Initial Mass Function

Initial Mass Function

Die Ursprüngliche Massenfunktion, auch Anfängliche Massenfunktion, englisch Initial Mass Function IMF, beschreibt, wie in einer neu entstehenden Sternpopulation die Verteilung der Sternmassen aussieht.

Edwin Salpeter leitete 1955 erstmals die ursprüngliche Massenfunktion für die Sonnenumgebung ab und schlug für Sterne zwischen etwa 0,4 und 10 Sonnenmassen einen Zusammenhang

dN \propto M^{-\alpha}dM

mit Exponent α = 2.35 vor, wobei dN die Anzahl der Sterne pro Volumeneinheit mit einer Masse zwischen M und M+dM ist. In dieser Salpeter-Funktion sind also massereiche Sterne deutlich seltener als massearme.

Würde dieser Zusammenhang zu sehr kleinen Massen hin fortgesetzt, dann wäre die gesamte stellare Masse von sehr massearmen Sternen dominiert. Heutige Bestimmungen der ursprünglichen Massefunktion deuten jedoch auf ein Abflachen dieser Beziehung unterhalb 0,5 Sonnenmassen hin.

Die Erklärung der ursprünglichen Massenfunktion ist eine wichtige Aufgabe für Modelle der Sternentstehung, besonders da sie nur wenig zwischen verschiedenen Sternentstehungsgebieten zu variieren scheint.

Literatur

  • Edwin Salpeter, The luminousity function and stellar evolution, Astrophysical Journal 121, 161 (1955)
  • Glen Miller & John Scalo, The initial mass function and stellar birthrate in the solar neighborhood, ApJS 41, 513 (1979)
  • John Scalo, The initial mass function of massive stars in galaxies. Empirical evidence, Luminous stars and associations in galaxies; Proceedings of the Symposium, Porto-Kheli, Greece, May 26-31, 1985. Dordrecht, D. Reidel Publishing Co., 1986, p. 451-466.
  • Pavel Kroupa, On the variation of the initial mass function, MNRAS 322, 231 (2001) arXiv preprint
  • Pavel Kroupa, The initial mass function of stars: evidence for uniformity in variable systems, Science 295, 82 (2002) arXiv preprint

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