The Evolution of L and T Dwarfs in Color-Magnitude Diagrams

By D. Saumon, M. Marley. 2008

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We present new evolution sequences for very low mass stars, brown dwarfs, and giant planets and use them to explore a variety of influences on the evolution of these objects. While the predicted adiabatic evolution of luminosity with time is very similar to results of previous work, the remaining disagreements reveal the magnitude of current uncertainty in brown dwarf evolution theory. We discuss the sources of those differences and argue for the importance of the surface boundary condition provided by atmosphere models including clouds. The L- to T-type ultracool dwarf transition can be accommodated within the Ackerman and Marley cloud model by varying the cloud sedimentation parameter. We develop a simple model for the evolution across the L/T transition. By combining the evolution calculation and our atmosphere models, we generate colors and magnitudes of synthetic populations of ultracool dwarfs in the field and in Galactic clusters. We focus on near-infrared color-magnitude diagrams (CMDs) and on the nature of the “second parameter” that is responsible for the scatter of colors along the Teff sequence. Instead of a single second parameter we find that variations in metallicity and cloud parameters, unresolved binaries, and possibly a relatively young population all play a role in defining the spread of brown dwarfs along the cooling sequence. We also find that the transition from cloudy L dwarfs to cloudless T dwarfs slows down the evolution and causes a pileup of substellar objects in the transition region, in contradiction with previous studies. However, the same model is applied to the Pleiades brown dwarf sequence with less success. Taken at face value, the present Pleiades data suggest that the L/T transition occurs at lower Teff for lower gravity objects, such as those found in young Galactic clusters. The simulated populations of brown dwarfs also reveal that the phase of deuterium burning produces a distinctive feature in CMDs that should be detectable in ~50-100 Myr old clusters.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/af9a346f2b39a705abdefa292b393a52a8d5e3ba

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Citations in the corpus

SPECTRAL AND PHOTOMETRIC DIAGNOSTICS OF GIANT PLANET FORMATION SCENARIOS (2011, background): “However, this mass depends on metallicity, helium fraction, the presence or absence of clouds, etc. (Saumon & Marley 2008; Spiegel et al. 2011).”
THE EXTREMELY RED, YOUNG L DWARF PSO J318.5338−22.8603: A FREE-FLOATING PLANETARY-MASS ANALOG TO DIRECTLY IMAGED YOUNG GAS-GIANT PLANETS (2013, methodology): “With a measured Lbol and an age estimate, we use the Saumon & Marley (2008) evolutionary models with fsed = 2 to compute the remaining physical properties.”
COSMOS2020: A Panchromatic View of the Universe to z ∼ 10 from Two Complementary Catalogs (2021, background): “Stellar templates with an effective temperature Teff 4000 K are rejected in the case that the physical parameters do not satisfy the constraints from Saumon & Marley (2008).”
THE DEUTERIUM-BURNING MASS LIMIT FOR BROWN DWARFS AND GIANT PLANETS (2010, background): “Saumon & Marley (2008) have contributed to this endeavor.”
On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets (2014, methodology): “The evolution of very low mass stars and brown dwarfs is reviewed by Burrows et al. (2001), while Saumon & Marley (2008) present more recent calculations.”
CLOUDS AND CHEMISTRY IN THE ATMOSPHERE OF EXTRASOLAR PLANET HR8799b (2011, background): “Evidence for a gravity dependence for the L-to-T transition has already been reported (Metchev & Hillenbrand 2006; Saumon & Marley 2008) and, recently, Stephens et al. (2009) found that low-gravity brown dwarfs in their sample remain cloudy at lower effective temperatures, with the L-to-T…”
LARGE-AMPLITUDE VARIATIONS OF AN L/T TRANSITION BROWN DWARF: MULTI-WAVELENGTH OBSERVATIONS OF PATCHY, HIGH-CONTRAST CLOUD FEATURES (2012, methodology): “This scenario is possible only for low primary masses (M1 10 MJup) and low mass ratios (q 0.05 − 0.1), such that a semi-detached binary with a 15.44 hr period would have to be a young ( 20 Myr), double planetary-mass system.”
GASEOUS MEAN OPACITIES FOR GIANT PLANET AND ULTRACOOL DWARF ATMOSPHERES OVER A RANGE OF METALLICITIES AND TEMPERATURES (2014, background): “…et al. (2008) (hereafter, F08) we presented a detailed discussion of atomic and molecular line opacities used by our group in modeling the atmospheres of brown dwarfs and giant planets (e.g. Marley et al. 2002; Fortney et al. 2005; Saumon & Marley 2008; Fortney et al. 2008; Marley et al. 2010).”
The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations (2012, background): “The introduction of “dusty” models was a leap forward in the study of brown dwarfs (see e.g. Allard et al. 2001; Kirkpatrick 2005; Saumon & Marley 2008), and our results suggests that a similar effort may be useful for hot planets like HD 189733b. c© 2012 RAS, MNRAS 000, 1–31”
THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS (2016, methodology): “Saumon & Marley (2008) provide a model atmosphere grid over a wide range of Teff , log(g), and cloud properties based on the cloud treatment of Ackerman & Marley (2001), which is parameterized by the sedimentation 14Dupuy et al. (2016a) have recently determined the individual component dynamical…”
MASSES, RADII, AND CLOUD PROPERTIES OF THE HR 8799 PLANETS (2012, methodology): “We note that the pile up of objects in the transition region reported in Saumon & Marley (2008) still occurs in this new calculation but it is more spread out in Teff , as would be expected from the broader span of the transition in Teff (Figure 11).”
MID-INFRARED PHOTOMETRY OF COLD BROWN DWARFS: DIVERSITY IN AGE, MASS, AND METALLICITY (2010, methodology): “Atmospheric and evolutionary models used in this analysis were generated by members of our team (Marley et al. 2002, Saumon & Marley 2008).”
The Field Substellar Mass Function Based on the Full-sky 20 pc Census of 525 L, T, and Y Dwarfs (2020, methodology): “In contrast to the results of Kirkpatrick et al. (2019), we now find that the evolutionary code of Saumon & Marley (2008) is highly favored over that of Baraffe et al. (2003), and the reason for this is the inclusion in this paper of space density measurements over the cloudyto-clear transition…”
THE HAWAII INFRARED PARALLAX PROGRAM. I. ULTRACOOL BINARIES AND THE L/T TRANSITION, (2012, background): “Although the CMDs most directly probe the color evolution of brown dwarfs (i.e., cloud dispersal), in the theoretical perspective of Saumon & Marley (2008) this pileup and gap are inextricably tied to luminosity evolution as well.”
PLANETS AROUND LOW-MASS STARS (PALMS). IV. THE OUTER ARCHITECTURE OF M DWARF PLANETARY SYSTEMS (2014, background): ““Hot-start” models (e.g., Burrows et al. 1997; Saumon & Marley 2008) slowly radiate their initial gravitational potential energy over time and therefore best represent formation via disk instability (e.g., Boss 1997; Mayer 2002).”
THE 0.8–14.5 μm SPECTRA OF MID-L TO MID-T DWARFS: DIAGNOSTICS OF EFFECTIVE TEMPERATURE, GRAIN SEDIMENTATION, GAS TRANSPORT, AND SURFACE GRAVITY (2009, methodology): “We have used the models of Saumon & Marley (2008) to generate and fit synthetic spectra to the red through mid-infrared spectra of 21 L and T dwarfs.”
QUANTITATIVELY ASSESSING THE ROLE OF CLOUDS IN THE TRANSMISSION SPECTRUM OF GJ 1214b (2013, background): “Studies of L dwarfs find thatfsed∼1– 3 for the majority of field L dwarfs (Stephens et al. 2009; Saumon & Marley 2008).”