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91.
J. L. Payne G. L. White M. D. Filipovi 《Monthly notices of the Royal Astronomical Society》2008,383(3):1175-1194
We use long-slit spectra from shocked regions of radio supernova remnants (SNRs) in the Large Magellanic Cloud to estimate electron density and derive an average 'metal' abundance of 10−3.9 based on diagnostic line ratio plots. These simple diagnostics may be especially useful to determine abundances in more distant galaxies. Abundance values listed in this paper, in units of log(x/H) + 12, for nitrogen (7.3) and oxygen (8.2) agree with those reported in the literature. These estimates – which we assume to be dominated by the interstellar medium with little evolutionary interference – were obtained from spectral analysis of ∼50 per cent of known radio SNRs using the double beam spectrograph on the 2.3-m Advanced Technology Telescope at Siding Spring Observatory in Australia and the Cassegrain spectrograph on the 1.9-m Radcliffe telescope at the South African Astronomical Observatory. We also found optical evidence of shocked regions near 2 of 20 radio SNR candidates (J053620−693136 and J053731−662740), strengthening their identification as true remnants. 相似文献
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J. B. Stevens M. J. Coe D. A. H. Buckley 《Monthly notices of the Royal Astronomical Society》1999,309(2):421-429
The fields of eight X-ray sources in the Magellanic Clouds believed to be Be/X-ray binaries have been searched for possible Be-star counterparts. BVR c and H α CCD imaging was employed to identify early-type emission stars through colour indices and H α fluxes. Spectroscopy of five sources confirms the presence of H α emission in each case. Based on the positional coincidence of emission-line objects with the X-ray sources, we identify Be-star counterparts to the ROSAT sources RX J0032.9-7348, RX J0049.1-7250, RX J0054.9-7226 and RX J0101.0-7206, and to the recently discovered ASCA source AX J0051-722. We confirm the Be star nature of the counterpart to the HEAO1 source H0544-66. In the field of the ROSAT source RX J0051.8-7231 we find that there are three possible counterparts, each showing evidence for H α emission. We find a close double in the error circle of the EXOSAT source EXO 0531.1-6609, each component of which could be a Be star associated with the X-ray source. 相似文献
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The ultraviolet (UV) spectra on cloudy days were compared to those on cloud free days to determine which part of the UV spectrum has the greatest enhancement due to the cloud compared to both corresponding measured clear sky spectra as well as other enhanced spectra. In this preliminary study, cloud enhanced UV spectra selected for maximum UVA enhancement compared to a clear sky UV spectrum at similar solar zenith angle (SZA) and ozone values, showed that the ratio of the two sets of spectral irradiances was approximately wavelength independent (approximately 1.1) above the cut-off wavelength of approximately 306 nm. Similarly, above 306 nm the average ratio of the spectral irradiances of a maximum UVB enhanced UV spectrum compared to a clear sky spectrum was 1.2 with maximum values generally above this average between 316 and 344 nm and generally below 1.2 above the wavelength of 344 nm. The UVA and UVB enhanced spectra were separated into five SZA ranges and the irradiance at each wavelength averaged for each range and compared to clear sky spectra in each of the ranges. Above approximately 306 nm, the ratios are wavelength independent for all SZA. However, with the exception of the SZA range centred on 20°, there is an increasing dependency with shorter wavelengths below the 306 nm. Also there appears to be two distinct groupings of the average irradiance ratios, corresponding to the SZA range centred on 20°, 37° and 49° (ratio of 1.2) and 32° and 42° (ratio 1.0), the latter cases suggesting that on average there is no enhancement for these SZA, except for wavelengths less than 306 nm. 相似文献
96.
夏季催化对流云雷达回波特征对比分析 总被引:2,自引:0,他引:2
对"江淮地区对流云人工增雨外场试验"中3次催化作业过程,催化云和对比云新一代天气雷达回波特征的对比分析结果表明:催化云的平均维持时间比对比云长51.2%,平均回波面积比对比云多17%,催化云每个体扫的平均总液态含水量要高于对比云,整个维持时间的总液态含水量高出对比云46%.从而认为:催化作业可以达到增加回波面积,延长回波的持续时间,增加云中液态含水量的目的.并且,从其中一组对比中发现,对流云催化作业要掌握好催化时机,对于处在减弱期的对流云,催化作业达不到增加含水量、延长生命期的目的. 相似文献
97.
Michael Feast 《Astrophysics and Space Science》1995,230(1-2):195-203
A review is given of some aspects of work in South Africa on the establishment, calibration and use of galactic and extragalactic distance indicators. 相似文献
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Michael Feast 《Astrophysics and Space Science》1995,230(1-2):205-213
A review is given of a few of the aspects of Magellanic Cloud research which have been carried out by South African astronomers or by others using South African facilities. 相似文献