Relativistic Fe Kα features in the XMM‐Newton spectrum of the intermediate Seyfert galaxy 4U 1344‐60

We present the analysis of optical and X‐ray XMM‐Newton data of the source 4U 1344‐60. On the basis of the optical data we propose to classify 4U 1344‐60 as a Seyfert 1.5 galaxy and we measured a redshift value z = 0.012 ± 0.001. The observed X‐ray spectrum is complex. The continuum emission can be described as a power law obscured by two neutral absorption components. 4U 1344‐60 exhibits a broad and skewed iron line at 6.4 keV most likely originated in a few gravitational radius of an accretion disc. The analysis also reveals the presence of two narrow emission line‐like features at ∼4.9 keV and ∼5.3 keV. Assuming that hot spots on the surface of the accretion disc, orbiting very close to the black hole is responsible of these emission lines, the accretion disc would present an inclination of 20° and the active regions would be located in the 6–10 R _g radius range. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An iras atlas of ysos in nearby dark clouds

We are using the newIRAS Sky Survey Atlas to construct a catalog of Galactic dark clouds and their associated Young Stellar Objects (YSOs). FromIRAS 100 and 60µm data we calculate images of the 100µm optical depth distribution in the clouds. Using theIRAS Faint Source Catalog we identify sources which have colors indicative of YSOs and have positions that lie inside cloud boundaries in the optical depth images. Here we present some preliminary results of applying this analysis to the Chamaeleon dark cloud complex.     

Nir spectroscopy and molecular shocks in Herbig-Haro 1

Near Infrared spectroscopic observations (1.2–2.4µm) of two condensations (HH 1A & HH 1G) of Herbig-Haro object 1 are used to explore the nature of its molecular shocks and extinction. The H₂ emission lines display a more complex behaviour than that accounted for C or J type shock models. The extinction, determined from the ratio of [Fe II] 1.257 & 1.644µm, is higher than what is expected from optical [S II] measurements, and it may indicate real discrepancies between the optical and IR regions of the ISM extinction curve.     

Solar spectrum distribution and optical depth of Bahrain's sky

The solar spectrum of wavelength 350–800 nm has been measured for the four seasons. The intensity of the solar radiation in W m^-2 nm^-1 has been calculated and used to estimate the monochromatic optical depth of Bahrain's sky. It was found that the optical depth (i.e., extinction coefficient,k) is least in winter and highest in summer. Comparison of the hourly variation of the optical depth between Bahrain's atmosphere and that of Dhahran (Saudi Arabia) shows that the abundance of small size particles in the former is more than in the latter. This causes more extinction effect in Bahrain than in Dhahran, especially in the wavelengths 350–525 nm. The relation betweenk and for each season in Bahrain is in the formk =A ⁿ , whereA is a constant andn is a negative integer, is reported in this study.     

Solution of Riemann–Hilbert problems for determination of new decoupled expressions of Chandrasekhar’s <Emphasis Type="Italic">X</Emphasis>- and <Emphasis Type="Italic">Y</Emphasis>-functions for slab geometry in radiative transfer

In radiative transfer, the intensities of radiation from the bounding faces of a scattering atmosphere of finite optical thickness can be expressed in terms of Chandrasekhar’s X- and Y-functions. The nonlinear nonhomogeneous coupled integral equations which the X- and Y-functions satisfy in the real plane are meromorphically extended to the complex plane to frame linear nonhomogeneous coupled singular integral equations. These singular integral equations are then transformed into nonhomogeneous Riemann–Hilbert problems using Plemelj’s formulae. Solutions of those Riemann–Hilbert problems are obtained using the theory of linear singular integral equations. New forms of linear nonhomogeneous decoupled expressions are derived for X- and Y-functions in the complex plane and real plane. Solutions of these two expressions are obtained in terms of one known N-function and two new unknown functions N ₁- and N ₂- in the complex plane for both nonconservative and conservative cases. The N ₁- and N ₂-functions are expressed in terms of the known N-function using the theory of contour integration. The unknown constants are derived from the solutions of Fredholm integral equations of the second kind uniquely using the new linear decoupled constraints. The expressions for the H-function for a semi-infinite atmosphere are obtained as a limiting case.     

Simultaneous linear and circular polarization observations of blazars 3C 66A,OJ 287 and Markarian 421

We present the first ever simultaneous optical linear and circular polarization observations of blazars. These polarizations have been measured simultaneously inUBVRI-bands in three blazars; 3C 66A, OJ 287 and Markarian 421. Measured linear polarization in 3C 66A was the largest ever observed, at PR = 33.1 ± 0.5 per cent. In 3C 66A we detected small circular polarization in the other bands, exceptU. In OJ 287 we detected variable circular polarization in theU-band.     

On the diffuse radiation of the Galaxy in far UV according to the investigations by S. Hayakawa,K. Yamashita and S. Yoshioka

It has been found that certain optical properties of interstellar grains obtained by Hayakawaet al. (1969) from their study of the diffuse radiation of the Galaxy in far UV are not in reality consistent with the more accurate theoretical calculations of diffuse radiation for the model of the Galaxy used by Hayakawaet al. in their work. A more complex model of the Galaxy may be required for interpretation of observations in far UV.Receipt delayed by postal strike in Great Britain.     

The equation of state of a cosmological selfgravitating fluid influenced by thermal or turbulent motion and the primeval background radiation

A variety of new optical observations have been made over the bright core of the supermassiveHii region 30 Doradus and the ionized filamentary material surrounding this object. In addition, a more detailed analysis of previously published interstellar absorption andHi emission profiles has been undertaken.The velocity and density structure of this complex region is discussed and the new results analysed here shown to be compatible to the model of 30 Doradus presented in Cantóet al. (1980) and Meaburn (1980).     

Measuring Seeing from Solar Scintillometry and the Spectral Ratio Technique

In principle, the optical transfer function can be described by a single parameter, the Fried parameter r ₀, which reveals the net effect of the turbulence along the line of sight. We present measurements of the Fried parameter obtained from the spectral ratio technique and compare them to data from solar scintillometry and from angle-of-arrival fluctuations. The measurements were performed at the Big Bear Solar Observatory (BBSO) in 1997 and 1998 – before and after a series of steps were taken to reduce dome seeing. The results show that the dome seeing was considerably reduced and now approaches the seeing conditions measured outside the dome. The Fried parameter as measured by the spectral ratio technique now frequently exceeds r ₀=10 cm at our lake site observatory. Accounting for the remaining dome and window seeing, the scintillometer and the angle-of-arrival data imply the potential for an r ₀>20 cm for BBSO during days of good seeing.     

Photometry of the open cluster NGC 6996 in the North America Nebula

Thirty stars in the direction of the open cluster NGC 6996 are measured in the Vilnius photometric system. Photometric spectral types, absolute magnitudes, interstellar reddenings, extinctions, and distances are determined for most of them. Fifteen stars are suspected to be cluster members. Their mean distance is 620±30 pc and mean extinctionA _v is 1.74 mag. The extinction within the cluster is variable. The age of the cluster is of the order of 10⁸ yr and this excludes the possibility that it is evolutionary related with the North America and Pelican Nebulae complex. The distance of this complex 550 pc is confirmed.     

X-ray and optical variability of the seyfert galaxy NGC 7469

Based on our UBV RI observations and X-ray data from the RXTE satellite, we have investigated the variability of the galaxy NGC 7469 over the period 1995–2009. In 1995–2000, the optical brightness of the galactic nucleus changed almost by 1 ^m in the U band. In 2000–2009, the amplitude of the optical variations was considerably lower. Regular X-ray observations began only in 2003. The X-ray fractional variability amplitude is higher than the optical one. The optical variability amplitude decreases with increasing wavelength. The full width at half maximum of the X-ray and B-band autocorrelation functions is about 8 and 62 days, respectively. The structure functions (SF) in the X-ray range on time scales up to 7 days and in the optical range on time scales up to 100 days have the form of a power law SF(τ) ∼ τ ^b , where τ is the time shift. On time scales of more than a day, where both structure functions have been determined rather reliably, their slopes differ markedly: b = 1.34 ± 0.06 and b = 0.25 ± 0.05 for the optical and X-ray ranges, respectively. The X-ray and B-band structure functions begin to flatten, respectively, near 6–8 days and on time scales of about 90 days. The observed structure functions can be described by the model of a superposition of independent Gaussian flares whose number changes with duration ω as n(ω) ∼ ω ^α and whose amplitudes depend on duration as A(ω) ∼ ω ^β. The flux distribution and the flux-amplitude relation are consistent with the model of a light curve in the form of a superposition of random flares. Once the fast intensity variations have been filtered out on long time scales, the X-ray light curve correlates well with the optical one. No lag of the X-ray variations relative to those in the B band is detected. The light variations in the R and I bands lag behind those in the B band calculated from the centroid of the cross-correlation function by 2.6 and 3.5 days, respectively, at a 3σ confidence level.     

On correlation of Hα, iron and oxygen line strengths in some B, Be and shell stars

We present the equivalent width measurements of the hydrogen H _α line, the oxygen near-IR triplet OI 7772–5 Å\AA and of a number of FeII lines in several B, Be, and shell stars in optical and near-infrared regions. A study of the correlations between all these measured quantities has been made. The correlations of strength of lines with collected data of the near-IR color excess, the rotational velocity and the intrinsic polarization are also obtained and presented.     

Parameters of irradiated accretion disks from optical and X-ray observations of GS 1826-238

We show that the set of observational characteristics for low-mass X-ray binaries in the optical and X-ray bands can be explained in terms of the model of an optically thick accretion disk with an atmosphere irradiated by a central X-ray source. We show that this set of observational data can be successfully used to measure the orbital inclination of a binary, the geometric parameters of its accretion disk, and the reprocessing time of X-emission to optical one. For the burster GS 1826-238, a low-mass X-ray binary with a neutron star, we have estimated the binary inclination and the thickness of the disk atmosphere at the outer edge from the mean optical flux and the amplitude of periodic modulations in the optical light curve: i = 62.5° ± 5.5° and H _d/R _d = 0.145 ± 0.009. The optical response time of the binary to an X-ray burst disagrees with the geometric delay in the propagation of X-ray photons in the binary. We believe that this points to a finite X-ray reprocessing/reradiation time, 1.0 s ≲ τ _repr ≲ 2.2 s, in the hot atmosphere above the accretion disk.     

New concept for testing General Relativity: the Laser Astrometric Test Of Relativity (LATOR) mission

This paper discusses a Fundamental physics experiment that will test relativistic gravity at the accuracy better than the effects of the second order in the gravitational field strength, ∝ G². The Laser Astrometric Test Of Relativity (LATOR) mission uses laser interferometry between two micro‐spacecraft whose lines of sight pass close by the Sun to accurately measure deflection of light in the solar gravity. The key element of the experimental design is a redundant geometry optical truss provided by a long‐baseline (100 m) multi‐channel stellar optical interferometer placed on the International Space Station (ISS). The spatial interferometer is used for measuring the angles between the two spacecraft and for orbit determination purposes. In Euclidean geometry, determination of a triangle's three sides determines any angle therein; with gravity changing the optical lengths of sides passing close by the Sun and deflecting the light, the Euclidean relationships are overthrown. The geometric redundancy enables LATOR to measure the departure from Euclidean geometry caused by the solar gravity field to a very high accuracy. LATOR will not only improve the value of the parameterized post‐Newtonian (PPN) γ to unprecedented levels of accuracy of 1 part in 10⁸, it will also reach ability to measure effects of the next post‐Newtonian order (c⁻⁴) of light deflection resulting from gravity's intrinsic non‐linearity. The solar quadrupole moment parameter, J₂, will be measured with high precision, as well as a variety of other relativistic effects including Lense‐Thirring precession. LATOR will lead to very robust advances in the tests of Fundamental physics: this mission could discover a violation or extension of general relativity, or reveal the presence of an additional long range interaction in the physical law. There are no analogs to the LATOR experiment; it is unique and is a natural culmination of solar system gravity experiments. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Numerical simulation of a permittivity probe for measuring the electric properties of planetary regolith and application to the near‐surface region of asteroids and comets

Abstract— We present a numerical simulation technique for the retrieval of the electric properties relative permittivity and conductivity of planetary, asteroid, and cometary regolith. Our simulation techniques aim at accompanying hardware development and conducting virtual experiments, e.g., to assess the response of arbitrary heterogeneous conductivity and permittivity distributions or to scrutinize possibilities for spatial reconstruction methods using inverse schemes. In a first step, we have developed a finite element simulation code on the basis of unstructured, adaptive triangular grids for arbitrary two‐dimensional axisymmetric distributions of conductivity and permittivity. The code is able to take into account the spatial geometry of the probe and allows for possible inductive effects. In previous studies, the non‐inductive approach has been used to convert potential and phase data into apparent material properties. By our simulations, we have shown that this approach is valid for the frequency range from 10² Hz to 10⁷ Hz and electric conductivities of 10^?8 S/m that are typical for the near‐surface region of asteroids and comets composed of chondritic materials and/or frozen volatiles such as H₂O and CO₂ ice. We prove the accuracy of our code to be better than 10%, using mixed types of boundary conditions and present a simulated vertical log through a horizontally stratified subsurface layer as a representative example of a heterogeneous distribution of the electrical properties. Resolution studies for the given electrode separation reveal that the material parameters of layers having thicknesses of less than about half the electrode spread are not reconstructible if only apparent quantities are considered. Therefore, spatial distributions of the complex sensitivity are presented having in mind a future data inversion concept that will permit the multi‐dimensional reconstruction of material parameters in heterogeneous environments.     

Optical constants of the mixture of ices

The Maxwell-Garnett mixing rule (MG) was applied to estimate the optical constant m ^* of the mixture of ices. A fairly good agreement between the resulting values of m ^* and those of our laboratory measurements suggests that the MG rule becomes a powerful tool to derive the unknown optical constants of natural dirty-ice, when there are no chemical bonds between the guest and host materials. Our results would provide the knowledge of the optical constants of dirty-ice for studies of icy substances on the surface of satellites, cometary nucleus and interplanetary dust grains based on their reflectance spectra.     

Optical approach to gravitational redshift

An optical approach begins by interpreting the gravitational redshift resulting to a change in the relative velocity of light due to the medium of propagation in the gravitational field. The discussion continues by pointing out an agreement in structure between the equation for rays in geometrical optics and the geodesic equation of general relativity. From their comparison we learn that the path of rays should be written in the form ds ²=n ²(r)dr ²+r ² dθ ², not ds ²=dr ²+r ² dθ ², in a medium with spherical symmetry of refractive index n(r). The development of an optical analogy suggests introducing n ²(r) in place of g _rr as an optical version of the Schwarzschild metric. In form and content, n ²(r) is different from g _rr . The optical point of view replaces the general-relativity explanations in terms of time and gravitation.     

Analytical Approach to Calculate Quasi-thermal Noise Spectrum in Irregular Plasma

Basic properties of quasi-thermal noise spectrum in irregular plasma have been investigated using an analytical point of view. A simple formula for the plasma frequency splitting effect has been obtained for ionospheric conditions. A passive electric antenna, immersed in a stable plasma, detects the fluctuations of the electric potential due to thermal motion of the ambient particles. Properties of this quasi-thermal noise spectrum in homogeneous plasma are relatively well known and are effectively used for diagnostics of space plasma (Aksenov et al., 1978; Trakhtengerts and Chugunov, 1978; Kellog, 1981; Meyer-Vernet and Perche, 1989). Especially, in the Earth's ionosphere or solar wind plasma, random irregularities of electron density are always present. These irregularities may substantially change properties of these media through electromagnetic radiation and may also modify quasi-thermal noise spectrum, which depends on the effective dielectric permittivity tensor. This tensor is defined as the dielectric permittivity tensor of some imaginary `effective' regular medium in which the field of point source is the same as the mean field in the medium with random irregularities (Ryzhov, Tamoikin and Tatarskii, 1965; Ryzhov 1968). Since the correlation function of electric field fluctuations in random medium may be expressed through the effective dielectric constant tensor (Ryzhov, 1968), it may be used for direct calculation of quasi-thermal noise spectrum. In Zabotin et al. (2000), the Born approximation was used to calculate numerically the effective dielectric permittivity tensor and the modified noise spectrum while we analytically estimate herein the modified noise spectrum. This revised version was published online in July 2006 with corrections to the Cover Date.     

The 2003 November 14 occultation by Titan of TYC 1343-1865-1: II. Analysis of light curves

We observed a stellar occultation by Titan on 2003 November 14 from La Palma Observatory using ULTRACAM with three Sloan filters: u^′, g^′, and i^′ (358, 487, and 758 nm, respectively). The occultation probed latitudes 2° S and 1° N during immersion and emersion, respectively. A prominent central flash was present in only the i^′ filter, indicating wavelength-dependent atmospheric extinction. We inverted the light curves to obtain six lower-limit temperature profiles between 335 and 485 km (0.04 and 0.003 mb) altitude. The i^′ profiles agreed with the temperature measured by the Huygens Atmospheric Structure Instrument [Fulchignoni, M., and 43 colleagues, 2005. Nature 438, 785–791] above 415 km (0.01 mb). The profiles obtained from different wavelength filters systematically diverge as altitude decreases, which implies significant extinction in the light curves. Applying an extinction model [Elliot, J.L., Young, L.A., 1992. Astron. J. 103, 991–1015] gave the altitudes of line of sight optical depth equal to unity: 396±7 and 401±20 km (u^′ immersion and emersion); 354±7 and 387±7 km (g^′ immersion and emersion); and 336±5 and 318±4 km (i^′ immersion and emersion). Further analysis showed that the optical depth follows a power law in wavelength with index 1.3±0.2. We present a new method for determining temperature from scintillation spikes in the occulting body's atmosphere. Temperatures derived with this method are equal to or warmer than those measured by the Huygens Atmospheric Structure Instrument. Using the highly structured, three-peaked central flash, we confirmed the shape of Titan's middle atmosphere using a model originally derived for a previous Titan occultation [Hubbard, W.B., and 45 colleagues, 1993. Astron. Astrophys. 269, 541–563].     

Multiwavelength observations of the two unidentified EGRET sources 3EG J0616-3310 and 3EG J1249-8330

We report on the X-ray and optical observation of the two unidentified EGRET sources 3EG J0616-3310 and 3EG J1249-8330. The X-ray coverage performed by the ESA space telescope XMM–Newton provided ∼150 X-ray sources within each of the two γ-ray error-circles. The optical follow-up carried on with the Wide Field Imager at the ESO/MPG 2.2 m telescope have found no candidate counterpart for 125 of these X-ray sources. Among these, we have selected 9 sources with f _X/f _opt≥100, which we consider promising INS candidates.