Neutral Iron Emission Lines from the Dayside of KELT-9b: The GAPS Program with HARPS-N at TNG XX

Abstract

We present the first detection of atomic emission lines from the atmosphere of an exoplanet. We detect neutral iron lines from the dayside of KELT-9b (T eq ∼4000 K). We combined thousands of spectrally resolved lines observed during one night with the HARPS-N spectrograph (R∼115,000), mounted at the Telescopio Nazionale Galileo. We introduce a novel statistical approach to extract the planetary parameters from the binary mask crosscorrelation analysis. We also adapt the concept of contribution function to the context of high spectral resolution observations, to identify the location in the planetary atmosphere where the detected emission originates. The average planetary line profile intersected by a stellar G2 binary mask was found in emission with a contrast of 84±14 ppm relative to the planetary plus stellar continuum (40% ± 5% relative to the planetary continuum only). This result unambiguously indicates the presence of an atmospheric thermal inversion. Finally, assuming a modeled temperature profile previously published, we show that an iron abundance consistent with a few times the stellar value explains the data well. In this scenario, the iron emission originates at the 10 −3-10 −5 bar level.

The Hubble WFC3 Emission Spectrum of the Extremely Hot Jupiter KELT-9b

“…For Fe, we find that Fe/H = 1.2 × 10 −8 , which is much lower than solar ratios. This ratio implies that the species must also be found in another form, which matches the findings in Pino et al (2020) who detected atomic Fe, even though their assumed self-consistent temperature structure from Lothringer et al (2018) differs from our retrieved ones.…”

“…Given the extreme temperatures, the majority of molecules are anticipated to be dissociated leaving only atomic species (Kitzmann et al 2018). Ground-based high-resolution observations have detected a number of metals including iron, titanium, and calcium (Hoeijmakers et al 2018(Hoeijmakers et al , 2019Cauley et al 2019;Yan et al 2019;Pino et al 2020;Turner et al 2020). Observations of KELT-9 b with TESS and Spitzer have revealed an asymmetric transit (Ahlers et al 2020), induced by the fast rotation of its host star.…”

“…It is subject to intense irradiation from the star and extreme atmospheric escape due to its large extended hydrogen envelope reaching the Roche-Lobe limit (Yan & Henning 2018;Wyttenbach et al 2020). Measurements of the neutral iron line by Pino et al (2020) imply the presence of a thermal inversion, as does modeling by Fossati et al (2020).…”

The PHOENIX Exoplanet Retrieval Algorithm and Using H− Opacity as a Probe in Ultrahot Jupiters

“…This corresponds to probing about an order of magnitude in pressure between 10 and 100mbar, useful for determining the presence and magnitude of temperature inversions which are predicted to be ubiquitous in the hottest Jovian planets (Lothringer et al 2018). Indeed, a temperature inversion has recently been detected in KELT-9b from ground-based high-resolution observations of neutral Fe (Pino et al 2020).…”

Detection of Fe i Emission in the Dayside Spectrum of WASP-33b*

“…The signature of Fe i has since been detected in the transmission spectrum of several hot Jupiters, including KELT-9b (Hoeijmakers et al 2018), WASP-121b (Gibson et al 2020;Cabot et al 2020;Bourrier et al 2020), WASP-76b (Ehrenreich et al 2020), and KELT-20b/MASCARA-2b (Nugroho et al 2020;Stangret et al 2020;Hoeijmakers et al 2020). Recently, Pino et al (2020) detected Fe i in the dayside spectrum of KELT-9b for the first time using the data taken with HARPS-N on the Telescopio Nazionale arXiv:2007.05508v1 [astro-ph.EP] 10 Jul 2020 Galileo. They also showed that the Fe i signature is in emission, which provides direct evidence of a thermal inversion.…”