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《天文学报》2017,(2)
对低温变星的脉动激发机制中的一些争议问题进行了评述:(1)大多数人相信γDoradus型变星是由所谓的阻塞对流机制所激发.研究表明,γDoradus和δScuti变星的激发机制不存在任何实质性的差别,他们是更大一类δScuti-γDoradus变星的2个次群:δScuti变星是p模脉动子群;而γDoradus是g模脉动子群.(2)大多数人相信太阳5分钟振荡和恒星的类太阳振荡被对流所阻尼,他们是由所谓湍流随机激发机制驱动的.研究表明,对流并非单纯只是脉动的阻尼机制,否则无法解释Mira变星和类Mira变星.利用非局部和非定常的恒星对流理论,不仅可以重现δScuti和γDoradus脉动不稳定区,也可重现低光度红巨星的类太阳振荡和高光度红巨星的类Mira振荡特性. 相似文献
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利用一种非局部和非定常的恒星对流理论,计算了太阳中低球谐阶(l＜25)模的非绝热脉动.结果表明,低阶(0＜l＜6)非径向p1模是脉动不稳定的,而与之相邻的g模、f模和p2-p5模都是脉动稳定的.根据累积功图的分析,发现振荡的激发来自对流区底部区域.太阳是否存在不稳定的低球谐阶p1模对判断太阳5 min振荡的激发机制有重要意义. 相似文献
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利用一种非定常的恒星非局部对流理论,对球状星团中低光度的红巨星进行了线性非绝热脉动理论计算．结果表明,对所有温度高于约5400 K模型的基音到4阶泛音都是脉动稳定的．随着恒星光度的增大,低阶泛音也变得脉动不稳定．对中低光度的红巨星,脉动稳定性非常低,接近中性稳定．因此他们将是不变星或非常小振幅的短周期变星(P<2天)． 相似文献
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《天文学报》2014,(4)
捅姜利用一种非局部和非定常的恒星对流理论,计算了3种不同氦丰度(Y=0.28,0.13,0.00)、太阳金属丰度(Z=0.02)、质量1.4~3.0 M_☉恒星演化模型的径向和低球谐阶F-p8模的线性非绝热脉动.数值计算结果表明,理论的δScuti变星脉动不稳定区红边界几乎不随氦丰度变化而改变.随着氦丰度降低,δScuti变星脉动不稳定区蓝边界向低温方向推移,脉动不稳定区中热方的高温星变得脉动更稳定;而冷方的低温星则变得脉动更不稳定.这似乎表明不大可能用氦弥散去解释δScuti脉动不稳定带中的不变星.然而脉动不稳定带热方和冷方中的不变星与变星的比例可能作为是否存在氦弥散的一种观测证据. 相似文献
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1 引言 太阳5分钟振荡是上世纪1个重要的发现[1],它使得人们可以通过观测太阳表面的振动来探测其内部的结构,日震学已取得了巨大的进展,然而我们至今仍不了解其脉动的激发机制,它依然是1个存在争议的问题.太阳位于造父变星脉动不稳定区之外,所以大多数人都相信,由于对流的阻尼,太阳是脉动稳定的,太阳和太阳型恒星的振荡都是由所谓的湍流随机激发机制所激发[2-8]. 相似文献
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依传统的局部混合长理论进行了对流包层模型计算,在黄红巨星和超巨星对流区的顶部出现超声速对流的情况,这与局部对流理论本身是不自恰的．文章详细分析了恒星大气超声速对流的成因,并按照星族Ⅰ恒星的演化轨迹,在赫罗图上给出了出现超声速对流的区域．其结果是。在演化过程中, (1)低质量星基本不出现超声速对流; (2)中等质量星的超声速对流主要出现在3．6相似文献
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根据非局部和非定常恒星对流理论,计算了质量3～30 M_⊙恒星演化模型低球谐阶(l=1～4)p4～g39非径向模的线性非绝热脉动,研究了对流对非径向脉动的影响.结果表明,对流对恒星非径向脉动稳定性有不可忽略的影响.然而假若不关注单个恒星和单个振动模的细节,从总体上粗略地看,理论的脉动不稳定区的大致位置和范围并未受到对流的明显影响. 相似文献
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长副周期变星是一类特殊的半规则变星,大量存在于银河系和大小麦哲伦云中,约占渐近巨星分支的25%～30%。该类变星有两个光变周期,短的主周期为30～200 d,由径向脉动的低阶模式导致;长的副周期长达400～1500 d。在长周期变星的周光关系中,长副周期变星处在D序列,平行于径向脉动的A、B和C序列,且与属于双星系统的E序列部分重叠。长副周期现象的起源一直是个谜,现存的解释模型有:径向脉动、非径向脉动、双星、磁活动、带有一个巨大黑子的转动红巨星、转动的椭球红巨星、κ机制等,但这些模型没有一种能完美地解释长副周期变星的起源。 相似文献
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锂在温度达到T＞2.5×106 K时即参与7Li(p,α)4He反应燃烧,经典恒星理论推测,当恒星演化到红巨星阶段时,由于向内非常延伸的对流包层的存在,锂的丰度A(Li)=12+ lg[n(Li)/n(H)]应为A(Li)＜0.5.但是,陆续有处于不同光谱型、不同演化阶段的富锂巨星被发现,其中一些巨星的锂丰度甚至远超出宇宙大爆炸的原初锂丰度,给经典恒星演化模型带来了难题.回顾了从恒星主序到巨星支的锂丰度观测研究历史,并详细介绍了我们对银河系矮星系中富锂巨星的最新发现,总结了所有富锂巨星的观测证据,以及为解决此难题所提出的理论解释. 相似文献
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Solar System Research - Finding and studying possible collisions of asteroids approaching the Earth requires a significant amount of computation. This paper describes the R0 program created to... 相似文献
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Magnetars are the neutron stars with the highest magnetic fields up to 1015–1016 G. It has been proposed that they are also responsible for a variety of extra-galactic phenomena, ranging from giant flares in nearby galaxies to fast radio bursts. Utilizing a relativistic mean field model and a variable magnetic field configuration, we investigate the effects of strong magnetic fields on the equation of state and anisotropy of pressure of magnetars. It is found that the mass and radius of low-mass magnetars are weakly enhanced under the action of the strong magnetic field, and the anisotropy of pressure can be ignored. Unlike other previous investigations, the magnetic field is unable to violate the mass limit of the neutron stars. 相似文献
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P. Maltby 《Solar physics》1972,26(1):76-82
Observations of the penumbral intensity of sunspots in 13 wavelength regions are presented. In 4 wavelength regions 54 sunspots are measured. In the other wavelength regions the number of sunspots considered ranges from 3–19.The penumbral intensity alters with position within the spot. This intensity variation is found to be comparable with the change in intensity from one spot to another. The penumbral intensity is found to be independent of spot size in the sample considered.The penumbra model of Kjeldseth Moe and Maltby (1969) with = 0.055 is supported by the measurements. 相似文献
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Many asteroids with a semimajor axis close to that of Mars have been discovered in the last several years. Potentially some of these could be in 1:1 resonance with Mars, much as are the classic Trojan asteroids with Jupiter, and its lesser-known horseshoe companions with Earth. In the 1990s, two Trojan companions of Mars, 5261 Eureka and 1998 VF31, were discovered, librating about the L5 Lagrange point, 60° behind Mars in its orbit. Although several other potential Mars Trojans have been identified, our orbital calculations show only one other known asteroid, 1999 UJ7, to be a Trojan, associated with the L4 Lagrange point, 60° ahead of Mars in its orbit. We further find that asteroid 36017 (1999 ND43) is a horseshoe librator, alternating with periods of Trojan motion. This asteroid makes repeated close approaches to Earth and has a chaotic orbit whose behavior can be confidently predicted for less than 3000 years. We identify two objects, 2001 HW15 and 2000 TG2, within the resonant region capable of undergoing what we designate “circulation transition”, in which objects can pass between circulation outside the orbit of Mars and circulation inside it, or vice versa. The eccentricity of the orbit of Mars appears to play an important role in circulation transition and in horseshoe motion. Based on the orbits and on spectroscopic data, the Trojan asteroids of Mars may be primordial bodies, while some co-orbital bodies may be in a temporary state of motion. 相似文献
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In the text-books of astronomy, sections generally related to the Moon deal with the orbital elements of the Earth-Moon system such asa, e, i, ,
and the time of perigee passage. While the MEAN of the first of the three elements do not vary, mean longitude of the ascending node-mean longitude of the lunar perigee and the time of perigee passage undergoes secular as well as periodic changes due predominantly to the action of the Sun's gravitational attraction. While to a certain degree, explanations related to the calculation of the lunar orbit parameters are given, not a single graphical representation of these short- or long-periodic changes are presented. We allow the number of data related to these periodic changes must cover a large span of time; and if regression of the line of nodes or advances of the line of apses are to be graphically seen, data covering 18.61 and 8.85 yr, respectively, are needed. In this work we particularly aim at the graphical representation of the periodic changes of the line of nodes. 相似文献
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