Publication: Water vapor detection in the transmission spectra of HD 209458 b with the CARMENES NIR channel
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2019-10
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EDP Sciences S A
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Abstract
Methods. The water vapor absorption lines from the atmosphere of the planet are Doppler-shifted due to the large change in its radial velocity during transit. This shift is of the order of tens of km s^(−1) , whilst the Earth’s telluric and the stellar lines can be considered quasi-static. We took advantage of this shift to remove the telluric and stellar lines using SYSREM, which performs a principal component analysis including proper error propagation. The residual spectra contain the signal from thousands of planetary molecular lines well below the noise level. We retrieve the information from those lines by cross-correlating the residual spectra with models of the atmospheric absorption of the planet.
Results. We find a cross-correlation signal with a signal-to-noise ratio (S/N) of 6.4, revealing H_(2)O in HD 209458 b. We obtain a net blueshift of the signal of –5.2^(+2.6)_(−1.3) km s^(−1) that, despite the large error bars, is a firm indication of day- to night-side winds at the terminator of this hot Jupiter. Additionally, we performed a multi-band study for the detection of H_(2)O individually from the three near infrared bands covered by CARMENES. We detect H_(2)O from its 0.96–1.06 µm band with a S/N of 5.8, and also find hints of a detection from the 1.06–1.26 µm band, with a low S/N of 2.8. No clear planetary signal is found from the 1.26–1.62 µm band.
Conclusions. Our significant H_(2)O signal at 0.96–1.06 µm in HD 209458 b represents the first detection of H_(2)O from this band individually, the bluest one to date. The unfavorable observational conditions might be the reason for the inconclusive detection from the stronger 1.15 and 1.4 µm bands. H_(2)O is detected from the 0.96–1.06 µm band in HD 209458 b, but hardly in HD 189733 b, which supports a stronger aerosol extinction in the latter, in line with previous studies. Future data gathered at more stable conditions and with larger S/N at both optical and near-infrared wavelengths could help to characterize the presence of aerosols in HD 209458 b and other planets.
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© A. Sánchez-López et al. 2019. Artículo firmado por 34 autores. CARMENES is funded by the German Max-PlanckGesellschaft (MPG), the Spanish Consejo Superior de Investigaciones Científicas (CSIC), the European Union through European Regional Fund (FEDER/ERF), the Spanish Ministry of Economy and Competitiveness, the state of Baden-Württemberg, the German Science Foundation (DFG), and the Junta de Andalucía, with additional contributions by the members of the CARMENES Consortium (Max-Planck-Institut für Astronomie, Instituto de Astrofísica de Andalucía, Landessternwarte Königstuhl, Institut de Ciències de l’Espai, Institut für Astrophysik Göttingen, Universidad Complutense de Madrid, Thüringer Landessternwarte Tautenburg, Instituto de Astrofísica de Canarias, Hamburger Sternwarte, Centro de Astrobiología, and the Observatorio de Calar Alto). Financial support was also provided by the Universidad Complutense de Madrid, the Comunidad Autónoma de Madrid, the Spanish Ministerios de Ciencia e Innovación and of Economía y Competitividad, the Fondo Europeo de Desarrollo Regional (FEDER/ERF), the Agencia estatal de investigación, and the Fondo Social Europeo under grants AYA2011-30 147-C03-01, -02, and -03, AYA2012- 39612-C03-01, ESP2013-48391-C4-1-R, ESP2014–54062–R, ESP 2016–76076– R, ESP2016-80435-C2-2-R, ESP2017-87143-R, BES–2015–073500, and BES– 2015–074542. IAA authors acknowledge financial support from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award SEV-2017-0709. L.T.-O. acknowledges support from the Israel Science Foundation (grant No. 848/16). Based on observations collected at the Observatorio de Calar Alto. We thank the anonymous referee for their insightful comments, which contributed to improve the quality of the manuscript.