file: diary.txt = notes on RJR's ITB course "solar line formation" July 2000 last: July 29 2000 site: ftp://cygnus.as.itb.ac.id/pub/rutten/course note: these are Rob Rutten's notes on his ITB course split between material / plan / done (= diary) these notes were updated while the course proceeded exercises: located in subdirectories ssa, ssb, ssc; require IDL subdirectory rridl: my personal IDL library (also psplot routines) material ======== books (all present at Bosscha Observatory Lembang) -------------------------------------------------- stellar spectra at introductory level: # Boehm-Vitense 1989 Introduction to stellar astrophysics. I. Basic Stellar Observations and Data # Boehm-Vitense 1989 Introduction to stellar astrophysics. II. Stellar Atmospheres stellar spectra at intermediate level: # Gray1992, The Observation and Analysis of Stellar Photospheres more observationally oriented then my courses, but similar level stellar spectra at advanced level: # Mihalas 1970 Stellar Atmospheres (1st edition) (Bosscha does not have the second edition (1978) but the first edition is in many respects preferable. The second edition contains more material on partial redistribution and on Sobolev theory) physics of radiation processes at advanced level: # Rybicki+Lightman 1979 Radiative Processes in Astrophysics Advanced astrophysics, but it also has an excellent first chapter summarizing radiative transfer with scattering. two sets of RJR lecture notes: ------------------------------ # "Generation and transport of radiation" - lower level introduction to radiation processes and transfer - two copies: one in classroom and one in library this volume is not (yet) available on WWW - essentially a long popularization of the first chapter of the book by Rybicki and Lightman above - contains many simple questions that help to focus, some are answered in the back - contains a selection of energy level diagrams at the end # "Radiative transfer in stellar atmospheres" - higher level text, often used in graduate courses in the US - mostly a popularization of the book of Mihalas above - Chapter 2 is an equation summary of the above lecture notes - web-available at http://www.astro.uu.nl/~rutten - problems given at the end three sets of computer exercises using IDL: ------------------------------------------- # Stellar Spectra A: all IDL programs are given (the files are in cygnus directory ~rutten/course/ssa) - a Windows stellar classification exercise from the US - explanation of the spectral type distribution from the Saha and Boltzmann ionization and excitation laws - spectral line modeling from a simple "reversing layer" model, including computation of the "curve of growth" # Stellar Spectra B: now you have to program IDL yourself! Answers are given at the end in the form of graphs. The files are in cygnus directory ~rutten/course/ssb. - stratification of the solar atmosphere: its properties, plus a comparison with the earth's atmosphere - continuous spectrum of the solar photosphere: you will follow Chandrasekhar and use H-minus extinction to model the solar continuous spectrum - spectral lines from the solar atmosphere: fairly advanced exercise to compute the Na D lines from the sun in detail assuming LTE. This exercise has been done by only a few students yet and may still have some errors. # Stellar Spectra C: a set that doesn't exist yet under this name and is not yet available on the web (the above two sets are on my website). Not written by me but by graduate students Mandy Hagenaar and Thijs Krijger, using programs from Phil Judge (Boulder) and Han Uitenbroek (Harvard). Advanced radiative transfer modeling including - inversion problems - Feautrier method - classical lambda iteration - accelerated lambda iteration. Instructions (latex) and solutions in dir ~rutten/course/ssc. Note: I do not know too much myself about these exercises! I also left (both at ITB and Bosscha) a SOHO CD-Rom with much information on solar physics including many movies from the SOHO mission. course plan =========== week 1 = introduction with cartoons - course contents - example Na D lines from flame basic photon-particle interactions process pairs - scattering in earth atmosphere - scattering in optically thick objects versus LTE assumption - exercises: SSA1, introduction IDL week 2 = thermal (LTE) radiation - Maxwell, Boltzmann, Saha TE distributions - Planck etc TE radiation laws - intensity, mean intensity, flux - emissivity, extinction coefficient, source function - optical thickness, optical depth - emergent intensity from thin/thick homogeneous medium - emergent intensity from stellar atmosphere LTE H-min continuum cool stars (red and infrared) - exercises: SSA2, SSA3 week 3 = NLTE scattering - Einstein coefficients and Einstein relations - 2-level atom scattering - coherent scattering and complete redistribution - radiative transfer in stellar atmospheres with scattering Thomson scattering hot stars solar continua ultraviolet (VALIII) - excercises: SSB1, SSB2 week 4 = other NLTE line formation - line formation in coronal conditions - radiative transfer with photon converson Bowen mechanism nebulium lines Zanstra mechanism planetary nebulae - remaining solar physics topics - exercises: complete SSB2 (SSB3? SSC??) intermezzo's = solar (and related stellar) topics ------------------------------------------------- - coronal radiation (white light, X-ray, radio) - solar granulation - solar oscillations - solar magnetism - cool-star activity - solar telescopes (seminar) - SOHO & TRACE movies (seminar) - current key areas of solar physics (seminar) actually done in the course =========================== Wed July 5 = introduction - spectral lines are major information carrier in astronomy - spectral lines from optically thick objects are not easy to understand - scattering makes radiation non-local - example: Rayleigh scattering in the earth's atmosphere brings sunlight into the classroom. Its spectrum still contains all the solar spectal lines. If you point a spectroscope at my nose, you observe the solar spectral lines - such as the Na D lines. You observe them from my nose but they were put into the spectrum in the sun: the radiative transfer between the thermal creation of the photons and the detection is complicated and very much non-local: my nose is not at 5000 K and is not made of natrium. - the course explains solar Na D lines in detail - but actually, their polarization has only recently been measured and is not understood Thu July 6 = start - natrium in laboratory flame without/with background illumination - main basic photon-matter interactions bound-bound 5 up-down processes bound-free idem free-free idem Thomson scattering off free electrons Rayleigh scattering off bound electrons Fri July 7 - pairs of 2-level bound-bound processes thermal photon creation thermal photon destruction photon scattering = redirection - Na emission lines from flame: thermal creation Na absorption lines from irradiated flame: scattering out of beam - Na absorption lines from sun: can't be the latter because the sun is not optically thin (= transparent) - easy way out: assume sun obeys LTE: no scattering sequences Sat July 8 = intermezzo = radiation from solar corona - inner white light corona Thomson scattering off free electrons redirects sunlight no spectral lines: washed out by 100 km/s Dopplershifts motions so large from hight temperature (1-2 10^6 K) - emission lines in optical = forbidden high-ionization lines - outer white light corona = sunlight scattered off dust particles (zodaical light), contains the normal solar spectrum - intrinsic coronal radiation: X-ray emission lines collision up + spontaneous deexcitation down thermal creation = photon loss (corona optically thin) loss = thermostat: photon loss cooling equals unknown energy input - observation in X-ray with TRACE satellite: all magnetism - details not understood! Tue July 11 - overview sofar - TE particle laws: Maxwell, Boltzmann, Saha - Cecilia Payne's explanation of Annie Cannon's spectral classification - cartoon LTE interpretation of the Ca II K line-center reversals - homework: why may the moon be dark red at the upcoming eclipse? Thu July 13 - red color of eclipsed moon = Rayleigh scattering along long path through earth atmosphere (cross-section lambda^-4) - white color of eclipsed moon = dust in atmosphere, Mie scattering; same causes white sky brighter near sun, not "coronal" - light on eclipsed moon = refraction of light in Earth atmosphere because it is much denser than the solar atmopshere (n=1) - solar "surface" = non-transparent for white light even though the earth atmopshere is much denser but transparent because H-minus (neutral atom + extra electron from ionized "metals" as Mg, Fe, Al, Ca) adds very large extinction cross-section (Chandrasekhar) - TE photon laws: Planck, Rayleigh-Jeans + Wien domains; Wien displacement - concepts flux and intensity = independent of distance (in vacuum) - definitions intensity, emissivity, extinction coeffcient, source function Fri July 14 = intermezzo: solar surface fine structure - high-resolution G-band movies: granules, magnetic elements, sunspots taken with new Dutch Open Telescope on La Palma (seminar) - MDI = Michelson Doppler Interferometer on board SOHO SOHO orbits around L1 sun-earth system to avoid Dopplershifts - MDI magnetogram and H Ly alpha emission: magnetism = bright chromosphere - fluxtube modeling, hot wall radiation - magnetic carpet: network evolution, coronal loop topology - cool star activity: star-star variations and basal flux - Cuntz et al modeling of stellar chromospheric emission: fluxtube waves plus basal acoustic waves fit well (1999ApJ...522.1053C) Sun July 16 = total lunar eclipse - mostly eclipsed by clouds alas - slight reddish color - good description of such phenomena: "The nature of light and colour in the open air" by M.G.J. Minnaert, in the Bosscha library Tue July 18 - definitions I, J, F; j, alpha, S; tau; radiative transport equation - 2-level atom gas: either thermal photon creation/destruction or scattering but no roundabout photon conversion - 2-level atoms: S = (1-eps) J + eps B - transport equation easy for S=B(T), difficult integro-differential equation for S=J=. Numerical iteration needed for scattering, as in Newton-Raphson iteration (but multi-dimensional) - radiative transfer through thin/thick homogeneous medium Thu July 20 - radiative transfer in optically thick atmosphere - optical depth versus optical thickness - standard transfer equation - formal integral solution - Eddington-Barbier approximation - graphical explanation of: solar limb darkening solar optical + infrared continuum due to H-minus extinction absorption lines from plane-parallel stellar atmosphere emission lines from plane-parallel stellar atmosphere Fri July 21 = intermezzo: solar oscillations and helioseismology - types of wave (restoring force), eigenmodes acoustic waves (pressure, buoyancy), p-modes internal gravity waves (gravitational accelerationy), g-modes Alfven waves (magnetic Lorentz force), fast+slow and many other modes - Dopplergrams from Michelson Doppler Interferometer on SOHO - 1960 Dopplergrams Leighton method - discovery 5-minute oscillation: photographic subtractions - identification 5-minute oscillation as 10^5 p-modes (n,l,m) - helioseismology: structure and rotation solar interior - local helioseismology: sunspots below surface and on solar backside - g-modes: GOLF on SOHO = NaD scattering cell; no success. Sat July 22 = colloquium Bosscha: optical solar telescopes - three problems: heating inside, heating outside, large f/D = size - solutions: vacuum or helium filling; lakes and trade winds; heliostats. - examples: Sacramento Peak = 100 m rotatable vacuum reflector, THEMIS = helium filled Ritchey-Cretien; Swedish Telescope = vacuum refractor; Dutch Open Telescope (DOT) = open reflector in trade wind. - history and first images = movie from DOT - DOT plans: 3-wavelength simultaneous imaging, G-band, Ca II K, H alpha; consistent speckle reconstruction = 100 frames/image, 500 Gb/day. - DOT niche: topology and dynamics magnetic structure in deep photospere, low chromosphere, high chromosphere; together with EUV and Xray imaging in space (SOHO and TRACE, in future Solar-B) Tue July 25 - repeat spectral lines from thick atmospheres - continua: hot stars (H ionized) = Thomson scattering = NLTE cool stars (H neutral): > 500 nm = H-minus = LTE < 400 nm = metals bf (Mg, Al, Fe, Si) - bf: LTE for H-minus, but scattering in UV (larger internal energy) - scattering: 2-level destruction parameter, source function - epsilon is small! Since collision frequency diminishes exponentially with height - source function at surface: S = sqrt(eps) B - physics: photon loss at surface propagates to deep layers through scattering (photons escape via scattering from tauu=1/eps - Avrett 2-level atom isothermal constant-epsilon graphs - complete frequency redistribution versus coherent scattering - formation of solar NaD lines: very dark line cores due to NLTE S << B in chromosphere due to scattering (S = J) NLTE tau=1 further out because ionization also with J << B (near-UV) Thu July 27 - VALIIIC continuum formation - bound-free scattering solar UV continua - definition lambda operator - lambda operator versus 2-level source function: Hubeny philsophy - classical lambda iteration - accelerated lambda iteration Fri July 28 - definition of Einstein coefficients - multi-level rate equations and coupled transfer equations - statistical equilibrum - complete linearisation of rate equations - standard codes: MULTI (Carlsson, Oslo); TLUSTY (Hubeny, Goddard) - population departure coefficients b - solar Na D lines: formation n terms of b(h) curves per level - emission lines from stars LTE: outward increasing temperature NLTE: outward increasing source function geometry: extneded atmosphere or disk P Cygni profiles = stellar wind, Sobolev approximation - Zanstra mechanism planetary nebulae: Balmer emission lines from nebula actually count Lyman continuum photons from central star very non-local both in wavelength and in location Sat July 29 = colloquium Bosscha: solar physics - overview of solar physics - results from global and local helioseismology - solar magnetism yak or yum? quotes from famous astrophysicists TRACE Fe IX movies - my own research = acoustic shocks in non-magnetic network interior results from Ca II K spectroscopy and numerical simulations now: TRACE near-UV image sequences