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31.
Martin Beech 《Astrophysics and Space Science》1985,117(1):69-81
The aim of this review is to discuss the properties of the known ellipsoidal variables. 相似文献
32.
Martin Beech 《Astrophysics and Space Science》1987,132(2):393-396
In general, the Lane-Emden equation for an arbitrary polytropic indexn does not admit of an analytic solution. Simple approximation to the numerical results can, however, be found; and, in particular,
affords a hitherto unreported good approximation to then=3 model. This term is accurate to within 10% of the tabulated values over 78% of the polytropic interior. 相似文献
33.
34.
Ceplecha Z Brown P Hawkes RL Wetherill G Beech M Mossman K 《Earth, Moon, and Planets》1996,72(1-3):395-404
Large Near-Earth-Asteroids have played a role in modifying the character of the surface geology of the Earth over long time scales through impacts. Recent modeling of the disruption of large meteoroids during atmospheric flight has emphasized the dramatic effects that smaller objects may also have on the Earth's surface. However, comparison of these models with observations has not been possible until now. Peekskill is only the fourth meteorite to have been recovered for which detailed and precise data exist on the meteoroid atmospheric trajectory and orbit. Consequently, there are few constraints on the position of meteorites in the solar system before impact on Earth. In this paper, the preliminary analysis based on 4 from all 15 video recordings of the fireball of October 9, 1992 which resulted in the fall of a 12.4 kg ordinary chondrite (H6 monomict breccia) in Peekskill, New York, will be given. Preliminary computations revealed that the Peekskill fireball was an Earth-grazing event, the third such case with precise data available. The body with an initial mass of the order of 10(4) kg was in a pre-collision orbit with a = 1.5 AU, an aphelion of slightly over 2 AU and an inclination of 5 degrees. The no-atmosphere geocentric trajectory would have lead to a perigee of 22 km above the Earth's surface, but the body never reached this point due to tremendous fragmentation and other forms of ablation. The dark flight of the recovered meteorite started from a height of 30 km, when the velocity dropped below 3 km/s, and the body continued 50 km more without ablation, until it hit a parked car in Peekskill, New York with a velocity of about 80 m/s. Our observations are the first video records of a bright fireball and the first motion pictures of a fireball with an associated meteorite fall. 相似文献
35.
The possibility of observing Venusian fireballs from Earth is examined. We estimate the steady-state flux of large, fireball-producing meteoroids at the orbit of Venus, and find that the prospects for observing such events from Earth with small, amateur-sized telescopes are not unreasonable. 相似文献
36.
Measurements of the bulk density, grain density, porosity, and magnetic susceptibility of 19 Gao-Guenie H5 chondrite meteorite samples are presented. We find average values of bulk density 〈ρbulk〉=3.46±0.07 g/cm3, grain density 〈ρgrain〉=3.53±0.08 g/cm3, porosity 〈P(%)〉=2.46±1.39, and bulk mass magnetic susceptibility 〈log χ〉=5.23±0.11. Measurements of the specific heat capacity for a 3.01-g Gao-Guenie sample, a 61.37-g Gao-Guenie sample, a 62.35-g Jilin H5 chondrite meteorite sample, and a 51.37-g Sikhote-Alin IIAB Iron meteorite sample are also presented. Temperature interpolation formula are further provided for the specific heat capacity, thermal conductivity, and thermal diffusivity of the 3.01-g Gao-Guenie sample in the temperature range 300<T (K)<800. We briefly review the possible effects of the newly deduced specific heat and thermal conductivity values on the ablation of meteoroids within the Earth's atmosphere, the modeling of asteroid interiors and the orbital evolution of meteoroids through the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect. 相似文献
37.
Martin Beech 《Earth, Moon, and Planets》2014,113(1-4):53-71
The origin of the Rio Cuarto crater field, Argentina has been widely debated since the early 1990s when it was first brought to public attention. In a binary on–off sense, however, the craters are either of a terrestrial origin or they formed via a large asteroid impact. While there are distinct arguments in favour of the former option being the correct interpretation, it is the latter possibility that is principally investigated here, and five distinct impact formation models are described. Of the impact scenarios it is found that the most workable model, although based upon a set of fine-tuned initial conditions, is that in which a large, 100–150-m initial diameter asteroid, entered Earth’s atmosphere on a shallow angle path that resulted in temporary capture. In this specific situation a multiple-thousand kilometer long flight path enables the asteroid to survive atmospheric passage, without suffering significant fragmentation, and to impact the ground as a largely coherent mass. Although the odds against such an impact occurring are extremely small, the crater field may nonetheless be interpreted as having potentially formed via a very low-angle, smaller than 5° to the horizon, impact with a ground contact speed of order 5 km/s. Under this scenario, as originally suggested by Schultz and Lianza (Nature 355:234, 1992), the largest of the craters (crater A) in the Rio Cuarto structure was produced in the initial ground impact, and the additional, smaller craters are interpreted as being formed through the down-range transport of decapitated impactor material and crater A ejecta. 相似文献
38.
Martin Beech 《Astrophysics and Space Science》1989,152(2):329-335
The V variations of ellipsoidal variables are investigated as a function of the spectral type of the primary. A model is developed on the assumption that the primary has near Main-Sequence characteristics. It is argued that the observed minimum in the V variations around spectral type F is real and is due to variations in the gravity-darkening exponent . The absolute upper limit to V variations is found to be 0.2 mag. 相似文献
39.
Martin Beech 《Astrophysics and Space Science》1992,192(1):103-111
Motivated by several recent studies on the geometry of molecular cloud structures, we perform two experiments that consider the projection of fractal images onto a two-dimensional screen. Evidence is presented to support the proposition that the dimensionD
P of the contours surrounding the projected images are given byD
s–1, whereD
s>2 is the fractal dimension of the object itself. A brief survey of the geometry of astrophysical cloud structures is also presented. 相似文献
40.
Martin Beech 《Astrophysics and Space Science》1988,147(1):163-171
In this study analytic models are used in an attempt to constrain the overshooting parameter in massive stars. It is found that core overshooting up to of order 20% is required to explain the non-existence of red supergiants withM
bol<–10. Furthermore, a critical mass of 60M
marks the upper mass limit for stars that can undergo a red supergiant phase. The analysis employed clearly demonstrates an important interplay between mass loss and core overhooting-highlighting the difficulty of establishing the uniqueness of a given set of results. 相似文献