Photometry of pluto in the last decade and before: evidence for volatile transport?     

B.J. Buratti  J.K. Hillier  A. Heinze  K.A. Tryka  J. Ward  J. Young 《Icarus》2003,162(1):171-182

Photometric observations of Pluto in the BVR filter system were obtained in 1999 and in 1990-1993, and observations in the 0.89-μm methane absorption band were obtained in 2000. Our 1999 observations yield lightcurve amplitudes of 0.30 ± 0.01, 0.26 ± 0.01, and 0.21 ± 0.02 and geometric albedos of 0.44 ± 0.04, 0.52 ± 0.03, and 0.58 ± 0.02 in the B, V, and R filters, respectively. The low-albedo hemisphere of Pluto is slightly redder than the higher albedo hemisphere. A comparison of our results and those from previous epochs shows that the lightcurve of Pluto changes substantially through time. We developed a model that fully accounts for changes in the lightcurve caused by changes in the viewing geometry between the Earth, Pluto, and the Sun. We find that the observed changes in the amplitude of Pluto’s lightcurve can be explained by viewing geometry rather than by volatile transport. We also discovered a measurable decrease since 1992 of ∼0.03 magnitudes in the amplitude of Pluto’s lightcurve, as the model predicts. Pluto’s geometric albedo does not appear to be currently increasing, as our model predicts, although given the uncertainties in both the model and the measurements of geometric albedo, this result is not firm evidence for volatile transport. The maximum of methane-absorption lightcurve occurs near the minimum of the BVR lightcurves. This result suggests that methane is more abundant in the brightest regions of Pluto. Pluto’s phase coefficient exhibits a color dependence, ranging from 0.037 ± 0.01 in the B filter to 0.032 ± 0.01 in the R filter. Pluto’s phase curve is most like those of the bright, recently resurfaced satellites Triton and Europa. Although Pluto shows no strong evidence for volatile transport now (unlike Triton), it is important to continue to observe Pluto as it moves away from perihelion.  相似文献   

The shape of the rotation curves of edge-on galaxies     

A. V. Zasov  A. V. Khoperskov 《Astronomy Letters》2003,29(7):437-446

We consider the effects of projection, internal absorption, and gas-or stellar-velocity dispersion on the measured rotation curves of galaxies with edge-on disks. Axisymmetric disk models clearly show that the rotational velocity in the inner galaxy is highly underestimated. As a result, an extended portion that imitates nearly rigid rotation appears. At galactocentric distances where the absorption is low (i.e., it does not exceed 0.3–0.5^m kpc^?1), the line profiles can have two peaks, and a rotation curve with minimum distortions can be obtained by estimating the position of the peak that corresponds to a higher rotational velocity. However, the high-velocity peak disappears in high-absorption regions and the actual shape of the rotation curve cannot be reproduced from line-of-sight velocity estimates. In general, the optical rotation curves for edge-on galaxies are of little use in reconstructing the mass distribution in the inner regions, particularly for galaxies with a steep velocity gradient in the central region. In this case, estimating the rotation velocities for outer (transparent) disk regions yields correct results.  相似文献   

The Orion nebula (M42) Herbig–Haro object, HH 201, within the tip of a molecular finger     

M. F. Graham  J. Meaburn  M. P. Redman 《Monthly notices of the Royal Astronomical Society》2003,343(2):419-426

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The young cluster in the CB34 globule: the clumps and the outflows     

C. Codella  F. Scappini 《Monthly notices of the Royal Astronomical Society》2003,344(4):1257-1263

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Dynamical implications of Jupiter's tropospheric ammonia abundance     

Adam P. Showman  Imke de Pater 《Icarus》2005,174(1):192-204

Groundbased radio observations indicate that Jupiter's ammonia is globally depleted from 0.6 bars to at least 4-6 bars relative to the deep abundance of ∼3 times solar, a fact that has so far defied explanation. The observations also indicate that (i) the depletion is greater in belts than zones, and (ii) the greatest depletion occurs within Jupiter's local 5-μm hot spots, which have recently been detected at radio wavelengths. Here, we first show that both the global depletion and its belt-zone variation can be explained by a simple model for the interaction of moist convection with Jupiter's cloud-layer circulation. If the global depletion is dynamical in origin, then important endmember models for the belt-zone circulation can be ruled out. Next, we show that the radio observations of Jupiter's 5-μm hot spots imply that the equatorial wave inferred to cause hot spots induces vertical parcel oscillation of a factor of ∼2 in pressure near the 2-bar level, which places important constraints on hot-spot dynamics. Finally, using spatially resolved radio maps, we demonstrate that low-latitude features exceeding ∼4000 km diameter, such as the equatorial plumes and large vortices, are also depleted in ammonia from 0.6 bars to at least 2 bars relative to the deep abundance of 3 times solar. If any low-latitude features exist that contain 3-times-solar ammonia up to the 0.6-bar ammonia condensation level, they must have diameters less than ∼4000 km.  相似文献   

DEVELOPMENT STRATEGIES OF WATER AND LAND RESOURCES IN THE HEXI REGION,CHINA     

肖洪浪  高前兆  李福兴 《中国地理科学(英文版)》1996,(1)

ＤＥＶＥＬＯＰＭＥＮＴＳＴＲＡＴＥＧＩＥＳＯＦＷＡＴＥＲＡＮＤＬＡＮＤＲＥＳＯＵＲＣＥＳＩＮＴＨＥＨＥＸＩＲＥＧＩＯＮ，ＣＨＩＮＡ肖洪浪，高前兆，李福兴ＤＥＶＥＬＯＰＭＥＮＴＳＴＲＡＴＥＧＩＥＳＯＦＷＡＴＥＲＡＮＤＬＡＮＤＲＥＳＯＵＲＣＥＳＩＮＴＨＥ...  相似文献   

Dwarf nova oscillations and quasi-periodic oscillations in cataclysmic variables – IV. Observations of frequency doubling and tripling in VW Hyi     

Brian Warner  Patrick A. Woudt 《Monthly notices of the Royal Astronomical Society》2006,367(4):1562-1576

We present new observations of the rapid oscillations in the dwarf nova VW Hyi, made late in outburst. These dwarf nova oscillations (DNOs) increase in period until they reach 33 s, when a transition to a strong 1st harmonic and weak fundamental takes place. After further period increase, the 2nd harmonic appears; often all three components are present simultaneously. This 1:2:3 frequency suite is similar to what has been seen in some neutron star and black hole X-ray binaries, but has not previously been seen in a cataclysmic variable. When studied in detail, the fundamental and 2nd harmonic vary similarly in phase, but the 1st harmonic behaves independently, though keeping close to twice the frequency of the fundamental. The fundamental period of the DNOs, as directly observed or inferred from the harmonics, increases to ∼100 s before the oscillation disappears as the star reaches quiescence. Its maximum period is close to that of the 'longer-period' DNOs observed in VW Hyi. The quasi-periodic oscillations (QPOs), which have fundamental periods 400–1000 s, behave in the same way, showing 1st and 2nd harmonics at approximately the same times as the DNOs. We explore some possible models. One in which the existence of the 1st harmonic is due to the transition from viewing a single accretion region to viewing two regions, and the rate of accretion on to the primary is modulated at the frequency of the 1st harmonic, as in the 'beat frequency model', can generate the suite of DNO frequencies observed. But the behaviour of the QPOs is not yet understood.  相似文献   

The tidal stripping of satellites     

J. I. Read  M. I. Wilkinson  N. W. Evans  G. Gilmore  Jan T. Kleyna 《Monthly notices of the Royal Astronomical Society》2006,366(2):429-437

We present an improved analytic calculation for the tidal radius of satellites and test our results against N -body simulations.
The tidal radius in general depends upon four factors: the potential of the host galaxy, the potential of the satellite, the orbit of the satellite and the orbit of the star within the satellite . We demonstrate that this last point is critical and suggest using three tidal radii to cover the range of orbits of stars within the satellite. In this way we show explicitly that prograde star orbits will be more easily stripped than radial orbits; while radial orbits are more easily stripped than retrograde ones. This result has previously been established by several authors numerically, but can now be understood analytically. For point mass, power-law (which includes the isothermal sphere), and a restricted class of split power-law potentials our solution is fully analytic. For more general potentials, we provide an equation which may be rapidly solved numerically.
Over short times (≲1–2 Gyr ∼1 satellite orbit), we find excellent agreement between our analytic and numerical models. Over longer times, star orbits within the satellite are transformed by the tidal field of the host galaxy. In a Hubble time, this causes a convergence of the three limiting tidal radii towards the prograde stripping radius. Beyond the prograde stripping radius, the velocity dispersion will be tangentially anisotropic.  相似文献   

Management of the UK mackerel fisheries: An economic perspective     

David J. Whitmarsh  James A. Young 《Marine Policy》1985,9(3):220-236

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The kinematics of the large western knot in the halo of the young planetary nebula NGC 6543     

Deborah L. Mitchell  M. Bryce  J. Meaburn  J. A. López  M. P. Redman  D. Harman  M. G. Richer  H. Riesgo 《Monthly notices of the Royal Astronomical Society》2005,362(4):1286-1294

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