Corrected Hawking radiation from a charged rotating black string

Using the Damour–Ruffini method, Hawking radiation from a four-dimensional charged rotating black string in asymptotically anti-de Sitter space–time is investigated. When energy, angular momentum, charge conservations, and the particles’ back-reaction to the space–time are taken into account, the exact emission spectrum near the horizon is calculated. The horizon is not spherical, but can be toroidal and cylindrical. Our results indicate that the spectrum is not purely thermal, which may be consistent with an underlying unitary theory. Moreover, it is a possible mechanism to explain the information loss paradox.     

Eigenvector Sky Subtraction

We develop a new method for estimating and removing the spectrum of the sky from deep spectroscopic observations. Our method does not rely on simultaneous measurement of the sky spectrum with the object spectrum. The technique is based on the iterative subtraction of continuum estimates and eigenvector sky models derived from singular value decompositions of sky spectra and sky spectra residuals. Using simulated data derived from small-telescope observations, we demonstrate that the method is effective for faint objects on large telescopes. We discuss simple methods to combine our new technique with the simultaneous measurement of sky to obtain sky subtraction very near the Poisson limit.     

Solar cycle changes in the high frequency spectrum

We present observations of high frequency, intermediate degree, Ca-K line solar intensity oscillations. We compare the peak frequencies determined from these 1991.4 observations with the peak frequencies from 1987.9 South Pole observations (Duvallet al., 1991) in that portion of the spatio-temporal diagram where the two datasets overlap (degrees between 30 and 150 and frequencies between 4 and 6.6 mHz). We find that temporal changes are detectable in the high frequency spectrum and are particularly large near 5.4 mHz. The m-averaged high frequency peaks decreased in frequency in 1991.4 compared to the peak frequencies measured in 1987.9. The magnitude of the frequency shift is of the order of 10 μHz near 5.4 mHz, increases with degree, and decreases to near zero both above and below 5.4 mHz. It is unlikely that these temporal changes in the high frequency spectrum are due to a change in the height of the subphotospheric acoustic source layer. A physical mechanism for these frequency shifts has not yet been identified.     

IRAS 17213-3841:晚型富碳星还是早型发射线星?

IRAS 17213-3841作为富碳星列于新版碳星星表中．然而该星的IRAS低分辨率光谱显示富氧的硅酸盐发射特征；光谱观测结果表明，该星是一个接近零龄主序的，光谱型为O9／B0的早型发射线星，而不是碳星，因此应从碳星星表中剔除．此外，将它证认为碳星的近红外-IRAS双色图方法并不是一个完全可靠的方法，用这一方法来证认碳星必须十分小心．     

Estimation of plasma parameters in an accretion column near the surface of accreting white dwarfs from their flux variability

We consider the behavior of matter in the accretion column that emerges under accretion in binary systems near the surface of a white dwarf. The plasma heated in a standing shock wave near the white dwarf surface efficiently radiates in the X-ray energy band. We suggest a method for estimating post-shock plasma parameters, such as the density, temperature, and height of the hot zone, from the power spectrum of its X-ray luminosity variability. The method is based on the fact that the flux variability amplitude for the hot region at various Fourier frequencies depends significantly on its cooling time, which is determined by the parameters of the hot zone in the accretion column. This allows the density and temperature of the hot matter to be estimated. We show that the characteristic cooling time can be efficiently determined from the break frequency in the power spectrum of the X-ray flux variability for accreting white dwarfs. The currently available X-ray instruments do not allow such measurements to be made because of an insufficient collecting area, but this will most likely become possible with new-generation large-area X-ray spectrometers.     

On the presence of silicon and carbon in the pre-maximum spectrum of the Type Ia SN 1990N

The spectrum of the normal Type Ia SN 1990N observed very early on (14 days before B maximum) was analysed by Fisher et al., who showed that the large width and the unusual profile of the strong line near 6000 Å can be reproduced if the line is assumed to be due to C  ii 6578, 6583 Å and if carbon is located in a high-velocity shell. This line is one of the characterizing features of SNe Ia, and is usually thought to be due to Si  ii . A Monte Carlo spectrum synthesis code is used to investigate this suggestion further. The result is that if a standard explosion model is used, the mass enclosed in the shell at the required high velocity (25 000–35 000 km s⁻¹) is too small to give rise to a strong C  ii line. At the same time, removing silicon has a negative effect on the synthetic spectrum at other wavelengths, and removing carbon from the lower velocity regions near the photosphere makes it difficult to reproduce two weak lines which are naturally explained as C  ii , one of them being the line which Fisher et al. suggested is responsible for the strong 6000-Å feature. However, synthetic spectra confirm that although Si  ii can reproduce most of the observed 6000-Å line, the red wing of the line extends too far to be compatible with a Si  ii origin, and that the flat bottom of the line is also not easy to reproduce. The best fit is obtained for a normal SN Ia abundance mix at velocities near the photosphere (15 500–19 000 km s⁻¹) and an outer carbon–silicon shell beyond 20 000 km s⁻¹. This suggests that mixing is not complete in the outer ejecta of an SN Ia. Observations at even earlier epochs might reveal to what extent a carbon shell is unmixed.     

Structure of the solar oscillation with period near 160 minutes

The solar oscillation with period near 160 min is found to be unique in a spectrum computed over the range of periods from about 71 to 278 min. Our best estimate of the period is 160.0095 ± 0.001 min, which is different from 160 min (1/9 of a day) by a highly significant amount. The width of the peak is approximately equal to the limiting resolution that can be obtained from an observation lasting 6 years, which suggests that the damping time of the oscillations is considerably longer than 6 years. A suggestion that this peak might be the result of a beating phenomenon between the five minute data averages and a solar oscillation with period near five minutes is shown to be incorrect by recomputing a portion of the spectrum using 15 s data averages.     

Multicolour Photometry of RX and During 1994/95

The cataclysmic star RX And was observed in the states standstill and quiescence. They differed not only in the light level but in the type of variations around this level. The standstill observed by us turned out quite near to the maximum light and its duration was unusually long. The energy distribution of RX And at the standstill seemed similar to the spectrum of an accretion disk. Two variabilities with periods 3 h 43 min and 1 h 26 min were found at the standstill but only the second of them was present at quiescence too. The star did not show light variability with the spectroscopic period. We tried to interpret some of the results by the supposition that the Z Cam-stars are an intermediate subtype of the cataclysmic stars evolving from UX UMa-subtype to U Gem-subtype and that probably RX And presents a pattern of Z Cam-star that is very near to the U Gem-subtype.     

A spectral comparison of (379) Huenna and its satellite

We present near-infrared spectral measurements of Themis family Asteroid (379) Huenna (D ∼ 98 km) and its 6 km satellite using SpeX on the NASA IRTF. The companion was farther than 1.5″ from the primary at the time of observations and was approximately 5 magnitudes dimmer. We describe a method for separating and extracting the signal of a companion asteroid when the signal is not entirely resolved from the primary. The spectrum of (379) Huenna has a broad, shallow feature near 1 μm and a low slope, characteristic of C-type asteroids. The secondary’s spectrum is consistent with the taxonomic classification of C-complex or X-complex. The quality of the data was not sufficient to identify any subtle feature in the secondary’s spectrum.     

Lunar conductivity models from the Apollo 12 magnetometer experiment

A number of conductivity models have been investigated for compatibility with the Apollo 12 magnetometer data. Except at the highest frequencies, a simple core-crust model is compatible with the observed dayside transfer function, which is expressed as the ratio of the lunar surface field spectrum to the interplanetary magnetic field spectrum. All conductivity profiles exhibit a peak near 1500 km, when the models are constrained to conform to the observed flat response at the higher frequencies. However, at frequencies above 0.01 Hz the long wavelength limitation of the theoretical model is no longer valid. A combination of dayside and nightside models and data indicate that a conductivity profile with a peak (0.003 mho/m) near 1500 km radius and a core conductivity of about 0.01 mho/m at 1000 km is compatible with the observations, as is a monotonic conductivity profile with 0.0005 mho/m at 1600 km and a core conductivity of 0.01 mho/m at 1000 km radius.A plausible explanation for the difference between the north-south and east-west transfer functions is that it is due to a time varying compression of the remanent (dc) field at the Apollo 12 site by fluctuations in the solar wind plasma. Providing that the spectrum of these compressive fluctuations is not strongly frequency dependent, the result of removing this effect will be to decrease slightly the estimated conductivity.Bellcomm, Inc., 955 L'Enfant Plaza North, S.W. Washington, D.C. 20024, U.S.A.     

Evidence for condensed-phase methane enhancement over Xanadu on Titan

We present evidence for condensed-phase methane precipitation near Xanadu using nine nights of observations from the SINFONI integral-field spectrograph at the Very Large Telescope and imaging analysis with empirical surface subtraction. Radiative transfer models are used to support the imaging technique by simulating the spectrometer datacubes and testing for variations in both the surface reflectivity spectrum and atmospheric opacity. We use the models and observations together to argue against artifacts that may arise in the image analysis. High phase angle observations from Cassini/VIMS are used to test against surface scattering artifacts that may be confused with sources of atmospheric opacity. Although changes in the surface reflectivity spectrum can reproduce observations from a particular viewing geometry on a given night, multiple observations are best modeled by condensed-phase methane opacity near the surface. These observations and modeling indicate that the condensed-phase methane opacity observed with this technique occurs predominantly near Xanadu and is most likely due to precipitation.     

Atmospheric emission from hydrogen-shell-burning white dwarfs as supersoft X-ray sources

The radiation spectra of supersoft X-ray sources based on a model for hydrogen burning on the white dwarf surface are investigated by solving hydrostatic equilibrium, radiative equilibrium, statistical equilibrium and radiative transfer self-consistently for various sets of mass, radius and luminosity. It is found that the radiation spectrum shows many bound–free emission/absorption features and greatly deviates from the blackbody spectrum at the effective temperature. By the effect of incoherent Compton scattering, the bound–free emission/absorption features do not appear in strong emission/absorption edges, as predicted by coherent models without Compton scattering, but appear as weak humps and relatively shallow absorption edges. The difference between the incoherent model and the coherent model is prominent for L 0.5 L _Edd. A calculated spectrum is fitted to the ASCA observations of RX J0925.7−4758. It is found that the entire spectrum of RX J0925.7−4758 cannot be reproduced by model atmospheres with any parameter sets. This suggests that the observed spectrum consists of two or more components. In this case, the atmospheric component is explained by the emission from a white dwarf near the Chandrasekhar limit (∼1.4 M_⊙) with L ∼0.2 L _Edd at a distance of 16–20 kpc.     

Origin of power-law X-ray emission in the steep power-law state of X-ray binaries

We present a new explanation for the origin of the steep power-law(SPL) state of X-ray binaries.The power-law component of X-ray emission is the synchrotron radiation of relativistic electrons in highly magnetized compact spots orbiting near the inner stable circular orbit of a black hole.It has a hard spectrum that extends to above MeV energies,which is determined by the electron acceleration rate.These photons are then down-scattered by the surrounding plasma to form an observed steep spectrum.We discuss ...     

Interplanetary dust particles near Jupiter

We calculate the expected counting rate of a flat micrometeoroid detector of finite sensitivity passing in hyperbolic orbit near a planet. We assume that the distribution of particle sizes, s, can be expressed as a power law spectrum of index p, i.e. dN(s) = Cs^?pds, and also that the particles encounter the sphere of influence of the planet with a certain speed v_∞. The results of the calculations are then compared with the results returned by Pioneer 10 in its flyby of Jupiter. The observed increase in impact rate near Jupiter can be completely explained in terms of gravitational “focusing” of particles which are in heliocentric orbits; i.e., they are not in orbit about Jupiter. The absolute concentration of particles near the orbit of Jupiter is of the same order as at 1 AU: the exact ratio being a function of particle speed and spectral index. Data from one flyby are insufficient to determine a unique value for both the spectral index, p, and the particle velocity, v_∞, but limits can be set. For reasonable encounter speeds (corresponding to eccentricities and inclinations of dust particles experienced near the Earth), the particles near Jupiter are characterized by a spectrum of index p ～ 3. The spectral index which best fits the data increases with increasing encounter speeds.     

Electron population aging models for wide-angle tails

Color–color diagrams have been useful in studying the spectral shapes in radio galaxies. At the workshop we presented color–color diagrams for two wide-angle tails, 1231+674 and 1433+553, and found that the standard aging models do not adequately represent the observed data. Although the JP and KP models can explain some of the observed points in the color–color diagram, they do not account for those found near the power-law line. This difficulty may be attributable to several causes. Spectral tomography has been previously used to discern two separate electron populations in these sources. The combination spectra from two such overlying components can easily resemble a range of power-laws. In addition, any non-uniformity in the magnetic field strength can also create a power-law-like spectrum. We will also discuss the effects that angular resolution has on the shape of the spectrum.     

HCN fluorescence on Titan

The HCN emission features near 3 μm recently detected by Geballe et al. (2003, Astrophys. J. 583, L39) are analyzed with a model for fluorescence of sunlight in the ν₃ band of HCN. The emission spectrum is consistent with current knowledge of the atmospheric temperature profile and the HCN distribution inferred from millimeter-wave observations. The spectrum is insensitive to the abundance of HCN in the thermosphere and the thousand-fold enhancement relative to photochemical models suggested by Geballe et al. (2003, Astrophys. J. 583, L39) is not required to explain the observations. We find that the spectrum can be matched with temperatures from 130 to 200 K, with slightly better fits at high temperature, contrary to the temperature determination of 130±10 K of Geballe et al. (2003, Astrophys. J. 583, L39). The HCN emission spectrum is sensitive to the collisional de-excitation probability, P₁₀, for the ν₃ state and we determine a value of 10⁻⁵ with an accuracy of about a factor of two. Analysis of absorption lines in the C₂H₂ν₃ band near 3 μm, detected in the same spectrum, indicate a C₂H₂ mole fraction near 0.01 μbar of 10⁻⁵ for P₁₀=10⁻⁴. The derived mole fraction, however, is dependent upon the value adopted for P₁₀ and lower values are required if P₁₀ at Titan temperatures is less than its room temperature value.     

Evolution of the Solar Flare Energetic Electrons in the Inhomogeneous Inner Heliosphere

Solar flare accelerated electrons escaping into the interplanetary space and seen as type III solar radio bursts are often detected near the Earth. Using numerical simulations we consider the evolution of energetic electron spectrum in the inner heliosphere and near the Earth. The role of Langmuir wave generation, heliospheric plasma density fluctuations, and expansion of magnetic field lines on the electron peak flux and fluence spectra is studied to predict the electron properties as could be observed by Solar Orbiter and Solar Probe Plus. Considering various energy loss mechanisms we show that the substantial part of the initial energetic electron energy is lost via wave–plasma processes due to plasma inhomogeneity. For the parameters adopted, the results show that the electron spectrum changes mostly at the distances before ～?20 R _⊙. Further into the heliosphere, the electron flux spectrum of electrons forms a broken power law relatively similar to what is observed at 1 AU.     

Methane Abundance on Titan, Measured by the Space Telescope Imaging Spectrograph

Although methane is the dominant absorber in Titan's reflection spectrum, the amount of methane in the atmosphere has only been determined to an order of magnitude. We analyzed spectra from the Space Telescope Imaging Spectrograph, looking at both a bright surface region (700-km radius) and a dark surface region. The difference between the spectra of the two regions is attributed to light that has scattered off the surface, and therefore made a round-trip through all of Titan's methane. Considering only absorption, the shape of the difference spectrum provides an upper limit on methane abundance of 3.5 km-am. Modeling the multiple scattering in the atmosphere further constrains the methane abundance to 2.63±0.17 km-am. In the absence of supersaturation and with a simplified methane vertical profile, this corresponds to a surface methane-mole fraction near 3.8% and a relative humidity of 0.32. With supersaturation near the tropopause, the surface methane mole fraction could be as low as 3%.     

Discrete ULF modes in the Earth’s magnetosphere near the Alfven frequency minimum

The equation of small oscillations of ULF waves in the Earth’s magnetosphere is derived accounting for a fast magnetosonic wave. The spectrum of discrete Alfven modes near the Alfven frequency minimum is studied on the basis of this equation.     

On poloidal mode coupling in the continuous spectrum of 2D equilibria

The continuous spectrum of linear ideal MHD is determined analytically in 2D magnetostatic models for coronal loops and arcades by means of a perturbation expansion. Poloidal mode coupling, induced by non-circularity of the cross-sections of the magnetic surfaces and/or variation of the plasma density along the magnetic field lines, is shown to occur in first order. The coupling is most pronounced on and near rational surfaces for particular poloidal and toroidal mode numbers and produces gaps in the continuous spectrum of ideal MHD.