共查询到20条相似文献，搜索用时 125 毫秒
1.
本从支配恒星内部物理过程的整套基本方程组出发，应用阵发混沌机制，研究其非线性特性，经过理论分析和数学演算，最后得出结论，即恒星结构方程本身，在一定参数范围内，能够自发出现阵发混沌脉动，这与已观测到的一些脉动变星的不规则光变性质，定性符合得很好。 相似文献
2.
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
3.
利用一种非局部和非定常的恒星对流理论,计算了0.6～3.0 M☉恒星演化模型的线性非绝热脉动.结果表明,赫罗图上脉动不稳定带右方的脉动不稳定的低温恒星可以分成2大类(群).一类由主序矮星、亚巨星和中低光度红巨星组成的类太阳振荡恒星,它们的中高阶(径向阶nr≥12)p模是脉动不稳定的,而低阶(nr≤ 5)模是脉动稳定的;另一类是由亮的红巨星和渐近巨星支星(AGB)组成的类长周期变星,它们的低阶模(nr≤5)是脉动不稳定的,而高阶模(nr≥12)却是脉动稳定的.能利用对流与脉动的耦合统一解释造父变星脉动不稳定带红边界、类太阳和类长周期变星脉动.对赫罗图右方的低温恒星的中低阶p模振荡,对流与脉动的耦合是主要的脉动激发和阻尼机制,而湍流的随机激发机制仅对类太阳振荡高阶p模重要. 相似文献
4.
ＡＧＢ长周期变星是中小质量恒星演化到晚期时形成的，由于它们存在强烈的振动和巨大的星风物质损失，研究这类变星对于了解恒星振动性质，星风产生机制及恒星晚期演化都有十分重要的意义，本文比较广泛地考查了最近十几年来国际上对于ＡＧＢ长周期变星观测和理论研究工作的现状，讨论了ＡＧＢ长周期变星的主要观测性质以及恒星振动和演化理论工作中所取得的进展，同时也分析了目前研究工作中存在的一些问题和困难，指出今后研究工作 相似文献
5.
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
6.
δScuti型变星是赫罗图上A3-F5区间的主序及其以上的一种周期短于0.3d的单周期或多周期小变幅脉动变星，与它们相关的变星有矮造父变星，γDol变星，蓝离散星，金属线星，A型特殊星，λBoo变星的δDel变星，有些赫比格Ae/Be星也存在类似的脉动，对自1964年起的研究工作进行了系统的总结，给出了1995年后新发现的相关变星数和最可靠的周期变化表，提出应当用双星轨道光时效应来解释实测得到的变星周期变化中的幅度很大的成分，统计表明自转越快变幅越小，因此年轻星团中不可能存在大变幅变星，变幅随周期的分布有3个极大值，最大变由是周期0.17d处的1.0mag，恒星系统内变星的平均周期越短系统的年龄越大，金属丰度也越低。 相似文献
7.
仙干座β型星是上部土序的一类短周期变星,它们的脉动起因是一个长期使人困惑的问题。本文评述了仙干座β型星的一些观测特性,如物理参数,不稳定带在赫罗图中的位置,演化阶段,周期和脉动模式等。我们同时也讨论了几个脉动激发机制,即恒星通过什么途径使别的能量转化为脉动的机械能。机制分深层和包层两类,重点讨论了不透明度机制。 相似文献
8.
本文以亮星星表1982年版的资料为依据,统计了双星比例随光谱型的变化。发现巨星的双星比例由B、A型的50％左右逐渐下降到M型的24％,而矮星的双星比例不随光谱型下降,都在50％左右。还发现各主要类型脉动变星中的双星比例比上述相应光谱区内的双星比例高约10％。这可能说明成双性与恒星演化和脉动特性均有某种关系。造父变星中双星比例高达53％是很值得仔细研究的问题。 相似文献
9.
10.
中等质量富金属AGB长周期变星的振动研究 总被引：1，自引：0，他引：1
本采用恒星演化计算与恒星振动计算相结合的方法，对中等质量富金属恒星演化到渐近巨星分支时的振动性质进行了分析研究，从理论上得出这类恒星的振动方式是处于一阶谐频振动，而振动的激发则是在氢电离区和氦的二次电离区由多种机制共同作用造成的，同时提出很长周期的ＡＧＢ长周期变星只能是由中等质量恒星演化到ＡＧＢ阶段形成的。我们的理论计算结果还比较支持在ＡＧＢ顶端存在巨大星风物质损失的观点，且这种星风物质损失很可 相似文献
11.
G. Handler W. W. Weiss R. R. Shobbrook E. Paunzen A. Hempel S. K. Anguma P. C. Kalebwe D. Kilkenny P. Martinez M. B. Moalusi R. Garrido R. Medupe 《Monthly notices of the Royal Astronomical Society》2006,366(1):257-266
We undertook a time-series photometric multisite campaign for the rapidly oscillating Ap (roAp) star HD 99563 and also acquired mean light observations over four seasons. The pulsations of the star, which show flatter light maxima than minima, can be described with a frequency quintuplet centred on 1557.653 μHz and some first harmonics of it. The amplitude of the pulsation is modulated with the rotation period of the star that we determine with 2.91179 ± 0.00007 d from the analysis of the stellar pulsation spectrum and of the mean light data. We break up the distorted oscillation mode into its pure spherical harmonic components and find it is dominated by the ℓ= 1 pulsation, and also has a notable ℓ= 3 contribution, with weak ℓ= 0 and 2 components. The geometrical configuration of the star allows us to see both pulsation poles for about the same amount of time; HD 99563 is only the fourth roAp star for which both pulsation poles are seen and only the third where the distortion of the pulsation modes has been modelled. We point out that HD 99563 is very similar to the well-studied roAp star HR 3831. Finally, we note that the visual companion of HD 99563 is located in the δ Scuti instability strip and may thus show pulsation. We show that if the companion was physical, the roAp star would be a 2.03-M⊙ , object, seen at a rotational inclination of 44°, which then predicts a magnetic obliquity . 相似文献
12.
M. Marconi V. Ripepi S. Bernabei A. Ruoppo M. J. P. F. G. Monteiro J. P. Marques F. Palla S. Leccia 《Astrophysics and Space Science》2010,328(1-2):109-111
The Herbig Ae star PDS2 was found to pulsate as a Pre-Main-Sequence delta Scuti star on the basis of R.E.M. telescope photometry. From the frequency analysis we have found four significant pulsation frequencies. We discuss these results and their interpretation through the adoption of nonradial pulsation models, deriving the first information on the intrinsic properties of this young star. 相似文献
13.
V. Van Grootel S. Charpinet G. Fontaine P. Brassard 《Astrophysics and Space Science》2010,329(1-2):217-224
The hot pulsating sdB star PG 1605+072 exhibits uncommon spectroscopic and pulsation properties, and is one of the biggest challenge in the field of sdB star modeling. Two hypotheses have been proposed to explain its unusually rich pulsation spectrum. The first is the natural explanation of a fast-rotating pulsator, which lifts the (2l+1)-fold degeneracy of the frequency components. Another approach, where PG 1605+072 can be seen as a slow rotator, considers that the numerous low amplitude frequency components are second- and third-order harmonics and nonlinear combinations of the highest amplitude frequencies. We investigated the two hypotheses in the light of asteroseismology, using our latest tools—including pulsation codes that incorporate star rotation and new generation complete sdB models. The results of both approaches are presented, showing interesting results and raising new questions for our understanding of this mysterious sdB star. 相似文献
14.
D. L. Terrett 《Astrophysics and Space Science》1980,70(2):393-399
The effective temperature of the short period cepheid SU Cas has been determined from a comparison of its spectral scans with appropriate model atmospheres. Using this temperature and an independent Wesselink radius determination, the luminosity of the star has been redetermined. The pulsation mass and the evolutionary mass of the star have been discussed. The evolutionary to pulsation mass ratio comes out to be greater than unity. 相似文献
15.
A.-Y. Zhou D. An J. R. Eggen M. D. Reed D. M. Terndrup S. L. Harms 《Astrophysics and Space Science》2006,305(1):29-36
We report on the discovery of a new short-periodic pulsating variable star in the field of the pulsating sdB star KPD 2109+4401. The star was observed on 10 consecutive nights. Based on the light curves, we detect three pulsation frequencies at 10.308, 4.023 and 11.075 cycle d−1 with amplitudes of 11.1, 4.3 and 4.2 milli-magnitudes, respectively. Using the existing data from other sky surveys, we estimate a spectral type of late F and other atmospheric parameters. Then we discuss the observational properties of the star. Finally it is classified to be a new low-amplitude multiperiodic δ Scuti star. A future interest addressed is to accurately determine the star's spectral type and then to judge a possible link to γ Doradus-type pulsation. 相似文献
16.
O'Donoghue Koen Lynas-Gray Kilkenny & van Wyk 《Monthly notices of the Royal Astronomical Society》1998,296(2):306-316
We report the discovery of rapid oscillations in the sdB star PG 1047+003. The oscillations are multiperiodic, with nine periods in the range 104–162 s. The optical spectrum of PG 1047+003 is consistent with that of a single sdB star. Line profile fitting yields an effective temperature of 35 000±1000 K and log g =5.9±0.1, although optical photometry and IUE spectrophotometry may indicate a cooler effective temperature. These properties demonstrate that PG 1047+003 is an EC 14026 star, a recently discovered class of sdB pulsators. Optical and infrared photometry constrains any cool companion to the sdB star to be a main-sequence star of spectral type M0 or later. With V =13.47 and a relatively rich pulsation spectrum, PG 1047+003 is an attractive target for an intensive photometric campaign to extract more periods from the light curve which, along with a suitable grid of pulsation models, will probe the interior structure of the star. 相似文献
17.
E. Pedretti † J. D. Monnier S. Lacour W. A. Traub W. C. Danchi P. G. Tuthill N. D. Thureau R. Millan-Gabet J.-P. Berger M. G. Lacasse P. A. Schuller F. P. Schloerb N. P. Carleton 《Monthly notices of the Royal Astronomical Society》2009,397(1):325-334
We have detected asymmetry in the symbiotic star CH Cyg through the measurement of precision closure phase with the Integrated Optics Near-Infrared Camera (IONIC) beam combiner, at the infrared optical telescope array interferometer. The position of the asymmetry changes with time and is correlated with the phase of the 2.1-year period found in the radial velocity measurements for this star. We can model the time-dependent asymmetry either as the orbit of a low-mass companion around the M giant or as an asymmetric, 20 per cent change in brightness across the M giant. We do not detect a change in the size of the star during a 3-year monitoring period neither with respect to time nor with respect to wavelength. We find a spherical dust shell with an emission size of 2.2 ± 0.1 D * full width at half-maximum around the M giant star. The star to dust flux ratio is estimated to be 11.63 ± 0.3. While the most likely explanation for the 20 per cent change in brightness is non-radial pulsation, we argue that a low-mass companion in close orbit could be the physical cause of the pulsation. The combined effect of pulsation and low-mass companion could explain the behaviour revealed by the radial velocity curves and the time-dependent asymmetry detected in the closure-phase data. If CH Cyg is a typical long secondary period variable then these variations could be explained by the effect of an orbiting low-mass companion on the primary star. 相似文献
18.
HR 7439 (HD 184705) is an F0V star which we have discovered to be a low amplitude Scuti star. This star is multi-periodic with frequencies in the range of 17 to 22 d–1 (periods in the range 65 to 85 min). These periods are relatively short for such a cool star. Calculation of the pulsation constant Q and comparison with models indicates pulsation in the fourth and fifth overtones. Interestingly, an appropriate model calculated by Stellingwerf shows highest growth rates for the fourth and fifth overtones. 相似文献
19.
If one zone models are available for some pulsating stars and the motion remains close to adiabaticity, we show the existence of odd frequencies in the power spectrum of these pulsating variable stars, and the frequency of free oscillation thus becomes dependent on the amplitude. We find 3 appearing in the power spectrum of the white dwarf PG 1351+489. Furthermore, the intrinsic stochasticity in the basic equations describing the structure of stars is discussed in this paper. We found that the pulsation of intermittent chaos can occur spontaneously in the basic equations of a star within certain intervals of values of its control parameters, and the intermittency can be used as an interpretation of pulsation in variable stars. 相似文献
20.
D. W. Kurtz 《Astrophysics and Space Science》1993,210(1-2):207-214
The rapidly oscillating Ap stars pulsate in high-overtone, low degreep-modes with their pulsation axes aligned with their oblique magnetic axes. They show non-linearity in their pulsation in three ways:
- The harmonics of the basic pulsation frequency are detectable.
- The pulsation phase seems to vary stochastically on a time scale of days to years depending on the star.
- The form of the nonradial surface distortion is not constant with time.