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171.
172.
173.
The photometric U orbital variations of the symbiotic binary AG Peg, caused by occultation of a bright gaseous region by the
M giant in this system, are used to determine the geometry of this region whose existence is explained in the framework of
the colliding winds model. The emission of the bright region varies and a particular value of its mean density of 2–3 1010 cm-3 has been derived. The causes for the irregular variations of the light in the orbital minimum and maximum are discussed.
It is also obtained, when the mass-loss rate of the hot companion of the system decreases to about 5 10-10
Ms
⊙ yr-1, this bright region will disappear.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
174.
175.
Theoretical line ratios involving 2s
2
S - 3p
2
P, 2p
2
P - 3s
2
S, and 2p
2
S - 3d
2
D transitions inCiv between 312 and 420 Å are presented. A comparison of these with solar active region observational data obtained during a rocket flight by the Solar EUV Rocket Telescope and Spectrograph (SERTS) reveals good agreement between theory and experiment, with discrepancies that average only 22%. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calculations, and also resolves discrepancies found previously when the theoretical results were compared with solar data from the S082A instrument on boardSkylab. The potential usefulness of theCIV line ratios as electron temperature diagnostics for the solar transition region is briefly discussed. 相似文献
176.
D.W. Crawford D.A. Purdie A.P.M. Lockwood P. Weissman 《Estuarine, Coastal and Shelf Science》1997,45(6):799-812
In the Southampton Water estuary (southern England, U.K.), red-tides caused by the planktonic, phototrophic ciliateMesodinium rubrum(=Myrionecta rubra) occur during most summers and sometimes in autumn. These events were investigated in detail between 1985 and 1987 and were characterized by levels of chlorophylla(chl a) of over 100 μg l−1, cell numbers ofM. rubrumof over 1×103 ml−1, oxygen saturations of around 150%, and depleted numbers of macrozooplankton. Initiation of red-water did not appear to be triggered by irradiance or nutrients, but coincided with an increase in temperature and water column stability. This enhanced stability was promoted by increased surface to bottom gradients of both temperature and salinity, and by reduced mixing during neap tides. Development of red-water was accompanied by removal of most of the dissolved NH+4from the water column, whereas some NO−3persisted, presumably maintained by freshwater input. NO−3and NH+4gradually returned to pre-bloom concentrations as the red-water declined in late summer. Maximal biomass ofM. rubrumappeared to be limited by irradiance, and self-shading probably imposed an upper limit of around 300 mg chl a m−2within the water column. At the observed levels of chl a, irradiance values within the population maximum between 1 and 3 m depth were only just of the order (≈15 μmol photons m−2 s−1) required to balance estimated respiratory demands. Oxygen concentration became undersaturated during the late bloom phase, with minimal values of 20–30% saturation recorded in deeper waters; however, despite this and reduced numbers of macrozooplankton, direct deleterious effects on other organisms were not observed. 相似文献
177.
178.
A. Bhatnagar R. M. Jain J. T. Burkepile I. M. Chertok A. Magun H. Urbarz P. Zlobec 《Astrophysics and Space Science》1996,243(1):209-213
The powerful cosmic ray flare of Sept. 29, 1989 occurred behind the limb and was observed over a wide spectral range. The analysis of optical, radio, and other relevant data suggest two phases of energy release. After an impulsive phase a prolonged post eruption energy release occurred in an extended region of the corona following the eruption of a large coronal mass ejection (CME). This phase is responsible for numerous coronal and interplanetary phenomena including the ground-level increase of cosmic rays. 相似文献
179.
Almudena Alonso-Herrero Marcia J. Rieke George H. Rieke Douglas M. Kelly 《Astrophysics and Space Science》2001,276(2-4):1109-1120
The irregular galaxy M82 is known as the archetypal starburst galaxy. Its proximity (3.5 Mpc) makes this galaxy an ideal laboratory
for studying the properties of its starburst. The detailed morphology of the [FeII] 1.644 μm and emission Paα (at 1.87 μm) is revealed by the NICMOS images. The peak of the 2.2 μm continuum brightness(evolved population) lies very
close to the dynamical centre. Most of the Paα emission (which traces the young population) is distributed in a ring of star formation (with a `hole' lacking line emission
at the centre of the galaxy). These observations support the scenario in which the starburst in M82 is propagating outwards.
It has long been suggested that the [FeII] emission in starburst galaxies can be used as a measure of supernova (SN) activity.
M82 shows a large number of radio supernova remnants (SNRs), approximately 50, lying in the plane of the galaxy. The comparison
of the positions of the bright compact [FeII] emitting regions with the location of the radio SNRs shows that there is no one-to-one spatial correspondence between
the two emissions, suggesting that the radio and [FeII] emissions trace two populations of SNRs with different ages. Young
(a few hundred years) SNRs are best traced by their radio emission, whereas the [FeII] stage lasts for at least a few 104 yr. The compact [FeII] sources contribute only some 20 % of the total [FeII] emission observed in M82. However, much of the remaining unresolved
[FeII] emission in the plane of the galaxy may arise from SNRs that expanded and merged into a general interstellar medium
within a few 104 yr. Presumably, as much as 70% of the total extinction-corrected [FeII]1.644 μm in M82 is associated with SNRs. The extended
and diffuse [FeII] component in M82 seems to be related with the superwind above and below the disc of the galaxy.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
180.
J.C. Vega Beltrán W.W. Zeilinger A. Pizzella E.M. Corsini F. Bertola J.G. Funes J.E. Beckman 《Astrophysics and Space Science》2001,276(2-4):1201-1210
In this paper we present the kinematics of the gas and/or the stars of a sample of 20 disc galaxies. We investigate whether there is any relation between the kinematics of the gas and stars and the classical morphological type of the galaxies in the sample. We deduce that, in most of the late-type spirals we have studied, the stars and the ionized gas are moving with virtually circular velocity, except when the spectroscopic slit crosses a bar region. On the other hand, we found in the central parts of early-type disc galaxies a wider variety of different behaviour of stars and gas. We find many possible factors that complicate the classification of the kinematical properties of the galaxies by their morphological type: the presence of counter-rotations (star vs. stars or star vs. gas), misalignment between the different kinematic components present in the galaxy, the presence of a bar structure and its orientation with respect to the line of nodes of the galaxy, and interactions and mergers or external accretion processes are some of the problems we find in the study of the kinematics of a galaxy. 相似文献