direct comparison of our new fluxes with independent literature
values gives excellent overall agreement. This gives confidence in the newly derived PMN fluxes when the selection criteria
are respected. We find a sharp drop off in the flux densities for Galactic SNRs beyond 4 Jy and then a fairly flat distribution
from 5 to 9 Jy, a slight decline and a further flat distribution from 9 to 20 Jy though the numbers of SNR in each Jy bin
are low. We also re-visit the contentious Σ–D (radio surface brightness–SNRs diameter) relation to determine a new power law index for a sub-sample of shell type SNRs
which yields β=−2.2±0.6. This new evaluation of the Σ–D relation, applied to the restricted sample, provides new distance estimates and their Galactic scale height distribution.
We find a peak in the SNR distribution between 7–11 kpc with most restricted to ±100 pc Galactic scale height. 相似文献
142.
143.
J. P. Phillips 《Monthly notices of the Royal Astronomical Society》2007,380(1):369-373
We have used recent radiative transfer solutions for cavity-centred shells to investigate the prevalence of density gradients in Galactic ultra-compact H ii regions. We find that an analysis of 5 and 1.4 GHz data, taken from the recent compilation of Giveon et al., implies that ∼76 per cent of sources may have appreciable density gradients. It would also seem that the central cavities of these sources must be relatively small, with radii no greater than ∼20 per cent of those of the outer shells. The remainder of these sources are presumably homogenous, have much larger cavities, or possess reverse density gradients (densities which increase with increasing radius). A good fraction of the H ii regions also appear to have high brightness temperatures, implying mean electron temperatures 〈 T e 〉 of the order of ≈1.3 × 104 K . This value is higher than has been determined for other such sources. 相似文献
144.
Elaine M. Sadler Russell D. Cannon Tom Mauch Paul J. Hancock David A. Wake Nic Ross Scott M. Croom Michael J. Drinkwater Alastair C. Edge Daniel Eisenstein rew M. Hopkins Helen M. Johnston Robert Nichol Kevin A. Pimbblet Roberto De Propris Isaac G. Roseboom Donald P. Schneider Tom Shanks 《Monthly notices of the Royal Astronomical Society》2007,381(1):211-227
145.
146.
A. Torres-Rodríguez C. M. Cress 《Monthly notices of the Royal Astronomical Society》2007,376(4):1831-1837
We investigate the potential of the Square Kilometer Array Telescope (SKA) to constrain the sound speed of dark energy. The Integrated Sachs Wolfe (ISW) effect results in a significant power spectrum signal when Cosmic Microwave Background (CMB) temperature anisotropies are cross-correlated with galaxies detectable with the SKA in H i . We consider using this measurement, the autocorrelation of H i galaxies and the CMB temperature power spectrum to derive constraints on the sound speed. We study the contributions to the cross-correlation signal made by galaxies at different redshifts and use redshift tomography to improve the signal-to-noise. We use a χ2 analysis to estimate the significance of detecting a sound speed different from that expected in quintessence models, finding that there is potential to distinguish very low sound speeds from the quintessence value. 相似文献
147.
On the origins of part-time radio pulsars 总被引:1,自引:0,他引:1
Bing Zhang Janusz Gil Jaroslaw Dyks 《Monthly notices of the Royal Astronomical Society》2007,374(3):1103-1107
148.
149.
2013年中国发射了首颗进行全球导航卫星系统(global navigation satellite system,GNSS)掩星观测的气象卫星风云3号C星(Fengyun-3C,FY-3C),且已发布自2014年6月以来的FY-3C掩星大气产品,但目前还未见将其应用于大气边界层的相关研究。首次尝试利用FY-3C折射率产品确定边界层高度并进一步进行空间分布分析。结果表明,在小波协方差变换法基础上,进行尖锐度约束,能够确定FY-3C掩星低层大气折射率廓线中可能存在的突变,反演边界层高度。所得到的2015―2018年各年边界层高度全球分布在不同纬度及海洋和陆地上的差异基本体现了边界层与地表气候及地形的关系,但FY-3C折射率产品在低层大气的精度和垂直分辨率相对较低。因此,反演成功率总体上较低,反演结果对边界层高度空间分布细节特征的呈现仍有待提升。 相似文献
150.