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1.
FRESIP (FRequency of Earth-Sized Inner Planets) is a mission designed to detect and characterize Earth-sizes planets around solar-like stars. The sizes of the planets are determined from the decrease in light from a star that occurs during planetary transits, while the orbital period is determined from the repeatability of the transits. Measurements of these parameters can be compared to theories that predict the spacing of planets, their distribution of size with orbital distance, and the variation of these quantities with stellar type and multiplicity. Because thousands of stars must be continually monitored to detect the transits, much information on the stars can be obtained on their rotation rates and activity cycles. Observations of p-mode oscillations also provide information on their age and composition. These goals are accomplished by continuously and simultaneously monitoring 500 solar-like stars for evidence of brightness changes caused by Earth-sized or larger planetary transits. To obtain the high precision needed to find planets as small as the Earth and Venus around solar-like stars, a wide field of view Schmidt telescope with an array of CCD detectors at its focal plane must be located outside of the Earth's at mosphere. SMM (Solar Maximum Mission) observations of the low-level variability of the Sun (1:100,000) on the time scales of a transit (4 to 16 hours), and our laboratory measurements of the photometric precision of charge-coupled devices (1:100,000) show that the detection of planets as small as the Earth is practical. The probability for detecting transits is quite favorable for planets in inner orbits. If other planetary systems are similar to our own, then approximately 1% of those systems will show transits resulting in the discovery of 50 planetary systems in or near the habitable zone of solar-like stars.  相似文献   

2.
C12 stars in the range 1.04–1.55M are evolved to simulate the core evolution of the possible precursors of planetary nebulae. The nuclear shell burning in stars above 1.2M advances to within about 0.2M of the surface, where the intense radiation interacts with the surface matter and causes mass loss. Comparison between our theoretical results and observations suggests that this may be a mechanism by which planetary nebulae are formed.Presented at the Trieste Colloquium on Mass Loss from Stars, September 12–16, 1968.  相似文献   

3.
The searches for extrasolar planetary systems by different methods based on the photometric monitoring of stars are reviewed. The search for extra-solar planets is, more or less consciously, the first step toward the search for other Minds in the Universe. A rational approach leads to the search for planets where structures with high complexity can emerge. In absence of any positive indication, it is safer to start this search by looking for planets within the habitable zone around main sequence stars where liquid water can be present. Of course, even if this future goal would fail, the detection of terrestrial planets would contribute to the characterization of other planetary systems and would constitute an interesting astrophysical goal by itself.  相似文献   

4.
A new radial velocity curve of V 1329 Cyg has been obtained from emission lines originating around an evolved star. The latter might be faced by an M-type mate, whose mass is larger than 23±6 solar masses. The system seems at |Z|>250 pc from the galactic plane. The 6830 unidentified band, found in V 1329 Cyg and among BQ [ ] stars, symbiotic stars and a few planetary nebulae, could be used as a diagnostic tool to identify very evolved stars. The close similarity of the optical spectrum of V 1329 Cyg to that of the optical counterpart of GX 1+4 is remarkable.On leave from Nagoya University, Japan.  相似文献   

5.
We report on our search for possible planetary system candidates in a volume-limited sample of 62 nearby A stars. Since the evolutionary lifetimes of A stars ( 109 yrs) roughly correspond to the era of planet formation and subsequent heavy bombardment in our solar system, our study could provide valuable insight into the origin of our own Solar System. From our ground-based visual and IUE high-resolution spectroscopy of all the northern nearby A stars, we have identified at least 12 stars with circumstellar gas. Combining these results with our previous IRAS survey we are probing the link between stars with circumstellar gas and those showing circumstellar dust disks. Our aim is not just to identify stars with gas, or stars with both gas and dust, but to identify systems with dynamic spectral activity similar to Pic, a well known proto-planetary system candidate. By measuring the gas dynamics in the disks of these Pic-like stars, we can begin to study the physics of accretion disks of young evolving systems.  相似文献   

6.
The HIPPARCOS program may contribute to dynamical astronomy in two different ways: by determining the positions of some bodies of the solar system or by improving the positions of the reference stars with respect to which observations of members of the solar system are made.It is shown that only minor planets may be observed validly by HIPPARCOS but these observations alone cannot contribute significantly to the determination of a reference frame. However, they can be useful for the improvement of orbits and as a complement to a major observational effort in preparation of a new determination of dynamical system of reference.HIPPARCOS will provide a new global reference frame and improved proper motions of stars. This may be used to rediscuss earlier observations and provide corrections to the theory of motion of the Moon and planets. Such corrections may be rather large and their possible effect is indicated for several cases. Furthermore, the celestial reference system of HIPPARCOS will allow to avoid, in future observations, many of the presently existing biases.Proceedings of the Conference on Analytical Methods and Ephemerides: Theory and Observations of the Moon and Planets. Facultés universitaires Notre Dame de la Paix, Namur, Belgium, 28–31 July, 1980.  相似文献   

7.
We have measured apparent fluctuations in stellar radial velocities with the ELODIE fiber-fed crossed-dispersion spectrograph and the 193-cm telescope of Observatoire de Haute-Provence. Within one given night, the fluctuations consist of two terms which may be sorted out. The first comes from imperfect scrambling of the stellar beam; the second arises from photon noise and agrees closely with our published calculations. So far, scrambler noise dominates for bright stars, but a perfect scrambler could be built by combining adatative optics and a single-mode fiber. The photon-noise results confirm that extrasolar planetary searching by the radial-velocity technique may be implemented with relatively small telescopes for a large number of stars. Consequences for the detection of astrophysical noise are discussed.  相似文献   

8.
Edison is a proposed large-aperture, radiatively-cooled space observatory planned to operate at wavelengths between 2 and 130m or longer. Current estimates for the telescope allow an aperture of 1.7 m which will achieve a final equilibrium temperature of about 30 K, although use of cryocoolers may permit temperatures below 20 K.Edison will be a powerful tool to investigate our Solar System, as well as planetary material around distant stars. At near- and mid-infrared wavelengths, where planetary material emits most of its radiation,Edison will be the most sensitive photometric and spectroscopic observatory under current consideration by the space agencies. With its large aperture,Edison will be able both to resolve the structure in nearby circumstellar Vega disks and to discriminate faint IR emission in the crowded environment of the galactic plane. With its long lifetime,Edison will allow extensive follow-up observations and increase the likelihood of catching transient events. We proposeEdison as a precursor to elements of a future space-based IR interferometer.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.  相似文献   

9.
We present the first results of a spectroscopy survey of iras sources with colours similar to those of planetary nebulae.Two new planetary nebulae, some H emission line stars, one peculiar source which is probably a pre-Main-Sequence object and a new Seyfert I galaxy have been found.Based on observations collected at the European Southern Observatory, La Silla, Chile.  相似文献   

10.
We investigate the geometry concerning the photometric method of extrasolar planet detection, i.e., the detection of dimunition of a parent star's brightness during a planetary transit. Under the assumption that planetary orbital inclinations can be defined by a Gaussian with a of 10° centered on the parent star's equatorial plane, Monte Carlo simulations suggest that for a given star observed at an inclination of exactly 90°, the probability of at least one Earth-sized or larger planet being suitably placed for transits is approximately 4%. This probability drops to 3% for a star observed at an inclination of 80°, and is still 0.5% for a star observed at an inclination of 60°. If one can select 100 stars with a pre-determined inclination 80°, the probability of at least one planet being suitably configured for transits is 95%. The majority of transit events are due to planets in small-a orbits similar to the Earth and Venus; thus, the photometric method in principle is the method best suited for the detection of Earthlike planets.The photometric method also allows for testing whether or not planets can exist within binary systems. This can be done by selecting binary systems observed at high orbital inclinations, both eclipsing binaries and wider visual binaries. For a real-world example, we look at the Centauri system (i = 79°.2). If we assume that the equatorial planes of both components coincide with the system's orbital plane, Monte Carlo simulations suggest that the probability of at least one planet (of either component) being suitably configured for transits is approximately 8%.In conclusion, we present a non-exhaustive list of solar-type stars, both single and within binary systems, which exhibit a high equatorial inclination. These objects may be considered as preliminary candidates for planetary searches via the photometric method.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.  相似文献   

11.
With the available data in planets, stars and galaxies, it is studied the functions of angular momentaJ(M) and amounts of actionA c(M) (associated to the non rotational terms in the kinetic energy). The results indicate that independently of how are these functionsJ(M),A c(M) their ratioA c/J remains a near invariant. It is independent also from the type of angular momenta: intrinsic spins of the bodies or the total angular (orbital) momenta of the bodies forming a system; for instance, the Solar System and the planets.The relationA c(M) for the Solar System are analogous to these in the FGK stars of the main sequence, and the relationJ(M) (also for the Solar System) is analogous to the lower possible limit for binary stars.The different types of binary stars from the short period, detached systems to contactary systems, gives a range of functionsJ(M),A c(M) that are the same that one can expect in stars with planetary systems. According to the detection limits given for planetary companions by Campbell, Walker and Yang (1988) (masses of less than 9 Jupiter masses and orbital periods of less than 50 years) we calculate the limits forJ(M) andA c(M) This gives a lower limitA c/J 1 associated to stars with planetary systems as 61 Cygni and to short period detached binaries. The upper limitA c/J 16 correspond to planetary systems as the ours and probably to cataclysmic binaries. There are reasons to suspect that systems as the ours and in range 4 A c/J 16 (with a lower limit analogous to contactary binaries as Algols and W Ursa Majoris) must be the most common type of planetary systems. The analogies with the functionsJ(M)A c(M) for galaxies suggest cosmogonical conditions in the stellar formation.Independently of this, one can have boundary conditions for the Jacobi problem when applied to a collapsing cloud. Namely, from the initial stage (a molecular cloud) to the final stage (a formed stellar system: binary or planetary) the angular momenta and amounts of action decayed to 10~4 the initial values, but in such a form thatA c(t)/J(t) remains a near invariant.  相似文献   

12.
In the present poster we suggest that some of the structures observed in the envelopes of planetary nebulae are caused by the interaction of central star wind and radiation with preplanetary nebula debris: planets, moons, minor objects and ring and ring arcs.Recently considerable amount of planetary material has been reported to exist around solar type stars, this debris could be evaporated during the envelope ejection and alter the chemical abundance and produce some of the envelope inhomogeneities.If there are massive enough rings of material surrounding the progenitor and planets in their vicinity, arc rings could be formed. If the rings are viewed pole on when the envelope is detached from the central star, it will interact with the arc ring material and produce ansae and pedal and garden-hose-shape structures observed in some planetaries.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.  相似文献   

13.
Numerical simulations are made within the framework of the plane restricted three-body problem, in order to find out if stable orbits for planets around one of the two components in double stars can exist. For any given set of initial parameters (the mass ratio of the two stars and the eccentricity of their orbit around each other), the phase-space of initial positions and velocities is systematically explored.In previous works, systematic exploration of the circular model as well as studies of more realistic (elliptic) cases such as Sun-Jupiter and the nearby Centauri and Sirius systems, large stable planetary orbits were found to exist around both components of the binary, up to distances from each star of the order or more than half the binary's periastron separation.The first results presented here for the Coronae Borealis system confirm the previous studies.  相似文献   

14.
The evolution of nuclei of planetary nebulae has been calculated from the end of the ejection stage that produces the nebulae to the white, dwarf stage. The structure of the central star is in agreement with the general picture of Finzi (1973) about the mass ejection from the progenitors of planetary nebulae. It has been found that in order to obtain evolutionary track consistent with the Harman-Seaton track (O'Dell, 1968) one has to assume that the masses of the nuclei stars are less than 0.7M . The calculated evolutionary time scale of the central stars of planetary nebulae is 2×104 yr. This time scale is negatively correlated with the stellar mass: the heavier the stellar mass, the shorter the evolutionary time scale.  相似文献   

15.
Many nearby main sequence stars are surrounded by cool dust radiating strongly in the far-IR. The characteristics of some of the prototype systems will be discussed. The dust is understood to represent debris related to planet formation, and the known disk systems may be dense analogs of the Kuiper Belt structure in our outer solar system. ISO observing programs plan to address questions regarding how common planetary material is around normal stars and how its amount and location depend on system age. These questions are central to an understanding of the place of the "Vega/β Pic" disks in stellar evolution. Preliminary results from the first year of ISO operation will be reported. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

16.
According to the work of Truran and Cameron, and of others, on the chemical evolution of the Galaxy, the first generation of stars in the Galaxy contained principally massive objects. If big-bang nucleosynthesis was responsible for the formation of helium, the first generation of stars would contain about 80% hydrogen and 20% helium, to be consistent with the approximately 22% helium found in recent stellar evolutionary studies of the Sun. The present investigation has followed the pre-main sequence evolution and the main sequence evolution of stars of 5, 10, 20, 30, 100, and 200M . Normal stars in this entire mass range normally convert hydrogen into helium by the CN-cycle on the main sequence. the present hydrogen-helium stars of 5 and 10M must reach higher central temperatures in order to convert hydrogen to helium by the proton-proton chains. Consequently, the mean densities in the stars are greater, and the surface temperatures are higher than in normal stars. In the stars of 20M and larger, the proton-proton chains do not succed in supplying the necessary luminosity of the stars by the time the contraction has produced a central temperature near 108K. At that point triple-alpha reactions generate small amounts of C12, which then acts as a catalyst in the CN-cycle, the rate of which is then limited by the beta-decays occurring within the cycle. During the evolution of these more massive stars, the central temperature remains in the vicinity of 108 K, and the surface temperature on the main sequence approaches 105 K. The star of 200M becomes unstable against surface mass loss through radiation pressure in the later stages of its main sequence evolution, and these mass loss effects were not followed. Young galaxies containing these massive stars will have a very high luminosity, but if they have formed at one-tenth the present age of the universe or later, then the light from them will mainly reside in the visible or ultraviolet, rather than in the infrared as has been suggested by Partridge and Peebles.  相似文献   

17.
Summary In the solar neighborhood, approximately half of all intermediate mass main sequence stars with initially between 1 and about 5 Mbecome carbon stars with luminosities near 104 L for typically less than 106 years. These high luminosity carbon stars lose mass at rates nearly always in excess of 10–7 M yr–1 and sometimes in excess of 10–5 M yr–1. Locally, close to half of the mass returned into the interstellar medium by intermediate mass stars before they become white dwarfs is during the carbon star phase. A much greater fraction of lower metallicity stars become carbon-rich before they evolve into planetary nebulae than do higher metallicity stars; therefore, carbon stars are much more importan t in the outer than in the inner Galaxy.  相似文献   

18.
When stars are being formed in a region of a molecular cloud, the presence of the gas of this cloud will influence the dynamics of these newly formed stars. We discuss an implementation of SPH or Smooth Particle Hydrodynamics within the framework ofN-body2, which will permit the study of this kind of mixed systems. It is our intention to include various gas removal processes, and to study their influence on the behaviour of stars and gas.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献   

19.
Optical identification of infrared sources from the IRAS Point Source Catalogue (PSC) is made by means of low-dispersion spectra of the First Byurakan Survey (FBS) and Palomar Observatory Sky Survey (POSS) red and blue images. The purpose of this work is to examine the composition of the PSC sample of fainter sources at high galactic latitudes and to reveal QSOs, infrared galaxies, red stars (C and M), planetary nebulae, for their further investigation at the optical range. 100 of 108 unknown IRAS sources in the region with 3h50m 7h40m and + 69° + 73° are optically identified. Optical coordinates, V magnitudes, color indices, and preliminary classes are determined. According to preliminary classification 3 objects turned out to be QSOs, 36 are galaxies with very interesting morphology, 5 are faint planetary nebulae, 9 are carbon stars, and 47 are late M-type stars.Published in Astrofizika, Vol. 38, No. 4, pp. 625–629, October–December, 1995.  相似文献   

20.
We develop a new thermodynamic approach to the problem of the last stages of star formation, when a collapsing fragment evolves adiabatically into its final state: single protostar, surrounded or not by protoplanetary disc, or binary system. In this context, we point out the crucial role of the angular momentum transfer: a very efficient mechanism tends to form double stars with small mass secondaries, while a total decoupling yields twin binaries. Intermediate assumptions allow the birth of both kinds of binary systems, as well as the formation of not very massive protoplanetary discs. Discs of larger mass, which would be required to produce protoplanetary systems as a consequence of dynamical instabilities, do not form under any circumstances. A representation of the outcomes as functions of the corresponding initial conditions on the usual – plane gives well definite regions for single stars, protoplanetary discs, unbalanced systems and twin binaries. On this ground, a preliminary estimate of the percentage of stars surrounded by planetary systems is possible. A particular numerical simulation confirms the bimodality of the mass ratio distribution as well as the main features of the – plane partition. A few suggestions about non-adiabatic effects are also given. Our thermodynamic approach, supported by the numerical one and by the analysis of the observational statistics, allow to define a first unitary sketch for the formation of binary systems and protoplanetary discs.  相似文献   

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