Sumários

Solving Exercise Series #1

12 Março 2020, 15:00 • Israel Matute

During the first half of this lab hour, the students worked on the questions and exercises of the 1st series of problems. 


The second half we went thought the most challenging of them in more detail.

Spectral lines (part 3) + the HR diagram

12 Março 2020, 14:00 • Israel Matute

The discussion on spectral lines concluded with the description of the diversity of lines from different species, their profiles, and effects on the continuum spectrum of stars, e.g. the Balmer break, effect of gravity and concepts line back-warming line blanketing.

The lecture continued with the introduction of the Hetzprung-Russel diagram: a luminosity vs temperature/color classification for stars. Among the topics discussed I list the following:

  • Main sequence;

  • The relation between size (radius) - temperature (T)  and luminosity (L);

  • First insight into the importance of star clusters and their HR diagrams;

  • Luminosity classes.

Spectral lines (part 2)

10 Março 2020, 13:00 • Israel Matute

This lecture discussed in detail the physical reason for the intensity of the lines and the equations that govern such emissions and intensities. 
In particular, we looked into:

- how the line intensity depends not only on the abundance of the species given origin to the line but also the "population" of that species, i.e. the fraction of electrons in the different orbital levels as well as the fraction of ionization of the species. Derivation and extensive discussion of the two equations that regulate such populations:

- The Boltzmann eq. regulating the orbital population and,
- The Saha eq. regulating the ionization states.

We looked into specfic examples of the applications of these equations and in particular how the combination of both can explain observables like the fraction of ionized Hydrogen on stars of different temperatures.

Stellar continuum (part 3) + Spectral lines (part 1 )

9 Março 2020, 13:00 • Israel Matute

To finish the part dedicated to the continuum emission of stars, I gave a brief introduction on the continuum observed in galaxies with what already seen in stars. Examples are shown to illustrate that galaxies are no others that the sum of the continuum of their stars.


Spectral lines (part 1)

The formation of spectral lines:

- Physical conditions in the atmospheres of stars
- The development of the theory for atoms and the need for one that can allow electrons to be in certain states of energy. 
- Mechanisms for spectral line formation.
 

Formação de riscas espectrais:

  • Condições físicas na atmosfera de uma estrela.

  • Precisa teoria atômica onde elétrons possam ocupar apenas certos estados de energia.

  • Formation of the Hydrogen line and its series: Lyman, Balmer, Paschen, etc.

  • mecanismo de formaçao de riscas: emission/absorption of photons, collissional excitation.

Stellar Continuum (part 2)

5 Março 2020, 15:00 • Israel Matute

Followed the introduction of the blackbody approximation to the stellar continuum and extensively discussed the color-temperature relation using the Wein displacement law. 

Other fundamental relations are discussed between the color and physical properties of the star using the Planks law.

The energy emitted by a blackbody (star) of given temperature through the Stephan-Boltzman law takes us to the definition of the observed Luminosity of a star as a function of a defined “effective temperature”. The exact meaning of this effective temperature will be described in more detail on the lectures dedicated the stellar atmospheres.

To finish the effects of the interstellar medium (ISM) in the observables are introduced: (i) composition of the ISM and the impact on measured fluxes; (ii)T the concepts and origin of extinction laws, optical depth and column density are described and discussed.


NOTE: This Lab hour was not dedicated to solving of exercises as the students did not have yet enough material to solve them. The "Teórico-Prático" lectures will start on the next week