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121.
We present timing measurements, astrometry, and high-resolution spectra of a number of nearby, thermally emitting, isolated
neutron stars. We use these to infer magnetic field strengths and distances, but also encounter a number of puzzles. We discuss
three specific ones in detail: (i) For RX J0720.4-3125 and RX J1308.6+2127, the characteristic ages are in excess of 1 Myr,
while their temperatures and kinematic ages indicate that they are much younger; (ii) For RX J1856.5-3754, the brightness
temperature for the optical emission is in excess of that measured at X-ray wavelengths for reasonable neutron-star radii;
(iii) For RX J0720.4-3125, the spectrum changed from an initially featureless state to one with an absorption feature, yet
there was only a relatively small change in T
eff. Furthermore, we attempt to see whether the spectra of all seven sources, in six of which absorption features have now been
found, can be understood in the context of strongly magnetised hydrogen atmospheres. We find that the energies of the absorption
features can be reproduced, but that it remains puzzling that, for J0720.4-3125 specifically, the spectrum was featureless
in one state, and that, generally, the spectra do not have high-energy tails that are harder than the Wien-like ones obseved.
相似文献
122.
123.
SMALL项目数字化地磁资料可靠性分析 总被引:4,自引:1,他引:3
在对中美合作 SMALL (中国低纬地磁台阵 )项目安装在北京地磁台 (白家疃 )和云南通海地磁台的磁通门磁力仪记录资料与磁变仪模拟记录资料进行了详细的对比分析后 ,得出的结果表明 ,两者的日变形态、日变幅有较好的一致性 ,所选特定事件的变化幅度非常一致 ,说明磁通门磁力仪记录到的变化磁场的资料是真实可靠的。尽管目前磁通门磁力仪的基线值存在温度影响和离散度较大的问题 ,但随温度变化有明显的规律性 ,若能采取改进观测条件和观测方法以及缩短观测时间等措施 ,并对基线值进温度校正 ,磁通门磁力仪完全可以提供长期连续可靠的资料。而其为地震预报 ,空间环境预报 ,为日地物理 ,空间物理和地磁学的研究提供的高精度、高分辨率、连续可靠的数字化变化磁场资料是磁变仪模拟记录无法比拟的。 相似文献
124.
D. W. Kurtz 《Journal of Astrophysics and Astronomy》2005,26(2-3):123-138
Asteroseismology studies stars with a wide variety of interior and surface conditions. For two decades asteroseismic techniques
have been applied to many pulsating stars across the HR diagram. Asteroseismology is now a booming field of research with
stunning new discoveries; I highlight a personal selection of these in this review, many of which are discussed in more detail
elsewhere in these proceedings. For many years the Nainital-Cape Survey for northern roAp stars has been running at ARIES,
so I emphasise new spectroscopic results for roAp stars and point out the outstanding prospects for the planned ARIES 3-m
telescope at Devastai. High precision spectroscopy has revolutionised the asteroseismic study of some types of stars — particularly
solar-like oscillators and roAp stars — while photometry is still the best way to study the frequency spectra that are the
basic data of asteroseismology. New telescopes, new photometers and space missions are revolutionising asteroseismic photometry.
In addition to the ground-based potential of asteroseismic spectroscopy, India has the knowledge and capability for space-based
asteroseismic photometry. The future for asteroseismology is bright indeed, especially for Indian astronomers. 相似文献
125.
Richard S. Lindzen 《地球物理与天体物理流体动力学》2013,107(3-4):303-355
Abstract In this, the first part of a three part study, we develop a model for the theoretical analysis of 3‐dimensional internal gravity waves in atmospheres with arbitrary distributions of basic temperature, molecular weight, viscosity and conductivity (both eddy and molecular), Newtonian cooling, anisotropic hydromagnetic (ion) drag, and thermal excitation. Attention is given to the physical bases for our models, and a detailed outline is given of the numerical method used to solve the resulting system of equations. As an application of the above development, we study the ability of five particular gravity waves (chosen for their observed importance in the neighborhood of 90–100 km—four of the waves are simulated tidal modes) to propagate from 90 km into the thermosphere. We choose to define the thermosphere as that portion of the atmosphere above the turbopause (ca. 110 km). Among the most significant results to emerge are the following: (i) the effects of molecular viscosity and conductivity appear to be more significant than the effects of hydromagnetic drag, and (ii) while most waves considered are significantly attenuated somewhere between 90 Ian and the thermosphere, the main semidiurnal tidal mode is not. In fact, semidiurnal temperature oscillations of only a few degrees amplitude at 90 km can give rise to oscillations of over a hundred degrees amplitude in the exosphere. 相似文献
126.
造父变星周光(PL)关系对于宇宙距离尺度研究和哈勃常数测定具有重要意义,所涉及的内容颇为广泛,可包括两类不同星族造父变星的PL关系,PL关系的绝对定标,周光色(PLC)关系,PL关系的金属度效应,多波段PL关系,极大光度PL关系和多相PL关系,以及非线性形式的PL关系,等等。 相似文献
127.
1988─1992年间,我们用云南天文台1m望远镜的Coude-CCD摄谱仪系统,对大角星的HeI10830A谱线进行了高分辨率光谱观测。从1991年6月2日的观测资料中发现谱线中出现明显的发射特征。该谱线显现出类似于天鹅座P型星的轮廓,有发射峰和吸收谷。发射峰的蓝移有相当于6km/s的向外速度。分析认为我们观测到的是大角星的一次以天计的短时标色球剧烈活动,它伴随着物质的向外抛射,也引起星周物质的向外运动。 相似文献
128.
Nicole St-Louis 《Astrophysics and Space Science》1994,221(1-2):197-214
In this paper, simultaneous optical and ultraviolet observations of spectral variability of the WN5 star HD 50896 are presented. Night-to-night and shorter timescale changes were found in the shape and intensity of most emission lines and P Cygni profiles in both wavelength ranges but there is no clear link between the ultraviolet and optical variability. There are some indications that the ultraviolet variations occur in phase with the well-known 3.766-day period often associated with this star. 相似文献
129.
130.