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151.
Interstellar transfer of planetary microbiota 总被引:2,自引:0,他引:2
152.
153.
R. J. Barber J. Tennyson G. J. Harris R. N. Tolchenov 《Monthly notices of the Royal Astronomical Society》2006,368(3):1087-1094
A computed list of H2 16 O infrared transition frequencies and intensities is presented. The list, BT2, was produced using a discrete variable representation two-step approach for solving the rotation–vibration nuclear motions. It is the most complete water line list in existence, comprising over 500 million transitions (65 per cent more than any other list) and it is also the most accurate (over 90 per cent of all known experimental energy levels are within 0.3 cm−1 of the BT2 values). Its accuracy has been confirmed by extensive testing against astronomical and laboratory data.
The line list has been used to identify individual water lines in a variety of objects including comets, sunspots, a brown dwarf and the nova-like object V838 Mon. Comparison of the observed intensities with those generated by BT2 enables water abundances and temperatures to be derived for these objects. The line list can also be used to provide an opacity for models of the atmospheres of M dwarf stars and assign previously unknown water lines in laboratory spectra. 相似文献
The line list has been used to identify individual water lines in a variety of objects including comets, sunspots, a brown dwarf and the nova-like object V838 Mon. Comparison of the observed intensities with those generated by BT2 enables water abundances and temperatures to be derived for these objects. The line list can also be used to provide an opacity for models of the atmospheres of M dwarf stars and assign previously unknown water lines in laboratory spectra. 相似文献
154.
We tested four criteria used for discrimination between asteroidal and cometary type of orbits: Whipple criterion K, Kresak
criterion Pe, Tisserand invariant T and aphelion distance Q. To estimate their reliability, all criteria were applied to classify
the 2225 orbits of NEAs and 582 orbits of comets, for several epochs spanning the time interval of 40 thousands years. The
Q-criterion produced the smallest number of exceptions and has shown the best stability. The biggest number of exceptions
and the biggest variations are obtained for the K-criterion. We applied the Q-criterion to classify meteor orbits from the
IAU Meteor Data Center and the video meteor orbits available on the Web sites. Among the sporadic radar orbits, as well as
among the mean orbits of meteor streams a strong preponderance of asteroid-type orbits was observed. In case of the photographic
and video meteors a weak preponderance of cometary and asteroidal orbits was found, respectively. 相似文献
155.
Piotr Gronkowski 《Astrophysics and Space Science》2004,294(3-4):135-150
Interaction between the strong solar wind and the dark side of a cometary nucleus was considered. It was calculated that the
potential of the dark side of the cometary nucleus could be numerically large and negative. Assuming that the nucleus of the
comet has surface mantle which consists of loose, fine dust-ice particles, it was shown that cometary particles could electrostatically
levitate over the nucleus. It was examined how this phenomenon affected the changes in the cometary brightness. Calculations
were carried out for realistically assumed values of a large range of cometary parameters. It was shown that the considered
mechanism could lead to the variations of cometary brightness, sometimes even to the outbursts of brightness. 相似文献
156.
157.
S.V. Jeffers S.P. Manley M.E. Bailey D.J. Asher 《Monthly notices of the Royal Astronomical Society》2001,327(1):126-132
An Öpik-based geometric algorithm is used to compute impact probabilities and velocity distributions for various near-Earth object (NEO) populations. The resulting crater size distributions for the Earth and Moon are calculated by combining these distributions with assumed NEO size distributions and a selection of crater scaling laws. This crater probability distribution indicates that the largest craters on both the Earth and the Moon are dominated by comets. However, from a calculation of the fractional probabilities of iridium deposition, and the velocity distributions at impact of each NEO population, the only realistic possibilities for the Chicxulub impactor are a short-period comet (possibly inactive) or a near-Earth asteroid. For these classes of object, sufficiently large impacts have mean intervals of 100 and 300 Myr respectively, slightly favouring the cometary hypothesis. 相似文献
158.
Several organic molecules have now been detected in the coma of Hale–Bopp. These species may either emanate from the nucleus, or, as has been suggested by Bockelée–Morvan et al., could be synthesized in the coma. We have modelled the gas phase chemistry which occurred in the coma of Hale–Bopp, concentrating on the observed organic molecules HCOOH, HCOOCH3 , HC3 N and CH3 CN. We find that gas phase chemical reactions are unable to synthesize the observed abundances of these molecules, so all these species are most probably present in the nuclear ice. We briefly discuss the implications of this result for the connection between cometary and interstellar ices. 相似文献
159.
160.
S.J. Collander-Brown A. Fitzsimmons E. Fletcher M.J. Irwin I.P. Williams 《Monthly notices of the Royal Astronomical Society》2001,325(3):972-978
On 1998 December 12 a new trans-Neptunian object, 1998 XY95, was discovered as part of a deep search. Recent observations of this object have placed it amongst the class of objects known as the scattered trans-Neptunian objects (TNOs). A total of 39 CCD images of 1998 XY95 were taken over two nights, and these were used to search for a light curve, but no significant periodicity was found. An examination of the possible orbital evolution gives no indication of how it may have arrived on its present orbit. The current best-fitting orbit is unstable, but remains within a band of semi-major axis approximately 2 au wide. The bottom of this band is due to 3:1 mean motion resonance with Neptune, while the reason for the top of the band remains unclear. 相似文献