MODEL ATMOSPHERES FOR MASSIVE GAS GIANTS WITH THICK CLOUDS: APPLICATION TO THE HR 8799 PLANETS AND PREDICTIONS FOR FUTURE DETECTIONS

By N. Madhusudhan, Adam Burrows, T. Currie. 2011

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We have generated an extensive new suite of massive giant planet atmosphere models and used it to obtain fits to photometric data for the planets HR 8799b, c, and d. We consider a wide range of cloudy and cloud-free models. The cloudy models incorporate different geometrical and optical thicknesses, modal particle sizes, and metallicities. For each planet and set of cloud parameters, we explore grids in gravity and effective temperature, with which we determine constraints on the planet's mass and age. Our new models yield statistically significant fits to the data, and conclusively confirm that the HR 8799 planets have much thicker clouds than those required to explain data for typical L and T dwarfs. Both models with (1) physically thick forsterite clouds and a 60 μm modal particle size and (2) clouds made of 1 μm sized pure iron droplets and 1% supersaturation fit the data. Current data are insufficient to accurately constrain the microscopic cloud properties, such as composition and particle size. The range of best-estimated masses for HR 8799b, HR 8799c, and HR 8799d conservatively span 2–12 MJ, 6–13 MJ, and 3–11 MJ, respectively, and imply coeval ages between ∼10 and ∼150 Myr, consistent with previously reported stellar ages. The best-fit temperatures and gravities are slightly lower than values obtained by Currie et al. using even thicker cloud models. Finally, we use these models to predict the near-to-mid-IR colors of soon-to-be imaged planets. Our models predict that planet-mass objects follow a locus in some near-to-mid-IR color–magnitude diagrams that is clearly separable from the standard L/T dwarf locus for field brown dwarfs.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/016c5f547a56442cc439c4af654c4c4bcd96b949

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Citations in the corpus

NEGLECTED CLOUDS IN T AND Y DWARF ATMOSPHERES (2012, background): “Several studies of the HR 8799 planets have shown that the iron and silicate clouds play a significant role in their atmospheres (Marois et al. 2008; Barman et al. 2011; Galicher et al. 2011; Bowler et al. 2010; Currie et al. 2011; Madhusudhan et al. 2011; Marley et al. 2012).”
HST SPECTRAL MAPPING OF L/T TRANSITION BROWN DWARFS REVEALS CLOUD THICKNESS VARIATIONS (2013, methodology): “4, see also Skemer et al. 2012; Barman et al. 2011a,b; Currie et al. 2011; Madhusudhan et al. 2011; Marley et al. 2012).”
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, background): “These properties are thought to arise from extreme atmospheric conditions tied to their young (≈10–30 Myr) ages and low gravities, e.g., enhanced vertical mixing, non-equilibrium chemistry, and unusual clouds (e.g. Barman et al. 2011b; Madhusudhan et al. 2011; Marley et al. 2012).”
SPECTRAL AND PHOTOMETRIC DIAGNOSTICS OF GIANT PLANET FORMATION SCENARIOS (2011, methodology): “For instance, the planets found in the HR8799 system (Marois et al. 2008, 2010) appear to be inconsistent with classical “cold-start” models (Dodson-Robinson et al. 2009; Bowler et al. 2010; Janson et al. 2010; Currie et al. 2011; Madhusudhan et al. 2011).”
LkCa 15: A YOUNG EXOPLANET CAUGHT AT FORMATION? (2011, result): “The same result has been found for moderately older direct-imaged exoplanets, such as Beta Pic b (Lagrange et al. 2009; Quanz et al. 2010; Currie et al. 2011a) and HR 8799 bcde (Marois et al. 2008; Bowler et al. 2010; Marois et al. 2010; Currie et al. 2011b; Madhusudhan et al. 2011).”
POSSIBLE DISINTEGRATING SHORT-PERIOD SUPER-MERCURY ORBITING KIC 12557548 (2012, background): “The first is by condensation of dust grains from a metal-rich vapor into clouds akin to those in brown dwarf or giant planet atmospheres; see, e.g., the modeling of forsterite clouds in Cooper et al. (2003) and Madhusudhan et al. (2011).”
ORBITAL MOTION OF HR 8799 b, c, d USING HUBBLE SPACE TELESCOPE DATA FROM 1998: CONSTRAINTS ON INCLINATION, ECCENTRICITY, AND STABILITY (2011, background): “Models using thick cloud layers that are not present in brown dwarfs tend to reproduce the planets’ SEDs with higher fidelity (Marois et al. 2008; Currie et al. 2011a; Barman et al. 2011; Madhusudhan et al. 2011).”
C/O RATIO AS A DIMENSION FOR CHARACTERIZING EXOPLANETARY ATMOSPHERES (2012, methodology): “Additionally, other hydrocarbons such as C2H2, C2H4, and HCN, which had not been considered by Madhusudhan et al. (2011a), are also expected to be present in the atmosphere of WASP-12b, as has also been suggested by previous studies (Madhusudhan et al. 2011b; Kopparapu et al. 2012).”
A NEAR-INFRARED SPECTROSCOPIC STUDY OF YOUNG FIELD ULTRACOOL DWARFS (2013, background): “It is interesting to note that spectroscopy and photometry of the HR 8799 planets are best matched by young, dusty atmospheres (e.g. Bowler et al. 2010; Madhusudhan et al. 2011; Barman et al. 2011).”
Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e (2020, methodology): “For example, using NIR and MIR photometry and a grid of self-consistent atmospheric models, Madhusudhan et al. (2011b) A131, page 16 of 28 P. Mollière et al.: Scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e find that HR 8799bcd are dominated by clouds much thicker than…”
MASSES, RADII, AND CLOUD PROPERTIES OF THE HR 8799 PLANETS (2012, methodology): “For these reasons a comparison of the cloudy HR 8799 planets to the “standard” L dwarf models, such as that presented by Madhusudhan et al. (2011) and Currie et al. (2011), does not address the question of whether the HR 8799 planets are really all that different from the cloudiest late L dwarfs…”
THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS (2016, background): “Theoretical work (e.g., Barman et al. 2011b; Madhusudhan et al. 2011; Marley et al. 2012; Lee et al. 2013; Zahnle & Marley 2014) has helped provide physical context for direct imaging observations.”
DIRECT IMAGING OF A COLD JOVIAN EXOPLANET IN ORBIT AROUND THE SUN-LIKE STAR GJ 504 (2013, background): “It has been proposed that planetary candidates with hot atmospheres (Teff ∼ 1000 K) around HR 8799 or 2M 1207 may have thick clouds (Barman et al. 2011a; Madhusudhan et al. 2011; Skemer et al. 2011; Marley et al. 2012) although their cloud properties are under discussion (Barman et al. 2011a,b).”