Exoplanetary atmospheric sodium revealed by orbital motion: Narrow-band transmission spectroscopy of HD 189733b with UVES

Khalafinejad, S. and von Essen, C. and Hoeijmakers, H. J. and Zhou, G. ORCID: https://orcid.org/0000-0002-4891-3517 and Klocova, T. and Schmitt, J. H. M. M. and Dreizler, S. and Lopez-Morales, M. and Husser, T. -O. and Schmidt, T. O. B. and Collet, R. (2017) Exoplanetary atmospheric sodium revealed by orbital motion: Narrow-band transmission spectroscopy of HD 189733b with UVES. Astronomy and Astrophysics, 598:A131. pp. 1-12. ISSN 0004-6361

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Abstract

Context. During primary transits, the spectral signatures of exoplanet atmospheres can be measured using transmission spectroscopy. We can obtain information on the upper atmosphere of these planets by investigating the exoplanets' excess sodium absorption in the optical region. However, a number of factors can affect the observed sodium absorption signature. We present a detailed model correcting for systematic biases to yield an accurate depth for the sodium absorption in HD 189733b. Aims. The goal of this work is to accurately measure the atomspheric sodium absorption light curve in HD 189733b, correcting for the effects of stellar differential limb-darkening, stellar activity, and a 'bump' caused by the changing radial velocity of the exoplanet. In fact, owing to the high cadence and quality of our data, it is the first time that the last feature can be detected even by visual inspection. Methods. We use 244 high-resolution optical spectra taken by the UVES instrument mounted at the VLT. Our observations cover a full transit of HD 189733b, with a cadence of 45 s. To probe the transmission spectrum of sodium we produce excess light curves integrating the stellar flux in passbands of 1 Å, 1.5 Å, and 3 Å inside the core of each sodium D-line. We model the effects of external sources on the excess light curves, which correspond to an observed stellar flare beginning close to mid-transit time and the wavelength dependent limb-darkening effects. In addition, by characterizing the effect of the changing radial velocity and Doppler shifts of the planetary sodium lines inside the stellar sodium lines, we estimate the depth and width of the exoplanetary sodium feature. Results. We estimate the shape of the planetary sodium line by a Gaussian profile with an equivalent width of ~0.0023 ± 0.0010Å, thereby confirming the presence of sodium in the atmosphere of HD 189733b with excess absorption levels of 0.72 ± 0.25%, 0.34 ± 0.11%, and 0.20 ± 0.06% for the integration bands of 1 Å, 1.5 Å, and 3 Å, respectively. Using the equivalent width of the planetary sodium line, we produce a first order estimate of the number density of sodium in the exoplanet atmosphere.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Faculty/School / Institute/Centre: No Faculty
Faculty/School / Institute/Centre: No Faculty
Date Deposited: 07 Feb 2022 03:17
Last Modified: 14 Feb 2022 00:14
Uncontrolled Keywords: Instrumentation: spectrographs; Methods: observational; Planets and satellites: atmospheres; Planets and satellites: individual: HD 189733b; Stars: activity; Techniques: spectroscopic; Astrophysics; - Earth and Planetary Astrophysics; Astrophysics - Solar and Stellar; Astrophysics
Fields of Research (2008): 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
Socio-Economic Objectives (2008): E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Socio-Economic Objectives (2020): 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280120 Expanding knowledge in the physical sciences
Identification Number or DOI: https://doi.org/10.1051/0004-6361/201629473
URI: http://eprints.usq.edu.au/id/eprint/45003

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