Volume 6, Issue 3
September 1985, pages 113-169
pp 113-130 September 1985
Nucleosynthetic yields and production rates of helium and heavy elements are derived using new initial mass functions which take into account the recent revisions in O star counts and the stellar models of Maeder (1981a, b) which incorporate the effects of massloss on evolution. The current production rates are significantly higher than the earlier results due to Chiosi & Caimmi (1979) and Chiosi (1979), and a near-uniform birthrate operating over the history of the galactic disc explains the currently observed abundances. However, the yields are incompatibly high, and to obtain agreement it is necessary to assume that stars above a certain mass do not explode but proceed to total collapse. Further confirmation of this idea comes from the consideration of the specific yields and production rates of oxygen, carbon and iron and the constraints imposed by the observational enrichment history in the disc as discussed by Twarog & Wheeler (1982). Substantial amounts of4He and14C, amongst the primary synthesis species, are contributed by the intermediate mass stars in their wind phases. If substantial numbers of them exploded as Type I SN, their contribution to the yields of12C and56Fe would be far in excess of the requirements of galactic nucleosynthesis. Either efficient massloss precludes such catastrophic ends for these stars, or the current stellar models are sufficiently in error to leave room for substantial revisions in the specific yields. The proposed upward revision of the12C (α,γ)16O rate may produce the necessary changes in stellar yields to provide a solution to this problem. Stars that produce most of the metals in the Galaxy are the same ones that contribute most to the observed supernova rate.
pp 131-135 September 1985
We present the higher-dimensional perfect fluid generalizations of the extended Bianchi type-VIh vacuum space-times discussed recently by Demaret & Hanquin (1985). It is shown that the Chodos-Detweiler mechanism of cosmological dimensional-reduction is possible in these cases.
pp 137-144 September 1985
We derive some new exact 7-dimensional cosmological solutions |R⊗ I ⊗N, whereN = I, II, VI0, VII0, VIII and IX are the various 3-dimensional Bianchi models. The solutions given are higher-dimensional generalizations of the mixmaster cosmologies. There is a strong influence of the extra spacesN, which results in a fundamental change of the 3-dimensional cosmology.
pp 145-151 September 1985
Three supernova remnants (SNR) have been mapped in the galaxy M33 with the Very Large Array* (VLA) at 20 cm. The angular resolution is ∼1.3 arcsec or ∼4 pc at a distance of 600 kpc and the rms noise is ∼0.04 mJy /beam. One of the radio sources shows evidence for a shell structure with a size of ∼15 pc, confirming the SNR nature of this source. The second object is extended and may well be a thick-shell SNR of size ∼12 pc. The third object is a small, presumably young SNR with a size of ∼4 pc.
pp 153-157 September 1985
VLA observations at 2 and 6 cm have been obtained for six hydrogen-deficient stars R CrB, HD 160641, BD — 9°4395, V348 Sgr, MV Sgr and Sgrv Upper limits to the massloss rates have been estimated for some of these using the upper limits to the radio flux density.
pp 159-164 September 1985
Photoelectric radial-velocity measurements show that the tenth-magnitude object HD 110195 is a double-lined spectroscopic binary. It consists of two very similar late-G dwarfs in an orbit having high eccentricity and a period of 18 days.
pp 165-169 September 1985
Changes in the radii of neutron stars due to variations in core temperature are studied qualitatively in a simple model. The resulting irregular changes in pulsar periods are compared with observed values. For the millisecond pulsar PSR 1937 + 214 the random changes in period due to temperature variation is estimated to be of the order of 10-14s yr-1 which is two orders of magnitude smaller than the steady variation due to loss of energy by radiation.
Volume 40 | Issue 5
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