The Zeeman effect in the Sobolev approximation: applications to spherical stellar winds     

R. Ignace  K. G. Gayley 《Monthly notices of the Royal Astronomical Society》2003,341(1):179-191

Modern spectropolarimeters are capable of detecting subkilogauss field strengths using the Zeeman effect in line profiles from the static photosphere, but supersonic Doppler broadening makes it more difficult to detect the Zeeman effect in the wind lines of hot stars. Nevertheless, the recent advances in observational capability motivate an assessment of the potential for detecting the magnetic fields threading such winds. We incorporate the weak-field longitudinal Zeeman effect in the Sobolev approximation to yield integral expressions for the flux of circularly polarized emission. To illustrate the results, two specific wind flows are considered: (i) spherical constant expansion with   v ( r ) = v _∞  and (ii) homologous expansion with   v ( r ) ∝ r   . Axial and split monopole magnetic fields are used to schematically illustrate the polarized profiles. For constant expansion, optically thin lines yield the well-known 'flat-topped' total intensity emission profiles and an antisymmetric circularly polarized profile. For homologous expansion, we include occultation and wind absorption to provide a more realistic observational comparison. Occultation severely reduces the circularly polarized flux in the redshifted component, and in the blueshifted component, the polarization is reduced by partially offsetting emission and absorption contributions. We find that for a surface field of approximately 100 G, the largest polarizations result for thin but strong recombination emission lines. Peak polarizations are approximately 0.05 per cent, which presents a substantial although not inconceivable sensitivity challenge for modern instrumentation.  相似文献   

Martian water vapor: Mars Express PFS/LW observations     

T. Fouchet  E. Lellouch  F. Forget  M. Tschimmel  V. Formisano  A. Maturilli 《Icarus》2007,190(1):32-49

We present the seasonal and geographical variations of the martian water vapor monitored from the Planetary Fourier Spectrometer Long Wavelength Channel aboard the Mars Express spacecraft. Our dataset covers one martian year (end of Mars Year 26, Mars Year 27), but the seasonal coverage is far from complete. The seasonal and latitudinal behavior of the water vapor is globally consistent with previous datasets, Viking Orbiter Mars Atmospheric Water Detectors (MAWD) and Mars Global Surveyor Thermal Emission Spectrometer (MGS/TES), and with simultaneous results obtained from other Mars Express instruments, OMEGA and SPICAM. However, our absolute water columns are lower and higher by a factor of 1.5 than the values obtained by TES and SPICAM, respectively. In particular, we retrieve a Northern midsummer maximum of 60 pr-μm, lower than the 100-pr-μm observed by TES. The geographical distribution of water exhibits two local maxima at low latitudes, located over Tharsis and Arabia. Global Climate Model (GCM) simulations suggest that these local enhancements are controlled by atmospheric dynamics. During Northern spring, we observe a bulge of water vapor over the seasonal polar cap edge, consistent with the northward transport of water from the retreating seasonal cap to the permanent polar cap. In terms of vertical distribution, we find that the water volume mixing ratio over the large volcanos remains constant with the surface altitude within a factor of two. However, on the whole dataset we find that the water column, normalized to a fixed pressure, is anti-correlated with the surface pressure, indicating a vertical distribution intermediate between control by atmospheric saturation and confinement to a surface layer. This anti-correlation is not reproduced by GCM simulations of the water cycle, which do not include exchange between atmospheric and subsurface water. This situation suggests a possible role for regolith-atmosphere exchange in the martian water cycle.  相似文献   

Long time-scale variability in GRS 1915+105     

M. R. Truss  G. A. Wynn 《Monthly notices of the Royal Astronomical Society》2004,353(4):1048-1054

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Ice-silicate fractionation among icy bodies due to the difference of impact strength between ice and ice-silicate mixture     

Masahiko Arakawa  Daisuke Tomizuka 《Icarus》2004,170(1):193-201

Laboratory experiments on the impact disruption of ice-silicate mixtures were conducted to clarify the accretion process of small icy bodies. Since the icy bodies are composed of ice and silicates with various porosities, we investigated the effect of porosity on the impact disruption of mixtures. We tested the mixture target with the mass ratio of ice to silicate, 0.5 and with 5 different porosities (0, 12.5, 25, 32, 37%) at the impact velocities of 150 to 670 m/s. The silicate mass ratio was changed from 0 to 0.5 in steps of 0.1 at a porosity of 12.5% and a constant impact velocity of about 300 m/s. The impact strength of the mixture was found to decrease with increasing porosity and the silicate mass ratio between 0.1 and 0.5 could enhance the strength of the icy target. The observed dependence of the impact strength on the porosity is opposite to that observed for pure ice. This difference could play an important role in ice-silicate fractionation during the accretion process. Because, ice rich bodies are easily broken as the porosity decreases in their evolution, the collisional growth could be prohibited. On the other hand, among the silicate rich bodies the collisional growth could be enhanced.  相似文献   

Thermonuclear reaction rates from (p,n) reactions on targets withA = 92–122     

S. Kailas 《Journal of Astrophysics and Astronomy》1986,7(2):53-57

From the experimentally measured (p,n) cross-sections for^92,94Zr,⁹³Nb,^95,96,98Mo,¹⁰³Rh,^107,109Ag,¹¹⁰Pd,¹¹⁵In,^117,122Sn nuclides, for proton energies below 7 MeV, thermonuclear reaction rates in the temperature range 1≤T ₉≤5(T₉=10⁹ K) have been extracted. These reaction rates have been fitted to a three parameter empirical expression proposed by Fowler.  相似文献   

仙女山-九畹溪断裂带附近地区地震活动性与静态库仑应力变化研究     

常婷  张丽芬  王秋良  何超枫 《大地测量与地球动力学》2020,40(10):1044-1048

基于仙女山-九畹溪断裂带附近地区地质构造,讨论三峡水库蓄水前后该断裂带附近地区的地震活动特征,同时分析该区域2014-03 M4.5与M4.7地震间的触发关系及2次地震对后续小震的影响。结果表明：1）M4.7地震可能由M4.5地震与库水渗流产生的较大孔隙压力共同触发。2）M4.5与M4.7两次地震的应力扰动导致研究区内地震活动增加,后续地震中约66.9%的地震发生于库仑应力增强区。3）2次地震产生的静态库仑应力变化导致仙女山断裂带附近地区地震活动增加,后续地震活动水平将处于背景地震活动水平之上;九畹溪断裂带活动性相对较弱,略小于背景地震活动水平,且处于应力积累阶段。  相似文献   

中国大陆地区GNSS ZTD对超强东部型厄尔尼诺事件的响应     

于腾丽  王勇  黄靖  杨军  占伟 《大地测量与地球动力学》2022,42(10):1015-1019

利用CMONOC提供的GNSS连续观测数据分析天顶对流层延迟（ZTD）代替水汽的可行性,并利用快速傅里叶变换（FFT）和小波变换(WT)开展GNSS ZTD对超强东部型厄尔尼诺事件的响应分析。结果表明,超强东部型厄尔尼诺事件会增加中国大陆地区水汽含量,在热带及亚热带地区响应更为显著;同时该事件会影响GNSS ZTD 的显著变化周期,使9个月的变化周期减弱,0.8~3个月内的变化周期增强。  相似文献   

2021年滦州M_S4.3地震和2015年昌黎M_S4.2地震震源参数及构造意义研究     

李赫  董一兵  王熠熙 《大地测量与地球动力学》2022,42(12):1281-1287

基于京津冀地震台网观测资料,利用CAP方法反演滦州M_S4.3地震、昌黎M_S4.2地震及其M_S3.3余震的震源机制,并利用近震深度震相获得更为准确的震源深度,结合双差定位法获得2个地震序列的震源分布结果,对发震构造及成因关联开展分析研究。结果显示：1）滦州M_S4.3地震的节面Ⅰ走向、倾角、滑动角分别为211°、85°、168°,节面Ⅱ分别为302°、78°、5°,震源错动类型为走滑型,震源深度为8 km,地震序列的震源分布呈NNE向,短轴剖面显示断层面倾角近垂直,认为其发震断层面为节面Ⅰ;昌黎M_S4.2地震及M_S3.3余震的节面Ⅰ分别为189°、68°、161°及190°、61°、170°,节面Ⅱ分别为286°、72°、23°及285°、81°、29°,震源错动类型同为走滑型,震源深度为10.5 km,地震序列的震源分布呈NNE向,短轴剖面显示断层面倾角近垂直,认为其发震断层面为节面Ⅰ;2）基于滦州M_S4.3地震、昌黎M_S4.2地震及滦州M_S7.1地震的震源参数结果,结合区域地质构造等资料分析认为,3次地震的发震构造不是上地壳先存断裂,而可能与震源区的深部构造背景密切相关,即壳内包体现象是孕育这些地震的共同基础。  相似文献   

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κ���  ��һ��  �ս��� 《大地测量与地球动力学》2014,34(5):17-20

??????M8.0????????????????????С???????????????????о???????????λ????????????????????ν???ие???????????????????1??M8.0??????????????????????????????????????С????????????????????????????????????????????????42°????????????????????????????20 km??2?????????????????????????????????????10 km?????????????????С??????????????????????????????????????????????????????λ?????????7 km??3??2??14??
ML3.7?????????????????93°?????????????????????С??????????????????????????????????2???????￡????????????????????????????????????????????????????????????????4??2??28??ML3.8?????????λ?????????????????????????????????????????????????????????￡????????????  相似文献   

Point pattern analysis of north polar crescentic dunes, Mars: A geography of dune self-organization     

Mark A. Bishop 《Icarus》2007,191(1):151-157

The geographic signature of dune distribution and self-organization as measured by the R-statistic offers a viewpoint on the geography of crescentic eolian systems and proposes an index from which to determine the degree of self-organization across a variety of spatial scales. Fields of simple dunes (dome, barchan, barchan-seif) are comparatively less regular in distribution than are those fields, or part thereof, that consist of compound (barchanoid) morphologies whose patterns are more highly regular.  相似文献