Spectrally resolved detection of sodium in the atmosphere of HD 189733b with the HARPS spectrograph

By A. Wyttenbach, David Ehrenreich, C. Lovis, S. Udry, F. Pepe. 2015

196 citations recorded by the source corpus.

Context. Atmospheric properties of exoplanets can be constrained with transit spectroscopy. At low spectral resolution, this technique is limited by the presence of clouds. The signature of atomic sodium (Nai), known to be present above the clouds, is a powerful probe of the upper atmosphere, where it can be best detected and characterized at high spectral resolution. Aims. Our goal is to obtain a high-resolution transit spectrum of HD 189733b in the region around the resonance doublet of Nai at 589 nm, to characterize the absorption signature that was previously detected from space at low resolution. Methods. We analyzed archival transit data of HD 189733b obtained with the HARPS spectrograph (R = 115 000) at the ESO 3.6-m telescope. We performed di erential spectroscopy to retrieve the transit spectrum and light curve of the planet, implementing corrections for telluric contamination and planetary orbital motion. We compared our results to synthetic transit spectra calculated from isothermal models of the planetary atmosphere. Results. We spectrally resolve the Nai D doublet and measure line contrasts of 0:64 0:07% (D2) and 0:40 0:07% (D1) and FWHMs of 0:52 0:08 A. This corresponds to a detection at the 10 level of excess of absorption of 0:32 0:03% in a passband of 2 0:75 A centered on each line. We derive temperatures of 2600 600 K and 3270 330 K at altitudes of 9800 2800 and 12 700 2600 km in the Nai D1 and D2 line cores, respectively. We measure a temperature gradient of 0.2 K km 1 in the region where the sodium absorption dominates the haze absorption from a comparison with theoretical models. We also detect a blueshift of 0:16 0:04 A (4 ) in the line positions. This blueshift may be the result of winds blowing at 8 2 km s 1 in the upper layers of the atmosphere. Conclusions. We demonstrate the relevance of studying exoplanet atmospheres with high-resolution spectrographs mounted on 4-m-class telescopes. Our results pave the way for an in-depth characterization of physical conditions in the atmospheres of many exoplanetary systems with future spectrographs such as ESPRESSO on the VLT or HiReS and METIS on the E-ELT.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/3c2e9e36ad5a86dde890645f2358768c34026474

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Citations in the corpus

Exoplanetary Atmospheres: Key Insights, Challenges, and Prospects (2019, methodology): “Similar measurements were made for the hot Jupiter HD 189733b using the Na absorption line observed in a high-resolution transmission spectrum in the optical (282) and initially”
A CONSISTENT RETRIEVAL ANALYSIS OF 10 HOT JUPITERS OBSERVED IN TRANSMISSION (2016, background): “We note that while we have assumed a uniform temperature for the retrieval, detailed analysis of the sodium line has revealed a hot thermosphere at the upper atmospheric layers for this planet ((Huitson et al. 2012; Wyttenbach et al. 2015).”
Mass–Metallicity Trends in Transiting Exoplanets from Atmospheric Abundances of H2O, Na, and K (2019, methodology): “Besides H2O, Na and K are the most observed chemical species in giant exoplanetary atmospheres using spaceand ground-based telescopes (e.g., Charbonneau et al. 2002; Redfield et al. 2008; Wyttenbach et al. 2015; Sing et al. 2016; Nikolov et al. 2018).”
Extremely Irradiated Hot Jupiters: Non-oxide Inversions, H− Opacity, and Thermal Dissociation of Molecules (2018, background): “…temperature of about 10,000 K. Evidence for this temperature inversion in the upper atmosphere has been obtained from observations of the sodium resonance doublet at 5890 and 5900 Å on HD209458b, HD189733b and WASP-49b (Vidal-Madjar et al. 2011; Wyttenbach et al. 2015; Wyttenbach et al. 2017).”
ROTATION AND WINDS OF EXOPLANET HD 189733 b MEASURED WITH HIGH-DISPERSION TRANSMISSION SPECTROSCOPY (2015, methodology): “At optical wavelengths, Wyttenbach et al. (2015) also claimed high-altitude winds in the atmosphere of HD 189733 b by measuring a blue-shift in the planet sodium absorption of ( 8± 2) km s 1.”