Im

Our goal is to obtain an expression for the luminosity of the star as a function of time the time dependence of the above equation is isolated in the time derivative of the core temperature. Our next step, then, is to relate the core temperature to the luminosity in an independent way then we will integrate with respect to time to obtain luminosity as a function of age. The above expression was derived for the degenerate core. Atop this core is the nondegenerate envelope, which contains (by...

Info

Evolutionary track of a post-AGB star that experiences a final helium shell flash while on the hot end of the white dwarf cooling track. Prom Iben (1991). contract (Schonberner 1983). For helium-burning central stars, the acceleration is more modest. Once the energy of the (now fossil) nuclear burning shell has diffused away, the evolution is steadily slowed by the decreasing luminosity (i.e. smaller rate of energy loss). The different rates at which hydrogen-burning and helium-burning...

Introduction

White dwarf stars represent the final stage of evolution of stars like our sun. They represent the ultimate fate of all stars with masses less than about 8 Mq, and are the natural consequence of the finite fuel supply of these stars. Upon exhaustion of their nuclear fuels of hydrogen and helium, these stars lack sufficient mass to take advantage of the limited return of carbon fusion, and are doomed to gravitational collapse. Upon reaching a radius comparable to that of the Earth, the inner...

White Dwarf Formation and Early Cooling

As discussed in the first section of this paper, there is overwhelming evidence that most white dwarfs represent the final stage of evolution of stars that have spent some time on the Asymptotic Giant Branch. For that reason, I will concentrate on the formation of white dwarfs from AGB stars. Other channels, no doubt, produce stars that are now classified as white dwarfs, and will produce stars with (initially) different thermal profiles in their interiors, and different elemental composition...

Date

Examples of timing noise in 11 pulsars (Helfand et al. 1980). Optical emission has been detected to date from three pulsars, and X-rays from about half-a-dozen pulsars. Regarding 7-ray emission from pulsars the picture is just emerging thanks to observations from the GRO. The average pulse profiles in the optical, X-ray and 7-ray for the Crab pulsar is shown in Fig. 16. The most remarkable thing to be noticed is that in all cases there is a main pulse and a subpulse separated by 140...

Db White Dwarf Helium Line

DA, DB, and DO stars are easy to understand. As in garden-variety A stars, the DA stars have spectra that are dominated by the Balmer lines of hydrogen. DB and DO stars show only lines of helium DB stars show strong Hel lines, and DO stars show lines of singly ionized helium. Beyond these all similarities to traditional spectral types end. DA stars have atmospheres that are almost pure hydrogen the dominance of the Balmer lines is not simply a temperature effect. Such pure spectra can result...

White Dwarf Cooling and the White Dwarf Luminosity Function

As Don Winget has stated many times, the history of star formation in the disk of our galaxy is written in the coolest white dwarf stars. These cool white dwarfs are the oldest stars in the disk of our galaxy by understanding their statistics, we can recreate the star formation rate and its changes over the entire history of the galaxy. In this section, we discuss the cooling of white dwarfs, with the goal of understanding the white dwarf luminosity function in terms of the cooling history of...

Physics of White Dwarf Interiors

This section reviews some results from statistical mechanics, which will eventually be used to derive equations of state for stellar material appropriate for the conditions found in white dwarf stars. We then treat the thermal properties of the material in white dwarfs, and the transport of radiation in their interiors. Several excellent texts on statistical mechanics, in addition to specialized texts in stellar interiors, are available for students of white dwarf stars. For the statistical...

The Baym-bethe-pethick Equation Of State

The secular evolution of the radio luminosity of pulsar-produced synchrotron nebulae such as the Crab nebula. The three phases mentioned in the text are clearly seen. In the figure on the left the luminosity evolution of three nebulae, all powered by central pulsars with the same initial period equal to the estimated initial period of the Crab pulsar , but with different magnetic fields are shown. In the right panel the magnetic fields of the central pulsars are the same, but the...

Stellar Remnants

Saas-Fee Advanced Course 25 Lecture Notes 1995 Swiss Society for Astrophysics and Astronomy Edited by Georges Meynet and Daniel Schaerer Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA Blegdamsvej 17, DK-2100 Copenhagen 0, Denmark Raman Research Institute RRI , Sadashivanagar, C.V. Raman Avenue, Bangalore 560 080, India Dr. Georges Meynet Dr. Daniel Schaerer Observatoire de Gen ve, 51 chemin des Maillettes, CH-1290 Sauverny, Switzerland This series is edited on...