For main sequence stars, the central nuclear processing generally has no effect on surface abundances. Later in the evolution, the newly synthetized elements may be revealed at the stellar surface by processes such as mass loss, convective dredge-up, overshooting, diffusion, rotational and tidal mixing, etc. The changes of CNO abundances are the most conspicuous and the easiest to observe spectroscopically; some abundance ratios like C/N, O/N may undergo changes by more than 102. On the whole, surface chemistry is a most powerful diagnostics of stellar evolution, model assumptions and nuclear cross sections.
We have considered a stationary outflowing
envelope accelerated by the radiative force in
arbitrary optical depth case. Introduced
approximations provide satisfactory description of
the behavior of the matter flux with partially
separated radiation at arbitrary optical depths.
The obtained systemof differential equations
provides a continuous transition of the solution
between optically thin and optically thick
regions. We analytically derivedapproximate
representation of the solution at the vicinity of
the sonic point. Using this representation we
numerically integrate the system of equations from
the critical point to the infinity. Matching the
boundary conditions we obtain solutions describing
the problem system of differential equations. The
theoretical approach advanced in this work could
be useful for self-consistent simulations of
massive star evolution with mass loss.
AbstractThe lowest metallicity massive stars in the Local Universe with $Z\sim \left( {{Z}_{\odot }}/50-{{Z}_{\odot }}/30 \right)$ are the crucial objects to test the validity of assumptions in the modern models of very low-metallicity massive star evolution. These models, in turn, have major implications for our understanding of galaxy and massive star formation in the early epochs. DDO68-V1 in a void galaxy DDO68 is a unique extremely metal-poor massive star. Discovered by us in 2008 in the HII region Knot3 with $Z={{Z}_{\odot }}/35\,\left[ 12+\log \left( \text{O/H} \right)\sim 7.14 \right]$, DDO68-V1 was identified as an LBV star. We present here the LBV lightcurve in V band, combining own new data and the last archive and/or literature data on the light of Knot3 over the 30 years. We find that during the years 2008-2011 the LBV have experienced a very rare event of ‘giant eruption’ with V-band amplitude of 4.5 mag ($V\sim {{24.5}^{m}}-{{20}^{m}}$).
The Point on the Theoretical Changes of Surface Chemistry During Massive Star Evolution