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1.
We show that the Auger Air Shower Array has the potential to detect neutrinos of energies in the 1019 eV range through horizontal air showers. Assuming some simple conservative trigger requirements, we obtain the acceptance for horizontal air showers as induced by high energy neutrinos by two alternative methods and we then give the expected event rates for a variety of neutrino fluxes as predicted in different models which are used for reference. 相似文献
2.
The expected proton and neutrino fluxes from decays of massive metastable relic particles are calculated using the HERWIG QCD event generator. The predicted proton spectrum can account for the observed flux of extremely high energy cosmic rays beyond the Greisen-Zatsepin-Kuzmin cutoff, for a decaying particle mass of
(1012) GeV. The lifetime required is of
(1020) yr if such particles constitute all of the dark matter (with a proportionally shorter lifetime for a smaller contribution). Such values are plausible if the metastable particles are hadron-like bound states from the hidden sector of supersymmetry breaking which decay through nonrenormalizable interactions. The expected ratio of the proton to neutrino flux is given as a diagonistic of the decaying particle model for the forthcoming Pierre Auger Project. 相似文献
3.
We present optical and near-infrared (NIR) surface brightness and colour profiles, in bands ranging from U to K, for the disk and bulge components of a complete sample of 30 nearby S0 to Sbc galaxies with inclinations larger than 50 °. We describe in detail the observations and the determination of colour parameters. Calibrated monochromatic and real-colour images are presented, as well as colour index maps. This data set, tailored for the study of the population characteristics of galaxy bulges, provides useful information on the colours of inner disks as well. In related papers, we have used them to quantify colour gradients in bulges, and age differentials between bulge and inner disk. 相似文献
4.
We propose a multicomponent analysis of starburst galaxies, based on a model that takes into account the young and evolved stellar components and the gas emission, with their respective extinction, in the frame of a coherent dust distribution pattern. Near-IR signatures are preferentially investigated, in order to penetrate as deep as possible into the dusty starburst cores. We computed the 1.4-2.5 μm spectra of synthetic stellar populations evolving through strong, short timescale bursts of star formation (continuum and lines, R ? 500). The evolution model is specifically sensitive to cool stellar populations (AGB and red supergiant stars). It takes advantage of the stellar library of Lançon & Rocca-Volmerange (1992) [A&ASS, 96, 593], observed with the same instrument (FTS/CFHT) as the analysed galaxy sample, so that the instrumental effects are minimised. The main near-IR observable constraints are the molecular signatures of CO and H2O and the slope of the continuum, observed over a range exceptionally broad for spectroscopic data. The H - K colour determined from the spectra measures the intrinsic stellar energy distribution but also differential extinction, which is further constrained by optical emission line ratios. Other observational constraints are the near-IR emission lines (Brγ, He I 2.06 μm, [Fe II] 1.64 μm, H2 2.12 μm) and the far-IR luminosity. The coherence of the results relies on the interpretation in terms of stellar populations from which all observable properties are derived, so that the link between the various wavelength ranges is secured. The luminosity LK is used for the absolute calibration.We apply this approach to the typical spectrum of the core of NGC 1614. Consistent solutions for the starburst characteristics (star-formation rate, IMF, burst age, morphology) are found and the role of each observational constraint in deriving satisfactory models is extensively discussed. The acceptable contamination of the K band light by the underlying population amounts ≥ 15% even through a 5 arcsec aperture. The model leads to a limit on the direct absorption of Lyman continuum photons by dust situated inside the ionised areas, which in turn, with standard gas-to-dust ratios, translates into small characteristic sizes for the individual coexisting H II regions of the massive starburst area (clusters containing ∼ 102 ionising stars). We show that room is left for IMFs extending to 120 M⊙, rather than truncated at ∼ 60 M⊙ as most conservative studies conclude. High internal velocity dispersions (≥ 20 km s−1) are then needed for the H II regions. An original feature of this work is to base the analysis of near-infrared spectral galaxy observations on a large wavelength range, using models constructed with spectral stellar data observed with the same instrument. However a broader use of this spectral evolution model on other spectral or photometric data samples is possible if the spectral resolution of the model is adapted to observations or if colours are derived from the energy distributions.Catherine J. Cesarsky 相似文献
5.
We report the detection of the LiI λ6708 resonance line in the K4V secondary of the black-hole binary Nova Muscae 1991. The LiI feature changes with orbital phase, being stronger (EW ∼ 400 mÅ) around φ = 0.0 (observing the dark side of the secondary) and weaker (EW ≤ 190 mÅ) around φ = 0.5 (observing the side facing the compact object). This effect is interpreted as LiI ionization induced by UV/X-ray illumination of the inner hemisphere of the companion star. From the strength of the LiI feature observed around φ = 0.0 we infer a photospheric lithium abundance of logN(Li) ∼ 3. This value should be considered in fact as a lower limit to the true Li abundance because we have not fully corrected for the LiI overionization expected from UV/X-ray illumination.High lithium abundances are becoming a common feature in the secondaries of black hole binaries. After the Li detections in V404 Cyg, A0620-00 and GS2000 + 25, our observations of Nova Muscae not only add a new case to the list, but also demonstrate the impact of irradiation on the formation of the LiI line for the first time. The LiI features observed in the other black hole binaries are probably also affected by irradiation, although not as strongly as in Nova Muscae, and their Li abundances are higher than previously thought.The most attractive scenario for explaining the origin of the high Li abundances in black hole binaries appears to be nucleosynthesis during the explosive accretion events that characterize these objects. We argue that our LiI detection in the secondary of X-ray Nova Muscae 1991, and the transient γ-ray narrow emission feature at 476 keV observed during the 1991 outburst, are both signatures of Li production around the black hole. We propose that the γ-ray emission line was due to 7Be electron capture which yielded excited 7Li atoms. This reaction is able to account for the central energy, narrow width and time scale of the observed γ-ray emission feature. The presence of Li on the surface of the secondary shows that Li atoms created during the outburst can escape and enrich the interstellar medium.Shrinivas Kulkarni 相似文献
6.
Michael D. Gregg 《New Astronomy》1997,1(4):363-371
The diameter-velocity dispersion relation in B, V, and K for three early-type galaxies in the Leo I (M96) group is derived from published photometry and kinematic data. The relations in all three colors have slopes which agree well with those for the Coma cluster. The RMS scatter of the Leo I galaxies in each color is extremely small, consistent with the group's compactness. These relations yield estimates of the Coma-Leo I distance ratio of 9.01 ± 0.51, 8.77 ± 0.43, and 8.82 ± 0.31, respectively, with a weighted mean of 8.84 ± 0.23. The general agreement among the three colors indicates that the early-type galaxies in Leo I and Coma have similar stellar populations.
The Coma-Leo I distance ratio coupled with estimates of the absolute distance to the Leo I group allows the Hubble constant to be determined, free of the uncertainties which arise when working with the Virgo cluster. Several high quality distance estimates are available from a variety of techniques: Cepheids in M96 (Tanvir, N.R., et al., 1995, Natur, 377, 27) and M95 (Graham, J.A., et al., 1997, ApJ, 477, 535), surface brightness fluctuations (Tonry, J.L., et al., 1997, ApJ, 475, 399), planetary nebulae luminosity functions (Ciardullo, R., et al., 1993, ApJ, 419, 479), and the luminosity of the red giant branch tip (Sakai, S., Freedman, W.L., & Madore, B.F., 1996, in: Formation of the Galactic Halo, Inside and Out, eds. H. Morrison & A. Sarajedini, PASP Conf. Series Vol. 92). Adopting a cosmic recession velocity of the Coma cluster in the microwave background frame of 7200 ± 300 km s−1, these distance estimates lead to values of the Hubble constant ranging from 70 to 81 km s−1 Mpc−1, with an unweighted mean of 75 ± 6 km s−1 Mpc−1. 相似文献
7.
Some problems in determining the orbits of inner satellites associated with the complex behavior of the target function, which is strongly ravine and which possesses multiple minima in the case of the satellite orbit is determined based on fragmentary observations distributed over a rather long time interval, are studied. These peculiarities of the inverse problems are considered by the example of the dynamics of the inner Jupiter satellites: Amalthea, Thebe, Adrastea, and Metis. Numerical models of the satellite motions whose parameters were determined based on ground-based observations available at the moment to date have been constructed. A composite approach has been proposed for the effective search for minima of the target function. The approach allows one to obtain the respective evaluations of the orbital parameters only for several tens of iterations even in the case of very rough initial approximations. If two groups of observations are available (Adrastea), a formal minimization of the target function is shown to give a solution set, which is the best solution from the point of view of representation of the orbital motion, which is impossible to choose. Other estimates are given characterizing the specific nature of the inverse problems. 相似文献
8.
We propose a new class of inflationary models in which the scalar field potential governing inflation is generated by the same nonperturbative gauge dynamics that may lead to supersymmetry breaking. Such models satisfy constraints from cosmic microwave background measurements for natural values of the fundamental parameters in the theory. In addition, they have two particularly interesting characteristics: a “blue” spectrum of scalar perturbations, and an upper bound on the total amount of inflation possible. 相似文献
9.
Helioseismological sound-speed profiles severely constrain possible deviations from standard solar models, allowing us to derive new limits on anomalous solar energy losses by the Primakoff emission of axions. For an axion-photon coupling gay 5 × 10−10 GeV−1, the solar model is almost indistinguishable from the standard case, while gay 10 × 10−10 GeV−1 is probably excluded, corresponding to an axion luminosity of about 0.20 L. This constraint on gay is much weaker than the well-known globular-cluster limit, but about a factor of 3 more restrictive than previous solar limits. Our result is primarily of interest to the large number of current or proposed search experiments for solar axions because our limit defines the maximum gay for which it is self-consistent to use a standard solar model to calculate the axion luminosity. 相似文献
10.
We study the correlation between near-Earth observations of interplanetary coronal mass ejections (ICMEs) detected by the
Wind and ACE spacecrafts and their counterparts of coronal mass ejections (CMEs) observed near the Sun by the SOHO/LASCO coronagraph during
1996–2002. The results have been compared with an empirical model given by Gopalswamy, et al. (2000; 2001) to predict the
1-AU arrival time of CMEs. In this paper, we use an expected data set with a wider range with initial velocities than that
considered in previous models. To improve the accuracy of the predicted arrival time, we divided the CME events into two groups
according to their effective acceleration and deceleration. The results show that our model works well for events with a negative
acceleration in the initial velocity range between 500 and 2500 km/s, while the model described by Gopalswamy is better for
events with initial velocities near the solar wind velocity.
Published in Russian in Astronomicheskii Vestnik, 2009, Vol. 43, No. 2, pp. 137–144.
The text was translated by the authors. 相似文献
11.
Molecular hydrogen formation on the surfaces of interstellar dust grains has been studied numerically. Different stochastic methods (analogue Monte Carlo methods, direct solutions of the chemical master equation, continuous-time random-walk simulations, etc.) have been recently applied to the astrochemistry of hydrogen formation; however, the computational efficiency of these approaches is usually low because they are extremely time consuming (Herbst and Shematovich, 2003). A kinetic version of the Monte Carlo method based on splitting by physical processes is presented in the study. Each of the basic physical processes—adsorption of atomic hydrogen on the surface, thermal diffusion, formation of molecular hydrogen, and hydrogen desorption from the surface-are considered as independent random Markovian-type processes and are simulated using stochastic algorithms. The suggested numerical model is computationally efficient allowing calculations to be held on model surfaces with up to 106 active centers, which corresponds to interstellar grains of up to 0.4 μm in diameter. Test calculations of the efficiency of molecular hydrogen formation were held for the two models of the surfaces of interplanetary grains, namely, for the homogeneous surfaces of olivine and amorphous carbon. It was confirmed that the effective formation of molecular hydrogen in diffuse molecular clouds is possible only within a narrow range of dust-particle temperatures. A comparison with the numerical results of other authors is presented. 相似文献
12.
M. I. Gritsevich 《Solar System Research》2008,42(5):372-390
To date, several meteorites have been found for which their flight in the atmosphere was recorded by special fireball camera networks. Because of this, a thorough analysis of the instrumentally registered falls is of current importance. For such fireballs, not only the high-quality photo images of the motion in the atmosphere exist, but also the density and the shape of the meteor body fragments reached the Earth’s surface are known for sure. In the present study, for the Innisfree, Lost City, and Pribram fireballs, new models of the entry to the atmosphere have been built. The values of the ballistic coefficient and the mass-loss parameter providing the best approximation for the observations of the luminous trajectory segment with the analytical solution of the meteor physics equations have been obtained. From recent results of the numerical experiments on the supersonic airflow of bodies of various shapes, the preatmospheric masses of the fireballs, as well as the dynamic estimates of the mass at the other trajectory points, were obtained. In particular, the terminal mass of the fireballs in the lower segment of the analyzed trajectories is in good agreement with the total mass of the meteorite material recovered in all of the cases considered. Moreover, to calculate the acceleration of the meteor bodies, a new analytical formula has been suggested, which allows the obtained theoretical time dependencies of the velocity and altitude to be compared with the observational data. 相似文献
13.
Gerald D. Quinlan 《New Astronomy》1996,1(3):255-270
The collapse time for a cluster of equal-mass stars is usually stated to be either 330 central relaxation times (trc) or 12-19 half-mass relaxation times (trh). But the first of these times applies only to the late stage of core collapse, and the second only to low-concentration clusters. To clarify how the time depends on the density profile, the Fokker-Planck equation is solved for the evolution of a variety of isotropic cluster models, including King models, models with power-law density cusps of ρ ∼ r−γ, and models with nuclei. The collapse times for King models vary considerably with the cluster concentration when expressed in units of trc or trh, but vary much less when expressed in units of trc divided by a dimensionless measure of the temperature gradient in the core. Models with cusps have larger temperature gradients and evolve faster than King models, but not all of them collapse: those with 0 < γ < 2 expand because they start with a temperature inversion. Models with nuclei collapse or expand as the nuclei would in isolation if their central relaxation times are short; otherwise their evolution is more complicated. Suggestions are made for how the results can be applied to globular clusters, galaxies, and clusters of dark objects in the centers of galaxies.Scott D. Tremaine 相似文献
14.
The stability and evolution of cold, shock-bounded slabs is studied using numerical hydrodynamic simulations. We confirm the analysis of Vishniac (1994) [ApJ, 428, 186], who showed that such slabs are unstable if they are perturbed by a displacement larger than their width. The growth rate of this nonlinear thin shell instability (NTSI) is found to increase with decreasing wavelength, in qualitative agreement with Vishniac's analysis. The NTSI saturates when the bending angle becomes large and the growth in the width of the slab pinches off the perturbation. After saturation, the slab remains greatly extended with an average density much less than the original slab density, supported primarily by supersonic turbulence within the slab. Linear perturbations are also found to be unstable in that they can lead to turbulent flow within the slab, although this response to linear perturbations is distinct from, and much less violent than the NTSI.Richard McCray 相似文献
15.
We measured the extragalactic 0.7 keV X-ray background by observing the X-ray shadow of a neutral gas cloud in the Magellanic Bridge region. Two ROSAT PSPC observations of total 104 ks were complemented by a detailed H I mapping of the cloud with both the Parkes 64 m telescope and the Australia Telescope Compact Array. From the detected anti-correlation between the observed background intensity and the H I column density of the cloud, we derived the unabsorbed extragalactic background intensity as ∼ 28 keV s−1 cm−2 keV−1 sr−1 at ∼ 0.7 keV. The 95% confidence lower limit 18 keV s−1 cm−2 keV−1 sr−1 is greater than the expected point-like source contribution ? 14 keV s−1 cm−2 keV−1 sr−1, constrained by the mean source spectrum together with the total background intensity in the 1-2 keV band. A significant fraction of the 0.7 keV background likely arises in a diffuse hot intergalactic medium of a few million degrees, as has been predicted in hydrodynamic simulations of cosmological structure formation.Richard McCray 相似文献
16.
We present the results of a CCD monitoring campaign of the continuum emission from the central region of the Crab nebula, amounting to 17 epochs spread over 3.5 years. The data provide clear evidence that the brightest wisps move outward from the pulsar at mildly relativistic velocities. This motion, combined with the shape of the wisps, supports the idea that they arise at a standing shock in an equatorial wind. The deprojected velocity of the wisps in the equatorial plane is c/3. We see only small changes in the so-called ‘thin wisps’ which leads us to suggest that these wisps may be the result of a back-flow from the shock in a toroidal cavity around the pulsar. 相似文献
17.
We report intermediate resolution H spectroscopy of the black hole candidate Nova Muscae 1991 during quiescence. We classify the companion star as a K3-K4V which contributes 85±6 percent to the total flux from the binary. The photospheric absorption lines are broadened by 106±13 kms−1 with respect to template field stars, leading to a system mass ratio of q =M1/M2 = 7.8−2.0+3.4. Doppler imaging of the H line shows strong emission coming from the secondary star (EW=3.1±0.6Å) which we associate with chromospheric activity. However, the hot-spot is not detected and this may indicate a lower mass transfer rate than in other X-ray transients of comparable orbital periods. The surface brightness distribution of the accretion disk in H follows a relation I∝R−1.1, less steep than typically observed in cataclysmic variables. Updated system parameters are also presented. 相似文献
18.
We report the observations of a coronal mass ejection (CME) using the Soft X-ray Telescope on board the Yohkoh Mission. The CME had the familiar three part structure (frontal loop, prominence core and a cavity). The erupting prominence was observed by the Nobeyama radioheliograph. We were able to determine the mass of the CME (2.6 × 1014 g) from X-ray observations which seems to be at the lower end of the range of CME masses reported before from white light observations. This is the first time the mass of a CME has been determined from X-ray observations. The height of onset of the CME was 0.3R⊙. The CME moved much faster than the erupting prominence while its acceleration was smaller than that of the erupting prominence.J. Leonard Culhane 相似文献
19.
From the data on bright stars of different spectral and luminosity classes from the 13-color photometry catalog, the selective extinction of light by the interstellar dust has been studied. The stars from the 1000-pc vicinity of the Sun were investigated. In the optical spectral range, the interstellar extinction curves show systematic deviations from the “λ?1” law, which allows one to sort them into three types. The observed curves of the interstellar dust extinction were compared with the theoretical curves calculated from the reflectance spectra of the asteroids under the approximation of the Rayleigh particles. The calculated extinction curves for the surface material of D-type asteroids and the Tagish Lake carbonaceous chondrite agree rather well with the observed curves of the interstellar extinction of the first type. 相似文献
20.
High-velocity comet and asteroid impacts onto the Moon are considered and the material masses ejected after such impacts at velocities above the second-cosmic velocity for the Moon (2.4 km/s) are calculated. Although the results depend on a projectile type and the velocity and angle of an impact, it has been demonstrated that, on average, the lunar mass decreases with time. The Moon has lost about 5 × 1018 kg, that is, about one-hundredth of a percent of its mass, over the last 3.8–3.9 billion years. The ejection of lunar meteorites and lunar dust, rich in 3He, is considered as well. The results of the study are compared to the results of earlier computations and data on lunar meteorites. 相似文献