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1.
A calculation of the expected signal due to Primakoff coherent conversion of solar axions into photons via Bragg scattering in several crystal detectors is presented. The results are confronted with the experimental sensitivities of present and future experiments concluding that the sensitivity of crystal detectors does not challenge the globular cluster limit on the axion-photon coupling gaγγ. In particular, in the axion mass window ma 0.03 eV explored with this technique (not accessible at present by other methods), gaγγ might be constrained down to 10−9 GeV−1 (the recent helioseismological bound) provided that significant improvements in the parameters and performances of these detectors be achieved and large statistics accumulated. This bound should be considered as a minimal goal for the sensitivity of future crystal experiments. Consequently, finding a positive signal at this level of sensitivity would necessarily imply revisiting other more stringent astrophysical limits derived for the same range of ma values.  相似文献   

2.
We compute the big bang nucleosynthesis limit on the number of light neutrino degrees of freedom in a model-independent likelihood analysis based on the abundances of 4He and 7Li. We use the two-dimensional likelihood functions to simultaneously constrain the baryon-to-photon ratio and the number of light neutrinos for a range of 4He abundances Yp = 0.225–0.250, as well as a range in primordial 7Li abundances from (1.6 to 4.1) ×10−10. For (7Li/H)p = 1.6 × 10−10, as can be inferred from the 7Li data from Population II halo stars, the upper limit to Nν based on the current best estimate of the primordial 4He abundance of Yp = 0.238 is Nν < 4.3 and varies from Nν < 3.3 (at 95% C.L.) when Yp = 0.225 to Nν < 5.3 when Yp = 0.250. If 7Li is depleted in these stars the upper limit to Nν is relaxed. Taking (7Li/H)p = 4.1 × 10−10, the limit varies from Nν < 3.9 when Yp = 0.225 to Nν 6 when Yp = 0.250. We also consider the consequences on the upper limit to Nν if recent observations of deuterium in high-redshift quasar absorption-line systems are confirmed.  相似文献   

3.
Recent rocket observations of the N2 V-K (Vegard-Kaplan) system in the aurora have been reinterpreted using an atmospheric model based on mass spectrometer measurements in an aurora of similar intensity at the same time of year. In contrast to the original interpretation, we find that population by cascade from the C3Πu and B3Πg states in the A3Σu+v=0,1 levels, as calculated using recently measured electron excitation cross sections, accurately accounts for the observed relative emission rates (IV-K/12PG0.0). In addition there is no need to change the production rate of A 3 Σ u+ molecules relative to that of C3Πuv=0 as a function of altitude in order to fit the profile of the deactivation probability to the atmospheric model. Quenching of A 3 Σ u+ molecules at high altitudes is dominated by atomic oxygen. The rate constants for the v=0 and v=1 levels are 8 × 10−11 cm3 sec−1 and 1.7 × 10−10 cm3 sec−1 respectively, as determined using the model atmosphere mentioned above. Recent observations with a helium cooled mass spectrometer suggest that conventional mass spectrometer measurements tend to underestimate the atomic oxygen relative concentration. The rate coefficients may therefore be too large by as much as a factor of 3. Below 130 Km we find that it is possible to account for the deactivation in bright auroras by invoking large nitric oxide concentrations, similar to those recently observed mass spectrometrically and using a rate constant of 8 × 10−11 cm3 sec−1 for both the v=1 levels. This rate constant is very nearly the same as that measured in the laboratory (7 × 10−11 cm3 sec−1). Molecular oxygen appears not to play a significant role in deactivating the lower A 3 Σ u+ levels.  相似文献   

4.
We calculate the event rates induced by a 51Cr νe source and by a 90Sr---90Y source in BOREXINO through elastic scattering on electrons, assuming a nonzero neutrino magnetic moment μν. We consider a source activity of about 2 MCi and estimate the solar ν (“source-off”) background for various oscillation scenarios. It is shown that values of μν as low as 0.5 × 10−10μB ( 0.2 × 10−10μB) can be proved with the 51Cr source (90Sr source) in about 100 days of data taking.  相似文献   

5.
Absolute values of the emission cross sections for five vibrational bands in the Meinel system of N2+,A2πu to X2Σg+, excited by electron impact are presented. From these, a value was obtained for the total excitation cross section of the A2πu state at 100 eV of 26·5 × 10−18 cm2. The results are compared with those of other workers and with theory. Collisional transfer of the excitation energy from the levels of the A2πu state was also observed with a transfer cross section of approximately 10−14 cm2.  相似文献   

6.
We have done extensive Monte Carlo simulations using the new simulation codes of CORSIKA and COSMOS to compare with the gamma-family data obtained at Mts. Fuji (3750 m above sea level) and Kanbala (5500 m above sea level). Then, we estimated the primary proton and helium spectra around the knee energy region using a multiple-layered feed-forward neural network as a classifier of primary particle kind. The selection efficiency of proton-induced family events is estimated to be 82%. The flux value of protons at 2×1015 eV is (5.5±1.5)×10−14 (m−2 s−1 sr−1 GeV−1). The result suggests heavy-enriched primary composition around the knee region.  相似文献   

7.
《Astroparticle Physics》2002,17(4):1083-475
Using data from the HEGRA air shower array, taken in the period from April 1998 to March 2000, upper limits on the ratio Iγ/ICR of the diffuse photon flux Iγ to the hadronic cosmic ray flux ICR are determined for the energy region 20–100 TeV. The analysis uses a gamma–hadron discrimination which is based on differences in the development of photon- and hadron-induced air showers after the shower maximum. A method which is sensitive only to the non-isotropic component of the diffuse photon flux yields an upper limit of Iγ/ICR (at 54 TeV) <2.0×10−3 (at the 90% confidence level) for a sky region near the inner galaxy (20°< galactic longitude <60° and |galactic latitude |<5°). A method which is sensitive to both the isotropic and the non-isotropic component yields global upper limits of Iγ/ICR (at 31 TeV) <1.2×10−2 and Iγ/ICR (at 53 TeV) <1.4×10−2 (at the 90% confidence level).  相似文献   

8.
Using the 13.7 m millimeter-wave telescope at the Qinghai Station of Purple Mountain Observatory, we have made observations of 13CO, C18O, HCO+ and N2H+ molecular lines towards IRAS 02232+6138. As the excitation density of the probe molecule increases from 13CO to HCO+, the size of the cloud core associated with IRAS 02232+6138 decreases from 2.40 pc to 0.54 pc, and the virial mass of the cloud core decreases from 2.2 × 103M to 5.1 × 102M. A bipolar molecular outflow is found towards IRAS 02232+6138. Using the power function n(r) ∝ r− to fit the spatial density structure of the cloud core, we obtain the power-law index  = 2.3 − 1.2; and we find that, as the probed density increases, the power function becomes more flat. The abundance ratio of 13CO to C18O is 12.4 ± 6.9, comparable with the values 11.8 ± 5.9 for dark clouds and the values 9.0–15.6 for massive cores. The abundance of N2H+ molecules is 3.5 ± 2.5 × 10−10, consistent with the value 1.0 − 5.0 × 10−10 for dark cloud cores and the value 1.2 − 12.8 × 10−10 for massive cores. The abundance of HCO+ molecules is 0.9 ± 0.5 × 10−9, close to the value 1.6 − 2.4 × 10−9 for massive cores. An increase of HCO+ abundance in the outflow region was not found. Combining with the IRAS data, the luminosity-mass ratio of the cloud core is obtained in the range 37–163(L/M). Based on the IRAS luminosity, it is estimated that a main-sequence O7.5 star is probably embedded in the IRAS 02232+6138 cloud core.  相似文献   

9.
Radio noise observations at frequencies of 0·700 Mc and 2·200 Mc were made at altitudes between 3000 and 11,000 km from a Blue Scout Jr. high-altitude rocket probe on 30 July 1963. A steady background flux of (7·5−3+6) × 10−19 W m−2)(c/s)−1 at 0·700 Mc and (1·8+1.0−0.5 × 10−19 W m−2 (c/s)−1 at 2·200 Mc was observed. Assuming a galactic origin of the observed fluxes at both frequencies, the averaged sky brightnesses are b(0·700 Mc) = (6−3+5) × 10−20 W m−2 (c/s)−1 sr−1b(2·200 Mc) = (1.4+1.0−0.5 × 10−20 W m−2 (c/s)−1 sr−1 The observed brightness at 2·200 Mc is in reasonable agreement with the results of other observers. The apparent brightness at 0·700 Mc is, however, greater than was expected from previous observations. An alternative source of the 0·700 Mc flux in the terrestrial exosphere, as well as characteristics of several noise bursts observed during the flight, is briefly discussed.  相似文献   

10.
A numerical analysis of cyclotron instabilities is carried out by computing the dispersion relation for a three component cold plasma-beam system. Rates of growth and damping for various values of the stream density are calculated from the dispersion relation. The rates of growth and damping increase monotonically as the number density of the proton stream increases. It is found that the frequencies at the rates of maximum growth and the damping decrease slightly to lower frequencies and a sharp peak at these frequencies becomes blunt. The minimum e-folding times of an ion cyclotron wave for (a) σs = 10−4, σi = 10−2 and (b) σs = 10−1, σi = 10−2 are about 3·84 and 0·16 sec respectively in the vicinity of the equatorial plane at 6 Re, where σs and σi are the ratios of the beam density Ns and the helium ion (H6+) density Ni to the total positive ions in the plasma-beam system.  相似文献   

11.
Rocket results are presented on the OI 6300 Å line and on the N2+ 3914 Å band in the dayglow. An altitude range of 78–335 km is covered. Theoretical interpretations are given, using results of simultaneous measurements of electron density and electron temperature. The apparent brightness of the 6300 Å line at the base of the emitting region is found to be 13 kR, of which 5.5 kR are ascribed to excitation through the Schumann-Runge dissociation of O2 by the solar UV radiations, 0.55 kR to the dissociative recombination of O2+ and NO+ ions, and 0.03 kR to the excitation of O by thermal electrons. An additional source of excitation above 280 km is suggested. The deactivation of O(1D) by O2(X3Σg−) is found to be appreciable below 200 km, and its rate coefficient is estimated to be 2 × 10−10 cm3/sec. The apparent brightness of the 3914 Å band at the base of the emitting region is found to be 6.5 kR, decreasing to 3.2 kR at 330 km. Assuming that fluorescent scattering of solar radiation is the mechanism involved the distribution of N2+ ions is calculated. The rate coefficients for the loss of these ions are hence calculated.  相似文献   

12.
The power spectral density of cosmic ray fluctuations observed at ground level during the years 1966–1968 has been calculated. In order to obtain the correct shape of the spectrum, the Fast Fourier Transform method with a triangular data window was used and corrections were made for uncorrelated errors and aliasing effects. When ignoring the Earth rotation peaks, the spectral index , for a sample of polar, middle latitude and equatorial stations, is − 1.96 in the frequency range 3 × 10−7–10−4 Hz. A possible break around 10−5 Hz, if existing, would be, on the whole, barely significant as a would change from − 1.96 to − 2.10. There are indications that beyond 10−4 Hz up to 7 × 10−3 Hz the spectrum continues with − 2.  相似文献   

13.
Venera 9, 10 measurements of the nightside ionospheric profile and the night airglow were used for investigating ionosphere formation processes. The upper ionospheric layer may be formed by HeI 584 Å radiation; the lower layer by meteorite ionization. Upper limits on the electron energy flux, <4 × 108eV cm−2 s−1, the helium ion flux <107 cm−2 s−1, the nitric oxide mixing ratio, <1.5 × 10−4 and the atomic sulphur mixing ratio, <10−6, are deduced for ionospheric altitudes.  相似文献   

14.
The diffused gamma halo around our Galaxy recently discovered by EGRET could be produced by annihilations of heavy relic neutrinos N (of fourth generation), whose mass is within a narrow range (MZ/2<mN<MZ). Neutrino annihilation in the halo may lead to either ultrarelativistic electron pairs whose Inverse Compton Scattering on infrared and optical galactic photons could be the source of observed GeV gamma rays, or prompt 100 MeV–1 GeV photons (due to neutral pion secondaries) born by reactions. The consequent gamma flux (10−7–10−6 cm−2 s−1 sr−1) is well comparable to the EGRET observed one, and it is also compatible with the narrow window of neutrino mass 45 GeV <mN<50 GeV, recently required to explain the underground DAMA signals.The presence of heavy neutrinos of fourth generation do not contribute much to solve the dark matter problem of the Universe, but may be easily detectable by outcoming LEP II data.  相似文献   

15.
If neutrinos have mass, we give reasons for a possible pattern of three (squaed) mass eigenvalues: m12 (2.8−5.8) (eV)2, m22 0.01 (eV)2, m32 (1.5−1) × 10−4 (eV)2. The flavor states νμ and νe are mixtures of the eigenstates with m2 and m3 with a significant mixing, corresponding to an effective mixing angle of about 0.45. The ντ is nearly the state with m1; the other two effective mixing angles are about an order of magnitude smaller than 0.45. There is a marked similarity to mixing in the quark sector.  相似文献   

16.
Using 1658 normal points of the McDonald lunar ranging data in the period 1971.6–1979.0, I calculated the Earth's rotation curve, and found an offset of −330 × 10−10 for UT1 – UTC. The difference between the UT1 values given by the lunar data and BIH is 3.6 ms. This difference and the standard error of single determinations increase with increasing interval length used in the data reduction. This is shown to be due to the neglect of the secular term in UT1-UTC. It appears that an interval length of 2 days is suitable when calculating the Earth's rotation.  相似文献   

17.
We describe a method of studying the variation in the rotation of the Earth in historical times using ancient records of central solar eclipses. From the records of central eclipses covering a period of some one thousand four hundred years (7th century B.C. to 7th century A.D.), given in the Chinese annals, we selected 88 entries and calculated the rotation variation parameter ΔT. Our result shows that the Earth is spinning down at a relative rate of − (1.88 ± 0.10) × 10−10/yr.  相似文献   

18.
Reflection and transmission coefficients of MHD waves are obtained at a stable, plane interface which separates two compressible, perfectly conducting media in relative motion to each other. The coefficients are evaluated for representative conditions of the quiettime, near-Earth magnetopause. The transmission coefficient averaged over a hemispherical distribution of incident waves is found to be 1–2 per cent. Yet the magnitude of the energy flux deposited into the magnetosphere in a day averaged over a hemispherical distribution of waves having amplitudes of say 2–3 gamma, is estimated to be of the order 1022 erg. Therefore the energy input of MHD waves must contribute significantly to the energy budget of the magnetosphere. The assumption that the boundary surface is a tangential discontinuity with no curvature limits the present theory to hydromagnetic frequencies higher than about 10−1 Hz. The ion gyrofrequencies for the models assumed here lie above 2 × 10−1 Hz. Therefore the present treatment applies to MHD waves near 10−1 Hz.  相似文献   

19.
Continuous observations of the amplitude and spectrum of naturally occurring radiation in the band 2–40 kc/s have been made during the period June to December 1958 near Sydney, Australia. A large number of isolated noise bursts lasting for some hours were detected. The intensity ranged from 6 × l0−19 to 6×10−-17W m−2 (c/s)−1 at 4·6 kc/s. Three main types of bursts were identified and classified on a basis of their spectra which usually extended from 3 to 5 kc/s, 4 to 8 kc/s and 2 to 30 kc/s, respectively. Major bursts, which were always of the latter two types, were clearly associated with strong auroral and magnetic activity and some showed a reproducible sequence of amplitude variation lasting about 36 hours. On three occasions, a detailed correspondence between the intensity of the noise and of simultaneously occurring red oxygen airglow was observed. Theories of the origin of the noise are discussed.  相似文献   

20.
To study the climatological role of ozone in the Precambrian atmosphere and the consequences of its reduction for the ultraviolet environment of the early biosphere, a coupled one-dimensional radiative-convective and photochemical model has been developed. Oxygen levels between 10−5 and 1 time the present atmospheric level (PAL) are considered. It is shown that when the ice-albedo feedback is taken into account, relatively important temperature decreases are associated with the ozone changes linked to the progressive decrease of the oxygen level from 1 PAL to smaller values.

A similar study is performed for enhanced atmospheric CO2 pressures (Pco2). In these conditions, the ozone column is increased at low O2 concentrations with respect to the Pco2 = 1 PAL case. Consequently, the larger CO2 concentration in the ancient atmosphere could have contributed to strengthen the ultraviolet screening of ozone. The surface temperature response to the ozone decrease, as well as the thermal profiles are also analyzed in these CO2-rich models. A possible evolutionary scenario of atmospheric O2 and CO2 is discussed.

The consequences of these calculations for the ultraviolet environment of the primitive biosphere is discussed with a quantitative model calculating bacterial surviving rates. According to this model, the minimum ozone column being tolerable by unprotected bacteria would fall between 1 × 1018 and 4 × 1018 cm−2, depending on the bacterial species considered and corresponding to an O2 level somewhat lower than 10−2 PAL. For the coccoid blue-green alga Agmenellum quadruplicatum, this minimum ozone column would be of 4.5 × 1018, a value which is only slightly less than the presently observed column in the spring time ozone hole of Antarctica.  相似文献   


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