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1.
This article is devoted to the Pulkovo astronomer, Prof. Aleksandr Nikolaevich Deich (Deutsch) (1899-1986), on the 110-th anniversary of his birth. Deich is known as the founder of the Pulkovo program for observing stars with invisible companions, as well as for his research on the star 61 Cyg, which was suspected, in his time, of having invisible companions with the masses of planets. Astrometric observations on the long focus astrograph and searches for exoplanets of nearby stars are reviewed. Modern methods of searching for exoplanets are summarized briefly. Instrument designs proposed by astronomers at Kharkiv (Scientific Research Institute of Astronomy at Kharkiv National University, NIIA KhNU) and Kazan (Institute of Astronomy, Kazan State University, AO KGU) for use in the search for low-mass dark components of stars are discussed. Examples are given of confirmations of invisible companions of stars which were first discovered by observation. A number of theoretical results on this topic from Kharkiv National University (Scientific Research Institute of Astronomy at Kharkiv and the Dept. of Astronomy) are noted.  相似文献   

2.
Stars in the Pulkovo Observatory program are observed with a 65-cm refractor during many years to study their positions and movements. We present examples of two visual binary stars, for which orbits and masses of components were determined, and two astrometric stars, for which masses of their unseen companions were estimated. The first two stars are ADS 14636(61 Cygni) and ADS 7251,and the others are Gliese 623 and ADS 8035(Alpha UMa). Direct astrometric methods are used for estimation of mass-ratio and masses.  相似文献   

3.
With more and more exoplanets being detected, it is paid closer attention to whether there are lives outside solar system. We try to obtain habitable zones and the probability distribution of terrestrial planets in habitable zones around host stars. Using Eggleton’s code, we calculate the evolution of stars with masses less than 4.00 M ⊙. We also use the fitting formulae of stellar luminosity and radius, the boundary flux of habitable zones, the distribution of semimajor axis and mass of planets and the initial mass function of stars. We obtain the luminosity and radius of stars with masses from 0.08 to 4.00 M ⊙, and calculate the habitable zones of host stars, affected by stellar effective temperature. We achieve the probability distribution of terrestrial planets in habitable zones around host stars. We also calculate that the number of terrestrial planets in habitable zones of host stars is 45.5 billion, and the number of terrestrial planets in habitable zones around K type stars is the most, in the Milky Way.  相似文献   

4.
Some results of the photographic observations of double stars with 65 cm refractor of Pulkovo observatory are presented. We use the apparent motion parameters (AMP) method which allows to determine the orbits and to carry out the dynamical investigation of wide binaries on the basis of a short arc of their orbital motion. We have determined more than 40 orbits for wide pairs and also the sum of masses and in some cases—the mass-ratio of components. The references to our works and the basic results of observations are contained in Kisselev et al. [2004. Catalogue of relative positions of visual double stars made on the observations with 26″ refractor of Pulkovo observatory. Strassbourg, I/297]. We apply two ways of revealing the hidden mass of our stars, namely: revealing of possible perturbations from comparison of observational and calculated positions using differences O-C (for instance, perturbations in the orbital motion of ADS 15571) and also by means of comparison of the sum of the masses obtained by us and the sum of the masses obtained by means of the mass-luminosity relation. An excess of masses of about 1-3 solar masses is detected for binaries: ADS 497, ADS 8450 and ADS 10329 by means of last method.The estimations of the masses for some binaries are discussed. Also we justify the necessity of precise parallaxes and relative radial velocities of stars, which could be measured by space telescopes such as the GAIA as the additional parameters for determination of orbits of binaries.  相似文献   

5.
Adrián Brunini 《Icarus》2005,177(1):264-268
The sample of known exoplanets is strongly biased to masses larger than the ones of the giant gaseous planets of the Solar System. Recently, the discovery of two extrasolar planets of considerably lower masses around the nearby Stars GJ 436 and ρ Cancri was reported. They are like our outermost icy giants, Uranus and Neptune, but in contrast, these new planets are orbiting at only some hundredth of the Earth-Sun distance from their host stars, raising several new questions about their origin and constitution. Here we report numerical simulations of planetary accretion that show, for the first time through N-body integrations that the formation of compact systems of Neptune-like planets close to the hosts stars could be a common by-product of planetary formation. We found a regime of planetary accretion, in which orbital migration accumulates protoplanets in a narrow region around the inner edge of the nebula, where they collide each other giving rise to Neptune-like planets. Our results suggest that, if a protoplanetary solar environment is common in the Galaxy, the discovery of a vast population of this sort of ‘hot cores’ should be expected in the near future.  相似文献   

6.
Planets which are old and close to their parent stars are considered as reflecting planets because their intrinsic temperature is extremely low but they are heated strongly by the impinging stellar radiation and hence radiation of such planets are the reflected star light that is governed by the stellar radiation, orbital distance and albedo of the planet. These planets cannot be resolved from the host stars. The second kind of exoplanets are those which are very young and hence they have high intrinsic temperature. They are far away from their star and so they can be resolved by blocking the star-light. It is now realized that radiation of such planets are linearly polarized due to atmospheric scattering and polarization can determine various physical properties including the mass of such directly detected self-luminous exoplanets. It is suggested that a spectropolarimeter of even low spectral resolution and with a capacity to record linear polarization of 0.5–1% at the thirty-meter telescope would immensely help in understanding the atmosphere, especially the cloud chemistry of the self-luminous and resolvable exoplanets.  相似文献   

7.
The development of principles, systems, and instruments enable the detection of exoplanets with 6–8 Earth masses or less. The launches of specialized satellites, such as CoRoT (2006) and Kepler (2009), into orbits around the Earth have enabled the discovery of new exoplanetary systems. These missions are searching for relatively low-mass planets by observing their transits over the disks of their parent stars. At the same time, supporting studies of exoplanets using ground-based facilities (that measure Keplerian components of radial velocities) are in progress. The properties of at least two objects discovered by different methods, Kepler-22 and GJ 1214b, suggested that there was another class of celestial bodies among the known types of extrasolar planets: planetans, or oceanic planets. The structure of Kepler-22 and GJ 1214b suggest that they can be these oceanic planets. In this paper, we consider to what extent this statement is valid. The consideration of exoplanet Gl 581g as an oceanic planet is more feasible. Some specific features of the physical nature of these unusual planets are presented.  相似文献   

8.
One of the goals of the Pulkovo program of research on stars with large proper motions is to reveal among the low-luminosity stars those that have evidence of binarity. Twelve astrometric binary candidates from the Pulkovo list have been included in the program of speckle observations with the BTA telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) and the 2.5-m telescope at the Caucasus Observatory (CO) of the Sternberg Astronomical Institute of the Moscow State University to confirm their binarity and then to determine the parameters of the revealed stellar pairs. The binarity of the brightest of these stars, J1158+4239 (GJ 3697), has been confirmed. Four sessions of speckle observations with the BTA SAO RAS telescope and one session with the 2.5-m CO telescope have been carried out in 2015–2016. The weighted mean estimates of the pair parameters are ρ = 286.5 ± 1.2 mas and θ = 230.24? ± 0.16? at the epoch B2015.88248. The magnitude difference between the pair stars is Δm = 0.55 ± 0.03 (a filter with a central wavelength of 800 nm and a FWHM of 100 nm) and Δm = 0.9 ± 0.1 (an R filter).  相似文献   

9.
The transit of exoplanets across a stellar disk will often occur in GAIA observations. A safe detection of the slight dimming of the star can be made many hundred times, i.e. in cases where the star is sufficiently constant in intensity, and the photometry is very precise. When combined with the simultaneous GAIA astrometry or ground-based radial velocities the scientific harvest is orbit, mass and mass density for hundreds of exoplanets. We have typically considered Jupiter-size planets at Earth-like distances from the stars. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

10.
日冕是太阳大气活动的关键区域,是日地空间天气的源头.受观测限制,对日冕低层大气等离子体结构和磁场状态的研究非常欠缺,国际上对于可见光波段日冕低层大气的亮度分层研究很少.利用丽江日冕仪YOGIS(Yunnan Green-line Imaging System)的日冕绿线(FeⅩⅣ5303?)观测资料,对内日冕区域(1.03R☉-1.25R☉,R☉表示太阳半径)亮结构及其中冕环进行了有效的强度衰减分析.对亮结构的强度在太阳径向高度上进行了指数衰减拟合,比较这些拟合结果发现所得到的静态内冕环的衰减指数在一固定值附近.然后将比较明显的冕环提取出来,通过对不同高度的绿线强度进行指数拟合,得出的衰减指数与亮结构中也比较相近,这对进一步研究日冕中的各项物理参数演化提供了参考.  相似文献   

11.
The search for habitable exoplanets centers on planets with Earth-like conditions around late type stars. Radial velocity searches for these planets require precisions of 1 m/s and better. That is now being achieved. At these precisions stellar surface motions might lead to false detections. Of particular interest are variable meridional flows on stellar surfaces. I review the available observations of solar surface meridional flows using both Doppler shift and local helioseismology techniques. Interpretation in terms of Doppler shifts in integrated starlight leads to estimates of the likelihood of false detections. It is unlikely that these false detections occur in the habitability zones of exoplanets. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

12.
The detection and investigation of EUV heated, extended and non-hydrostatic upper atmospheres around terrestrial exoplanets would provide important insights into the interaction of the host stars plasma environment as well as the evolution of Earth-type planets their atmospheres and possible magnetic environments. We discuss different scenarios where one can expect that Earth-like planets should experience non-hydrostatic upper atmosphere conditions so that dynamically outward flowing neutral atoms can interact with the stellar plasma flow so that huge hydrogen coronae and energetic neutral atoms (ENA) can be produced via charge exchange. By observing the size of the extended upper atmospheres and related ENA-clouds and by determining the velocities of the surrounding hydrogen atoms, conclusions can be drawn in respect to the origin of these features. Due to the large number of M-type stars in our neighbourhood and their long periods of strong and moderate stellar activity in comparison to G-stars, we expect that M-type stars represent the most promising candidates for the detection of hydrogen ENA-clouds and the subsequent study of the interaction between the host star and the planets?? upper atmosphere. We show that the low mass of M-type stars also makes them preferable targets to observe extended hydrogen clouds around terrestrial exoplanets with a mass as low as one Earth mass. Transit follow-up observations in the UV-range of terrestrial exoplanets around M-type stars with space observatories such as the World Space Observatory-UV (WSO-UV) would provide a unique opportunity to shed more light on the early evolution of Earth-like planets, including those of our own Solar System.  相似文献   

13.
The space telescope Search for Terrestrial Exo-Planets (STEP) employed a method of sub-pixel technology which ensures that the astrometric accuracy of the telescope on the focal plane is at the order of 1 μas. This kind of astrometric precision is promising to detect the earth-like planets beyond the solar system. In this paper, we analyze the influence of some key factors, including the errors in the stellar proper motion, parallax, the optical center of the system, and the velocity and position of the satellite, on the detection of exoplanets. We propose a relative angular distance method to evaluate the non-linear terms in the variation of star-pair's angular distance caused by the possibly existing exoplanet. This method could avoid the direct influence of measuring errors of the position and proper motion of the reference stars. Supposing that there are eight reference stars and a target star with a planet system in the same field of view, we simulate their five-year observational data, and use the least square method to get the parameters of the planet orbit. Our results show that the method is robust to detect terrestrial planets based on the 1 μas precision of STEP.  相似文献   

14.
The proposed baseline GAIA mission will be able to detect the astrometric signature of Jupiter-size planets around of the order of a million stars, using either global or narrow-angle astrometry. If the mission can realize the higher astrometric accuracy that photon statistics allows for bright stars, lower-mass planets (from Earth size to ten times larger) can be found around ten to a few hundred stars.  相似文献   

15.
SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems) is a five-year M-class mission proposed to ESA Cosmic Vision. Its purpose is to image and characterize long-period extrasolar planets and circumstellar disks in the visible (450?C900 nm) at a spectral resolution of about 40 using both spectroscopy and polarimetry. By 2020/2022, present and near-term instruments will have found several tens of planets that SPICES will be able to observe and study in detail. Equipped with a 1.5 m telescope, SPICES can preferentially access exoplanets located at several AUs (0.5?C10?AU) from nearby stars (<25 pc) with masses ranging from a few Jupiter masses to Super Earths (??2 Earth radii, ??10 M??) as well as circumstellar disks as faint as a few times the zodiacal light in the Solar System.  相似文献   

16.
We provide an overview of the main results obtained as part of the programs for astrometric observations of bodies in the Solar system at the Pulkovo Observatory over the period 1898–2005. We summarize the results of photographic observations and show new possibilities for astrometric observations in connection with the transition to CCD detectors on Pulkovo instruments. Observing and data reduction techniques are considered. A database with Pulkovo observations of bodies in the Solar system has been created and opened to users. The database is accessible at http://www.puldb.ru.  相似文献   

17.
The general approach to studying the dynamics of moons of planets and asteroids consists in developing more and more accurate models of motion based on observational data. Not only the necessary ephemerides, but also some physical parameters of planets and moons are obtained this way. It is demonstrated in the present study that progress in this field is driven not only by the increase in accuracy of observations. The accuracy of ephemerides may be increased by expanding the observation time interval. Several problems arise on the way toward this goal. Some of them become apparent only when the procedure of observational data processing and use is examined in detail. The method used to derive astrometric data by processing the results of photometric observations of mutual occultations and eclipses of planetary moons is explained below. The primary contribution to the error of astrometric results is produced by the unaccounted noise level in photometric readings and the inaccuracy of received values of the albedo of moons. It is demonstrated that the current methods do not allow one to eliminate the noise completely. Extensive additional photometric measurements should be performed at different angles of rotation of moons and in different spectral bands of the visible wavelength range in order to obtain correct values of the albedo of moons. Many new distant moons of the major planets have been discovered in the early 21st century. However, the observations of these moons are scarce and were performed over short time intervals; as a result, some of the moons were lost. The necessity of further observations of these Solar System bodies is pointed out in the present study. Insufficient knowledge of asteroid masses is an obstacle to improving the accuracy of the ephemerides of Mars. The basic method for determining the masses of large asteroids consists in analyzing their influence on the motion of Mars, the Earth, and spacecraft. The masses of more than 100 large asteroids were determined this way. One of the principal techniques for Earth-based measurement of the masses of asteroids involves astrometric observations of binary asteroids. The determination of relative coordinates is made rather difficult by the apparent proximity of components. The success of these efforts depends on the availability of instrumentation and the expertise of observers skilled in adaptive optics and speckle interferometry. Collaboration between different research teams and observers is absolutely necessary.  相似文献   

18.
We investigate the migration of massive extrasolar planets caused by gravitational interaction with a viscous protoplanetary disc. We show that a model in which planets form at 5 au at a constant rate, before migrating, leads to a predicted distribution of planets that is a steeply rising function of log( a ), where a is the orbital radius. Between 1 and 3 au, the expected number of planets per logarithmic interval in a roughly doubles. We demonstrate that, once selection effects are accounted for, this is consistent with current data, and then extrapolate the observed planet fraction to masses and radii that are inaccessible to current observations. In total, approximately 15 per cent of stars targeted by existing radial velocity searches are predicted to possess planets with masses  0.3< M p sin( i )<10 M J  and radii  0.1< a <5 au  . A third of these planets (around 5 per cent of the target stars) lie at the radii most amenable to detection via microlensing. A further  5–10  per cent of stars could have planets at radii of  5< a <8 au  that have migrated outwards. We discuss the probability of forming a system (akin to the Solar system) in which significant radial migration of the most massive planet does not occur. Approximately  10–15  per cent of systems with a surviving massive planet are estimated to fall into this class. Finally, we note that a smaller fraction of low-mass planets than high-mass planets is expected to survive without being consumed by the star. The initial mass function for planets is thus predicted to rise more steeply towards small masses than the observed mass function.  相似文献   

19.
超短周期(ultra-short-period,USP)行星是指轨道周期小于1 d的系外行星,是近年来系外行星研究领域中一个新的前沿目标。USP行星的搜寻与确认需要借助傅里叶变换(Fourier transform,FT)和盒最小二乘法(the box least,BLS)等光变曲线分析算法,以筛选和确认精准的周期信号。利用统计方法可得到目前USP行星的轨道周期、行星半径、宿主恒星类型等分布特征。大部分USP行星半径小于2R⊕,受行星质量限制,大多数USP行星无法通过视向速度信号测得精确的行星质量。根据已有的观测结果可算出,部分USP行星的质量小于10M⊕,由此推测这些USP的组成更接近金属与岩石混合的类地行星。由于密近轨道可能发生光致蒸发等物质损失过程,USP行星大气的存在情况尚不明确。目前,USP行星被认为起源于热木星(hot-Jupiters)或亚海王星(sub-Neptunes),但USP行星与热木星的主星金属丰度的分布存在较大差异,亚海王星的光致蒸发起源理论可能性更高。USP行星轨道演化机制包括低偏心率轨道迁移和潮汐耗散的原位起源模型等。  相似文献   

20.
About 20 years after the discovery of the first extrasolar planet, the number of planets known has grown by three orders of magnitude, and continues to increase at neck breaking pace. For most of these planets we have little information, except for the fact that they exist and possess an address in our Galaxy. For about one third of them, we know how much they weigh, their size and their orbital parameters. For less than 20, we start to have some clues about their atmospheric temperature and composition. How do we make progress from here?We are still far from the completion of a hypothetical Hertzsprung–Russell diagram for planets comparable to what we have for stars, and today we do not even know whether such classification will ever be possible or even meaningful for planetary objects. But one thing is clear: planetary parameters such as mass, radius and temperature alone do not explain the diversity revealed by current observations. The chemical composition of these planets is needed to trace back their formation history and evolution, as happened for the planets in our Solar System. As in situ measurements are and will remain off-limits for exoplanets, to study their chemical composition we will have to rely on remote sensing spectroscopic observations of their gaseous envelopes.In this paper, we critically review the key achievements accomplished in the study of exoplanet atmospheres in the past ten years. We discuss possible hurdles and the way to overcome those. Finally, we review the prospects for the future. The knowledge and the experience gained with the planets in our solar system will guide our journey among those faraway worlds.  相似文献   

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