SIMULTANEOUS DETECTION OF WATER, METHANE, AND CARBON MONOXIDE IN THE ATMOSPHERE OF EXOPLANET HR 8799 b

By Travis S. Barman, Q. Konopacky, B. Macintosh, C. Marois. 2015

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Absorption lines from water, methane, and carbon monoxide are detected in the atmosphere of exoplanet HR 8799 b. A medium-resolution spectrum presented here shows well-resolved and easily identified spectral features from all three molecules across the K band. The majority of the lines are produced by CO and H2O, but several lines clearly belong to CH4. Comparisons between these data and atmosphere models covering a range of temperatures and gravities yield log mole fractions of H2O between −3.09 and −3.91, CO between −3.30 and −3.72, and CH4 between −5.06 and −5.85. More precise mole fractions are obtained for each temperature and gravity studied. A reanalysis of H-band data, previously obtained at a similar spectral resolution, results in a nearly identical water abundance as determined from the K-band spectrum. The methane abundance is shown to be sensitive to vertical mixing and indicates an eddy diffusion coefficient in the range of 106–108 cm2 s−1, comparable to mixing in the deep troposphere of Jupiter. The model comparisons also indicate a carbon-to-oxygen ratio (C/O) between ∼0.58 and 0.7, encompassing previous estimates for a second planet in the same system, HR 8799 c. Super-stellar C/O could indicate planet formation by core-accretion; however, the range of possible C/O for these planets (and the star) is currently too large to comment strongly on planet formation. More precise values of the bulk properties (e.g., effective temperature and surface gravity) are needed for improved abundance estimates.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/3881765647c5155976bde1b57da784503a3f50c0

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In Astronomy and Astrophysics

1. Jon Fortney
2. N. Madhusudhan
3. Th. Henning
4. M. Line
5. B. Bowler
6. E. Lopez
7. Laura Kreidberg
8. J. Lustig-Yaeger

Citations in the corpus

• CHARACTERIZING TRANSITING EXOPLANET ATMOSPHERES WITH JWST (2015, background): “There has yet to be unambiguous evidence for high C/O (C/O > 1) within the current ensemble of observed exoplanets (Konopacky et al. 2013; Barman et al. 2015; Madhusudhan et al. 2011; Line et al. 2014a; Stevenson et al. 2014; Kreidberg et al. 2015; Benneke 2015).”
• Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e (2020, background): “Likewise, Konopacky et al. (2013); Barman et al. (2015) derive a C/O of 0.65+0.10−0.05 for HR 8799c and a value between 0.58 and 0.7 for HR 8799b, which is consistent with the value we derive for HR 8799e.”
• 2018 Census of Interstellar, Circumstellar, Extragalactic, Protoplanetary Disk, and Exoplanetary Molecules (2018, unknown): “…[33] Thi et al. (1999) [34] Thi et al. (2011) [35] Walsh et al. (2016) [36] van Zadelhoff et al. (2001) References: [1] Barman et al. (2011) [2] Barman et al. (2015) [3] Deming et al. (2013) [4] Haynes et al. (2015) [5] Kreidberg et al. (2014) [6] Kreidberg et al. (2015) [7] Lanotte et al.…”
• An Accurate, Extensive, and Practical Line List of Methane for the HITEMP Database (2020, methodology): “…below ∼1300 K (Burrows & Sharp 1999), yet observations of CH4 have only been reported in the spectra of five exoplanets to date: HD 189733b (Swain et al. 2008), HD 209458b (Swain et al. 2009), XO-1b (Tinetti et al. 2010), HR 8799b (Barman et al. 2015) and 51 Eridani b (Macintosh et al. 2015).”
• THE MASS–METALLICITY RELATION FOR GIANT PLANETS (2015, background): “…either in bulk composition (Guillot et al. 2006; Burrows et al. 2007; Miller & Fortney 2011; Mordasini et al. 2014), or atmospheric composition (Madhusudhan et al. 2011; Fortney et al. 2013; Konopacky et al. 2013; Kreidberg et al. 2014; Barman et al. 2015) as shown in a schematic way in Figure 1.”
• Imaging Extrasolar Giant Planets (2016, background): “Other fertile avenues for high-contrast imaging include precise measurements of atmospheric composition (Konopacky et al. 2013; Barman et al. 2015), doppler imaging (Crossfield 2014; Crossfield et al. 2014), photometric monitoring to map variability of rotationally-modulated features (e.g., Apai et…”