Radiative processes

Algemeen

Dit vak wordt gegeven door prof. H. Van Winckel. Het examen is open boek. Vergeet vooral geen rekenmachine mee te brengen.

Examens

Examen 15 januari 2010 Voormiddag

• Short Questions

*Show that if stimulated emission is neglected, so that there are only two Einstein coefficients left in the transfer  equation. An appropriate relation between the Einstein coefficients will be consistent with the Thermal equilibrium  between the atom and the radiation field of a Wien spectrum, not a Planck spectrum.

• • The strength of CO lines in the IR increases in metal poor objects. This seems contradictory. Can you explain this.

• Describe the continuum processes in the stellar atmospheres which are relevant for the Sun. Compare the effects for a star with the same effective temperature but with a metalicity of 1/1000 solar.

• There is a plasma stream falling on to a White Dwarf (WD) of 0.5 M_solar and R = 8000 Km. The energy of the infalling matter is absorbed onto an area of 1% of the total WD surface. The mass transfer is $10^{-9}{M}_{solar}/year$ The energy of the mass is absorbed in the region of 1m deep into the surface. This region is heated by the plasma and is optically thin. The density of this area is: $\rho =10^{-2}$

*What is the number density in the shock absorbing region. Assume the plasma consists of H only.
*Calculate the potential energy per second (J/s) from accreting material by a fall from infinity.
*The potential energy is converted fully to thermal energy. What is the power dropped in $1m^3$?
*The radiative power of the shock absorbing region is all from the accretion power. Use the integrated volume emissivity of the thermal bremsstralung to find the temperature and the piek in the radiation. (Gauntfactor is 1).

• Explain a hermes spectrum. (From a nova)