Most planets we know of are within 0.5 kpc of the sun but our galaxy has a radius > 25 kpc
Is our sun special? Most search programs for extrasolar planets concentrate on solar-like stars in the solar neighbourhood but is our sun special? The two most atypical properties of the Sun are its mass and orbit around the galaxy. The Sun is more massive than 95%+/-2% of nearby stars, and its orbit around the Galaxy is less eccentric than 93%+/-1% of FGK stars within 40 pc.
Intermezzo I: The rotation of spiral galaxies As the name indicates spiral galaxies have spiral arms. Spiral arms are the sites of star formation. We see the better well in the blue, because of the young luminous OB stars inhabiting them. Spiral galaxies are found in low-density regions of the universe.
Lindblad: star formation caused by density waves of stars.
Star formation in spiral arms Gas clouds are swept up by spiral arms (clouds move into regions of enhanced density of stars) This increases density of matter in clouds and may even results in cloud- cloud collisions. The high density makes the collapse of clouds more likely which triggers star-formation.
Intermezzo II: The formation of galaxies (bottom up process) Grows of primordial fluctuations (universe contains dark energy, dark matter, hydrogen, helium) As universe cools dark matter condenses Gas flows into denser regions. Dark matter stays in outer regions because it can only interact gravitationally. Small proto-galaxies form Galaxies grew by accreting smaller galxies
Universe at 0.47, 2.1 and 13.4 Gyrs (simulation, box size 90 Mpc)
As a galaxy gains mass by accreting smaller galaxies the dark matter stays mostly on the outer parts. This is because the dark matter can only interact gravitationally, and thus will not dissipate. The gas however can quickly contract, and as it does so it rotates faster, until the final result is a very thin, very rapidly rotating disk. It is currently not known what process stops the contraction, in fact theories of disk galaxy formation are not yet successful at producing the rotation speed and size of disk galaxies (possibly AGN activity, star-formation, or the gravitation pull of the dark matter stops it).
The role of mergers In recent years, a great deal of focus has been put on understanding merger events in the evolution of galaxies. Our own galaxy has a tiny satellite galaxy (the Sagittarius Dwarf Elliptical Galaxy) which is currently gradually being ripped up and "eaten" by the Milky Way, it is thought these kinds of events may be quite common in the evolution of large galaxies.
Sagittarius Dwarf Elliptical Galaxy The Sagittarius dwarf galaxy is orbiting our galaxy at almost a right angle to the disk. It is currently passing through the disk; stars are being stripped off of it with each pass and joining the halo of our galaxy. There are other examples of these minor accretion events, and it is likely a continual process for many galaxies. Such mergers provide "new" gas, stars and dark matter to galaxies. Evidence for this process is often observable as warps or streams coming out of galaxies.
Determine the mass of the host star by using the oscillations
Another problem: spots can cause RV-variations V = –V rot V = +V rot V = 0
Activity of the star can be monitored in CaIIH and K: Sunspots in white light and in CaIIH and K
Ca II line Strong absorption lines are formed higher up in the stellar atmosphere. The core of the lines are formed even higher up (wings are formed deeper). Ca II is formed very high up in the atmospheres of solar type stars.
Activity can also be monitored in X-rays: The Sun in X-rays
The amplitude of the RV-variations of a sunspot is larger in the optical then in the IR
Fried Parameter r 0 : Zenit Distanz Da der Brechungsindex eine Funktion der H ö he in der Atmosph ä re ist, f ü hrt man den Parameter C n ein. C n : Strukturkonstante der Variationen des Brechungsindex integriert ü ber die turbulenten Schichten.
Die Aberration der Phase l ä sst sich als Summe orthogonaler Pylonome (Zernicke Polynome) (in Polarkoordinaten r,q) darstellen.
Konzept eines Spektrographen Aufl ö sung: Die Bildelemente des Detektors m ü ssen klein genug sein, um diese feinen Details auch aufzul ö sen (bzw. die Brennweite der Kamera lang genug): Zentralwellenl ä nge ( n+1 ) in der n+1 ten Ordnung ist gegeben durch n/(n+1) n
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