Results 1 - 10 of 3144
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[en] The results of the observations in the environments of the five cometary nebulae: MacC H12, MacC sH15, GM 1-14, RNO 33, Pars 17, are presented. This search was performed in the frames of the continuing survey of the new HH-objects in the star formation regions. Nine previously unknown HH-objects were found. Nearly all these objects belong to directed outflows, the sources of which are with high probability the central stars of the listed above nebulae. In the cases of MacC H12 and GM 1-14 the outflows have distinct bipolar structure. The position of the sources on J-H/H-K diagram is discussed
[en] The aggregation, fragmentation and thermal processing of dust in protoplanetary disks is believed to be the first step on the long road from dust to planets. Models of this process in the literature have so far been applied mostly to the early solar system, and were mostly limited to a static 'minimum mass solar nebula' model of the protoplanetary disk. We present the initial results of a campaign to extend such a modeling to evolving protoplanetary disks, to improve the realism and detail of coagulation/fragmentation models compared to models in the literature so far and to link these models to observations
[en] The expansion velocity-radius (R-V) relation for planetary nebulae is examined using the existing measurements of expansion velocities and recent calculations of radii. It is found that some of the previously alleged R-V relations for PN are not convincingly established. The scatter in the R-V plots may be due largely to stratification of ions in individual nebulae and to heterogeneity in the planetary nebula population. In addition, from new echelle/CCD observations of planetary nebulae, it is found that spatial information is essential in deriving the internal kinematic properties. Future investigations of R-V relations should be pursued separately for groups of planetaries with similar physical properties, and they should employ observations of appropriate low excitation lines in order to measure the expansion velocity at the surface of the nebula. 26 references
[en] Within the framework of the nebular theory of the origin of the solar system, conservation laws are applied to the condensation of a ring-shaped cloud of orbiting particles. The final configuration is assumed to be a point-like planet in a circular orbit around the Sun. On this ground, it is possible to relate the masses of the planets with the interplanetary distances. This relation is confirmed satisfactorily by the observed masses and orbital radii of several planets and satellites of the solar system. (Auth.)
[en] The paper presents new B- and/or V-magnitudes for the nuclei of 51 planetary nebulae, as well as limits for 10 others, from absolute photometry with the University of Illinois 1 m telescope, and a superior method of extracting stellar continuum fluxes from a bright nebular background. The errors and the limitations of the method are carefully examined. The results are compared with the widely circulated list of preliminary central-star magnitudes determined by Shao and Liller, which are shown to suffer frequently from severe contamination from the nebular continuum, and a calibration is provided for older photographic magnitudes. Finally, the nebular contribution to the continuum in the context of the evolution of central stars on the log L-log T plane is examined, and the implications for future observations of hot and/or young planetary nuclei are discussed. 35 references
[en] Chondrules are important early Solar System materials that can provide a wealth of information on conditions in the solar nebula, if their formation mechanism can be understood. The theory most consistent with observational constraints, especially thermal histories, is the so-called shock model, in which chondrules were melted in solar nebula shocks. However, several problems have been identified with previous shock models. These problems all pertained to the treatment of the radiation field, namely, the input boundary condition to the radiation field, the proper treatment of the opacity of solids, and the proper treatment of molecular line cooling. In this paper, we present the results of our updated shock model, which corrects for the problems listed above. Our new hydrodynamic shock code includes a complete treatment of molecular line cooling due to H2O. Previously, shock models including line cooling predicted chondrule cooling rates exceeding 105 K hr-1. Contrary to these expectations, we have found that the effect of line cooling is minimal; after the inclusion of line cooling, the cooling rates of chondrules are 10-1000 K hr-1. The reduction in the otherwise rapid cooling rates attributable to line cooling is due to a combination of factors, including buffering due to hydrogen recombination/dissociation, high column densities of water, and backwarming. Our model demonstrates that the shock model for chondrule formation remains consistent with observational constraints.
[en] Stellar perturbations affect planet formation in binary systems. Recent studies show that the planet-formation stage of mutual accretion of km-sized planetesimals is most sensitive to binary effects. In this paper, the condition for planetesimal accretion is investigated around α CenB, which is believed to be an ideal candidate for detection of an Earth-like planet in or near its habitable zone (0.5-0.9 AU). A simplified scaling method is developed to estimate the accretion timescale of the planetesimals embedded in a protoplanetary disk. Twenty-four cases with different binary inclinations (iB = 0, 0.01, 1.00, and 100), gas densities (0.3, 1, and 3 times of the Minimum Mass of Solar Nebula, MMSN hereafter), and with and without gas depletion, are simulated. We find that (1) re-phasing of planetesimals orbits is independent of gas depletion in α CenB, and it is significantly reached at 1-2 AU, leading to accretion-favorable conditions after the first ∼ 105 yr; (2) the planetesimal collision timescale at 1-2 AU is estimated as: TBcol ∼ (1 + 100iB ) x 103 yr, where 00 < iB < 100; (3) disks with gas densities of 0.3-1.0 MMSN and inclinations of 10-100 with respect to the binary orbit are found to be the favorable conditions in which planetesimals are likely to survive and grow up to planetary embryos; and (4) even for the accretion-favorable conditions, accretion is significantly less efficient as compared to the single-star case, and the time taken by accretion of km-sized planetesimals into planetary embryos or cores would be at least several times of TBcol, which is probably longer than the timescale of gas depletion in such a close binary system. In other words, our results suggest that formation of Earth-like planets through accretion of km-sized planetesimals is possible in α CenB, while formation of gaseous giant planets is not favorable.