Harvard Astronomy 201b

AY208 Notes

The outline below is for the course Astronomy 208. All the notes from this course may be found here in pdf format. You may also use the course outline below to get lecture notes on particular topics. Note: So, far I have only added half of the lecture notes below, but I will complete this soon.

  1. Introduction: Defining Features of “a” galactic ISM

    1. Earliest Observations
      (Notes on Earliest Observations, 1.1, 1.2 intro)
    2. The “Modern” View & How we Got It
      (Notes: Tour of Milky Way, 1.2 cont.)
      a. Composition 

      1. Gas, Dust, Electrons, Cosmic Rays, Photons

      b. Extent

      1. Scale Height & Radial Distribution
      2. Interstellar “Clouds”
      3. Extragalactic Perspective
      4. Comparison with Stellar Distribution

      c. Temperature Structure

      1. The “Hot,” “Cold,” and “Warm” ISM

      d. Ionization State
      (Notes on Ionization & Disassociation, Temperature Ionization, 1.2d-1.2f)

      1. Interactions with of ISM & Stars
        1. example: Stroemgren Sphere Analysis
      2. Influence of Cosmic Rays

      e. Density Structure

      1. Measures of Column Density and Volume Density
      2. Hierarchy of Interstellar “Clouds”

      f. Velocity Structure

      1. Galactic Scales
      2. Within Individual “Clouds”

      g. Magnetic Field Structure

      1. Flux-freezing & Ambipolar Diffusion
      2. Measurement Techniques
      3. Confinement of Cosmic Rays & “Support” of Clouds

      h. Time Scales & Stability
      (Notes on Time Scales & Stability, Virial Equilibrium, Kinetic Equilibrium & Radiative Processes, 1.2h-2.1)

      1. Virial Equilibrium
      2. Instabilities (e.g. Jeans)
    3. Nature of the ISM: Above “Variables” Inseparable
  2. Kinetic Equilibrium & Radiative Processes: Overview

    1. Thermodynamic Equilibrium
      a. Partition Function 

      1. Kinetic, Excitation, Color, Antenna, Bolometric, and Other “Temperatures”

      b. Non-equilibrium Distributions

    2. Excitation Processes
      (Notes on Excitation Processes, Radiative Transfer Definitions, 2.2-2.3b)
      a. Collisional
      b. Recombination
      c. Non-LTE (Pumping)
    3. Radiative Processes
      (Notes on Absorbtion and Emission and Radiative Transfer in terms of Einstein Coefficient, 2.3a-3.0 )
      a. Radiative Transfer Definitions
      b. Emission & Absorption Coefficients
      c. Continuum Emission 

      1. Thermal
      2. Bremsstrahlung & Synchrotron

      d. Scattering Processes
      e. The Influence of Shocks

      1. In SNe, Star-forming Regions, and in Accretion Disks (more below)

      f. What combination of the above will be observed where?

      1. Depends on l.o.s. Temperature, Density, Abundance, and Velocity Distribution
  3. The ISM of the Milky Way

    (Notes on The Multi-Phase Paradigm and The “Cold” ISM, 3.1, 3.2)

    1. Introduction: The Multi-Phase Paradigm
      a. Basic Assumptions
      b. Pressure, Mass, and Energy Balance
      c. Time Dependence
    2. The “Cold” ISM
      a. History and Definitions 

      1. “Out the window”
      2. Permitted and Forbidden Transitions
      3. Critical Density

      b. Atomic Gas (H I)

      1. Origin of the 21-cm Line: Flipping a Spin
      2. 21-cm line Surveys
        1. Collisional Excitation
          (Handout on Collisional Excitation, Molecular Gas, 3.2b.1-3.2c)
        2. Optical Depth Considerations
      3. High-Velocity and High-Latitude Clouds
        1. Detection
        2. Origin & Evolution

      c. Molecular Gas

      1. The Difficulty in Directly Observing H2
      2. Role of “Trace” Species”
        1. Molecular Line Mapping
        2. Masers (more in AGN discussion)
    3. Dust
      a. What is dust? 

      1. Cause of interstellar extinction
      2. Range of Sizes from “Big Molecules” to Planetesimals

      b. Measured/Measurable Properties

      1. Optical Efficiency Factors
        1. Cross-sections for emission, absorption & scattering
        2. Albedo
      2. Extinction as a function of l
        1. Total-to-Selective Extinction
        2. Spectral “features”
      3. Thermal Emission as a function of l
        1. Is the blackbody approximation adequate?
        2. Are grains fractal?
      4. Polarization as a function of l
        1. Polarization due to Scattering
        2. Polarization due to Aligned Grains
          1. Polarization of Background Starlight
          2. Polarization of Thermal Emission

      c. Using Polarization to Map B

    4. Molecules & Dust Together
      a. Formation of Molecules 

      1. on Dust
      2. in the Gas Phase

      b. Destruction of Molecules

      1. by cosmic rays
      2. by photons
      3. by electrons & collisions
    5. Heating & Cooling
      1. Atomic & Molecular Coolants
      2. Dust Heating & Cooling
    6. The “Hot” ISM
      a. The Warm Neutral Medium: Broad H I lines
      b. The Warm Ionized Medium: Absorption Line Observations
      c. Radio Continuum Emission & Pulsars as Probes 

      1. Distinguishing Bremsstrahlung from Synchrotron from Thermal Emission
      2. Polarization of Synchrotron Emission
      3. Rotation and Dispersion Measure
        1. Faraday Rotation
        2. RM/DM of Pulsars as a Probe of B
    7. X-rays as a “Probe” of the ISM
      a. X-ray “Shadows” of Molecular Clouds
      b. Calibration of the CO/H2 ratio (a.k.a. the “X-factor”)
    8. How Appropriate are Multi-Phase Models?
  4. Interaction of Photons with the ISM

    1. H II Regions & Photon-Dominated Regionsa. Stroemgren Spheres
      b. “Clumpy” H II Regions
      c. Radio Recombination Lines
      d. General Shock Physics (Basic Equations, More Later)
      e. Compact and Ultra-Compact H II Regions 

      1. Cometary H II Regions & Bow shock models

      f. Champagne-flow models

    2. Heating and Cooling in H II Regions
    3. Ionization Fraction & Chemical Balance in PDRsa. Measurements & Theories
      b. Effects on Ion-Neutral Coupling
    4. The Effect of High-Energy Photons on Molecular Clouds (e.g. in AGNe)
  5. Star Formation in Molecular Clouds

    1. Giant Molecular Clouds, Dark Clouds, Cloud Cores & the “Modern” Star Formation Paradigm
    2. Cloud Support & Dynamics
      a. “Larson’s Laws” & Virial Equilibrium 

      1. Role of Magnetic Fields (Part I)

      b. Pressure Confinement
      c. Self-similar Structure
      d. Rotation

    3. The Role of Magnetic Fields in Star-Forming Regions (Part II)
      a. What matters: Static Fields, Turbulence and/or Waves?
      b. Measurements of Field Strength
      c. Measurements of Field Structure
      d. MHD Simulations
    4. Disks
      a. Radiated Spectrum & Dependence on Viewing Angle 

      1. The Role of Scattered Light

      b. Fragmentation & Instabilities
      c. Planet Formation

    5. Infall & Outflow
      a. Expectations & Observations of Inflow
    6. What Determines the Initial Mass Function of Stars?
      a. Agglomeration Theories
      b. Fragmentation Scenarios
      c. “Fractal” Scenarios & Speculation
  6. Interaction of Stellar Winds with the ISM

    1. Winds from Young Stars
      a. Observed Properties of Outflows (on ~pc scales) 

      1. Comparison of Outflow Mechanical Luminosity & Protostar’s Luminosity
      2. Aspect Ratio
      3. “Hubble Flow”

      b. Observed Properties of Jets (on ~0.1 pc scales)

      1. Emission from Herbig-Haro Objects and “Shocked” H2
        1. Continuum and Line Radiation Produced in Shocks
        2. Temperature, Ionization & Velocity Structure of Jets

      c. Energy dissipated
      d. Collimation Mechanism

      1. The “X-wind Model”
      2. Other proposals
      3. Origin of the Relevant B-field: Stellar or Interstellar?

      e. Jet-driven Outflows

      1. (M)HD Simulations of Jets & Outflows

      f. FU Orionis Activity & Episodic Jets: Magnetic Variability?

    2. Mass Loss from Main Sequence & Evolved Stars
      a. Production of Dust 

      1. Variety
      2. Subsequent Processing to Produce Observed I-S Dust

      b. Planetary Nebulae

    3. Supernova Remnants
      a. Observations 

      1. Multi-Wavelength Radiation
        1. Optical Line & Continuum Emission
        2. Synchrotron Radiation

      b. Shock Physics & Chemistry

      1. Time Evolution: Phases in the Expansion

      c. Energy Deposited into ISM
      d. Simulations

  7. The ISM in External Galaxies at z~0

    1. Variations with the Realm of “Normal” Galaxies
      a. Density Structure
      b. Velocity Structure & Rotation Curves 

      1. Origin of High-velocity Clouds

      c. Metallicity Variations
      d. Magnetic Field Structure

    2. “Active” and “Starburst” Galaxies
      a. The Cause(s) of Starbursts
      b. Jets and Disks in AGNe
  8. The Intergalactic Medium

    1. Observations: Present & Future
      a. Lyman-a clouds, Lyman Limit systems and the Lyman Forest
      b. Metal-line systems
    2. Relationship of the ISM & IGM
      a. Coronal Gas?
      b. Intracluster Gas in Galaxy Clusters
  9. The “ISM” at z>>0

    1. Observations
      a. Highly Redshifted CO
      b. Future Prospects: Other lines, other techniques
    2. Cosmological Predictions
      a. Lower Metallicity?
      b. Origin of the Intergalactic & Interstellar Magnetic Fields
      c. Observational Feasibility Estimates
    3. Polarization of the Microwave Background

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