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Miguel Cerviño 《Astrophysics and Space Science》2003,284(2):897-900
Evolutionary synthesis models have been used to study the physical properties of unresolved populations in a wide range of
scenarios. Unfortunately, their self-consistency is difficult to test and there are some theoretical open questions without
an answer: (1) The change of the homology relations assumed in the computation of isochrones due to the effect of stellar
winds (or rotation) and the discontinuities in the stellar evolution are not considered. (2) There is no consensus about how
the isochrones must be integrated. (3) The discreteness of the stellar populations (that produce an intrinsic statistical
dispersion) usually are not taken into account, and model results are interpreted in a deterministic way instead of a statistical
one. The objective of this contribution is to present some inconsistencies in the computation and some cautions in the application
of the results of such codes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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The integrated optical spectrum of the Crab nebula and evidence for its fading synchrotron continuum
Nathan Smith † 《Monthly notices of the Royal Astronomical Society》2003,346(3):885-889
A flux-calibrated optical spectrum integrated over the entire Crab nebula was obtained by making drift scans with a long-slit spectrograph. Compared to observations obtained over the past 40 years, these new data confirm an earlier controversial result that the [O iii ] λλ4959, 5007 equivalent width is increasing with time, although the rate of ∼0.9 per cent yr−1 is somewhat slower than that measured previously. Additionally, the Hβ equivalent width is increasing at a comparable rate, but the measured fluxes of both Hβ and [O iii ] have changed less than their respective equivalent widths. The different rates of change in the measured fluxes and equivalent widths of these lines suggest that the optical synchrotron continuum from the Crab nebula is indeed fading rapidly. The apparent decline is consistent with a rate around −0.5 (±0.2) per cent yr−1 at wavelengths near 5000 Å inferred independently from measurements of the optical continuum flux during the same time period. 相似文献
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