NEAR-INFRARED SPECTROSCOPY OF THE EXTRASOLAR PLANET HR 8799 b

By B. Bowler, Michael C. Liu, T. Dupuy, M. Cushing. 2010

155 citations recorded by the source corpus.

We present 2.12–2.23 μm high contrast integral field spectroscopy of the extrasolar planet HR 8799 b. Our observations were obtained with OSIRIS on the Keck II telescope and sample the 2.2 μm CH4 feature, which is useful for spectral classification and as a temperature diagnostic for ultracool objects. The spectrum of HR 8799 b is relatively featureless, with little or no methane absorption, and does not exhibit the strong CH4 seen in T dwarfs of similar absolute magnitudes. The spectrum is consistent with field objects from early-L to T4 (3σ confidence level), with a best-fitting type of T2. A similar analysis of the published 1–4 μm photometry shows the infrared spectral energy distribution (SED) matches L5–L8 field dwarfs, especially the reddest known objects which are believed to be young and/or very dusty. Overall, we find that HR 8799 b has a spectral type consistent with L5–T2, although its SED is atypical compared to most field objects. We fit the 2.2 μm spectrum and the infrared SED using the Hubeny & Burrows, Burrows et al., and Ames-Dusty model atmosphere grids, which incorporate non-equilibrium chemistry, non-solar metallicities, and clear and cloudy variants. No models agree with all of the data, but those with intermediate clouds produce significantly better fits. The largest discrepancy occurs in the J band, which is highly suppressed in HR 8799 b. Models with high eddy diffusion coefficients and high metallicities are somewhat preferred over those with equilibrium chemistry and solar metallicity. The best-fitting effective temperatures range from 1300 to 1700 K with radii between ∼0.3 and 0.5 RJup. These values are inconsistent with evolutionary model-derived values of 800–900 K and 1.1–1.3 RJup based on the luminosity of HR 8799 b and the age of HR 8799, a discrepancy that probably results from imperfect atmospheric models or the limited range of physical parameters covered by the models. The low temperature inferred from evolutionary models indicates that HR 8799 b is ∼400 K cooler than field L/T transition objects, providing further evidence that the L/T transition is gravity-dependent. With an unusually dusty photosphere, an exceptionally low luminosity for its spectral type, and hints of extreme secondary physical parameters, HR 8799 b appears to be unlike any class of field brown dwarf currently known.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/ecebb554a2436ac1961baa6053e050f8d1d582ea

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In Astronomy and Astrophysics

1. Michael C. Liu
2. B. Bowler
3. T. Dupuy
4. M. Marley
5. Jon Fortney
6. N. Madhusudhan
7. A. Burgasser
8. K. Luhman

Citations in the corpus

• THE EFFECTS OF SNOWLINES ON C/O IN PLANETARY ATMOSPHERES (2011, background): “Spectra of HR 8799b, situated at 68 AU, show a lack of CH4 absorption, possibly indicating a low C/O ratio (Bowler et al. 2010).”
• A COMBINED SUBARU/VLT/MMT 1–5 μm STUDY OF PLANETS ORBITING HR 8799: IMPLICATIONS FOR ATMOSPHERIC PROPERTIES, MASSES, AND FORMATION (2011, methodology): “The K-band spectrum of HR 8799b is not well matched by typical L and T-type brown dwarf spectra (Bowler et al. 2010).”
• THE BROWN DWARF KINEMATICS PROJECT (BDKP). III. PARALLAXES FOR 70 ULTRACOOL DWARFS (2012, background): “HR 8799b as well as the early L dwarf companion to AB Pic are also underluminous while some earlier L and M dwarfs such as HD 130948B and CD-35 2722 B are overluminous on color magnitude diagrams (Bowler et al. 2010; Chauvin et al. 2005; Dupuy et al. 2008; Wahhaj et al. 2011).”
• 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).”
• THE GEMINI/NICI PLANET-FINDING CAMPAIGN: THE FREQUENCY OF PLANETS AROUND YOUNG MOVING GROUP STARS (2013, background): “…HR 8799 planets; Chauvin et al. 2005a; Marois et al. 2008, 2010) have lacked methane absorption and show extremely red colors, likely due to dust clouds and/or non-equilibrium chemistry in their atmospheres (Bowler et al. 2010; Skemer et al. 2011; Barman et al. 2011a, 2011b; Currie et al. 2011).”
• LARGE-AMPLITUDE VARIATIONS OF AN L/T TRANSITION BROWN DWARF: MULTI-WAVELENGTH OBSERVATIONS OF PATCHY, HIGH-CONTRAST CLOUD FEATURES (2012, background): “Second, low-gravity L dwarfs (Faherty et al. 2011, submitted) and directly imaged planets (e.g. Bowler et al. 2010; Skemer et al. 2011) have been found to be less luminous than “normal” field BDs of a given spectral type.”
• SPECTRAL AND PHOTOMETRIC DIAGNOSTICS OF GIANT PLANET FORMATION SCENARIOS (2011, result): “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).”
• 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).”
• CLOUDS AND CHEMISTRY IN THE ATMOSPHERE OF EXTRASOLAR PLANET HR8799b (2011, methodology): “While certainly not perfect, the model comparisons presented here are better representations of the observations than those presented by Bowler et al. (2010) and Currie et al. (2011).”
• C/O RATIO AS A DIMENSION FOR CHARACTERIZING EXOPLANETARY ATMOSPHERES (2012, background): “…2012), thermal phase curves (Knutson et al. 2007, 2012; Showman et al. 2009; Cowan et al. 2012), and direct imaging (e.g. Marois et al. 2008,2010; Bowler et al. 2010; Currie et al. 2011; Janson et al. 1 Department of Physics and Department of Astronomy, Yale University, New Haven, CT 06511…”
• Imaging Extrasolar Giant Planets (2016, background): “…massive stars analogous to the well-established correlation at small separations (Johnson et al. 2007; Lovis & Mayor 2007; Johnson et al. 2010; Bowler et al. 2010b), this trend is not yet statistically significant at wide orbital distances and requires larger sample sizes in each stellar mass…”
• FUNDAMENTAL PARAMETERS AND SPECTRAL ENERGY DISTRIBUTIONS OF YOUNG AND FIELD AGE OBJECTS WITH MASSES SPANNING THE STELLAR TO PLANETARY REGIME (2015, background): “…poorly reproduced regions such as the H-band peak and λ< 0.9 μm result in sometimes highly discrepant best fit parameters (e.g., Teff and surface gravity) and consequently unreliable or unphysical radii estimates (e.g., Bowler et al. 2010; Barman et al. 2011; Dupuy & Kraus 2013; Liu et al. 2013).”
• MODEL ATMOSPHERES FOR MASSIVE GAS GIANTS WITH THICK CLOUDS: APPLICATION TO THE HR 8799 PLANETS AND PREDICTIONS FOR FUTURE DETECTIONS (2011, background): “…giant planets at large orbital distances, and, hence, with low stellar irradiation, could have been expected to have had similar spectral characteristics to low temperature brown dwarfs, recent observations are proving otherwise (Marois et al. 2008 & 2010, Bowler et al. 2010, Currie et al. 2011).”
• ExoMol line lists – XVIII. The high-temperature spectrum of VO (2016, background): “There has been considerable recent debate (Spiegel et al. 2009; Fortney et al. 2010; Bowler et al. 2010; Madhusudhan & Seager 2010; Huitson et al. 2012; Spiegel & Burrows 2013; Gibson et al. 2013; Parmentier et al. 2013; Agúndez et al. 2014; Hoeijmakers et al. 2015; Schwarz et al. 2015; Haynes et…”
• SIMULTANEOUS DETECTION OF WATER, METHANE, AND CARBON MONOXIDE IN THE ATMOSPHERE OF EXOPLANET HR 8799 b (2015, background): “The two outer most planets, b and c, have the most comprehensive wavelength coverage including near-infrared (near-IR) spectroscopy at low, R ∼ 50 − 100 (Bowler et al. 2010; Barman et al. 2011a; Oppenheimer et al. 2013) and medium, R ∼ 4000 (Konopacky et al. 2013) resolutions.”
• A New High Contrast Imaging Program at Palomar Observatory (2010, background): “Direct imaging enables spectroscopy (see, e.g., Janson et al. 2010; Bowler et al. 2010), which is the key to unlocking the detailed properties of the objects themselves.”