Evolutionary models for low-mass stars and brown dwarfs: uncertainties and limits at very young ages

By Isabelle Baraffe, G. Chabrier, F. Allard, Peter Hauschildt. 2001

520 citations recorded by the source corpus.

We analyse pre-Main Sequence evolutionary tracks for low mass stars with masses $m \\le 1.4 \\msol$ based on the Baraffe et al. (1998) input physics. We also extend the recent Chabrier et al. (2000) evolutionary models based on dusty atmosphere to young brown dwarfs down to one mass of Jupiter. We analyse current theoretical uncertainties due to molecular line lists, convection and initial conditions. Simple tests on initial conditions show the high uncertainties of models at ages $\\simle$ 1 Myr. We find a significant sensitivity of atmosphere profiles to the treatment of convection at low gravity and $\\te < 4000$ K, whereas it vanishes as gravity increases. This effect adds another source of uncertainty on evolutionary tracks at very early phases. We show that at low surface gravity ($\\log g \\simle 3.5$,) the common picture of vertical Hayashi lines with constant $\\te$ is oversimplified. The effect of a variation of initial deuterium abundance is studied. We compare our models with evolutionary tracks available in the literature and discuss the main differences. We finally analyse to which extent current observations of young systems provide a good test for pre-Main Sequence tracks.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/3128de49632981d5c86b7c8301885184cb545c67

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In Astronomy and Astrophysics

1. K. Luhman
2. Eric Mamajek
3. Michael C. Liu
4. B. Bowler
5. Jon Fortney
6. L. Hillenbrand
7. M. Marley
8. A. Burgasser

Citations in the corpus

• Embedded Clusters in Molecular Clouds (2003, background): “Unfortunately, the theoretical trajectories of PMS stars on the HRD can be highly uncertain, particularly for cluster ages of 1 Myrs or less and for low-mass stars and substellar objects (e.g., Baraffe et al. 2002).”
• Spectroscopy of Very Low Mass Stars and Brown Dwarfs in IC 2391: Lithium Depletion and Hα Emission (2004, methodology): “Using our new age estimate and models by Baraffe et al. (2002), the interstellar reddening, and the cluster distance, the substellar limit is located at IC ¼17:06.”
• BAYESIAN ANALYSIS TO IDENTIFY NEW STAR CANDIDATES IN NEARBY YOUNG STELLAR KINEMATIC GROUPS (2012, methodology): “Thus, to extend the color sequence of the young associations beyond M3V up to M9V, we used the evolutionary models of Baraffe et al. (1998, 2002), shifting the isochrones (typically by 0.5 mag) to match the known members between K5V and M5V dwarfs.”
• On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets (2014, background): “…brown dwarf and giant planet atmospheres is more straightforward than in the stellar structure literature (e.g., Hansen et al. 2004, Chapter 5), since the ideal gas law applies and the convection is, to a good approximation, adiabatic (Baraffe et al. 2002; Ludwig et al. 2006; Freytag et al. 2010).”
• The Effect of Jupiter's Formation on the Distribution of Refractory Elements and Inclusions in Meteorites (2017, methodology): “For a passively heated disk, we adopt a profile using the approach of Chiang & Goldreich (1997): Tpassive = 163 ( L 1L )2/7 ( r 1 AU )−3/7 K, (8) 12 and adopt the luminosity L(t) = 1.2 (t/1 Myr)−0.5 L (Baraffe et al. 2002).”
• THE EVOLUTION OF CATACLYSMIC VARIABLES AS REVEALED BY THEIR DONOR STARS (2011, methodology): “Thus we again adopt the standard NextGen atmosphere models (Hauschildt et al. 1999) down to Teff = 2300 K, the AMES-DUSTY models (Chabrier et al. 2000) between 1800 K Teff 2000 K, and the AMES-COND models (Baraffe et al. 2003) for temperatures Teff 1700 K.”
• The Luminosity and Mass Function of the Trapezium Cluster: From B Stars to the Deuterium-burning Limit (2002, background): “The luminosity evolution at the youngest ages (<1 Myr) will depend, however, on the initial conditions of the contracting PMS star as it leaves its protostellar stage, although these differences are quickly erased (Baraffe et al. 2002).”
• THE DEUTERIUM-BURNING MASS LIMIT FOR BROWN DWARFS AND GIANT PLANETS (2010, methodology): “…by the application of nongray radiative transfer theory (Burrows et al. 1997, 1998; Burrows & Sharp 1999; Burrows 1999; Burrows et al. 2001, 2003; Baraffe et al. 2002, 2003; Allard et al. 2003; Chabrier et al. 2000b,a; Chabrier & Baraffe 2000; Sharp & Burrows 2007; Barman 2008) and sophisticated…”
• A REVISED AGE FOR UPPER SCORPIUS AND THE STAR FORMATION HISTORY AMONG THE F-TYPE MEMBERS OF THE SCORPIUS–CENTAURUS OB ASSOCIATION (2011, methodology): “…below the limiting mass for thermonuclear fusion of F-Type Members of Sco-Cen 13 we use our revised age for Upper Sco of 11 Myr and the object’s reported Teff of 1800±200 K (Lafrenière et al. 2010) to obtain a mass of 13+2−3 MJup using the DUSTY models (Chabrier et al. 2000; Baraffe et al. 2002).”
• The Formation and Early Evolution of Low-Mass Stars and Brown Dwarfs (2012, methodology): “…for a few dozen pre-main-sequence stars, and compilations of these data have been used to characterize the sizes of systematic errors in various sets of models and the possible sources of those errors (Baraffe et al. 2002, Hillenbrand & White 2004, Luhman et al. 2003b, Mathieu et al. 2007).”
• Gravitational Instabilities in Circumstellar Disks (2016, methodology): “The stellar masses are estimated using the isochrones from D’Antona & Mazzitelli (1997); Baraffe et al. (2002) and Siess et al. (2000).”
• Characterization of exoplanets from their formation - I. Models of combined planet formation and evolution (2012, background): “…of evolution, the planets could be going through regions in the surface gravity-effective temperature parameter space where the formation of H2 leads to a nonlinear response of A111, page 3 of 23 the atmospheric structure, which influences the degree of superadiabaticity (Baraffe et al. 2002).”
• Sub-arcsec imaging of the AB Aur molecular disk and envelope at millimeter wavelengths: a non Keplerian disk (2005, methodology): “For example, using the brightness profile published by (Fukagawa et al. 2004) in the H band, and the evolution models from Baraffe et al. (1998, 2002), we find a (conservative, especially at large radii) upper limiton any coeval companion of less than 0.02 M⊙ in the field of view of the Subaru…”
• The Interior Structure, Composition, and Evolution of Giant Planets (2009, background): “It is not known if these thermal evolution models are accurate at young ages–they are relatively untested, which has been stressed by Baraffe et al. (2002) for brown dwarfs and Marley et al. (2007) for planets.”