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Brown Dwarfs and Extrasolar Planets

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Brown Dwarfs and Extrasolar Planets Substellar objects: Basic information Brown dwarfs and extrasolar planets •Class web site: http://www.mpia-hd.mpg.de/homes/goldman/course/ • Material: slides, bibliography, useful links •Max-Planck-Institut für Astronomie, Königstuhl • large dept for young stellar objects, brown dwarfs and Bertrand Goldman exoplanets, theory and observations •Email: Thomas Henning •Schedule: ? • in ARI: astrometry, nearby star catalogue, microlensing Talk Th.Henning Thursday, 11:00, here 1 2 Current schedule Scales and units: wavelengths • Lecturer might change The electromagnetic spectrum • Topic distribution might change– suggestions welcomed 3 4 Filters Colours The Planck radiation law (1900): 2# h c 2 F" = hc "5 e " kT $1 2 4 => Stefan’s law: L = 4"RBD.#.Teff 2.99mm and Wien’s law: " = ! max T ! ! 5 6 Scales and units: distance Other useful scales • Stellar space velocities (with respect to the Sun): Most observed BDs and • Sun • thin disk: 30 km/s (typical) exoplanets: within 100 pc • thick disk: 80 km/s really locally stellar halo/spheroid: 200 km/s • v (km / s) • proper motion: angular velocity: µ(arcsec / yr) " # 5.d(pc) Some exceptions: • Angular positional accuracy: transit and microlensing • • absolute: 0.1” for CCD-based catalogues, worst for plates detections 7.5 kpc • relative: 1–10 milliarcseconds (object not [yet] imaged) 1! • parallax: "(arcsec) # d(pc) • Masses: • Sun/Jupiter: 1 M!=1047 M! Jupiter/Earth: 1 M!= 318 M" M31 Andromeda • ! • Saturn/Earth: 1 M"= 95 M" 7 8 Yerkes MKK Definition of brown dwarfs Hertzprung-Russell diagram (luminosity) classification Morgan-Keenan spectral classification • Main parameter: mass 50% Deuterium burned • slightly function of 50% Lithium burned metallicity stars • proposed in 1910 Criteria: • BDs • stable H burning 2 • 22,000 nearby stars with • 1H = De burning planets Hipparcos parallaxes Luminosity and Gliese stars. ! z!: for solar metallicity Age Burrows, 2001 9 10 Brown dwarf colour-magnitude diagram Stellar classification J • Two new spectral classes M • Specific species: M • Ms: TiO L • Ls: dust, FeH, H2O • Ts: methane, H2O T Golimowski, Cool Stars 13, 2005 models by Ackerman & Marley, 2001 Cushing, Cool Stars #13, 2005 11 12 Brown dwarf and Detection of brown dwarfs exoplanet radius • Unusual colours • model predicted • contamination by warmer stars and galaxies • Companions of nearby stars • requires high contrast ratio with high angular resolution Degenerate electron gas of High proper motions objects cooler cores prevents • further contraction • incomplete, bias towards older populations • requires some patience and twice telescope time • Late type objects in young clusters • known types, but lower gravity • contamination by field stars 13 14 A very recent field First (cool) brown dwarf Gl 229B (1995) First young brown dwarf in the Pleiades (1995) companion to Gl 229A, a M1/M2 dwarf at 5.8!pc r i z Ks 7.6” =43 AU 15 16 Definition of “planet” Detection of extrasolar planets • Solar system: cf. IAU in Prag: • Imaging: direct detection • => 1–4? • Movements of the host star • pulsar (1992,1994) • Acceleration of the host star • Extrasolar planets: various options: • 198 (1995…) • formation? • Occultation of the host star • association (with a host star) • 14 (2004…) • mass (not burning De): • Gravitational lensing (microlensing) of a background star <13 MJupiter • !4 (2004…) Int’l Herald Trib. 17/08/06 17 18 Wobbling of the host star First extrasolar planet (around a pulstar) • Time-delay: milli-second pulsars • Astrometry: • Ground based projects: VLT, Keck, LBT • Long-term space projects: • GAIA • TPF-I, Darwin 19 20 First extrasolar planet Radial velocities surveys around a main-sequence (variable) star 51 Pegasi B, 1995 561 papers • Extremely successful • Sensitivity keeps increasing • Puzzling results 21 22 Transits Microlensing • Small (geometric) efficiency • Requires tens of 1000s of stars • Extremely fruitful: • radius, mass (RV) => density and composition • atmospheric composition • temperature(s) 23 24 Fundamental physics Current results and expectations that we’ll use • quantum physics: • degenerate gas • light-matter interactions • electromagnetism, radiation laws • thermodynamics • convection • statistics For extrasolar planets: • Keplerian mechanics Keith Horne 25 26 Readings for next week: Spectral classification • Popular: • Die neuen Spektraltypen L und T, Bailer-Jones & Bastian, Sterne & Weltraum, May 2004, p.20 • Book New Light of dark stars: • §§2.1, 2.2: quick introduction • §4: basic principles • Professional literature: difficult, but try the introduction: • Kirkpatrick et al., ApJ 319, p. 802 (1999), especially §5: L type • Martín et al., AJ 118, p. 2466 (1999), especially §§3,4: L type • Burgasser et al., ApJ 637, p.1067 (2006): §4: method, and §5: T type 27.
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