The partial volatilization of Mercury     

A.G.W. Cameron 《Icarus》1985,64(2):285-294

During recent years my research on the primitive solar nebular has followed two main themes: (1) Very early in the development of the nebula conditions probably favored the occurence of major gaseous instabilities leading to the formation of giant gaseous protoplanets, but the rapid rise of the external temperature soon evaporated the envelopes of these protoplanets, possibly leaving behind precipitated solids which formed the cores and mantles of the terrestrial planets. (2) Models of the nebula indicate a later stage when conditions in the inner Solar System became very hot; at the position of Mercury the temperature was probably in the range 2500–3500°K. This leads to the hypothesis that the original protomercury was a body substantially more massive than the present planet and of normal composition, but that when it was immersed in the high-temperature field of the dissipating solar nebula, most of the rocky mantle was vaporized and mixed into the solar nebula gases and carried away by them. This hypothesis is investigated in the present paper. For simplicity the vaporization of a mantle composed of enstatite, MgSiO₃, was computed for a planet with 2.25 the mass of Mercury at a temperature of 3000°K. It is argued that the mantle could probably be largely removed in the available time of 3 × 10⁴ years. Subsequent accretion would restore some magnesium silicates to the mantle of the planet.  相似文献   

Multisite observations of surface structures on AB Doradus in 1994 November     

A. Collier Cameron  F. M. Walter  O. Vilhu  T. Böhm  C. Catala  S. Char  F. J. Clarke  P. Felenbok  B. H. Foing  K. K. Ghosh  J. Hao  L. Huang  D. A. Jackson  E. Janot-Pacheco  S. Jiang  A.-M. Lagrange  N. Suntzeff  D. S. Zhai 《Monthly notices of the Royal Astronomical Society》1999,308(2):493-509

We present time-resolved optical spectroscopy and broad-band photometry of the rapidly rotating southern K0 dwarf star AB Doradus, obtained during 1994 November. The data were obtained as part of a collaboration dedicated to MUlti-SIte COntinuous Spectroscopy (MUSICOS), and entailed coordinated observations on three continents to obtain the fullest phase coverage possible subject to limitations of local weather conditions. The Doppler images from the three consecutive nights of the run show excellent mutual agreement, with a dark polar cap and numerous intermediate- and low-latitude features. Simultaneous optical photometry showed numerous short-duration U -band flares, and two longer duration optical flares with durations of the order of hours. The latter produced broad-band continuum enhancements throughout the optical spectrum. Where simultaneous spectroscopy was available, both types of flare were seen to have counterparts in H and the Ca  ii H line. Simultaneous time-resolved ultraviolet spectroscopy from the Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope , reported elsewhere, shows that at least one of the short-duration U -band flares was also observed in C  iv with the GHRS. Time-series H spectra showed significant evolution of the circumstellar prominence system over five consecutive stellar rotations. One prominence underwent a dramatic increase in distance from the stellar rotation axis. We speculate that this event may have been associated with one of the long-duration flares.  相似文献   

Magnetic topology and prominence patterns on AB Doradus     

J.-F. Donati  A. Collier Cameron  G. A. J. Hussain  M. Semel 《Monthly notices of the Royal Astronomical Society》1999,302(3):437-456

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Optical and ultraviolet observations of a strong flare in the young, single K2 dwarf LQ Hya     

D. Montes  S. H. Saar  A. Collier Cameron  Y. C. Unruh 《Monthly notices of the Royal Astronomical Society》1999,305(1):45-60

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The potential magnetic field of AB Doradus: comparison with Zeeman--Doppler images     

Moira Jardine  John R. Barnes  Jean-Francois Donati  Andrew Collier Cameron 《Monthly notices of the Royal Astronomical Society》1999,305(1):L35-L39

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Tomographic studies of exoplanet atmospheres     

A. Collier Cameron  Ch. Leigh 《Astronomische Nachrichten》2004,325(3):252-255

We review the current state of models for the optical and near‐infrared reflection spectra of exoplanetary atmospheres, with particular reference to the close‐orbiting giant planets that offer the best prospects for high‐resolution spectroscopic detection.We describe the main steps in the tomographic procedures that have been used in recent attempts to separate these faint signals from the direct spectra of the parent stars.We compare recent, deep upper limits on planetary albedos with model predictions, and discuss prospects for future attempts to detect and characterise the reflection, transmission and thermal emission spectra of these planets at optical and infrared wavelengths. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Applying Zeeman Doppler imaging to solar spectra     

G. A. J. Hussain  S. H. Saar  A. Collier Cameron 《Astronomische Nachrichten》2004,325(3):245-245

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Dissipation of thick accretion disks     

A. G. W. Cameron 《Astrophysics and Space Science》1983,93(2):295-303

A thick accretion disk which is isentropic cannot have simple laminar flow because fluid elements follow orbits which intersect the orbits of other fluid elements, leading to turbulence in astrophysical disks which have very large Reynolds numbers. The turbulence in such disks is estimated using molecular analogies for the behavior of the fluid elements. The usual empirical dissipation parameter ‘α’ is found to be equal to 0.25 under normal circumstances. Characteristic local disk parameters are calculated for a variety of conditions at different distances from a central star of one solar mass. Circumstances involving low midplane optical depths or external heating which can lead to large reductions in the turbulence are discussed.  相似文献   

Editorial     

A. G. W. Cameron  Z. Kopal  M. D. Moutsoulas 《Earth, Moon, and Planets》1983,28(1):v-v

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1980s' oceans policy — resources and technology: ‘The decade of the oceans’, 16th annual conference of the Marine Technology Society,Washington, DC,USA, 6–8 October 1980     

Hugh Cameron  Glyn Ford 《Marine Policy》1981,5(2):159-161

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