## 765649S

# Astrophysics

an advanced course (10 credits)

at the Space Physics and Astronomy research unit, University of Oulu

#### The course period: January 10 – April 26, 2024

#### Lectures, exercise and practical sessions take place usually on Monday, Wednesday, and Thursday at 14-16, see Peppi for detail. However, classes on Thursday will only occur when I announce them!

#### The course is lectured in English

#### Teacher: Vitaly Neustroev, MA 308, vitaly[-at-]neustroev.net

Course plan:

- Stellar structure and evolution
- Radiative processes
- Stellar photospheres
- Interstellar Medium
- etc…

Theoretical and practical considerations will be supplemented with the home exercises which constitute the important part of the course.

Literature:

Textbook choice for this course is largely a matter of personal taste. I provide below a list of recommended books. Study them in parallel with the lectures.

- Stellar Structure and Evolution – Onno Pols, Utrecht, 2014 (Free)
- An Introduction to the Theory of Stellar Structure and Evolution – Dina Prialnik
- Introduction to Stellar Astrophysics: Vol 2 – E. Böhm-Vitense
- Introduction to Stellar Astrophysics: Vol 3 – E. Böhm-Vitense
- Observations and analysis of stellar photospheres – D. F. Gray [E-Book]
- Lecture notes (Part I) – not enough!
- Lecture notes (Part II) – not enough!
- Lecture notes (Part III) – not enough!

Schedule

**Lecture 1: January 10:**Introduction (What is Astrophysics and Theoretical Astrophysics? Astronomical units). Stars (Role of stars; Definition; What can we learn from observations?).

PDF**Lecture 2: January 11:**Stars (Properties of stars; Stellar timeline; basic assumptions, mass conservation, hydrostatic equilibrium).

PDF**January 15:**NO CLASS**January 17:**NO CLASS**Lecture 3: January 18:**Stars (Virial theorem. Timescales of stellar evolution. Conditions in stellar interiors).

PDF**Lecture 4: January 22:**Stars (Energy generation. The equation of conservation of energy). Basics about radiative transfer (Specific intensity).

PDF

**Compulsory problems:**Set 1 (return by January 29).**Lecture 5: January 24:**Basics about radiative transfer (Radiation terms, specific intensity, interaction radiation – matter, parallel-ray radiative transfer equation, solution of the parallel-ray RTE)

PDF**January 25:**NO CLASS**Lecture 6: January 29:**Basics about radiative transfer (Mean Intensity, Flux, and K-integral. RTE in plane-parallel atmosphere. The temperature gradient for radiative transport).

PDF**Lecture 7: January 31:**The equations of stellar structure and possible ways to solve them. Boundary conditions. Convection and conditions for its occurrence. Equation of state (EOS).

PDF**February 1:**NO CLASS**Lecture 8: February 5:**Solution of HW1. Lecture: the equations of stellar structure (EOS, degeneracy pressure, stellar opacity)

PDF**Lecture 9: February 7:**Nuclear Energy Production (Basics on nuclear reactions, the binding energy, Quantum tunnelling, Reaction cross-section, the Gamow peak, Nuclear Reaction Rates, Electron shielding)

PDF

**Compulsory problems:**Set 2 (return by February 19).**Lecture 10: February 12:**Nuclear reactions in stellar interiors (Energy generation, PP-chains & CNO-cycle, Helium burning, Carbon burning and beyond, iron and heavier elements, Composition changes)

PDF**Lecture 11: February 14:**Solution of the Equations of Stellar Structure (The stellar structure equations and how to solve them? Simple stellar models. Polytropic models. Lane-Emden equation. Different relationships for polytropic stars. Chandrasekhar mass. Dynamical stability of stars)

PDF (Updated on 15.02.2024)**Lecture 12: February 15:**Stellar evolution codes. Schematic stellar evolution. Star formation.

PDF * EZ-Web**Lecture 13: February 21:**Star formation (cont). Identification of Young Stars. Pre-main sequence star evolution (the Hayashi track and the Henyey track).

PDF**Lecture 14: February 22:**Main Sequence stars. Evolution of low-mass stars.

PDF**Lecture 15: February 26:**Evolution of high-mass stars. The initial mass function. Solution of HW2.

PDF**February 28:**Mid-term exam**Lecture 16: February 29:**The end point: stellar remnants. White dwarfs, Supernovae, Neutron stars, Black holes.

PDF**Lecture 17: March 11:**What is a stellar atmosphere? Why should we care about it? What can we learn from observations? Radiative transfer (Radiative transfer equation in plane-parallel atmosphere. Limb darkening).

PDF**Lecture 18: March 13:**Limb darkening (cont.), Solution to transfer equation, Eddington-Barbier relation. Grey atmosphere. Radiative equilibrium.

PDF**Lecture 19: March 18:**The depth dependence of the source function. Eddington approximation. Temperature structure of the grey atmosphere. LTE (Maxwellian distribution in velocities, Boltzmann equation, Saha formula).

PDF (Updated on 21.03.2024)

**Compulsory problems:**Set 3 (return by March 25).**Lecture 20: March 20:**Stellar Opacity (Bound-bound, bound-free and free-free absorptions).

PDF

**Compulsory problems:**Set 4 (return by April 3).**Lecture 21: March 25:**Lyman edge and Balmer jump. Negative hydrogen ion H^{–}as the sources of opacity. Other sources of opacity (He and Metallic absorptions, Scattering, Effect of nongreyness of the temperature structure, Balmer jump).

PDF**Lecture 22: March 27:**Spectral lines (Equivalent Width, FWHM, FWZI, Radial Velocity). Spectral line formation (Einstein coefficients. Natural Line Width, Natural broadening, Doppler broadening).

PDF * Homework: slide 192**Lecture 23: March 28:**Spectral line formation (Convolution of different broadening processes, Pressure broadening, Ingis-Teller relation, Rotational and Instrumental broadening).

PDF**Lecture 24: April 4:**Simple line transfer, Schuster-Schwarzschild model, Theory of line formation, Curve of Growth. Scattering in lines, Transfer Equation including lines, The Milne-Eddington model, Residual flux of the line, Absorption and scattering lines, Schuster Mechanism for Line Emission.

PDF**Lecture 25: April 8:**Non-LTE (Statistical equilibrium, Two-level approximation, the line source function, LTE versus non-LTE). Spectral type sequence.

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**Compulsory problems:**Set 5 (return by April 15).**Lecture 26: April 10:**Towards the Model Photosphere (Hydrostatic equilibrium. Gas and electron pressure). Measuring temperatures and surface gravities (Direct measurement of radii. Determining teff and surface gravity, Model-independent methods, Model-dependent methods, Atmospheric models, Photometric methods, Spectroscopic methods).

PDF * Spectral classification**Lecture 27: April 15:**A short introduction to the Interstellar Medium (ISM).

PDF**Lecture 28: April 17:**ISM: Interstellar Absorption Lines and DIBs. 21 cm hydrogen line. Ionized regions. Strömgren Spheres.

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