共查询到20条相似文献,搜索用时 31 毫秒
1.
N.C. Wickramasinghe M. Wainwright J.V. Narlikar P. Rajaratnam M.J. Harris D. Lloyd 《Astrophysics and Space Science》2003,283(3):403-413
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. 相似文献
2.
Thai-Q -Tung Dinh-V -Trung Nguyen-Q -Rieu V. Bujarrabal T. Le Bertre E. Gerard 《Astrophysics and Space Science》1997,255(1-2):329-330
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. 相似文献
3.
Francesca Primas 《Astrophysics and Space Science》2002,281(1-2):195-198
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. 相似文献
4.
Francesco Haardt Emanuele Ripamonti Monica Colpi Andrea Ferrara 《Astrophysics and Space Science》2002,281(1-2):479-482
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 1033-34 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. 相似文献
5.
Sabine Richling 《Astrophysics and Space Science》2003,284(2):361-364
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. 相似文献
6.
S. Jane Arthur 《Astrophysics and Space Science》2002,281(1-2):267-270
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. 相似文献
7.
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. 相似文献
8.
P. Fabiani Bendicho 《Astrophysics and Space Science》1998,263(1-4):223-226
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. 相似文献
9.
Bruno P. Besser Mikhail I. Pudovkin Valentina V. Lebedeva Svetlana A. Zaitseva Claudia-Veronika Meister 《Astrophysics and Space Science》2000,274(1-2):399-405
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. 相似文献
10.
Danielle Alloin Carme Gallart Emmanuel Fleurence Emanuela Pompei Daniel Raimann Uta Fritze- Von Alvensleben Sukyoung Yi 《Astrophysics and Space Science》2002,281(1-2):109-113
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. 相似文献
11.
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. 相似文献
12.
Eric Quémerais Bill R. Sandel J.L. Bertaux R. Lallement 《Astrophysics and Space Science》2000,274(1-2):123-132
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. 相似文献
13.
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. 相似文献
14.
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. 相似文献
15.
José J. Rodes Guillermo Bernabeu Juan Fabregat 《Astrophysics and Space Science》1998,263(1-4):259-262
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. 相似文献
16.
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. 相似文献
17.
Qian Shengbang 《Astrophysics and Space Science》2002,282(2):399-409
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. 相似文献
18.
19.
Yves Grosdidier Anthony F.J. Moffat Agnès Acker 《Astrophysics and Space Science》1998,260(1-2):181-184
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. 相似文献
20.
K. Justtanont J. Cami I. Yamamura T. De Jong L.B.F.M. Waters 《Astrophysics and Space Science》1997,255(1-2):351-357
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. 相似文献