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Title: RE-VISIT OF HST FUV OBSERVATIONS OF THE HOT-JUPITER SYSTEM HD 209458: NO Si iii DETECTION AND THE NEED FOR COS TRANSIT OBSERVATIONS

Abstract

The discovery of O i atoms and C ii ions in the upper atmosphere of HD 209458b, made with the Hubble Space Telescope Imaging Spectrograph (STIS) using the G140L grating, showed that these heavy species fill an area comparable to the planet’s Roche lobe. The derived ∼10% transit absorption depths require super-thermal processes and/or supersolar abundances. From subsequent Cosmic Origins Spectrograph (COS) observations, C ii absorption was reported with tentative velocity signatures, and absorption by Si iii ions was also claimed in disagreement with a negative STIS G140L detection. Here, we revisit the COS data set showing a severe limitation in the published results from having contrasted the in-transit spectrum against a stellar spectrum averaged from separate observations, at planetary phases 0.27, 0.72, and 0.49. We find variable stellar Si iii and C ii emissions that were significantly depressed not only during transit but also at phase 0.27 compared to phases 0.72 and 0.49. Their respective off-transit 7.5% and 3.1% flux variations are large compared to their reported 8.2 ± 1.4% and 7.8 ± 1.3% transit absorptions. Significant variations also appear in the stellar line shapes, questioning reported velocity signatures. We furthermore present archive STIS G140M transit data consistent withmore » no Si iii absorption, with a negative result of 1.7 ± 18.7 including ∼15% variability. Silicon may still be present at lower ionization states, in parallel with the recent detection of extended magnesium, as Mg i atoms. In this frame, the firm detection of O i and C ii implying solar or supersolar abundances contradicts the recent inference of potential 20–125× subsolar metallicity for HD 209458b.« less

Authors:
 [1];  [2]
  1. University of Arizona, Dept. of Planetary Sciences, Lunar and Planetary Laboratory, 1541 E University Blvd., Tucson, AZ 85721-0063 (United States)
  2. UPMC Univ. Paris 06, UMR7095, Institut d’Astrophysique de Paris, F-75014 Paris (France)
Publication Date:
OSTI Identifier:
22522437
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 804; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ATOMS; CARBON; COMPARATIVE EVALUATIONS; DETECTION; ELEMENT ABUNDANCE; JUPITER PLANET; MAGNESIUM; METALLICITY; OXYGEN; ROCHE EQUIPOTENTIALS; SATELLITE ATMOSPHERES; SILICON; SILICON IONS; SPACE; STARS; TELESCOPES; ULTRAVIOLET RADIATION

Citation Formats

Ballester, G. E., and Ben-Jaffel, L., E-mail: gilda@lpl.arizona.edu, E-mail: bjaffel@iap.fr. RE-VISIT OF HST FUV OBSERVATIONS OF THE HOT-JUPITER SYSTEM HD 209458: NO Si iii DETECTION AND THE NEED FOR COS TRANSIT OBSERVATIONS. United States: N. p., 2015. Web. doi:10.1088/0004-637X/804/2/116.
Ballester, G. E., & Ben-Jaffel, L., E-mail: gilda@lpl.arizona.edu, E-mail: bjaffel@iap.fr. RE-VISIT OF HST FUV OBSERVATIONS OF THE HOT-JUPITER SYSTEM HD 209458: NO Si iii DETECTION AND THE NEED FOR COS TRANSIT OBSERVATIONS. United States. doi:10.1088/0004-637X/804/2/116.
Ballester, G. E., and Ben-Jaffel, L., E-mail: gilda@lpl.arizona.edu, E-mail: bjaffel@iap.fr. Sun . "RE-VISIT OF HST FUV OBSERVATIONS OF THE HOT-JUPITER SYSTEM HD 209458: NO Si iii DETECTION AND THE NEED FOR COS TRANSIT OBSERVATIONS". United States. doi:10.1088/0004-637X/804/2/116.
@article{osti_22522437,
title = {RE-VISIT OF HST FUV OBSERVATIONS OF THE HOT-JUPITER SYSTEM HD 209458: NO Si iii DETECTION AND THE NEED FOR COS TRANSIT OBSERVATIONS},
author = {Ballester, G. E. and Ben-Jaffel, L., E-mail: gilda@lpl.arizona.edu, E-mail: bjaffel@iap.fr},
abstractNote = {The discovery of O i atoms and C ii ions in the upper atmosphere of HD 209458b, made with the Hubble Space Telescope Imaging Spectrograph (STIS) using the G140L grating, showed that these heavy species fill an area comparable to the planet’s Roche lobe. The derived ∼10% transit absorption depths require super-thermal processes and/or supersolar abundances. From subsequent Cosmic Origins Spectrograph (COS) observations, C ii absorption was reported with tentative velocity signatures, and absorption by Si iii ions was also claimed in disagreement with a negative STIS G140L detection. Here, we revisit the COS data set showing a severe limitation in the published results from having contrasted the in-transit spectrum against a stellar spectrum averaged from separate observations, at planetary phases 0.27, 0.72, and 0.49. We find variable stellar Si iii and C ii emissions that were significantly depressed not only during transit but also at phase 0.27 compared to phases 0.72 and 0.49. Their respective off-transit 7.5% and 3.1% flux variations are large compared to their reported 8.2 ± 1.4% and 7.8 ± 1.3% transit absorptions. Significant variations also appear in the stellar line shapes, questioning reported velocity signatures. We furthermore present archive STIS G140M transit data consistent with no Si iii absorption, with a negative result of 1.7 ± 18.7 including ∼15% variability. Silicon may still be present at lower ionization states, in parallel with the recent detection of extended magnesium, as Mg i atoms. In this frame, the firm detection of O i and C ii implying solar or supersolar abundances contradicts the recent inference of potential 20–125× subsolar metallicity for HD 209458b.},
doi = {10.1088/0004-637X/804/2/116},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 804,
place = {United States},
year = {2015},
month = {5}
}