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1.
Ahmad Rami El-Nabulsi 《Astrophysics and Space Science》2010,327(1):111-115
We investigate five-dimensional Brans–Dicke cosmology with spacetime described by the homogeneous, anisotropic and flat spacetime
with the topology M
1×R
3×S
1 where S
1 is taken in the form of a circle. We conjecture throughout this letter that the extra-dimension compactifies as the visible
dimensions expand like b(t)≈a
−1(t) and that the non-minimal coupling between the scalar field and the matter is of the form f(φ)∝
φ
2. The model gives rise to a transition from a decelerated epoch to an accelerated epoch for large values of the Brans–Dicke
parameter ω. The model predicts crossing of the phantom divided barrier unless the universe is governed by a growing matter field. 相似文献
2.
Simultaneous measurements of the nightglow profiles of the O2(b1Σg+?X3Σg?) A-band, the atomic oxygen green line and the OH (8?3) Meinel band are presented. The altitude profiles are used to determine both the excitation mechanisms for the oxygen emissions and the atomic oxygen altitude distribution. It is shown that the measurements are consistent with a green line excitation through the Barth mechanism and that the molecular oxygen emission is excited through oxygen recombination and the reaction between OH1 and atomic oxygen. The derived atomic oxygen concentrations,6.2 × 1011cm?3at 98km, are consistent with the Jacchia (1971) model. 相似文献
3.
Two monochromatic pictures of the Comet Kohoutek (1973f) were taken on January 15, 1974 in the resonance light (A2Σ ? X2 ∏) of the radical OH with a photographic telescope placed on board the NASA 990 Convair airplane. From an intensity profile we derive the production rate of OH radicals QOH = 4 xsx 1028 moleculesec ?1sr?1 at 0.6 AU and the lifetime of the OH radical which is τOH = 4.5 × 104 sec at 0.6 AU. This short lifetime (very similar to the lifetime of H2O) combined with the high total production rate of gas in comets can explain the observed velocity of 8km sec?1 for the H-atoms: The H-atoms produced by photodissociation of H2O are thermalized at short distancesfrom the nucleus; the H-atoms produced by photodissociation of OH have a velocity of ?8km sec?1 and can reach the outer part of the hydrogen envelope. 相似文献
4.
We investigate the interacting NADE model in non-flat universe. The effects of spatial curvature Ω
k
, interaction coefficient α and the main parameter of NADE, n, on EoS parameter w
d
and deceleration parameter q are studied. We obtain a minimum value for n in both early and present time, in order to that our DE model crosses the phantom divide. Also in a closed universe, changing
the sign of q is strongly dependent on α. It has been shown that the quantities w
d
and q have a different treatment for various spatial curvature. At last, we calculate the statefinder diagnostic and w−w
′ analysis in non flat universe. In non flat universe, the statefinder trajectories are discriminated by both n and α. 相似文献
5.
KAr and/or 40Ar39Ar plateau ages of Allende samples—whole rock, matrix, chondrules, white inclusions–range from 3.8 AE for matrix of ?5 AE for some white inclusions, but cluster strongly near 4.53 AE. This age marks the dominant KAr resetting of Allende materials. Age spectra show disturbances due to 39Ar recoil or some other argon redistribution processes. Possible explanations for the apparent presolar ages (>4.6 AE) include: ?20% loss of 39Ar; ?40% loss of 40K ～3.8 AE ago with no loss of 40Arl trapped argon of unique 40Ar/36Ar isotopic composition; admixture of “very old” presolar grains. 相似文献
6.
7.
8.
New far-infrared observations of the NH3 rotation-inversion manifolds in the spectrum of Jupiter have been inverted with the use oftthe detailed ammonia line opacity. A temperature of 160°K at a 1-bar pressure level and a temperature of 105°K for the minimum temperature of the inversion level at 0.15 bars have been derived for gaseous absorption due to NH3, H2, and He. The overall fit to the brightness temperature as a function of frequency σ is within ±1°K for 100 ≤ σ ≤ 400 cm?1 except for the centers of the NH3 rotation-inversion manifolds where for J ≥ 7 the fit is about 5°K too high. In the continuum for 400 ≤ σ ≤ 630 cm?1 the fit is within 2.5°K. Consideration of an ammonia ice haze, photodissociation of NH3 by uv radiation, NH3 abundance variation, different He/H2 ratios, and uncertainties in the data effect the temperatures at 1 bar and the temperature at the inversion layer by <7°K. The presently derived temperature at 1 bar of 160°K is consistent with Jovian interior models which can match the gravitational moment, J2. 相似文献
9.
G. Lodato A. R. King J. E. Pringle 《Monthly notices of the Royal Astronomical Society》2009,392(1):332-340
In this paper, we revisit the arguments for the basis of the time evolution of the flares expected to arise when a star is disrupted by a supermassive black hole. We present a simple analytic model relating the light curve to the internal density structure of the star. We thus show that the standard light curve proportional to t −5/3 only holds at late times. Close to the peak luminosity the light curve is shallower, deviating more strongly from t −5/3 for more centrally concentrated (e.g. solar type) stars. We test our model numerically by simulating the tidal disruption of several stellar models, described by simple polytropic spheres with index γ. The simulations agree with the analytical model given two considerations. First, the stars are somewhat inflated on reaching pericentre because of the effective reduction of gravity in the tidal field of the black hole. This is well described by a homologous expansion by a factor which becomes smaller as the polytropic index becomes larger. Secondly, for large polytropic indices wings appear in the tails of the energy distribution, indicating that some material is pushed further away from parabolic orbits by shocks in the tidal tails. In all our simulations, the t −5/3 light curve is achieved only at late stages. In particular, we predict that for solar-type stars, this happens only after the luminosity has dropped by at least 2 mag from the peak. We discuss our results in the light of recent observations of flares in otherwise quiescent galaxies and note the dependence of these results on further parameters, such as the star/hole mass ratio and the stellar orbit. 相似文献
10.
Ground-based observations of Venus were made with a 5-cm drive Michelson interferometer during December 1970 and December 1973. The thermal emission spectrum of the central portion of the apparent disk was recorded from 450–1250 cm?1 with an apodized spectral resolution of 0.25 cm?1. All statistically significant sharp line absorption features in the spectrum have been identified with gaseous CO2. Comparison between the observed spectrum and a synthetic spectrum computed from a model atmosphere, assuming gaseous CO2 and a sulfuric acid haze as opacity sources, indicates good agreement. A broad diffuse absorption feature associated with the sulfuric acid haze is evident in the 870- to 930 cm?1 region. With the exception of the rotational lines of the 927-cm?1 CO2 band, the above feature appears as a continuum down to 0.25 cm?1 resolution. In the 750- to 1250-cm?1 range, the spectrum exhibits moderate thermal contrast with maximum brightness temperatures of 234–238°K occurring near 825 cm?1. These temperatures are in general agreement with previous measurements. 相似文献
11.
13C(α,n)16O反应是小质量渐近巨星分支(asymptotic giant branch,AGB)星(M/M⊙≤3,M和M⊙分别表示AGB星的质量和太阳质量)内s过程(慢中子俘获过程)的主要中子源。在对流热脉冲间隔期间,一个储层(即所谓的“13C袋”)内的13C在辐射条件下(约8 keV)燃烧并释放中子。到目前为止,13C袋的物理形成过程仍远未被充分理解,因此13C袋的结构也一直无法被完全确定。在后处理核合成计算中,13C袋通常是利用观测数据通过自由的参数化来约束。从基本原理、主要效果及局限性等方面综述了不同观测证据对13C袋的约束作用,最后展望了13C中子源约束问题未来可能的研究方向。 相似文献
12.
Pawe? Wajer 《Icarus》2009,200(1):147-153
We study the dynamical evolution of Asteroid 2002 AA29. This object moves in the co-orbital region of the Earth and is the first known asteroid which experiences recurrent horseshoe-quasi-satellite transitions. The transitions between the HS and QS states are unique among other known Earth co-orbital asteroids and in the QS state 2002 AA29 remains very close to Earth (within 0.2 AU for several decades [Connors, M., Chodas, P., Mikkola, S., Wiegert, P., Veillet, C., Innanen, K., 2002. Meteorit. Planet. Sci. 37, 1435-1441]). Based on results obtained analytically by Brasser et al. [Brasser, R., Heggie, D.C., Mikkola, S., 2004b. Celest. Mech. Dynam. Astron. 88, 123-152] we developed a simple analytical method to describe and analyze the motion of 2002 AA29. We distinguish a few moments in time crucial for understanding its dynamics. Near 2400 and 2500 this object will be close to going through the maxima of the averaged disturbing function and it will either change its co-orbital regime by transition from the HS into QS state, or leave the librating mode. These approaches generate instability in the motion of 2002 AA29. By means of 66 observations, covering a two-year interval, we extend the analysis of the long term evolution of this object presented by Connors et al. [Connors, M., Chodas, P., Mikkola, S., Wiegert, P., Veillet, C., Innanen, K., 2002. Meteorit. Planet. Sci. 37, 1435-1441] and Brasser et al. [Brasser, R., Innanen, K.A., Connors, M., Veillet, C., Wiegert, P., Mikkola, S., Chodas, P.W., 2004a. Icarus 171, 102-109]. Our analysis is based on a sample of 100 cloned orbits. We show that the motion of 2002 AA29 is predictable in the time interval [−2600,7100] and outside of this interval the past and future orbital history can be studied using statistical methods. 相似文献
13.
14.
The 5ν1 absorption band of NH3 is displayed from 6418 to 6550 Å. The total band intensity has been measured: SB = 0.66 cm?1m?1amagat?1. Line intensities and self-broadening coefficients have been measured for some of the prominent lines. Our line intensities are in good agreement with those of Rank et al. (1966), but are about 2 times greater than those of Mason (1970). The spectrum displayed was obtained photoelectrically at a pressure of 0.061 atm, and shows many more lines than the spectrum obtained by McBride and Nicholls (1972a) at a pressure of 0.39 atm. Therefore, our new measurements can provide the basis for making a more complete rotational analysis than those of McBride and Nicholls (1972a).Since the total band absorption has previously been measured by others on moderate resolution photoelectric scans of the spectra of Jupiter and Saturn, we can use the band intensity to derive the NH3 abundance in the atmospheres of these two planets. The NH3 abundances in a single vertical path obtained by this method are about 10m amagat for Jupiter and 2m amagat for Saturn. These results are in agreement with previous results obtained from higher resolution photographic spectra. 相似文献
15.
To settle the question of disulfur monoxide and sulfur monoxide deposition and occurrence on Io's surface, we performed series of laboratory experiments reproducing the condensation of S2O at low temperature. Its polymerization has been monitored by recording infrared spectra under conditions of temperature, pressure, mixing with SO2 and UV-visible radiation simulating that of Io's surface. Our experiments show that S2O condensates are not chemically stable under ionian conditions. We also demonstrate that SO and S2O outgassed by Io's volcanoes and condensing on Io's surface should lead to yellow polysulfuroxide deposits or to white deposits of S2O diluted in sulfur dioxide frost (i.e., S2O/SO2 < 0.1%). Thus S2O condensation cannot be responsible for the red volcanic deposits on Io. Comparison of the laboratory infrared spectra of S2O and polysulfuroxide with NIMS/Galileo infrared spectra of Io's surface leads us to discuss the possible identification of polysulfuroxide. We also recorded the visible transmission spectra of sulfur samples resulting from polysulfuroxide decomposition. These samples consist in a mixture of sulfur polymer and orthorhombic sulfur. Using the optical constants extracted from these measurements, we show that a linear combination of the reflectance spectra of our samples, the reflectance spectrum of orthorhombic S8 sulfur and SO2 reflectance spectrum, leads to a very good matching of Io's visible spectrum between 330 and 520 nm. We conclude then that Io's surface is probably mainly composed of sulfur dioxide and a mixture of sulfur S8 and sulfur polymer. Some polysulfuroxide could also co-exist with these dominant components, but is probably restricted to some volcanic areas. 相似文献
16.
R.L. Branham 《Astronomische Nachrichten》2012,333(2):118-124
Comet C/1853 E1 (Secchi) has a hyperbolic orbit with eccentricity 1.01060 and perihelion outside of the Earth's orbit. Integrating the orbit with barycentric coordinates backwards to 50000 AU, the approximate edge of the Oort cloud, shows that the orbit remains hyperbolic. This is still true even if plutoids additional to Pluto are included in the integration. Nor does including Galactic tidal and disc effects and possible nongravitational forces change the orbit to a high eccentricity ellipse. Although certain factors, such as unknown massive plutoids, gravitational effects by interstellar gas clouds, or unmodelled nongravitational forces operating on the comet, could change this situation, the tentative conclusion that the origin of this comet is extrasolar remains the one most consistent with the observations (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
17.
18.
Z. Osmanov 《New Astronomy》2010,15(4):351-355
We investigate the role of centrifugal acceleration of electrons in producing the very high energy (VHE) radiation from the BL Lac object 1ES 0806+524, recently detected by VERITAS. The efficiency of the inverse Compton scattering (ICS) of the accretion disk thermal photons against rotationally accelerated electrons is examined. By studying the dynamics of centrifugally induced outflows and by taking into account a cooling process due to the ICS, we estimate the maximum attainable Lorentz factors of particles and derive corresponding energetic characteristics of the emission. Examining physically reasonable parameters, by considering the narrow interval of inclination angles (0.7–0.95°) of magnetic field lines with respect to the rotation axis, it is shown that the centrifugally accelerated electrons may lead to the observational pattern of the VHE emission, if the density of electrons is in a certain interval. 相似文献
19.
N. S. Soboleva E. K. Majorova O. P. Zhelenkova A. V. Temirova N. N. Bursov 《Astrophysical Bulletin》2010,65(1):42-59
We use two independent methods to reduce the data of the surveys made with RATAN-600 radio telescope at 7.6 cm in 1988–1999
at the declination of the SS433 source. We also reprocess the data of the “Cold” survey (1980–1981). The resulting RCR (RATAN
COLD REFINED) catalog contains the right ascensions and fluxes of objects identified with those of the NVSS catalog in the
right-ascension interval 7
h
≤ R.A. < 17
h
. We obtain the spectra of the radio sources and determine their spectral indices at 3.94 and 0.5 GHz. The spectra are based
on the data from all known catalogs available from the CATS, Vizier, and NED databases, and the flux estimates inferred from
the maps of the VLSS and GB6 surveys. For 245 of the 550 objects of the RCR catalog the fluxes are known at two frequencies
only: 3.94 GHz (RCR) and 1.4 GHz (NVSS). These are mostly sources with fluxes smaller than 30mJy. About 65% of these sources
have flat or inverse spectra (α > −0.5). We analyze the reliability of the results obtained for the entire list of objects and construct the histograms of
the spectral indices and fluxes of the sources. Our main conclusion is that all 10–15 mJy objects found in the considered
right-ascension interval were already included in the decimeter-wave catalogs. 相似文献
20.
I. Negueruela P. Roche J. Fabregat M. J. Coe 《Monthly notices of the Royal Astronomical Society》1999,307(3):695-702
We present optical and infrared observations of BQ Cam, the optical counterpart to the Be/X-ray transient system V0332+53. BQ Cam is shown to be an O8–9Ve star, which places V0332+53 at a distance of ∼7 kpc. H α spectroscopy and infrared photometry are used to discuss the evolution of the circumstellar envelope. Owing to the low inclination of the system, parameters are strongly constrained. We find strong evidence for a tilt of the orbital plane with respect to the circumstellar disc (presumably on the equatorial plane). Even though the periastron distance is only ≈10 R * , during the present quiescent state the circumstellar disc does not extend to the distance of periastron passage. Under these conditions, X-ray emission is effectively prevented by centrifugal inhibition of accretion. The circumstellar disc is shown to be optically thick at optical and infrared wavelengths, which, together with its small size, is taken as an indication of tidal truncation. 相似文献