排序方式： 共有6条查询结果，搜索用时 46 毫秒
1
1.
R. Ferlet A. Lecavelier Des Etangs G. Perrin A. Vidal-Madjar F. Sèvre F. Colas J. E. Arlot C. Buil H. Beust A. M. Lagrange-Henri J. Lecacheux M. Deleuil C. Gry 《Astrophysics and Space Science》1994,212(1-2):173-180
The inner regions of the circumstellar disk around Pictoris might be dust-free due to a possible planet which may have cleared up dust particles. We present a new observational technique based on the use of an anti-blooming CCD in order to directly image this zone. The structure of the disk is revealed down to 2 arcsec from the star (30 AU). We show that the Pic disk brightness is neutral inV, R, andI
C
, but drops down when going inward inB, possibly related to a change in the dust composition. Also, a slight disk asymmetry is present but inverted from the outer to the inner zones.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A. 相似文献
2.
3.
Repeated time-variable redshifted absorption features in the spectrum of β Pictoris (β Pic) have been attributed to comet-like bodies falling toward the star, when evaporating in its immediate vicinity. This model explains now a large number of observational characteristics, but the exact mechanism that could generate these numerous star-grazers is still controversial, even if planetary perturbations are thought to be the basic process. The different models proposed up to now are here reviewed, and we discuss in particular a recent one, involving the effect of secular resonances in the β Pic system. We stress that it seems highly improbable that such a mechanism could apply to the β Pic case, because the extremely strong power of secular resonances is connected to the very specific structure of the Solar System. Therefore, the secular resonance mechanism is highly non-generic. Conversely, we propose a model involving the eccentricity-pumping effect of mean-motion resonances with a massive planet on a moderately eccentric orbit. We show in particular that the 4:1 mean-motion resonance is a very active source of star-grazers as soon as the eccentricity of the perturbing planet is ?0.05, while the 3:1 mean-motion resonance is less efficient. We stress that this mechanism is very generic. These theoretical predictions are confirmed by numerical integrations using the Extended Schubart Integrator. The time-scale of the process is discussed, and we show that if the eccentricity of the perturbing planet fluctuates, due to secular perturbations, this time-scale is compatible with the age of β Pic's system. 相似文献
4.
R. Signer F. v. Beust Ulrich A. Corti 《Aquatic Sciences - Research Across Boundaries》1951,13(1):31-35
Summary The investigation with an electron-microscope of the scales of the fresh water fish,Leuciscus rutilus L., showed that their ventral “smooth” surface scems to be formed like a corrugated plate with a distance between the ridges
of 1–2 μ. The dorsal “rough” side of the scales shows a very fine roughness. It is interrupted by pointed combs of the same
structure in a regular distance of 16–27 μ. The thickness of these combs is of about 1 μ at their base, their height of about
5–10 μ. It seems probable that the surface of scales is partially covered with laminas of hyalodentine or guanine.
13. Mitteilung siehe diese Zeitschrift,13, 29–30 (1951). 相似文献
13. Mitteilung siehe diese Zeitschrift,13, 29–30 (1951). 相似文献
5.
We present high-resolution spectra (1.0 km s−1 FWHM) of the circumstellar Ca K line towards β Pictoris obtained on 1997 June 19 and 20. On the former date a strong absorption component was found at a heliocentric velocity of v helio = +8 km s−1 , that is blueshifted by 14 km s−1 with respect to the main, 'stable', circumstellar component at v helio = +22 km s−1 . To our knowledge, this is the first detection of a blueshifted Ca ii component with a strength comparable to the more frequently observed redshifted events. On the following night a blueshifted component was still present, but its strength had decreased significantly; in addition, a strong redshifted component had appeared at v helio = +54 km s−1 which was absent on the previous night. The implications of these observations for the evaporating 'comet' model of spectral variations in the β Pictoris disc are discussed. 相似文献
6.
H. Beust A. Vidal-Madjar R. Ferlet A. M. Lagrange-Henri 《Astrophysics and Space Science》1994,212(1-2):147-157
Repeated spectroscopic observations of Pictoris have been performed since 1985 and revealed the presence, in many metallic lines likeCa II, Mg II, Fe II, ..., of strong sporadic circumstellar absorption, redshifted by tens to hundreds of km s–1 with respect to the star, and highly time-variable (time-scales of days or hours).We have tentatively interpreted these variable events as the spectral signature of infalling cometary-like bodies, when evaporating in the vicinity of the star. This scenario has been furthermore theoretically studied, and we showed that it could indeed explain correctly the observations with their peculiar characteristics, like (1) the behavior difference between visible and UV lines, (2) the unusual line ratios, (3) the surprising presence of Al III absorption lines. Constraints deduced from both observational data and theoretical study allowed us to suggest that a planet within the disk could be responsible, by perturbations, of this high rate infall of small bodies towards the star (> 100 per year).Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A. 相似文献
1