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2.9.13 Star and Planet Formation Master course 2013 Carsten Dominik 8 weeks (2.9. - . – 25.10.2013) 2 lectures per week (Monday 13:00 & Thursday 9:00, G2.04) 2 problem session/project meetings per week (Monday 15:100 G5.29, Friday 15:00 A1.08) Exam on Thirsday, 24.10, 13-16, room B0.207 Star and Planet Formation Course outline: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. Introduction: The Solar System Context Molecular clouds Cloud equilibrium and Stability Collapse of clouds Protostars & pre-main-sequence evolution High-mass Star Formation Viscous Accretion Disks Irradiated Disks Observations of Disks From dust to planetesimals From planetesimals to planets Giant Planet Formation Planet-Disk interaction, Migration Population Synthesis Star and Planet Formation Exercise hours: Problems should have been worked out before, solutions will be discussed. The projects will be discussed there as well. Projects: Small programming project. Details in todays problem session. 1 2.9.13 Star and Planet Formation Books: S.W.Stahler & F.Palla “The Formation of Stars”, Wiley-VCH, ~85 € P.Armitage “Astrophysics of Planet Formation”, Cambridge University Press, ~48 € Syllabus (written in collaboration with Inga Kamp): Online. First half is finished, second half comes later All material will be on Blackboard. People who provided material: The Solar System Context 1. A historical perspective I. II. 2. 3. The Sun as a star Models of Solar System Formation Observational Constraints I. Regularity II. Composition III. Asteroid Belt IV. Ages from radioactive dating V. Deuterium VI. Dynamics of Small Bodies VII. Angular Momentum VIII. Minimum Mass Solar Nebula How did the Sun form? I. II. III. IV. 4. Molecular Clouds Starless Cores Young Stellar Objects Jets & Outflows How did the planets form? I. Protoplanetary Disks II. Debris Disks III. Exoplanets 1. A historical perspective Our Solar System 2 2.9.13 1. A historical perspective The geocentric model Before the 16th century: geocentric model (Earth at the center) only Aristarchos of Samos (280 BC) had suggested a heliocentric model Cosmographia (1539) 1. A historical perspective The geocentric model Aristotele’s school: 1. If the Earth rotates around the Sun, birds should actually stay behind because of the movement of the Earth on its orbit. 2. If the Earth rotates around its axis (as required to explain day and night), things should fly off the spinning planet. 3. If the Earth rotates around the Sun, we should observe parallaxes for the fixed stars. " 1. A historical perspective The geocentric model Aristotele’s school: 1. If the Earth rotates around the Sun, birds should actually stay behind because of the movement of the Earth on its orbit. 2. If the Earth rotates around its axis (as required to explain day and night), things should fly off the spinning planet. 3. If the Earth rotates around the Sun, we should observe parallaxes for the fixed stars. " In which of these statements was he right ? 3 2.9.13 1. A historical perspective The geocentric model Aristotele’s school: 1. If the Earth rotates around the Sun, birds should actually stay behind because of the movement of the Earth on its orbit. Inadequate understanding of physics ! 2. If the Earth rotates around its axis (as required to explain day and night), things should fly off the spinning planet. Inadequate understanding of physics ! 3. If the Earth rotates around the Sun, we should observe parallaxes for the fixed stars. " 1. A historical perspective The geocentric model Aristotele’s school: 1. If the Earth rotates around the Sun, birds should actually stay behind because of the movement of the Earth on its orbit. Inadequate understanding of physics ! 2. If the Earth rotates around its axis (as required to explain day and night), things should fly off the spinning planet. Inadequate understanding of physics ! 3. If the Earth rotates around the Sun, we should observe parallaxes for the fixed stars. " True, but parallax too small to be observed at that time. Largest parallax: 0.77” for Proxima Centauri (1.3 pc) 1. A historical perspective The heliocentric model Nicolaus Copernicus (1473 - 1543) 4 2.9.13 1. A historical perspective The heliocentric model Johannes Kepler (1571 - 1630) 1. A historical perspective Kepler’s laws 1. The planets revolve on elliptical orbits around the Sun, with the Sun in one focus. periastron" apastron" periastron " 2. The area swept out by the radius vector from the Sun to the apastron" distance" distance" planet per unit time is constant 3. The square of the orbital period T divided by the cube of the mean distance from the Sun a is the same for all planets 1. A historical perspective Kepler’s laws 1. The planets revolve on elliptical orbits around the Sun, with the Sun in one focus. 2. The area swept out by the radius vector from the Sun to the planet per unit time is constant 3. The square of the orbital period T divided by the cube of the mean distance from the Sun a is the same for all planets 5 2.9.13 1. A historical perspective Kepler’s laws 1. The planets revolve on elliptical orbits around the Sun, with the Sun in one focus. 2. The area swept out by the radius vector from the Sun to the planet per unit time is constant. 3. The square of the orbital period T divided by the cube of the mean distance from the Sun a is the same for all planets. 1.I The Sun as a star The Sun as a star Ancient greeks: The Sun and the stars belong to the same category; they are stones of fire. 1.I The Sun as a star The Sun’s temperature Surface temperature estimates: To measure the Sun’s temperature, one needs to measure the total energy received on Earth per surface area. TSun = 4 x 106 K (William Herschel, 1738-1822) TSun = 1500-1800 K (Claude Pouillet, 1838) Solar constant S = 1.76 cal cm-2 min-1 ice (insulation)" glass window" thermometer" opaque layer with hole" Today’s value of the Solar constant S = 1.94 cal cm-2 min-1 6 2.9.13 1.I The Sun as a star The Sun’s temperature Surface temperature estimates: To measure the Sun’s temperature, one needs to measure the total energy received on Earth per surface area. TSun = 4 x 106 K (William Herschel, 1738-1822) TSun = 1500-1800 K (Claude Pouillet, 1838) TSun = 7338 K (actinometer, begin of the 20th century) 1.I The Sun as a star Spectroscopy Joseph von Fraunhofer (1787-1826) 1.I The Sun as a star Spectroscopy Kirchoff’s laws (1959): 1. A hot solid body produces a simple continuous spectrum without lines. 2. A hot gas produces a spectrum with bright lines at discrete wavelengths. The position and number of lines depends on the nature of the gas. 3. If a continuous spectrum shows dark lines, it originated from a hot solid body surrounded by a gas that is cooler than the hot solid body before reaching us. Again, the number and position of the dark lines depends on the chemical nature of the surrounding cooler gas. Planck’s law (1901): 7 2.9.13 1.I The Sun as a star The Sun and the Star’s Diameter: From eclipses measured to be RSun = 7 x 1010 m Mass: From planetary orbits using Kepler’s 3rd law MSun = 2 x 1033 g ⇒ Density ρ = 1.4 g/cm3 indicative of a gas ball Spectroscopy: • The Sun is a gas ball. • Spectra enabled studies of the chemical composition of the Sun. • Spectra confirmed that stars are indeed other “Sun’s”. Differences in spectra were attributed to different sizes, masses, surface temperatures, chemical composition and most likely ages. 1.I The Sun as a star Energy source of the Sun Radioactive dating of Earth: Age of Earth ~4.5 x 109 yr (begin 20th century) Implication for the Sun and stars: Stability over a very long timescale Gravitational energy: Nuclear fusion: ⇒ Lifetime of the Sun 1.03 x 1011 yr 1.II Models of Solar System Formation Historical theories 8 2.9.13 1.II Models of Solar System Formation Historical theories 1.II Models of Solar System Formation Historical theories Kant 1724-1804 Laplace 1749-1827 1.II Models of Solar System Formation Observed “solar nebulae” Protoplanetary disks Sizes: 50-few 100 AU Masses: 0.1-0.001 M* 9 2.9.13 1.II Models of Solar System Formation Core accretion / gravitational instability Massive nebula (Cameron) Low mass nebula (Safronov) Mass: 0.1-1 M* Mass: ~0.01 M* Planets form like stars through gravitational instabilities Km-sized planetesimals form through collisional accretion of small dust Planets form fast (~1000s of yr) Planetary cores ~10 MEarth can attract the surrounding gas and form giant planets Planets form slowly (~107-108 yr) 2. Observational Constraints Regularity AU 2. Observational Constraints Regularity • Spin axis within 30o perpendicular to the ecliptic (except Uranus) • Prograde rotation except Venus and Uranus AU 10 2.9.13 2. Observational Constraints Composition Rocky planets Gas and ice giants Dwarf planets 2. Observational Constraints Radioactive Dating & Deuterium Meteorites: 4.55 x 109 yr Chondrules: 4.56 x 109 yr Rocks on Earth: 4.3 x 109 yr Rocks on Moon: 4.4 x 109 yr ⇒ Sun and planets formed at the same time (within 106 yr inside a few AU) D/H ratios in the SS: ⇒ Planets formed from interstellar matter (D is rapidly destroyed inside stars) 2. Observational Constraints Dynamics of small bodies [The Nice model: Gomes et al. 2005] a) Before Jupiter (green) and Saturn (yellow) reach their 2:1 resonance b) Scattering of planetesimals into inner Solar System when resonance occurs c) After ejection of planetesimals (Uranus: cyan, Neptunus: blue) Dynamics of small bodies carries imprint of early SS dynamics 11 2.9.13 2. Observational Constraints Minimum Mass Solar Nebula [Desch 2007] [Kuchner 2004] 3. How did the Sun form Cosmic matter cycle 3. How did the Sun form Molecular clouds 12 2.9.13 3. How did the Sun form Starless cores Jeans radius: 3. How did the Sun form Young stellar objects Collapse phase: [K band speckle interferometry, Preibisch] free-fall phase ends when R~500 RSun (for 1 MSun star) Hayashi phase (vertical track) 3. How did the Sun form Collapse 500 Msun 0.8 pc tff = 190000 yr t = 285000 yr 13 2.9.13 3. How did the Sun form Jets and outflows 3. How did the Planets form Protoplanetary disks gas Dust 3. How did the Planets form Planet formation 14 2.9.13 3. How did the Planets form Planet formation 500 AU gas (?) + dust gas + dust 100 AU gas (?) + dust 100 AU debris disk / zodiacal dust 3. How did the Planets form Exoplanets [Udry & Santos 2007] Exoplanets from Kepler 15 2.9.13 Exoplanets from Kepler Compact systems, e.g. Kepler 11 3. How did the Planets form Exoplanets Planetary systems in young debris disks [Michaud & Macintosh 2008, Kalas et al. 2008, Lagrange et al. 2009, Lafreniere et al. 2009] 16