How many cosmological parameters?     

Andrew R. Liddle 《Monthly notices of the Royal Astronomical Society》2004,351(3):L49-L53

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Stellar contents of two young open clusters: NGC 663 and 654     

A. K. Pandey  K. Upadhyay  K. Ogura  Ram Sagar  V. Mohan  H. Mito  H. C. Bhatt  B. C. Bhatt 《Monthly notices of the Royal Astronomical Society》2005,358(4):1290-1308

UBVRI CCD photometry in a wide field around two young open clusters, NGC 663 and 654, has been carried out. Hα and polarimetric observations for the cluster NGC 654 have also been obtained. We use the photometric data to construct colour–colour and colour–magnitude diagrams, from which we can investigate the reddening, age, mass and evolutionary states of the stellar contents of the these clusters. The reddening across the cluster regions is found to be variable. There is evidence for anomalous reddening law in both clusters; however, more infrared and polarimetric data are needed to conclude about the reddening law. Both clusters are situated at about a distance of 2.4 kpc. Star formation in both clusters is found to be a continuous process. In the case of NGC 663, star formation seems to have taken place sequentially, in the sense that formation of low-mass stars precedes the formation of most massive stars. Whereas, in the case of NGC 654, formation of low-mass stars did not cease after the formation of most massive stars in the cluster.  相似文献   

The photometric properties of isolated early-type galaxies     

Fatma M. Reda  Duncan A. Forbes  Michael A. Beasley  Ewan J. O'Sullivan  Paul Goudfrooij 《Monthly notices of the Royal Astronomical Society》2004,354(3):851-869

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The non-radially pulsating primary of the cataclysmic variable GW Librae     

L. van Zyl  B. Warner  D. O'Donoghue  C. Hellier  P. Woudt  D. Sullivan  J. Pritchard  J. Kemp  J. Patterson  W. Welsh  J. Casares  T. Shahbaz  F. van der Hooft  S. Vennes 《Monthly notices of the Royal Astronomical Society》2004,350(1):307-316

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Mass and density of Asteroid 121 Hermione from an analysis of its companion orbit     

F. Marchis  D. Hestroffer  J. Berthier  I. de Pater 《Icarus》2005,178(2):450-464

We report on Adaptive Optics observations of the satellite of Asteroid 121 Hermione with the ESO-Paranal UT4 VLT and the Keck AO telescopes. The binary system, belonging to the Cybele family, was observed during two observing campaigns in January 2003 and January 2004 aiming to confirm its trajectory and accurately determine its orbital elements. A precessing Keplerian model was used to describe the motion of S/2002 (121) 1. We find that the satellite of Hermione revolves at a=768±11 km from the primary in P=2.582±0.002 days with a roughly circular and prograde orbit (e=0.001±0.001, i=3±2° w.r.t. equator primary). These extensive astrometric measurements enable us to determine the mass of Hermione to be 0.54±0.03×¹⁰¹⁹ kg and its pole solution (λ₀=1.5°±2.00, β₀=10°±2.0 in ecliptic J2000). Additional Keck AO observations taken close to the asteroid opposition in December 2003 give us direct insight into the structure of the primary which presents a bilobated shape. Since the angular resolution is limited to the theoretical angular resolution of the telescope (43 mas corresponding to a spatial resolution of 80 km), two shape models (called snowman and peanut) are proposed based on the images which were deconvolved with MISTRAL deconvolution process. Assuming a purely synchronous orbit and knowing the mass of the primary, the peanut shape composed of two separated components is quite unlikely. Additionally the J₂ calculated from the analysis of the secondary orbit is not in agreement with the peanut model, but close to the snowman shape. The bulk density of the primary as derived from the observed size of the snowman shape is estimated to ρ∼1.8±0.2 g/cm³ implying a porosity ∼14% for this C-type asteroid, corresponding to a fractured asteroid. Considering the IRAS diameter, the density is lower (ρ=1.1±0.3 g/cm³) leading to a high porosity (p=30-60%) with a nominal value of p=48%, which indicates a completely loose rubble-pile structure for the primary. Further work is necessary to better constrain the size, shape, and then internal structure of Hermione's primary.  相似文献   

Laboratory production of δ and θ alumina grains and their characteristic infrared spectra     

Mami Kurumada  Chiyoe Koike  Chihiro Kaito 《Monthly notices of the Royal Astronomical Society》2005,359(2):643-647

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Search for spatial variation in the jovian N/N ratio from Cassini/CIRS observations     

Thierry Fouchet  Patrick G.J. Irwin  Simon B. Calcutt  Conor A. Nixon 《Icarus》2004,172(1):50-58

We have used the spectra obtained by the Composite Infrared Spectrometer (CIRS) onboard the Cassini spacecraft to search for latitudinal variation in the ¹⁵N/¹⁴N ratio on Jupiter. We found no variations statistically significant given the observational and model uncertainties. The absence of latitudinal variations demonstrates that ¹⁵NH₃ is not fractionated in Jupiter's atmosphere, and that the measured ¹⁵N/¹⁴N represents Jupiter's global value. Our mean value for the global jovian ¹⁵N/¹⁴N ratio of (2.22±0.52)×10⁻³ agrees with previous measurements made by Fouchet et al. (2000, Icarus 143, 223-243) and Owen et al. (2001, Astrophys. J. 553, L77-L79). We argue that the jovian isotopic ¹⁵N/¹⁴N ratio must represent the solar nitrogen isotopic composition. The solar ¹⁵N/¹⁴N ratio hence significantly differs from the terrestrial value: (¹⁵N/¹⁴N)_⊕=3.68×10⁻³. This supports the proposition that terrestrial nitrogen originates from a nitrogen reservoir isolated from the main nitrogen reservoir in the proto-solar nebula. The origin and carrier of this isolated reservoir are still unknown.  相似文献   

Surface-bounded atmosphere of Europa     

V.I. Shematovich  R.E. Johnson  M.C. Wong 《Icarus》2005,173(2):480-498

A 1-D collisional Monte Carlo model of Europa's atmosphere is described in which the sublimation and sputtering sources of H₂O molecules and their molecular fragments are accounted for as well as the radiolytically produced O₂. Dissociation and ionization of H₂O and O₂ by magnetospheric electron, solar UV-photon and photo-electron impact, and collisional ejection from the atmosphere by the low-energy plasma are taken into account. Reactions with the surface are discussed, but only adsorption and atomic oxygen recombination are included in this model. The size of the surface-bounded oxygen atmosphere of Europa is primarily determined by a balance between atmospheric sources from irradiation of the satellite's icy surface by the high-energy magnetospheric charged particles and atmospheric losses from collisional ejection by the low-energy plasma, photo- and electron-impact dissociation, and ionization and pick-up from the surface-bounded atmosphere. A range of sources rates for O₂ to H₂O are used with a larger oxygen-to-water ratio than suggested by laboratory measurements in order to account for differences in adsorption onto grains in the regolith. These calculations show that the atmospheric composition is determined by both the water and oxygen photochemistry in the near-surface region, escape of suprathermal oxygen and water into the jovian system, and the exchange of radiolytic water products with the porous regolith. For the electron impact ionization rates used, pick-up ionization is the dominant oxygen loss process, whereas photo-dissociation and atmospheric sputtering are the dominant sources of neutral oxygen for Europa's neutral torus. Including desorption and loss of water enhances the supply of oxygen species to the neutral torus, but hydrogen produced by radiolysis is the dominant source of neutrals for Europa's torus in these models.  相似文献   

The young open cluster Markarian 50     

Gustavo Baume  Rubén A. Vázquez  Giovanni Carraro 《Monthly notices of the Royal Astronomical Society》2004,355(2):475-484

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The dependence of the substellar initial mass function on the initial conditions for star formation     

E. J. Delgado-Donate  C. J. Clarke  M. R. Bate 《Monthly notices of the Royal Astronomical Society》2004,347(3):759-770

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