On the universal outcome of star formation: is there a link between stars and brown dwarfs?     

Pavel Kroupa †  Jerome Bouvier  Gaspard Duchêne  Estelle Moraux 《Monthly notices of the Royal Astronomical Society》2003,346(2):354-368

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Identification of a 12–17 d time-scale in X-ray observations of GRS 1915+105     

J. Greenhough  S. C. Chapman  S. Chaty  †  R. O. Dendy  G. Rowlands 《Monthly notices of the Royal Astronomical Society》2003,340(3):851-855

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The possiblity of detection of ultracool dwarfs with the UKIRT Infrared Deep Sky Survey     

N. R. Deacon  N. C. Hambly 《Monthly notices of the Royal Astronomical Society》2006,371(4):1722-1730

We present predictions for the numbers of ultracool dwarfs in the Galactic disc population that could be detected by the WFCAM/UKIDSS Large Area Survey and Ultra Deep Survey. Simulated samples of objects are created with masses and ages drawn from different mass functions and birthrates. Each object is then given absolute magnitudes in different passbands based on empirically derived bolometric correction versus effective temperature relationships (or model predictions for Y dwarfs). These are then combined with simulated space positions, velocities and photometric errors to yield observables such as apparent magnitudes and proper motions. Such observables are then passed through the survey selection mechanism to yield histograms in colour. This technique also produces predictions for the proper motion histograms for ultracool dwarfs and estimated numbers for the as yet undetected Y dwarfs. Finally, it is shown that these techniques could be used to constrain the ultra-low-mass mass function and birthrate of the Galactic disc population.  相似文献   

Probing the evolution of the near-infrared luminosity function of galaxies to z≃ 3 in the Hubble Deep Field-South     

P. Saracco  A. Fiano  G. Chincarini  E. Vanzella  M. Longhetti  S. Cristiani  A. Fontana  E. Giallongo  M. Nonino 《Monthly notices of the Royal Astronomical Society》2006,367(1):349-365

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Origin of the metallicity distribution of the NGC 5128 stellar halo     

K. Bekki  William E. Harris  Gretchen L. H. Harris 《Monthly notices of the Royal Astronomical Society》2003,338(3):587-598

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Infrared stellar populations in the central parts of the Milky Way galaxy     

Jacco Th. van Loon  G. F. Gilmore  A. Omont  J. A. D. L. Blommaert  I. S. Glass  M. Messineo  F. Schuller  M. Schultheis  I. Yamamura  H. S. Zhao 《Monthly notices of the Royal Astronomical Society》2003,338(4):857-879

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On the dynamics of magnetorotational turbulent stresses     

G. I. Ogilvie 《Monthly notices of the Royal Astronomical Society》2003,340(3):969-982

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Latitudinal transport by barotropic waves in Titan's stratosphere.: II. Results from a coupled dynamics-microphysics-photochemistry GCM     

D. Luz  F. Hourdin  S. Lebonnois 《Icarus》2003,166(2):343-358

We present a 2D general circulation model of Titan's atmosphere, coupling axisymmetric dynamics with haze microphysics, a simplified photochemistry and eddy mixing. We develop a parameterization of latitudinal eddy mixing by barotropic waves based on a shallow-water, longitude-latitude model. The parameterization acts locally and in real time both on passive tracers and momentum. The mixing coefficient varies exponentially with a measure of the barotropic instability of the mean zonal flow. The coupled GCM approximately reproduces the Voyager temperature measurements and the latitudinal contrasts in the distributions of HCN and C₂H₂, as well as the main features of the zonal wind retrieved from the 1989 stellar occultation. Wind velocities are consistent with the observed reversal time of the North-South albedo asymmetry of 5 terrestrial years. Model results support the hypothesis of a non-uniform distribution of infrared opacity as the cause of the Voyager temperature asymmetry. Transport by the mean meridional circulation, combined with polar vortex isolation may be at the origin of the latitudinal contrasts of trace species, with eddy mixing remaining restricted to low latitudes most of the Titan year. We interpret the contrasts as a signature of non-axisymmetric motions.  相似文献   

Studying Hydrodynamic Instability Using Shock-Tube Experiments     

O. Sadot  K. Levy  A. Yosef-Hai  D. Cartoon  Y. Elbaz  Y. Srebro  G. Ben-Dor  D. Shvarts 《Astrophysics and Space Science》2005,298(1-2):305-312

The hydrodynamic instability, which develops on the contact surface between two fluids, has great importance in astrophysical phenomena such as the inhomogeneous density distribution following a supernova event. In this event acceleration waves pass across a material interface and initiate and enhance unstable conditions in which small perturbations grow dramatically. In the present study, an experimental technique aimed at investigating the above-mentioned hydrodynamic instability is presented. The experimental investigation is based on a shock-tube apparatus by which a shock wave is generated and initiates the instability that develops on the contact surface between two gases. The flexibility of the system enables one to vary the initial shape of the contact surface, the shock-wave Mach number, and the density ratio across the contact surface. Three selected sets of shock-tube experiments are presented in order to demonstrate the system capabilities: (1) large-initial amplitudes with low-Mach-number incident shock waves; (2) small-initial amplitudes with moderate-Mach-number incident shock waves; and (3) shock bubble interaction. In the large-amplitude experiments a reduction of the initial velocity with respect to the linear growth prediction was measured. The results were compared to those predicted by a vorticity-deposition model and to previous experiments with moderate- and high-Mach number incident shock waves that were conducted by others. In this case, a reduction of the initial velocity was noted. However, at late times the growth rate had a 1/t behavior as in the small-amplitude low-Mach number case. In the small-amplitude moderate-Mach number shock experiments a reduction from the impulsive theory was noted at the late stages. The passage of a shock wave through a spherical bubble results in the formation of a vortex ring. Simple dimensional analysis shows that the circulation depends linearly on the speed of sound of the surrounding material and on the initial bubble radius.  相似文献   

Models for the magnitude‐distribution of brightest cluster galaxies     

J. P. Bernstein †  Suketu P. Bhavsar ‡ 《Monthly notices of the Royal Astronomical Society》2001,322(3):625-630

The brightest, or first-ranked, galaxies (BCGs) in rich clusters show a very small dispersion in luminosity, making them excellent standard candles. This small dispersion raises questions about the nature of BCGs. Are they simply the extremes of normal galaxies formed via a stochastic process, or do they belong to a special class of atypical objects? If they do, are all BCGs special, or do normal galaxies compete for the first rank? To answer these questions, we undertake a statistical study of BCG magnitudes using results from extreme value theory. Two-population models do better than one-population models. A simple scenario where a random boost in the magnitude of a fraction of bright normal galaxies forms a class of atypical galaxies best describes the observed distribution of BCG magnitudes.  相似文献