The Hertzsprung-Russell diagram of the Large Magellanic Cloud compiled recently by Fitzpatrick & Garmany (1990) shows that
there are a number of supergiant stars immediately redward of the main sequence although theoretical models of massive stars
with normal hydrogen abundance predict that the region 4.5 ≤ logTeff ≤ 4.3 should be un-populated (“gap”). Supergiants having surface enrichment of helium acquired for example from a previous
phase of accretion from a binary companion, however, evolve in a way so that the evolved models and observed data are consistent
— an observation first made by Tuchman & Wheeler (1990). We compare the available optical data on OB supergiants with computed
evolutionary tracks of massive stars of metallicity relevant to the LMC with and without helium-enriched envelopes and conclude
that a large fraction (≈ 60 per cent) of supergiant stars may occur in binaries. As these less evolved binaries will later evolve into massive X-ray
binaries, the observed number and orbital period distribution of the latter can constrain the evolutionary scenarios of the
supergiant binaries. The distributions of post main sequence binaries and closely related systems like WR + O stars are bimodal-consisting
of close and wide binaries in which the latter type is numerically dominating. When the primary star explodes as a supernova
leaving behind a neutron star, the system receives a kick and in some cases can lead to runaway O-stars. We calculate the
expected space velocity distribution for these systems. After the second supernova explosion, the binaries in most cases,
will be disrupted leading to two runaway neutron stars. In between the two explosions, the first born neutron star’s spin
evolution will be affected by accretion of mass from the companion star. We determine the steady-state spin and radio luminosity
distributions of single pulsars born from the massive stars under some simple assumptions. Due to their great distance, only
the brightest radio pulsars may be detected in a flux-limited survey of the LMC. A small but significant number of observable
single radio pulsars arising out of the disrupted massive binaries may appear in the short spin period range. Most pulsars
will have a low velocity of ejection and therefore may cluster around the OB associations in the LMC. 相似文献
Based on spacecraft observations of the giant planets we call attention to an apparent regular mass-luminosity relation for the large planets (giant planets plus Earth). It can provide important clues and constraints on the question of their energy source, including various relevant theories and their difficulties. We describe in some detail a new thermonuclear reaction mechanism, valid for plasma fusions at both super—high and low temperatures, and including the original thermonuclear mechanism as a particular case. It can explain not only the internal energy souce of the large planets, but also many anomalous fusion phenomena observed in the laboratory and in astronomical bodies. Although these appear in various guises, their basic principle is the same, that is, they can all be understood in terms of the new mechanism. 相似文献
We present a series of RXTE observations of the nearby obscured Seyfert galaxies ESO103-G35, IC5063, NGC 4507 and NGC 7172. The period of monitoring ranges from seven days for NGC 7172 up to about seven months for ESO103-G035. The spectra of all galaxies fit well with a highly obscured ( N H>1023 cm−2) power-law and an Fe line at 6.4 keV. We find strong evidence for the presence of a reflection component in ESO103-G35 and NGC 4507. The observed flux presents strong variability on day time-scales in all objects. Spectral variability is also detected in the sense that the spectrum steepens with increasing flux similar to the behaviour witnessed in some Seyfert 1 galaxies. 相似文献
We describe the implementation of two High Time Resolution modes for ESO's new generation CCD controller FIERA. These new modes have been used to perform phase-resolved high speed photometry and spectroscopy of pulsars with the FORS instruments at the VLT. 相似文献
New major and trace element data for the Permo–Triassic basalts from the West Siberian Basin (WSB) indicate that they are strikingly similar to the Nadezhdinsky suite of the Siberian Trap basalts. The WSB basalts exhibit low Ti/Zr (50) and low high-field-strength element abundances combined with other elemental characteristics (e.g., low Mg#, and negative Nb and Ti anomalies on mantle-normalised plots) typical of fractionated, crustally contaminated continental flood basalts (CFBs). The major and trace element data are consistent with a process of fractional crystallisation coupled with assimilation of incompatible-element-enriched lower crust. Relatively low rates of assimilation to fractional crystallisation (0.2) are required to generate the elemental distribution observed in the WSB basalts. The magmas parental to the basalts may have been derived from source regions similar to primitive mantle (OIB source) or to the Ontong Java Plateau source. Trace element modelling suggests that the majority of the analysed WSB basalts were derived by large degrees of partial melting at pressures less than 3 GPa, and therefore within the garnet-spinel transition zone or the spinel stability field.
It seems unlikely that large-scale melting in the WSB was induced through lithospheric extension alone, and additional heating, probably from a mantle plume, would have been required. We argue that the WSB basalts are chemically and therefore genetically related to the Siberian Traps basalts, especially the Nadezhdinsky suite found at Noril'sk. This suite immediately preceded the main pulse of volcanism that extruded lava over large areas of the Siberian Craton. Magma volume and timing constraints strongly suggest that a mantle plume was involved in the formation of the Earth's largest continental flood basalt province. 相似文献