Progress towards the vindication of panspermia

Theories of panspermia are rapidly coming into vogue, with the possibility of the transfer of viable bacterial cells from one planetary abode to another being generally accepted as inevitable. The panspermia models of Hoyle and Wickramasinghe require the transfer of viable bacterial cells from interstellar dust to comets and back into interplanetary and interstellar space. In such a cycle a viable fraction of as little as 10^-18 at the inception of a newly formed comet/planet system suffices for cometary panspermia to dominate over competing processes for the origin and transfer of life. The well-attested survival attributes of microbes under extreme conditions, which have recently been discovered, gives credence to the panspermia hypothesis. The prediction of the theory that comets bring microbes onto the Earth at the present time is testable if aseptic collections of stratospheric air above the tropopause can be obtained. We describe a recent collection of this kind and report microbiological analysis that shows the existence of viable cells at 41 km, falling to Earth at the rate of a few tonnes per day over the entire globe. Some of these cells have been cultured in the laboratory and found to include microorganisms that are not too different from related species on the Earth. This is in fact what the Hoyle-Wickramasinghe theory predicts. The weight of evidence goes against the more conservative explanation that organisms are being lofted to the high atmosphere from the ground. This revised version was published online in July 2006 with corrections to the Cover Date.     

Excitation of Far-Infrared Lines of OH and Maser Pumping Efficiency in Circumstellar Envelopes

We present the results obtained with a radiative transfer model to investigate the excitation of OH molecules. Maser pumping efficiencies are estimated from the model and compared to the value calculated using recent OH far-infrared (FIR) observations with ISO and OH maser data. This revised version was published online in August 2006 with corrections to the Cover Date.     

Tracing Cosmic-Rays and SNe with Be Abundances

We present the results of a new analysis of Be abundances in a large sample of stars, spanning the metallicity range -2.5 ≤ [Fe/H] ≤ - 0.7. The observations were taken with the Ultraviolet and Visible Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT). With this new set of high quality data we aim at further investigating the trend of Be with metallicity, the possible presence of dispersion, and their implications for cosmic-ray and supernovae physics. This revised version was published online in September 2006 with corrections to the Cover Date.     

The collapse of primordial stars: importance of radiation

We simulate the collapse of a primordial protostellar cloud by means of a 1D hydrodynamics code accounting for chemical evolution, radiative transfer and radiation pressure. We find that the role of radiation pressure is negligible throughout the whole simulations, i.e. Until shortly after the formation of a central hydrostatic core. We also estimate the luminosity and the spectrum of such collapsing clouds. The luminosity is initially due to a number of H₂ lines and is of the order of 10^33-34 erg s^-1. It then grows to values ≳10³⁶ erg s^-1 by the time the core forms, and results from both HH lines and continuum radiation. This revised version was published online in September 2006 with corrections to the Cover Date.     

Modeling the Lyα radiation of high-redshift galaxies

The Lyα line emission of high-redshift galaxies depends on the density and temperature distribution of the gas, the kinematics and the dust content. We use a finite element method to model theLyα radiation of different 3D configurations considering complete frequency redistribution and the influence of velocity fields. Our results show that the central absorption feature of the double-peaked Lyα line profile observed in many radio galaxies with z=2-4 is probably the consequence of frequency redistribution rather than foreground absorption. The blue peak of the profile is enhanced for models with in fall motion and the red peak for models with outflow motion. In particular, we attempt to model the extendedLyα emission of high-redshift radio galaxies, where we consider results of corresponding hydrodynamical simulations to select possible model configurations. We find that Lyα photons scattered outside a jet-influenced low-density region are able to produce an extended Lyα halo. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photoionized Regions Around Supernova Remnants

The radiation produced by the gas cooling behind a fast supernova remnant shock in the interstellar medium is capable of ionizing the undisturbed medium ahead of the shock wave. In this work I investigate the nonequilibrium evolution of these photoionized precursor regions by means of radiation-hydrodynamic simulations of supernova remnant evolution. This revised version was published online in September 2006 with corrections to the Cover Date.     

Radiative Transfer Models of Dust Shells Around Post-AGB Stars

We present a radiative transfer analysis of circumstellar dust shells around the Post-AGB stars HD 179821, HD 56126, HD 101584 and early R star HD 100764, using the code DUSTY. Parameters like mass-loss, shell inner radius, dust temperature, outflow velocity etc., are derived for HD 179821and HD 56126 whose observed SED could be reproduced by our models. This revised version was published online in July 2006 with corrections to the Cover Date.     

Radiative Transfer Under Inhomogeneous Configurations

We present, for the first time, three dimensional (3D) radiative transfer (RT) results with realistic atomic models (multilevel) and without using the local thermodinamical equilibrium approximation (non-LTE). We have developed a new code based on efficient iterative methods (Trujillo Bueno, and Fabiani Bendicho 1995; Fabiani Bendicho, Trujillo Bueno and Auer 1997) characterized by a very high convergence rate. With this 3D multilevel code and using a schematic atmospheric model we are able to demonstrate that one may need self-consistent multidimensional RT calculations in order to interpret high spatial resolution solar spectroscopic observations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Magnetosheath Structure in an Anisotropic Plasma Model

Variations of the magnetic field and plasma parameters across the Earth's magnetosheath are calculated for an anisotropic plasma in the Chew-Goldberger-Low approximation. Additionally, proton pitch-angle diffusion is taken into account as the energy transfer mechanism between the direction perpendicular and parallel to the magnetic field. We discuss the main characteristics of the magnetic barrier for different temperature relaxation times and their dependence on the interplanetary magnetic field orientation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Deriving Star Formation Histories: Evolutionary or Population Synthesis Codes versus Color-Magnitude Diagrams

The goal of this project is to analyze the integrated-light spectrum of a region in the LMC bar, for which HST images are already available yielding color-magnitude diagrams reaching the oldest main-sequence turnoff. Then, we can derive the star formation history in this field through evolutionary/population synthesis of the integrated light from 330 to 990 nm by a variety of independent methods and compare the results with the - in principle - more reliable results derived from the analysis of the color-magnitude diagram (CMD). This confrontation is the key ‘truth-test’ needed for the understanding of the abilities and the limitations of the evolutionary/population synthesis methods that must be applied of necessity to unresolved nearby and far-away galaxies. We report here on the observational part of the project. This revised version was published online in September 2006 with corrections to the Cover Date.     

Comparison of Velocity Fields of the Galaxies From the Catalogs RFGC and MarkIII

A distribution of matter up to 100 h ^-1 Mpc could be obtained from the large-scale galaxy peculiar motions. The best picture of such motion is given for today by two galaxy catalogs, namely MarkIII and RFGC. We compare their velocity fields and show they are very similar and have not only practically the same multipole structure but also a corresponding small-scale motions . We estimate a mean radial component of this small-scale motion as 500–700 kms. An additional comparison of distances to common galaxies is made. This revised version was published online in July 2006 with corrections to the Cover Date.     

Outer Heliosphere Ly-α Measurements: 1993 to 1998

We present the Lyman α sky background data obtained by the UV spectrometers on the Voyager 1 and 2 spacecraft between 1993 and early 1998. These data which consist of special maneuvers dedicated to the study of the Lyα pattern in the outer heliosphere represent a unique opportunity to constrain the hydrogen distribution in the outer heliosphere.A first analysis of the data is presented. This consists of a comparison with a Hot Model of the hydrogen distribution combined with a radiative transfer calculation in the hypothesis of Complete Frequency Redistribution. We confirm previous measurements showing the existence of an excess in Lyα background in the upwind direction. The radial variation of the upwind intensity measurements found from the two Voyager data sets are different. The Voyager 1 data show a radial decrease following r ^-1.4 whereas the Voyager 2 data yield r ^-0.79. These values have been derived after correction for solar flux variations using the SOLSTICE/UARS data set. This revised version was published online in July 2006 with corrections to the Cover Date.     

2D/3D Dust Continuum Radiative Transfer Codes to Analyze and Predict VLTI Observations

Radiative Transfer (RT) codes with image capability are a fundamental tool for preparing interferometric observations and for interpreting visibility data. In view of the upcoming VLTI facilities, we present the first comparison of images/visibilities coming from two 3D codes that use completely different techniques to solve the problem of self-consistent continuum RT. In addition, we focus on the astrophysical case of a disk distorted by tidal interaction with by-passing stars or internal planets and investigate for which parameters the distortion can be best detected in the mid-infrared using the mid-infrared interferometric device MIDI. This revised version was published online in July 2006 with corrections to the Cover Date.     

Centrifugal Forces and Optical Geometry in Neutron Stars

In this paper centrifugal forces and the geometry of light ray trajectories in neutron stars are discussed. The general behavior of centrifugal forces and angular momentum transfer is closely linked to the geometry of photon trajectories, such a behavior is here graphically depicted for realistic neutron stars, shown to be quite different from the non-relativistic case and to depend on the particular form of the equation of state. This revised version was published online in July 2006 with corrections to the Cover Date.     

Radial Velocity Measurements with FXCOR

We present measured radial velocities of two peculiar early B type stars, to check their membership to the open cluster NGC 663. The radial velocities have been obtained with the cross correlation technique, using as a template stars from the list of Liu et al. (1989). We have obtained accuracies around 3-4 km/s in our radial velocity measurements. From our results we conclude that both stars are probably non members of the cluster. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cosmic Roulette: Comets In The Main Belt Asteroid Region

We have produced top ten ranked lists of impact velocity, mainbelt asteroid region dwell times and impact probabilities for a selection of short period comets. The comet with the combined highest ranking with respect to impact probability and impact velocity is Comet C/1766 G1 Helfenzrieder. Since it is not clear that this comet still exists, the highest ranked, presently active, comet with respect to the likelihood of suffering impacts from meter-sized objects while in the main belt asteroid region is Comet 28P/Neujmin 1. We find no evidence to support the existence of a distinctive sub-set of the short period comets liable to show repeated outburst or splitting behavioursdue to small body, meter-sized, asteroid impacts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Period Changes in Four Algol-Type Binaries: SX Dra, AV Del, CU Peg and DK Peg

Orbital period changes of four neglected short-period semidetached Algols, SX Dra, AV Del, CU Peg and DK Peg, are presented based on the analysis of their O–C observations. It is found that the three systems, AV Del, CU Peg and DK Peg, show rapid period increase at rates of dP/dt =+3.15 × 10^-6, +2.00 × 10^-6 and +4.88 × 10^-7days/year respectively. For the other system, SX Dra, a possible periodic variation in the orbital period is discovered to superimpose on a very rapid period increase (dP/dt = +1.09 × 10^-5 days/year). The period increases of the four Algols can be explained by a mass transfer from the secondary to the more massive primary, which is in agreement with the semi-detached configurations of these systems. However, since the period increases are rather rapid, the mass transfer should be on a dynamical time scale. The cyclic period change in SX Dra suggests that there may exist a third body in this system. This revised version was published online in July 2006 with corrections to the Cover Date.     

临潼-蒲城数字微波时间传输系统建设及初步结果

中国科学院国家授时中心的临潼--蒲城微波时间传输系统承担着守时基准钟房(临潼)与发播控制钟房(蒲城)之间的时间同步比对任务.截至2006年底,该系统已经连续工作了28年,由于设备老化等原因,系统的可靠性和性能指标严重下降.概括介绍了微波时间传输系统的技术改造方案和数字微波系统实现的功能,初步结果表明改造后的微波时间传输系统的性能得到了提高.     

Hubble Space Telescope-WFPC2/Hα Observations of the Ejected Nebula M1-67

We present HST-WFPC2/Hα deep images of the ejected nebula M1-67. Our data suggest that M1-67 is the imprint of a previous, slow LBV wind ejected from the central star WR124, now a WN8 star. We find evidence that the LBV wind is highly variableand anisotropic. Some dense, persisting clumps have possibly been ejected directly from the stellar surface. This revised version was published online in July 2006 with corrections to the Cover Date.     

Spectroscopic Study of Carbon Stars with the ISO-SWS

We have observed ten carbon stars with different mass-loss rates using the Short Wavelength Spectrometer (SWS) on board ISO. We found that not only the spectral energy distribution and the dust features, but that also that the strength and/or shape of molecular absorption features in the infrared spectrum varies with the near-infrared color temperature, i.e. with the thickness of the circumstellar envelope. This revised version was published online in August 2006 with corrections to the Cover Date.