MODERN DEVELOPMENTS IN SOLAR AND STELLAR SPECTROSCOPY

Lectures at the Astronomical Institute, Slovak Academy of Sciences

May 17—21, 2010

Outline of course

Ken Phillips

LECTURE 1: BASICS and INTRODUCTORY ATOMIC PHYSICS (Monday, May 17 @ 1400; 1 ½ hours)

Units, definitions (we will use cgs units but will relate them to SI units; irradiance/radiance and flux/specific intensity). Examples of spectra. Atoms and ions. Absorption and emission spectra; Kirchhoff's laws. Wavelength ranges. Electron volt. Ion and spectrum notation.

Bohr atom - basic assumptions, Bohr orbits, dimensions and energies. Orbital angular momentum. Electron spin. Rydberg constant, unit of energy. Hydrogen atom, hydrogen isoelectronic sequence. Energy level diagrams.

LECTURE 2: FURTHER ATOMIC PHYSICS, He AND MORE COMPLEX ATOMS (Tuesday, May 18 @ 0930; 1 ½ hours)

Fine structure. Wave mechanics. De Broglie wavelength of electron, Heisenberg uncertainty principle. Wave functions. Schrödinger equation. Electron spin.

Helium atom and more complex atoms. Pauli Principle. Notation (n, l, m_s, m_l; 1,2,3... s,p,d,...)

Periodic table of elements.

LECTURE 3: ATOMIC STATES; SOME SPECTRAL LINES (Tuesday, May 18 @ 1400; 1 ½ hours)

LS coupling, combination of angular and spin momenta.

Electron transitions; selection rules.

Common lines in solar spectra, photosphere, chromosphere, and corona

Notation used to describe atomic states and transitions.

Coronal forbidden lines including the “green line”.

What we see with TRACE and SOHO/EIT: which spectral lines are included in various filters.

Continua: free-free, free-bound.

LECTURE 4: SOLAR SPECTRA: PHOTOSPHERE and CHROMOSPHERE (Wednesday, May 19 @ 0930; 1 ½ hours)

Total solar radiation, black-body distribution, and effective temperature.

Absorption (Fraunhofer) line spectra: optical depth, strengths of lines. Equivalent widths. Curve of growth.

Limb darkening.

Thermal equilibrium, LTE, NLTE, coronal equilibrium.

Spectral line formation in LTE. Chromospheric absorption lines and non-LTE.

Eddington-Barbier relation.

How the solar chromosphere is observed in the Ca II H and K lines.

Chromospheric network in Ca II and in the ultraviolet.

LECTURE 5: EXCITATION OF CORONAL SPECTRA (Wednesday, May 19 @ 1400; 1 ½ hours)

Ionization equilibrium in the solar and stellar coronae: chief processes.

Coronal emission line spectra in the EUV, UV and SXR. Collision excitation of coronal ions by electrons; contribution or G(T) function. Ion fractions.

Emission measure, differential emission measure.

LECTURE 6: DIAGNOSING PLASMAS FROM THEIR SPECTRA (Thursday, May 20 @ 0930; 1 ½ hours)

Electron temperatures of emitting regions: ratios of spectral lines emitted by highly ionized ions in the corona or coronal active regions. Temperature of flares.

Electron densities: line ratios in the X-ray spectra of solar flares; line ratios in solar UV spectra of active regions and the quiet Sun; using X-ray images of flares.

Line broadening: thermal Doppler broadening - ion temperature. Plasma flows and turbulence.

LECTURE 7: ELEMENT ABUNDANCES (Thursday, May 20 @ 1400; 1 ½ hours)

Element formation: How elements in the Sun and Earth were formed -- fusion reactions in the Big Bang and in stars.

Photospheric abundances are determined from curve-of-growth methods, but more recently model atmospheres are used.

Coronal element abundances are determined from coronal excitation conditions. Recent developments: abundances from the RESIK and RHESSI spacecraft instruments.

Element abundances from solar energetic particles and meteorites.

How the abundance determinations compare: the FIP (first ionization potential) effect. Theories of how the FIP effect arises.

LECTURE 8: SPACECRAFT SPECTROMETERS: SUN-LIKE STARS (Friday, May 21 @ 0930; 1 ½ hours)

UV and X-ray spectrometers – instrumentation and spacecraft. GOES, RHESSI, crystal spectrometers, UV spectrometers on SOHO etc.

Requirements for instruments: wavelength ranges.

Sun-like Stars: visible-light spectroscopy. X-ray and ultraviolet spectroscopy.

Reasons for their Sun-like characteristics.

Stellar flares and prominences.

WRAP-UP SESSION: Questions and discussion. (1100—1115).