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?

By Isabelle Baraffe, G. Chabrier, José A. Gallardo. 2009

219 citations recorded by the source corpus.

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 Teff. 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 ∼10 Myr age spread for non-accreting objects. We also predict a significant spread in radius at a given Teff, 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.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/95bd773e9dac4a994e0c9227212b4fee5446bcf7

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Citations in the corpus

VARIABLE PROTOSTELLAR ACCRETION WITH EPISODIC BURSTS (2015, methodology): “For instance, variable accretion can help to explain the luminosity spread of young clusters without invoking a significant age spread (Baraffe et al. 2009, 2012).”
RADIATION MAGNETOHYDRODYNAMIC SIMULATIONS OF PROTOSTELLAR COLLAPSE: PROTOSTELLAR CORE FORMATION (2012, methodology): “Our results can be used as the initial and boundary conditions for the stellar evolution simulations (e.g., Baraffe et al. 2009; Hosokawa et al. 2011).”
On the diversity and statistical properties of protostellar discs (2018, background): “This should be born in mind by observers since they have no choice but to look at a starforming region at a particular time, and ages of individual protostars usually cannot be reliably determined (Hartmann et al. 1997; Tout et al. 1999; Baraffe et al. 2009).”
The Pisa pre-main sequence tracks and isochrones - A database covering a wide range of Z, Y, mass, and age values (2011, unknown): “1997; D’Antona et al. 2000; Siess 2001; Stahler & Palla 2004; Baraffe et al. 2009; Hosokawa et al. 2011).”
New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit (2015, methodology): “This supposes that early history of accretion has not altered their structure (Baraffe et al., 2009, 2012) and that their position in a CMD or L − Teff diagram can be reproduced by non-accreting evolutionary models.”
Observations of Cool-Star Magnetic Fields (2012, background): “However, Baraffe et al. (2009) show that episodic accretion can lead to a luminosity spread that can be misinterpreted as an age spread on the order of 10 Myr, hence age and radius estimates have large uncertainties in this regime.”
MESA ISOCHRONES AND STELLAR TRACKS (MIST). I. SOLAR-SCALED MODELS (2016, background): “However, there is evidence that early accretion episodes affect the location and evolution of PMS stars on the HR diagram (e.g., Baraffe et al. 2009; Hosokawa et al. 2011), possibly complicating the comparison to PMS at these young ages.”
Stellar, brown dwarf and multiple star properties from a radiation hydrodynamical simulation of star cluster formation (2011, background): “Studies of such bursty accretion have become quite popular recently (e.g. Vorobyov & Basu 2005; Zhu, Hartmann & Gammie 2009; Baraffe et al. 2009).”
The stellar and sub-stellar IMF of simple and composite populations (2011, background): “The uncertainties due to such processes have been partially discussed though (Baraffe et al. 2002, 2009; Baraffe & Chabrier 2010).”
Star Formation in the Milky Way and Nearby Galaxies (2012, methodology): “Assumptions about accretion and initial conditions may also have substantial consequences for the usual methods of determining ages of young stars (Baraffe et al. 2009; Baraffe & Chabrier 2010; Hosokawa et al. 2011).”
SOLAR MODELS WITH ACCRETION. I. APPLICATION TO THE SOLAR ABUNDANCE PROBLEM (2011, background): “One is simplicity: this choice corresponds to quiescent accretion rates well below 10−7 M⊙ yr −1, allowing us to neglect the energy deposition on the outer layers of the star and associated effects that could alter final internal structure of the model (Baraffe et al. 2009).”
RESOLVING THE LUMINOSITY PROBLEM IN LOW-MASS STAR FORMATION (2011, background): “Such calculations can now be performed for any arbitrary accretion history (e.g., Baraffe et al. 2009), and will be explored in a future paper.”