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Title: EPISODIC ACCRETION AT EARLY STAGES OF EVOLUTION OF LOW-MASS STARS AND BROWN DWARFS: A SOLUTION FOR THE OBSERVED LUMINOSITY SPREAD IN H-R DIAGRAMS?

Abstract

We present evolutionary models for young low-mass stars and brown dwarfs taking into account episodic phases of accretion at early stages of the evolution, a scenario supported by recent large surveys of embedded protostars. An evolution including short episodes of vigorous accretion followed by longer quiescent phases can explain the observed luminosity spread in H-R diagrams of star-forming regions at ages of a few Myr, for objects ranging from a few Jupiter masses to a few tenths of a solar mass. The gravitational contraction of these accreting objects strongly departs from the standard Hayashi track at constant T{sub eff}. The best agreement with the observed luminosity scatter is obtained if most of the accretion shock energy is radiated away. The obtained luminosity spread at 1 Myr in the H-R diagram is equivalent to what can be misinterpreted as an {approx}10 Myr age spread for non-accreting objects. We also predict a significant spread in radius at a given T{sub eff}, as suggested by recent observations. These calculations bear important consequences for our understanding of star formation and early stages of evolution and on the determination of the initial mass function for young ({<=} a few Myr) clusters. Our results also showmore » that the concept of a stellar birthline for low-mass objects has no valid support.« less

Authors:
;  [1];  [2]
  1. Ecole Normale Superieure, Lyon, CRAL (UMR CNRS 5574), Universite de Lyon (France)
  2. Observatorio Astronomico Cerro Calan, Departamento de AstronomIa, Universidad de Chile, Casilla 36-D Santiago (Chile), E-mail: ibaraffe@ens-lyon.fr, E-mail: chabrier@ens-lyon.fr, E-mail: gallardo@das.uchile.cl
Publication Date:
OSTI Identifier:
21333820
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal (Online)
Additional Journal Information:
Journal Volume: 702; Journal Issue: 1; Other Information: DOI: 10.1088/0004-637X/702/1/L27; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1538-4357
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; FUNCTIONS; JUPITER PLANET; LUMINOSITY; MASS; PROTOSTARS; STAR EVOLUTION; STARS

Citation Formats

Baraffe, I., Chabrier, G., and Gallardo, J. EPISODIC ACCRETION AT EARLY STAGES OF EVOLUTION OF LOW-MASS STARS AND BROWN DWARFS: A SOLUTION FOR THE OBSERVED LUMINOSITY SPREAD IN H-R DIAGRAMS?. United States: N. p., 2009. Web. doi:10.1088/0004-637X/702/1/L27; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Baraffe, I., Chabrier, G., & Gallardo, J. EPISODIC ACCRETION AT EARLY STAGES OF EVOLUTION OF LOW-MASS STARS AND BROWN DWARFS: A SOLUTION FOR THE OBSERVED LUMINOSITY SPREAD IN H-R DIAGRAMS?. United States. doi:10.1088/0004-637X/702/1/L27; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Baraffe, I., Chabrier, G., and Gallardo, J. Tue . "EPISODIC ACCRETION AT EARLY STAGES OF EVOLUTION OF LOW-MASS STARS AND BROWN DWARFS: A SOLUTION FOR THE OBSERVED LUMINOSITY SPREAD IN H-R DIAGRAMS?". United States. doi:10.1088/0004-637X/702/1/L27; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
@article{osti_21333820,
title = {EPISODIC ACCRETION AT EARLY STAGES OF EVOLUTION OF LOW-MASS STARS AND BROWN DWARFS: A SOLUTION FOR THE OBSERVED LUMINOSITY SPREAD IN H-R DIAGRAMS?},
author = {Baraffe, I. and Chabrier, G. and Gallardo, J.},
abstractNote = {We present evolutionary models for young low-mass stars and brown dwarfs taking into account episodic phases of accretion at early stages of the evolution, a scenario supported by recent large surveys of embedded protostars. An evolution including short episodes of vigorous accretion followed by longer quiescent phases can explain the observed luminosity spread in H-R diagrams of star-forming regions at ages of a few Myr, for objects ranging from a few Jupiter masses to a few tenths of a solar mass. The gravitational contraction of these accreting objects strongly departs from the standard Hayashi track at constant T{sub eff}. The best agreement with the observed luminosity scatter is obtained if most of the accretion shock energy is radiated away. The obtained luminosity spread at 1 Myr in the H-R diagram is equivalent to what can be misinterpreted as an {approx}10 Myr age spread for non-accreting objects. We also predict a significant spread in radius at a given T{sub eff}, as suggested by recent observations. These calculations bear important consequences for our understanding of star formation and early stages of evolution and on the determination of the initial mass function for young ({<=} a few Myr) clusters. Our results also show that the concept of a stellar birthline for low-mass objects has no valid support.},
doi = {10.1088/0004-637X/702/1/L27; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)},
journal = {Astrophysical Journal (Online)},
issn = {1538-4357},
number = 1,
volume = 702,
place = {United States},
year = {2009},
month = {9}
}