Stellar Atmosphere & Spectra Analysis

Stellar Atmosphere & Spectra Analysis

Course Code: 031M4004H

Course Name: Stellar Atmosphere & Spectra Analysis

Credits: 3.0

Level: Graduate

Pre-requisite: The Basic Astronomy, The Radiation Processes in Astrophysics

Lecture Time: 20 weeks, 3 hours/week, 60 hours in total

Instructors: Prof. Feilu WANG

Course Description

This course is designed to give a fundamental understanding to the physics in stars for the graduate student whose mayor is astrophysics or similar. The stellar physics is a wide-ranged topic, and this course will focus on the stellar atmosphere and spectra analysis. The topics include: the fundamental theories of the stellar atmosphere, the basic concepts of the stellar spectra, and the analyzing methods. By completing this course, the students will have a basic understanding to the stellar atmospheres, stellar spectra, and the analyzing methods, which are of great importance to their future academic careers.

Topics and Schedule

Part I. The chemical evolution of the Milky Way (15 hours)

Lecture 1: The origin of elements, nucleosynthesis, and metal-poor stars (3 hours)
Highlights: The process of the nucleosynthesis, the nature of metal-poor stars.
Difficulties: The process of nuclear reaction.

Lecture 2: The evolution of the stars (3 hours)
Highlights: The evolution of the stars; H-R diagram.
Difficulties: Master the H-R diagram.

Lecture 3: The isochrones and the ages of stars (3 hours)
Highlights: The stellar evolutionary model; deriving the stellar ages.
Difficulties: How to use isochrones to derive the ages of stars.

Lecture 4: The stellar populations and structures of the Milky (3 hours)
Highlights: The stellar populations; the history of assembling and evolving of our Galaxy.
Difficulties: The evolution of the Galaxy.

Lecture 5: The galactic chemical evolution (GCE) models. (3 hours)
Highlights: Introductions to the GCE models; how to use GCE model to study the Galactic evolutionary history.
Difficulties: The applications and differences of various GCE models.

Part II. The stellar atmospheric models and their computations (21 hours)

Lecture 1: An introduction to the stellar radiation field (3 hours)
Highlights: The physical parameters to describe the radiation field on the macroscopic scale, including the radiation intensity, flux, radiation pressure, and the energy density. The microcosmic definition of the radiation field.
Difficulties: Understanding the fundamental parameters of the radiation fields and their applications in astronomical observations.

Lecture 2: The local thermodynamic equilibrium (LTE) and opacity (3 hours)
Highlights: The derivation of the Boltzmann Equation and Saha Equation; the application of these LTE equations in the spectra analysis; the definition of absorption and scattering, and the related microcosmic physical processes; the opacity and its application.
Difficulties: Understand the LTE theories; be able to interpret the spectral features of different stellar types with LTE theories; understand the nature of absorption coefficient on both microcosmic and macroscopic scale.

Lecture 3: The radiation transfer equation (3 hours)
Highlights: The deviation of the radiation transfer equation under the parallel-plane assumption; the definition of source function; the interpretation of the limb darkening of the Sun; the solution and boundary of the transfer equation; the moment of the radiation transfer equation; the commonly used operators in the radiation transfer theory.
Difficulties: Understand the nature of absorption line and emission line; the Schwarzschild-Milne equations.

Lecture 4: The radiative and hydrostatic equilibrium equations, the convection, and the grey atmosphere assumption (3 hours)
Highlights: The deviation of the radiative equilibrium equation and its transformation; the distribution of the temperature and the approximation of the intensity; the Rosseland mean opacity; the convective energy transfer.
Difficulties: The condition of the convective energy transfer.

Lecture 5: The continuum opacity (3 hours)                                             
Highlights: The continuum absorptions of the H and He atoms; the absorptions of metals; the scatterings of free electrons and molecules.
Difficulties: The continuum absorption of the H- ions; the sources of the absorption in different types of stellar spectra.

Lecture 6: The non-local thermodynamic equilibrium (NLTE), the movement of the atmosphere and the stellar wind (3 hours)                                                                                             
Highlights: The departures to LTE; the velocity distribution of the particles in the atmosphere; the statistical equilibrium equation and its application; NLTE source function.
Difficulties: The establishing of the statistical equilibrium equation and its application.

Lecture 7: Model atmosphere (3 hours)                                                   
Highlights: The correction to the temperature distribution; the linearization method; the accelerated-lambda iteration method; the line blanketing effect; the stellar atmosphere theory and semi-experiential models; the numerical method.
Difficulties: Close connections between model atmospheres and observed stellar spectra.

Part III. Modern Spectrograph and Spectrum Reduction (6 hours)

Lecture 1: The spectrograph and optical fibers (2 hours)                       
Highlights: An introduction to the echelle spectrograph and fibers.
Difficulties: None.

Lecture 2: The spectrum observation (2 hours)                                        
Highlights: The measurements of continuum and spectral lines, including the error estimation, correction to the instrumental profile, and recognizing lines of different wavelengths; understanding the wavelength calibration.
Difficulties: The recognition of spectral lines

Lecture 3: The spectrum reduction (2 hours)                                           
Highlights: Understand the extraction of 1D spectrum from a 2D CCD image; be able to reduce spectrum alone.
Difficulties: learn to use IDL; wavelength calibration.

Part IV. The Quantificational Spectrum Analysis (18 hours)

Lecture 1: The line profiles and the broadening mechanisms (3 hours)
Highlights: Line profile; equivalent width; line broadening mechanisms; theoretical growth curve.
Difficulties: The broadening of line absorption; determine the elemental abundance from growth curve.

Lecture 2: The equivalent width and line profiles (6 hours)                    
Highlights: A discussion to the relation between equivalent width and stellar parameters (e.g., effective temperature, surface gravity, and metallicity); the calculation of line profile under LTE; the line profile affected by stellar rotation and macro- turbulence, the line profile affected by the isotopic shifting and hyperfine structure.
Difficulties: The comparison between the theory and the observation.

Lecture 3: NLTE line synthesize (6 hours)                                                 
Highlights: The importance of NLTE effects and the physical processes that may lead to a departure from LTE.
Difficulties: Understanding the physical processes involved in NLTE.

Lecture 4: The Quantificational Analysis to Stellar Spectra (3 hours)     
Highlights: Derive the stellar parameters; determination of the elemental abundance.
Difficulties: The analysis to the stellar parameters.

Textbook & References

1. Runqian Huang, Stellar Physics, Science Press, 1998 (Only in Chinese)

2. Erika Böhm-Vitense, Introduction to stellar astrophysics, Cambridge University Press, New York, 1989.

3、Eva Novotny, Introduction to stellar atmospheres and interiors, Oxford university Press, New York, 1973.

4、David F. Gray, The observation and analysis of stellar photospheres, John Wiley & Sons company, New York, 1976; 1992.

5、Allen’s Astrophysical Quantities, Arthur N. Cox, Editor, AIP Press, Springer, 2000.

6、John T. Jefferies, Spectral line formation, Blaisdell publishing company, London, 1986.

Introduction to the Instructors: None.