TESS空间卫星单扇区变星的周期性研究

TESS (Transiting Exoplanet Survey Satellite)空间卫星提供的短曝光、高精度光度测量为寻找并区分变星与搜寻行星提供了良好的数据.利用变星源的光变曲线,使用周期频谱分析与光变折叠等一系列方法分析了TESS空间卫星21扇区19995颗拥有高质量光变数据的目标源,并对这些源进行了分类,共获得4624颗变星,其中食双星322颗、脉动变星470颗、行星凌星37颗.所得变星结果与VSX (The International Variable Star Index)变星表进行了交叉比较,共交叉匹配了625颗变星源,这些交叉源中共有131颗为食双星系统、31颗为脉动变星,并通过周期频谱分析获取了双星绕转以及脉动周期.另外在59颗变星中发现明显耀发现象,交叉源中有8颗变星为行星凌星并同样通过周期频谱分析获取了行星绕转周期,从而验证了TESS空间卫星数据对变星分析的可行性.通过利用TESS空间卫星21扇区获得的变星周期结果与VSX变星表中提供的变星周期对比,发现与VSX变星表中绝大部分变星的周期一致,有一部分结果与VSX变星表中的结果差别较大,对这些变星周期结果做了进一步修正,并给出了变星表未列出的变星周期结果.     

20个激变变星或相关天体的分光证认

在２０个研究得很少的激变变星或者曾经被分类为激变变星的相关天体的光谱中,１３个被证实为属于激变变星（６５％）,另外７个似乎应该被排除（表１第８列）,不像其他研究者那样,仅给出非激变变星或热天体,还以更强的证据和更多的光谱特征征认出１个ＤＡ型白矮星,４个双星系统及其子星的光谱型。新的光谱资料不支持ＦＹ Ｐｅｒ的Ｈｅｒｂｉｇ Ａｅ／Ｂｅ分类,它是一个激变变星。对于ＰＧ１７１２＋４９３,不仅给出星和云的     

δScuti变星和相关天体

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0.3 d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、γ Dol变星、蓝离散星、金属线星、A型特殊星、λBoo变星和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,最大变幅是周期0.17d处的1.0 mag.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.     

δScuti变量和相关天体

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。     

红巨星中长副周期变星的起源

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。     

仙王β型变星的观测物理特性和研究进展

仙王β型变星是一类早型(08-B6,Ⅰ—Ⅴ)、短周期、低变幅的脉动变星。本文综述了这类变星的观测物理特性,并着重从实测方面介绍了近年来一些研究进展,新变星的寻找,高精度测光,高分辨率的光谱观测研究,光学偏振,紫外,红外,X射线探测等。仙王β型变星的脉动机制至今尚未解决。     

δScuti型变星的观测与模型(英文)

本文报告了δScuti型变星V6 5 0Tau的测光研究结果并讨论了这类变星振幅的变化。根据Arets2 0 0 0的综述“通过谱线变化做模式证认” ,介绍了光谱观测研究δScuti型变星的方法。最后介绍了熊大闰和邓李才的理论模型及δScuti型变星理论的脉动不稳定带     

脉动稳定性对恒星对流包层氦丰度的依赖

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.     

球状星团M3水平支脉动不稳定带红边界附近的小变幅变星

半个世纪以前,Ｒｏｂｅｒｔｓ 和Ｓａｎｄａｇｅ 在验证Ｓｃｈｗａｒｚｓｃｈｉｌｄ 的理论发现时,在水平支ＲＲＬｙｒａｅ 变星缺口段的红端发现了两颗小变幅的变星。当时定不出类型,标以“？”。以后Ｓａｎｄａｇｅ 在做ＲＲ Ｌｙｒａｅ 变星统计研究时,竟不加解释地当作ＲＲａｂ 型星处理。半个世纪之间,没有人对这颗星的反常加以注意。我们用国内的ＣＣＤ 观测,又发现了一颗类似的小变幅变星,但变幅更小,周期更长。这颗星与以前发现的两颗一起,似乎构成ＲＲ Ｌｙｒａｅ 星的又一个次型。现有的变星脉动理论还不能对之加以解释。我们预计,这将再一次推动脉动理论发展。     

激变变星

激变变星是密近双星系统,包含一颗白矮星主星和一颗晚型星伴星。晚型星伴星充满了其Roche瓣,并向主星转移物质,在主星周围形成一个吸积盘。这类双星对于我们认识吸积过程、密近双星的演化等是相当重要的。本文主要从实测角度综述激变变星研究的现状,并讨论一些尚待解决的问题。     

The secondary stars in cataclysmic variables and low-mass X-ray binaries

We critically re-examine the available data on the spectral types, masses and radii of the secondary stars in cataclysmic variables (CVs) and low-mass X-ray binaries (LMXBs), using the new catalogue of Ritter &38; Kolb as a starting point. We find there are 55 reliable spectral type determinations and only 14 reliable mass determinations of CV secondary stars (10 and 5, respectively, in the case of LMXBs). We derive new spectral type–period, mass–radius, mass–period and radius–period relations, and compare them with theoretical predictions. We find that CV secondary stars with orbital periods shorter than 7–8 h are, as a group, indistinguishable from main-sequence stars in detached binaries. We find that it is not valid, however, to estimate the mass from the spectral type of the secondary star in CVs or LMXBs. We find that LMXB secondary stars show some evidence for evolution, with secondary stars which are slightly too large for their mass. We show how the masses and radii of the secondary stars in CVs can be used to test the validity of the disrupted magnetic braking model of CV evolution, but we find that the currently available data are not sufficiently accurate or numerous to allow such an analysis. As well as considering secondary star masses, we also discuss the masses of the white dwarfs in CVs, and find mean values of ⁻ M  = 0.69 ± 0.13 M_⊙ below the period gap, and ⁻ M  = 0.80 ± 0.22 M_⊙ above the period gap.     

Contact binaries at different evolutionary stages

Contact binaries consist of two strongly interacting component stars where they are filling their critical Roche lobes and sharing a common envelope. Most of them are main-sequence stars, but some of them are post main-sequence systems. They are good astrophysical laboratories for studying several problems such as the merging of binary stars, evolution of the common envelope, the origin of luminous red nova outbursts and the formation of rapidly rotating single stars with possible planetary systems. A large number of contact binary candidates were detected by several photometric surveys around the world and many of them were observed by the LAMOST spectroscopic survey. Based on follow-up observations,the evolutionary states and geometrical structures of some systems were understood well. In this review,we will introduce and catalog new stellar atmospheric parameters(i.e., the effective temperature(Teff), the gravitational acceleration(log(g)), metallicity([Fe/H]) and radial velocity(Vr)) for 9149 EW-type contact binaries that were obtained based on low-and medium-resolution spectroscopic surveys of LAMOST. Then we will focus on several groups of contact binary stars, i.e., marginal contact binary systems, deep and low-mass ratio contact binary stars, binary systems below the short-period limit of contact binaries and evolved contact binaries. Marginal contact binaries are at the beginning of the contact stage, while deep and low-mass ratio contact binary stars are at the final evolutionary stage of tidally locked binaries. Several statistical relations including the period-temperature relation are determined well by applying LAMOST data and their formation and evolutionary states are reviewed. The period-color relation of M-type binaries reveals that there are contact binaries below the short-period limit. Searching for and investigating contact binaries near and below this limit will help us to understand the formation of contact binary systems and a new prediction for the short-period limit is about 0.15 d. Some evolved contact binaries were detected by the LAMOST survey where both components are sub-giants or giants. They provide a good opportunity to investigate evolution of the common envelope and are the progenitors of luminous red novae like V1309 Sco.     

A new method of determining the inclination angle in interacting binaries

We describe a method of determining the system parameters in non-eclipsing interacting binaries. We find that the extent to which an observer sees the shape of the Roche lobe of the secondary star governs the amount of distortion of the absorption-line profiles. The width and degree of asymmetry of the phase-resolved absorption-line profiles show a characteristic shape, which depends primarily on the binary inclination and gravity darkening exponent. We show that, in principle, by obtaining high spectral and time resolution spectra of quiescent cataclysmic variables or low-mass X-ray binaries in which the mass-losing star is visible, fitting the shape of absorption-line profiles will allow one to determine not only the mass function of the binary, but also the binary inclination and hence the mass of the binary components.     

Radial velocity measurements of white dwarfs

We present 594 radial velocity measurements for 71 white dwarfs obtained during our search for binary white dwarfs and not reported elsewhere. We identify three excellent candidate binaries, which require further observations to confirm our preliminary estimates for their orbital periods, and one other good candidate. We investigate whether our data support the existence of a population of single, low-mass (≲0.5 M_⊙) white dwarfs (LMWDs). These stars are difficult to explain using standard models of stellar evolution. We find that a model with a mixed single/binary population is at least ~20 times more likely to explain our data than a pure binary population. This result depends on assumed period distributions for binary LMWDs, assumed companion masses and several other factors. Therefore, the evidence in favour of the existence of a population of single LMWDs is not sufficient, in our opinion, to firmly establish the existence of such a population, but does suggest that extended observations of LMWDs to obtain a more convincing result would be worthwhile.     

Identification of temperature anomaly RR Lyrae stars in LAMOST survey,misclassification and binarities

RR Lyrae stars,a well-known type of pulsating variable stars,have been known about for more than a century.A large amount of photometric data on RR Lyrae stars has been accumulated by space-and ground-based sky surveys,but the spectral data are relatively poor.Fortunately,the LAMOST sky survey project provides an opportunity to view them from the point of view of spectra.We collect the atmospheric parameters of 1685 RR Lyrae stars provided by the LAMOST catalog,and carry out research by using the reliable T_(eff).We find that there is a clear correlation between their Teff and pulsation periods,which is consistent with the pulsation and evolution theories of RR Lyrae stars.In addition,we focus on those RR Lyrae stars with abnormal temperatures.After analyzing the data from several photometric surveys,we find that some of these temperature anomalies are misclassified variable stars(e.g.,eclipsing binaries,pulsating stars on main sequence),and some are RR Lyrae binary candidates.For the latter,the temperatures of potential companions should be lower and their luminosities should not be neglected(e.g.,red giant stars).We obtain that the ratio of temperature anomaly stars to all the sample stars is 4%,which means that the impact on the further analysis(e.g.,kinematics analysis) is low.We also present the catalogs of spectral anomaly RR Lyrae stars.     

A catalogue of close binaries located in the δ Scuti region of the Cepheid instability strip

A catalogue of close eclipsing binary systems (detached and semidetached) with at least one of the components located in the δ Scuti region of the Cepheid instability strip is presented. The positions of the stars in the instability strip are determined by their accurate temperatures and luminosities. Observationally detected binaries (20 semidetached, four detached and one unclassified) with oscillating components were included in the catalogue as a separate table. The primaries of the oscillating Algols tend to be located near the blue edge of the instability strip. Using reliable luminosities and temperatures determined by recent photometric and spectroscopic studies, we have found that at least one or two components of 71 detached and 90 semidetached systems are located in the δ Scuti region of the Cepheid instability strip. In addition, 36 detached or semidetached systems discovered by the Hipparcos satellite were also given as a separate list. One of their components is seen in the δ Scuti region, according to their spectral type or   B − V   colours. They are potential candidate binaries with the δ Scuti-type pulsating components which need further photometric and spectroscopic studies in better precision. This catalogue covers information and literature references for 25 known and 197 candidate binaries with pulsating components.     

The Progenitors of sdB Binaries: Confronting Theory with Observations

We have re-examined the main binary evolution channels that produce sdB stars (by stable and unstable mass transfer, the merging of two helium white dwarfs). We find that all three main channels are of comparable importance, but produce slightly different mass distributions and dominate at different times. We show how the short-period sdB binaries can be used to constrain the efficiency of common-envelope ejection and discuss various observational tests that will allow further testing and constrain the binary evolution parameters that go into binary population synthesis simulations.     

Reconstructing the evolution of white dwarf binaries: further evidence for an alternative algorithm for the outcome of the common-envelope phase in close binaries

We determine the possible masses and radii of the progenitors of white dwarfs in binaries from fits to detailed stellar evolution models and use these to reconstruct the mass-transfer phase in which the white dwarf was formed. We confirm the earlier finding that in the first phase of mass transfer in the binary evolution leading to a close pair of white dwarfs, the standard common-envelope formalism (the α-formalism) equating the energy balance in the system (implicitly assuming angular momentum conservation) does not work. An algorithm equating the angular momentum balance (implicitly assuming energy conservation) can explain the observations. This conclusion is now based on 10 observed systems rather than three. With the latter algorithm (the γ-algorithm) the separation does not change much for approximately equal-mass binaries. Assuming constant efficiency in the standard α-formalism and a constant value of γ, we investigate the effect of both methods on the change in separation in general and conclude that when there is observational evidence for strong shrinkage of the orbit, the γ-algorithm also leads to this. We then extend our analysis to all close binaries with at least one white dwarf component and reconstruct the mass-transfer phases that lead to these binaries. In this way we find all possible values of the efficiency of the standard α-formalism and of γ that can explain the observed binaries for different progenitor and companion masses. We find that all observations can be explained with a single value of γ, making the γ-algorithm a useful tool to predict the outcome of common-envelope evolution. We discuss the consequences of our findings for different binary populations in the Galaxy, including massive binaries, for which the reconstruction method cannot be used.     

Very low mass stars in binaries: a theoretical look

We have undertaken a series of hydrodynamic + N ‐body simulations in order to explore the binary properties of young stars. We find that multiple stars are a natural outcome of collapsing turbulent flows, with a high incidence of N > 2 multiples, specially among the higher mass objects. We find a positive correlation of multiplicity with primary mass and a companion frequency that decreases with age, during the first few Myr after formation. Binary brown dwarfs are rarely formed, in conflict with observations. Brown dwarfs as companions are predominantly found orbiting binaries or triples at large separations. The paucity of ultra low mass and low mass ratio binaries has been investigated further, and we tentatively conclude that their formation is intricately related to an appropriate selection of initial conditions and an accurate modelling of disc accretion and evolution. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The University of New South Wales Extrasolar Planet Search: a catalogue of variable stars from fields observed between 2004 and 2007

We present a new catalogue of variable stars compiled from the data taken for the University of New South Wales Extrasolar Planet Search. From 2004 October to 2007 May, 25 target fields were each observed for one to four months, resulting in ∼87 000 high-precision light curves with 1600–4400 data points. We have extracted a total of 850 variable light curves, 659 of which do not have a counterpart in the General Catalogue of Variable Stars, the New Suspected Variables catalogue or the All Sky Automated Survey southern variable star catalogue. The catalogue is detailed here, and includes 142 Algol-type eclipsing binaries, 23 β Lyrae-type eclipsing binaries, 218 contact eclipsing binaries, 53 RR Lyrae stars, 26 Cepheid stars, 13 rotationally variable active stars, 153 uncategorized pulsating stars with periods <10 d, including δ Scuti stars, and 222 long period variables with variability on time-scales of >10 d. As a general application of variable stars discovered by extrasolar planet transit search projects, we discuss several astrophysical problems which could benefit from carefully selected samples of bright variables. These include (i) the quest for contact binaries with the smallest mass ratio, which could be used to test theories of binary mergers; (ii) detached eclipsing binaries with pre-main-sequence components, which are important test objects for calibrating stellar evolutionary models and (iii) RR Lyrae-type pulsating stars exhibiting the Blazhko effect, which is one of the last great mysteries of pulsating star research.