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1.
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
2.
3.
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
4.
5.
J.W. BeemanF. Bellini L. Cardani N. Casali I. DafineiS. Di Domizio F. Ferroni F. OrioG. Pessina S. PirroC. Tomei M. Vignati 《Astroparticle Physics》2012,35(9):558-562
TeO2 crystals have proven to be superb bolometers for the search of neutrinoless double beta decay in many respects. However, if used alone, they do not exhibit any feature that allows to discriminate an α energy deposit from a β/γ one. This fact limits their ability to reject the background due to natural radioactivity and eventually affects the sensitivity of the search. In this paper we show the results of a TeO2 crystal where, in coincidence with its bolometric heat signal, also the luminescence light escaping the crystal is recorded. The results show that we are able to measure the light produced by β/γ particles, which can be explained as due to Cerenkov emission. No light is detected from α particles, allowing the rejection of this background source. 相似文献
6.
The zirconium oxide (ZrO) is well known for its astrophysical importance. The radiative transition parameters that include
Franck-Condon (FC) factor, r-centroid, electronic transition moments, Einstein coefficient, band oscillator strengths, radiative
life time and effective vibrational temperature have been estimated for e
1Π–X
1Σ+ and 1Σ+–X
1Σ+ band systems of 90ZrO molecule for the experimentally known vibrational levels using RKR potential energy curves. A reliable numerical integration
method has been used to solve the radial Schr?dinger equation for the vibrational wave functions of upper and lower electronic
states based on the latest available spectroscopic data and known wavelengths. The estimated radiative transition parameters
are tabulated. The effective vibrational temperatures of these band systems of 90ZrO molecule are found to be below 4200 K. Hence, the radiative transition parameters help us to ascertain the presence of
90ZrO molecule in the interstellar medium, S stars and sunspots. 相似文献
7.
N2 2P fluorescent intensity was monitored as a function of incident photon energy from 40 to 70 eV. A structure was seen near 52.2 eV. This feature is attributed to the scattering of photoelectrons originating from the N2 2σg molecular orbital with a binding energy of about 37.7 eV. The kinetic energy of these photoelectrons corresponds to the peak of the 2P excitation cross section at 14.5 eV. 相似文献
8.
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
9.
Doran J. Baker William R. Pendleton Gerald J. Romick Vincent B. Wickwar Murray I. Baron 《Planetary and Space Science》1978,26(7):619-634
The ground-level zenith radiance of the atmospheric emission at λ1.27 μm was radiometrically observed to increase by a factor of approximately two with the onset of an IBC III+ auroral breakup above Chatanika, Alaska, on 10 March 1975. Time-resolved optical spectra clearly show that the slow component of the enhancement is associated with the (0,0) band of the infrared atmospheric system of O2. Photometric and incoherent scatter radar data are used to define the energy-deposition profile and the absolute energy flux for the event. The magnitude of the O2λ1.27-μm enhancement compares favourably with the predictions of an auroral excitation model which includes only secondary-electron excitation of molecular oxygen in the O2(a1Δg) source term. 相似文献
11.
Based on a set of 11 CME events we study the impact of projection effects by tracking CME leading edge features in the plane of sky (traditional CME tracking) from combined STEREO-SECCHI and SOHO-LASCO observations up to 20R ⊙. By using CME observations from two vantage points and applying triangulation techniques, the source region location of the CME on the solar surface was determined (heliospheric longitude and latitude) to correct for projection effects. With this information, the directivity and “true” speed of a CME can be estimated in a simple way. The comparison of the results obtained from the spacecraft pairs SOHO-LASCO/STEREO-A and SOHO-LASCO/STEREO-B allows us to study the reliability of the method. The determined CME source region is generally coincident within ?10°. 相似文献
12.
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
13.
With the sample of 105 emission line galaxies selected from the Sloan Digital Sky Survey Data Release 4 (SDSS DR4), we have investigated the relations of the [OII]λ3727/Hα flux ratio with the dust extinction, the ionization state of interstellar gas and the metal abundance of galaxies. It is found that the dust extinction correction has a significant effect on the [OII]λ3727/Hα flux ratio. Before and after the dust distinction correction is made, the mean [OII]λ3727/Hα flux ratios are 0.48 and 0.89, respectively. After the dust extinction is corrected, the dispersion of the distribution of F([OII]λ3727) as a function of F(Hα) is obviously reduced. The [OII]λ3727/Hα flux ratio of metal-poor galaxies decreases with the increasing ionization degree of interstellar gas, but this relation does not exist in metal-rich galaxies. Besides, it is found that the [OII]λ3727/Hα flux ratio is correlated with the metal abundance. When 12 + lg(O/H) > 8.5, the [OII]λ3727/Hα flux ratio decreases with the increasing metal abundance; for the galaxies of 12 + lg(O/H) > 8.5, the spectral flux ratio correlates positively with the metal abundance. Finally, by using the parameters of gas ionization degree and metal abundances of galaxies, the formulae for calculating the [OII]λ3727/Hα flux ratios of different types of galaxies are given. With the [OII]λ3727/Hα flux ratio given by these formulae, the star formation rate can be derived by using the [OII]λ3727-line flux, for the galaxies of the redshift z > 0.4, such as the large number of galaxies to be observed by the LAMOST telescope. 相似文献
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15.
W. J. Wagner R. M. E. Illing C. B. Sawyer L. L. House N. R. Sheeley Jr. R. A. Howard M. J. Koomen D. J. Michels R. N. Smartt M. Dryer 《Solar physics》1983,83(1):153-166
Multi-telescope observations of the coronal transient of 15–16 April, 1980 provide simultaneous data from the Solar Maximum Mission Coronagraph/Polarimeter, the Solwind Coronagraph, and the new Emission Line Coronagraph of the Sacramento Peak Observatory. An eruptive prominence-associated white light transient is for the first time seen as an unusual wave or brightening in Fe x
gl6374 (but not in Fe xiv
gl5303). Several interpretations of this fleeting enhancement are offered.The prominence shows a slowly increasing acceleration which peaks at the time of the Fe event. The white light loop transient surrounding the prominence expands at a well-documented constant speed to 10R
, with an extrapolated start time at zero height coincident with the surface activity.This loop transient exemplifies those seen above 1.7R
in that leading the disturbance is a bright (N
e-enhanced) loop rather than dark. This is consistent with a report of the behavior of another eruptive event observed by Fisher and Poland (1981) which began as a density depletion in the lower corona, with a bright loop forming at greater altitudes. The top of the bright loop ultimately fades in the outer corona while slow radial growth continues in the legs.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
16.
We use the Cerenkov line emission mechanism to give a new explanation of the observed intensity ratios, particularly the L/H ratio, of the emission lines of quasars. We give equations that restrict the choice of the parameter values. The parameters are the characteristic energy of the relativistic electrons, the number density of neutral hydrogen and its relative level populations. With reasonable choice of the parmaeters, we can obtain calculated L/H, H/H, P/H ratios in agreement with observed values. Our estimate for the gas density in the broad line region of quasars is 1015 cm–3, very different from previous estimates. Unlike previous theories, such a high density causes no difficulties with the Cerenkov line emission. 相似文献
17.
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
18.
Supergranulation is a component of solar convection that manifests itself on the photosphere as a cellular network of around
35 Mm across, with a turnover lifetime of 1 – 2 days. It is strongly linked to the structure of the magnetic field. The horizontal,
divergent flows within supergranule cells carry local field lines to the cell boundaries, while the rotational properties
of supergranule upflows may contribute to the restoration of the poloidal field as part of the dynamo mechanism, which controls
the solar cycle. The solar minimum at the transition from cycle 23 to 24 was notable for its low level of activity and its
extended length. It is of interest to study whether the convective phenomena that influence the solar magnetic field during
this time differed in character from periods of previous minima. This study investigates three characteristics (velocity components,
sizes and lifetimes) of solar supergranulation. Comparisons of these characteristics are made between the minima of cycles
22/23 and 23/24 using MDI Doppler data from 1996 and 2008, respectively. It is found that whereas the lifetimes are equal
during both epochs (around 18 h), the sizes are larger in 1996 (35.9 ± 0.3 Mm) than in 2008 (35.0 ± 0.3 Mm), while the dominant
horizontal velocity flows are weaker (139 ± 1 m s−1 in 1996; 141 ± 1 m s−1 in 2008). Although numerical differences are seen, they are not conclusive proof of the most recent minimum being inherently
unusual. 相似文献
19.
The large-scale post-perihelion evolution of the dust tail in Comet C/1995 O1 (Hale–Bopp) was monitored with Schmidt telescope exposures at the European Southern Observatory (ESO) La Silla in Chile. In early October 1997 signatures of a peculiar dust-tail appeared as straight, but diffuse extensions in the northern and southern coma hemisphere. With the approach of the Earth to the orbital plane of the comet a needle-like anti-tail with a similar, but much longer counterpart in the region of the normal dust tail formed. In early January 1998, i.e., close to the plane crossing, the anti-tail pointed towards position angle 190° and was at least 0.4°long, its counter part extended over more than 5° into oppositedirection. During February and March 1998 the position angles of both features increased by more than 40$°– while their appearance became shorter, wider and more diffuse again. Thepeculiar dust tail was last observed in April 1998.Modeling of the dust tail dynamics shows that the anti-tail andpeculiar tail phenomenon observed is formed by a neck-line structureof heavy dust grains released around perihelion passage. Two scenariiare introduced to explain the extension of the anti-tail feature:(1) grains ejected about 20 days post-perihelion with a initial velocity of 170 m/s in radial direction towards the Sun and(2) grains released about 60–80 days before perihelion at a speed of70m/s into the orbital plane and against the motion directionof the comet. The out-of-plane velocity component of the dust wasless than 25 m/s. Both scenarios require dust of < 0.001to be involved, i.e., grains of at least mm-size. The rather symmetric shading of the neck-line structure before and after passage of theEarth through the orbital plane of the comet in early January 1998 supports the idea that dust of both scenarii may have contributed to the phenomenon. 相似文献
20.
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