Almost since the beginning, massive stars and their resultant supernovae have played a crucial role in the Universe. These objects produce tremendous amounts of energy and new, heavy elements that enrich galaxies, encourage new stars to form and sculpt the shapes of galaxies that we see today. The end of millions of years of massive star evolution and the beginning of hundreds or thousands of y...

We have investigated the relation between the orbital periods (Porb) and the spin periods (Ps) of wind-fed X-ray pulsars in high-mass X-ray binaries (HMXBs), based on population synthesis calculations of the spin evolution of neutron stars during the pre-HMXB stage. We show that most of the neutron stars either have steady accretion or still reside in the radio pulsar phase when the donor star ...

The primordial elements, H, He and Li, are included in a low-temperature equation of state and monochromatic opacity function. The equation of state and opacity function are incorporated into the stellar evolution code NG-ELMS, which makes use of a non-grey model atmosphere computed at runtime. NG-ELMS is used to compute stellar evolution models for primordial and lithium-free element mixtures ...

We adopt up-to-date Li yields from asymptotic giant branch stars in order to study the temporal evolution of Li in the solar neighbourhood in the context of a revised version of the two-infall model for the chemical evolution of our galaxy. We consider several lithium stellar sources besides the asymptotic giant branch stars such as Type II supernovae, novae, low-mass giants as well as Galactic...

We present stellar evolution calculations for Population III stars for both singleand binarystar evolutions. Our models include 10and 16.5-M single stars and a 10-M model star that undergoes an episode of accretion resulting in a final mass of 16.1 M . For comparison, we present the evolution of a solar heavy element abundance model. We use the structure from late-stage evolution models to calc...

Star-disk interaction is thought to drive the angular momentum evolution of young stars. In this review, I present the latest results obtained on the rotational properties of low mass and very low mass pre-main sequence stars. I discuss the evidence for extremely efficient angular momentum removal over the first few Myr of pre-main sequence evolution and describe recent results that support an ...

The chemical evolution of the Universe is governed by the chemical yields from stars, which in turn is determined primarily by the initial stellar mass. Even stars as low as 0.9M⊙ can, at low metallicity, contribute to the chemical evolution of elements. Stars less massive than about 10M⊙ experience recurrent mixing events that can significantly change the surface composition of the envelope, w...

New observations from the Hubble ultra deep field suggest that the star formation rate at z > 7 drops off faster than previously thought. Using a newly determined star formation rate for the normal mode of Population II/I stars (PopII/I), including this new constraint, we compute the Thomson scattering optical depth and find a result that is marginally consistent with WMAP5 results. We also rec...

Part of the mystery around the Bulge carbon stars from Azzopardi et al. (1991) is solved, if they are related to the Sagittarius dwarf galaxy. The carbon stars are in that case not metal-rich as previously thought, but they have a metallicity comparable to the LMC, with an age between 0.1 – 1 Gyr. A significant fraction of the carbon stars still have luminosities fainter than the lower LMC limi...

Part of the mystery around the Bulge carbon stars from Azzopardi et al. (1991) is solved, when they belong to the Sagittarius dwarf galaxy. The carbon stars are not metal-rich as previously thought, but they have a metallicity comparable to the LMC, with an age between 0.1 – 1 Gyr. A significant fraction of the Sagittarius dwarf carbon stars have luminosities fainter than the lower LMC and SMC ...