Simulating colour variations in pulsating sdB stars     

B. Ramachandran  C.S. Jeffery 《Astrophysics and Space Science》2004,289(3-4):441-444

After briefly recalling basic facts about the metallicity gradients inspiral galaxies, we summarize two recent N-body gas-dynamical modelsthat implement a non-instantaneous gas recycling and point our their potential for an improved treatment of the chemical evolution ingalactic disks.  相似文献   

On the transmission-dominated to reprocessing-dominated spectral state transitions in Seyfert 2 galaxies   总被引：1，自引：0，他引：1  

M. Guainazzi  A. C. Fabian  K. Iwasawa  G. Matt  F. Fiore 《Monthly notices of the Royal Astronomical Society》2005,356(1):295-308

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Optical properties of solid and liquid sulfur at visible and infrared wavelengths     

R. Sasson  R. Wright  E.T. Arakawa  B.N. Khare  Carl Sagan 《Icarus》1985,64(3):368-374

Knowledge of the optical constants of elemental sulfur has potential applications to Venus, Jupiter, Io, Amalthea, and the Earth. The real part, n, of the index of refraction of liquid sulfur (at 133°C) and of solid orthorhombic sulfur (at 25°C) for the wavelength range 0.4–2.0 μm were measured ellipsometrically. The imaginary part, k, of the refractive index of liquid sulfur was obtained by transmittance measurements at the same temperature and wavelength range. The reflectance of semi-infinite slabs of solid and liquid sulfur is calculated using the measured n and k values. We confirm that sulfur melts on Io would be classified as “black” by the Voyager imaging system.  相似文献   

Eclipsing binaries in extrasolar planet transit surveys: the case of SuperWASP     

B. Willems  U. Kolb  S. Justham 《Monthly notices of the Royal Astronomical Society》2006,367(3):1103-1112

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Progress in coronal physics     

Jack B. Zirker 《Solar physics》1985,100(1-2):281-287

This paper reviews research highlights of the past five years. Considerable progress has been made in observing and interpreting coronal mass ejections. The stability of coronal loops is much better understood and new observations of the onset of wind streams in coronal holes have been made. Observations from the Solar Maximum Mission should helpt to clarify the physics of the active corona.The mechanisms that heat the corona and accelerate the high-speed wind streams remain to be identified, however.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.  相似文献   

Infrared spectrophotometry of Comet IRAS-Araki-Alcock (1983d): a bare nucleus revealed?     

M.S. Hanner  D.K. Aitken  R. Knacke  S. McCorkle  P.F. Roche  A.T. Tokunaga 《Icarus》1985,62(1):97-109

Spectra of the central core and surrounding coma of Comet IRAS-Araki-Alcock (1983d) were obtained at 8–13 μm on 11 May and 2–4 μm on 12 May 1983. Spatially resolved measurements at 10 μm with a 4-arcsec beam showed that the central core was more than 100 times brighter than the inner coma only 8 arcsec away; for radially outflowing dust, the brightness ratio would be a factor of 8. The observations of the central core are consistent with direct detection of a nucleus having a radius of approximately 5 km. The temperature of the sunlit hemisphere was > 300 K. Spectra of the core are featureless, while spectra of the coma suggest weak silicate emission. The spectra show no evidence for icy grains. The dust producton rate on 11.4 May was ～ 10⁵ g/sec, assuming that the gas flux from the dust-producing areas on the nucleus was ～ 10^?5 g/cm²/sec.  相似文献   

Relative and absolute ages of individual craters and the rate of infalls on the moon in the post-imbrium period     

Ralph B. Baldwin 《Icarus》1985,61(1):63-91

This paper contains a reasonably successful attempt to determine relative ages and then absolute ages of individual craters younger than Imbrium, and the rate of infalls onto the Moon as a function of time. After the tail of the massive premare bombardment became depleted before 3 aeons (1 aeon = 10⁹ years) ago, there was a period of minimal numbers of infalls. The rate of infalls increased rather steadily from this minimum to the present. The rate in the geologically recent past (0.3 aeon) was about two times that found for the period immediately after the last of the major lave outpourings (3.2 aeons). Absolute ages were determined for large craters (?8 km) from crater counts on the surfaces within and on the rims of the large craters. Key dates were 0 and 0.3 aeon for terrestrial meteoritic craters, 3.2, 3.5, 3.8, and 3.82 aeons for the various mare surfaces according to the determinations of D.E. Wilhelms (1980, Geologic history of the Moon, U.S. Geol. Surv. Prof. Pap.) and 3.85 aeons from the formation of Imbrium.  相似文献   

The Second International Hydrographic Technical Conference: Plymouth, 3–7 September 1984     

P.B. Beazley 《Marine Policy》1985,9(1):78-79

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Contrasting the chemical evolution of the Milky Way and Andromeda     

Agostino Renda  Daisuke Kawata  Yeshe Fenner  Brad K. Gibson 《Monthly notices of the Royal Astronomical Society》2005,356(3):1071-1078

The chemical evolution history of a galaxy hides clues about how it formed and has been changing through time. We have studied the chemical evolution history of the Milky Way (MW) and Andromeda (M31) to find which are common features in the chemical evolution of disc galaxies as well as which are galaxy-dependent. We use a semi-analytic multizone chemical evolution model. Such models have succeeded in explaining the mean trends of the observed chemical properties in these two Local Group spiral galaxies with similar mass and morphology. Our results suggest that while the evolution of the MW and M31 shares general similarities, differences in the formation history are required to explain the observations in detail. In particular, we found that the observed higher metallicity in the M31 halo can be explained by either (i) a higher halo star formation efficiency (SFE), or (ii) a larger reservoir of infalling halo gas with a longer halo formation phase. These two different pictures would lead to (i) a higher [O/Fe] at low metallicities, or (ii) younger stellar populations in the M31 halo, respectively. Both pictures result in a more massive stellar halo in M31, which suggests a possible correlation between the halo metallicity and its stellar mass.  相似文献   

The Martian hydrologic cycle: Effects of CO₂ mass flux on global water distribution     

Philip B. James 《Icarus》1985,64(2):249-264

The Martian CO₂ cycle, which includes the seasonal condensation and subsequent sublimation of up to 30% of the planet's atmosphere, produces meridional winds due to the consequent mass flux of CO₂. These winds currently display strong seasonal and hemispheric asymmetries due to the large asymmetries in the distribution of insolation on Mars. It is proposed that asymmetric meridional advection of water vapor on the planet due to these CO₂ condensation winds is capable of explaining the observed dessication of Mars' south polar region at the current time. A simple model for water vapor transport is used to verify this hypothesis and to speculate on the effects of changes in orbital parameters on the seasonal water cycle.  相似文献