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971.
Artie P. Hatzes & William D. Cochran 《Monthly notices of the Royal Astronomical Society》1998,293(4):469-478
The shape of the Ti i 6303.8-Å spectral line of Aldebaran as measured by the line bisector was investigated using high signal-to-noise ratio, high-resolution data. The goal of this study was to understand the nature of the 643-d period in the radial velocity for this star reported by Hatzes & Cochran. Variations in the line bisector with the radial velocity period would provide strong evidence in support of rotational modulation or stellar pulsations as the cause of the 643-d period. A lack of any bisector variability at this period would support the planet hypothesis.
Variations in the line asymmetries are found with a period of 49.93 d. These variations are uncorrelated with the 643-d period found previously in the radial velocity measurements. It is demonstrated that this 50-d period is consistent with an m =4 non-radial sectoral g-mode oscillation. The lack of spectral variability with the radial velocity period of 643 d may provide strong evidence in support of the hypothesis that this variability stems from the reflex motion of the central star due to a planetary companion having a mass of 11 Jupiter masses. However, this long-period variability may still be the result of a low-order ( m =2) pulsation mode as these would cause bisector variations of less than the error measurement. 相似文献
Variations in the line asymmetries are found with a period of 49.93 d. These variations are uncorrelated with the 643-d period found previously in the radial velocity measurements. It is demonstrated that this 50-d period is consistent with an m =4 non-radial sectoral g-mode oscillation. The lack of spectral variability with the radial velocity period of 643 d may provide strong evidence in support of the hypothesis that this variability stems from the reflex motion of the central star due to a planetary companion having a mass of 11 Jupiter masses. However, this long-period variability may still be the result of a low-order ( m =2) pulsation mode as these would cause bisector variations of less than the error measurement. 相似文献
972.
Chochol Teodorani Strafella Errico & Vittone 《Monthly notices of the Royal Astronomical Society》1998,293(4):L73-L77
High-resolution, time-resolved spectroscopic observations of Z CMa carried out on 1997 January 14–17 are presented. Large night-to-night and hour-to-hour variations in Hα, Hβ and Na i D P Cygni absorptions, as well as an Hβ emission peak, were observed. Variations in the red wings of the hydrogen emission lines were also detected. The high-velocity wide-emission component on the blue side of Hα appeared on January 17. The observations are discussed in the framework of current wind models. 相似文献
973.
Effective collision strengths for electron-impact excitation of the N-like ion Ne iv are calculated in the close-coupling approximation using the multichannel R-matrix method. Specific attention is given to the 10 astrophysically important fine-structure forbidden transitions among the 4 So , 2 Do and 2 Po levels in the 2s2 2p3 ground-state configuration. The expansion of the total wavefunction incorporates the lowest 11 LS eigenstates of Ne iv , consisting of eight n = 2 terms with configurations 2s2 2p3 , 2s2p4 and 2p5 , together with three n = 3 states of configuration 2s2 2p2 3s. We present in graphical form the effective collision strengths obtained by thermally averaging the collision strengths over a Maxwellian distribution of velocities, for all 10 fine-structure transitions, over the range of electron temperatures log T (K) = 3.6 to log T (K) = 6.1 (the range appropriate for astrophysical applications). Comparisons are made with the earlier, less sophisticated close-coupling calculation of Giles, and excellent agreement is found in the limited temperature region where a comparison is possible [log T (K) = 3.7 to log T (K) = 4.3]. At higher temperatures the present data are the only reliable results currently available. 相似文献
974.
D. G. Hummer & P. J. Storey 《Monthly notices of the Royal Astronomical Society》1998,297(4):1073-1078
A new calculation of photoionization cross-sections is described for the ground and excited states of atomic helium up to principal quantum number n =25 and angular momentum quantum number l =5. These cross-sections are used to calculate total recombination and cooling coefficients for atomic helium for electron temperatures given by log( T )=1(0.2)4.4. A comparison of the threshold photoionization cross-sections obtained here with extrapolations of the highly accurate bound–bound oscillator strength calculations by Drake shows that the new calculations are in error by no more than 1 per cent. The accuracy of the photoionization cross-sections used by previous workers to derive recombination coefficients is also discussed. 相似文献
975.
An analysis is described which can derive optical thicknesses and associated quantities from measured intensities and linewidths using convenient expressions for photon escape probabilities and for opacity-broadened line halfwidths. An associated analysis of the effect of observational errors is provided. The analysis treats intensities and linewidths independently so that internal consistency of results can provide a measure of observational accuracy, which is shown here to be a stringent requirement. As examples, first applications are made to Si II lines in a solar prominence and to some high-resolution observations of the solar He II 303.78-Å resonance line. 相似文献
976.
977.
我国境外旅游本底趋势线的建立及科学意义 总被引:49,自引:4,他引:45
提出了旅游本底趋势线的概念,依据1978 ̄1996年共计19境外客流量统计数据,经过“滤波”订正,建立了外国人,港澳台胞,华侨及境外客流总量4条本底趋势线;利用旅游本底趋势表“晴雨表”功能说明‘89风波地我国境外旅游业的影响,利用预测功能预估了未来4年我国境外旅游业的发展趋势。 相似文献
978.
卢伙胜 《广东海洋大学学报》1998,(1)
为正确分析和改进设计网具,采用悬链线与拖网配纲形状比较的方法,引伸配纲形变系数对设计网配纲进行合理性检验。并对有关计算方法进行推导和论证。 相似文献
979.
目前利用计算机绘制图形的软件很多,特别是作平面等值线图的软件,如SURFER、GRA-PHER等,但这些软件在平面上作图时均不考虑地质构造线,因此这些图件远不能满足地质工作者的需要。为此,本文为了解决上述问题从数学方法、原理方面作一简要说明,对于计算机处理过程作了较完整的叙述。 相似文献
980.
湖南凤凰寒武纪Fischer点图及其意义 总被引:2,自引:0,他引:2
湖南凤凰早寒武世为外陆棚环境,中、晚寒武世为台缘斜坡,经过一定校正编绘的Fischer点图获得的海平面变化曲线显示寒武纪全球海平面上升的趋势,海洋可容空间不断加大,这与三叶虫演经有耦合关系,早寒武世区域性三叶虫多,生物分区明显,三叶虫带不能进行洲际对经,晚寒武世则相反,两个重要海进面(536Ma和517.2Ma)是统间界线最佳线点,与北美R2曲线比较可确认515-517Ma 寒武大海泛期(长山期内 相似文献