OBSERVATIONS OF MASS LOSS FROM THE TRANSITING EXOPLANET HD 209458b

By J. Linsky, Hao Yang, K. France, C. Froning, J. Green, J. Stocke, S. Osterman. 2010

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Using the new Cosmic Origins Spectrograph on the Hubble Space Telescope, we obtained moderate-resolution, high signal/noise ultraviolet spectra of HD 209458 and its exoplanet HD 209458b during transit, both orbital quadratures, and secondary eclipse. We compare transit spectra with spectra obtained at non-transit phases to identify spectral features due to the exoplanet's expanding atmosphere. We find that the mean flux decreased by 7.8% ± 1.3% for the C ii 1334.5323 Å and 1335.6854 Å lines and by 8.2% ± 1.4% for the Si iii 1206.500 Å line during transit compared to non-transit times in the velocity interval −50 to +50 km s−1. Comparison of the C ii and Si iii line depths and transit/non-transit line ratios shows deeper absorption features near −10 and +15 km s−1 and less certain features near −40 and +30–70 km s−1, but future observations are needed to verify this first detection of velocity structure in the expanding atmosphere of an exoplanet. Our results for the C ii lines and the non-detection of Si iv 1394.76 Å absorption are in agreement with Vidal-Madjar et al., but we find absorption during transit in the Si iii line contrary to the earlier result. The 8% ± 1% obscuration of the star during transit is far larger than the 1.5% obscuration by the exoplanet's disk. Absorption during transit at velocities between −50 and +50 km s−1 in the C ii and Si iii lines requires high-velocity ion absorbers. Assuming hydrodynamic model values for the gas temperature and outflow velocity at the limb of the outflow as seen in the C ii lines, we find mass-loss rates in the range (8–40)×1010 g s−1. These rates assume that the carbon abundance is solar, which is not the case for the giant planets in the solar system. Our mass-loss rate estimate is consistent with theoretical hydrodynamic models that include metals in the outflowing gas.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/de1351d7d93fefec38204e01f5c0f1dc709f219f

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Citations in the corpus

• POSSIBLE DISINTEGRATING SHORT-PERIOD SUPER-MERCURY ORBITING KIC 12557548 (2012, background): “For example, the hot Jupiter HD 209458b is known to emit a gaseous wind (Vidal-Madjar et al. 2003; Ben-Jaffel 2008; Linsky et al. 2010).”
• THE ULTRAVIOLET RADIATION ENVIRONMENT AROUND M DWARF EXOPLANET HOST STARS (2012, background): “…an older solar-type transiting planet host star such as HD 209458 has been shown to have very steady transition region emission (observed in Si IV; Linsky et al. 2010), UV variability on younger, less-massive transiting planet hosts like HD 189733 may significantly hinder the ability to detect…”
• Temporal variations in the evaporating atmosphere of the exoplanet HD 189733b (2012, background): “…is further compounded by the limited number of observations (Vidal-Madjar et al. 2004; Ballester et al. 2007; Ehrenreich et al. 2008; Fossati et al. 2010; Linsky et al. 2010), which include non-spectrally resolved Lyman-α observations of the exoplanet HD 189733b (Lecavelier des Etangs et al. 2010).”
• LYα TRANSIT SPECTROSCOPY AND THE NEUTRAL HYDROGEN TAIL OF THE HOT NEPTUNE GJ 436b (2014, background): “These inflated atmospheres contain many atomic species, such as H, C+, O, and Si2+, that absorb the stellar radiation in UV resonance lines (Vidal-Madjar et al. 2004; Linsky et al. 2010).”
• A NEW APPROACH TO ANALYZING HST SPATIAL SCANS: THE TRANSMISSION SPECTRUM OF HD 209458 b (2015, background): “Other UV observations suggested that the planetary atmosphere is in hydrodynamic escape (e.g. Vidal-Madjar et al. 2003; Holmström et al. 2008; Ben-Jaffel & Sona Hosseini 2010; Linsky et al. 2010).”
• A FRAMEWORK FOR CHARACTERIZING THE ATMOSPHERES OF LOW-MASS LOW-DENSITY TRANSITING PLANETS (2013, background): “Most prominent are the observations that hot Jupiters lose atmospheric mass (Vidal-Madjar et al. 2003; Linsky et al. 2010; Lecavelier Des Etangs et al. 2010; Lecavelier des Etangs et al. 2012), as has been observed in the UV with the HST.”
• The escape of heavy atoms from the ionosphere of HD209458b. I. A photochemical–dynamical model of the thermosphere (2012, background): “If this were the887 case, the transit depths in the O I, C II, and Si III lines (Vidal-Madjar et al.,888 2004; Linsky et al., 2010) should not be significantly higher than the transit889 depth at visible wavelengths.”
• A New Window into Escaping Exoplanet Atmospheres: 10830 Å Line of Helium (2017, background): “…obtained for a handful of exoplanets to date in the form of a strong absorption signal detected in the wings of the hydrogen Lyα line, but also in some UV lines of metals (Vidal-Madjar et al. 2003, 2004; Lecavelier Des Etangs et al. 2010; Linsky et al. 2010; Fossati et al. 2010; Kulow et al. 2014).”
• A CORRELATION BETWEEN STELLAR ACTIVITY AND HOT JUPITER EMISSION SPECTRA (2010, background): “…including HD 189733b (Lecavelier des Etangs et al. 2010) and HD 209458b (Vidal-Madjar et al. 2003, 2004; Ehrenreich et al. 2008; France et al. 2010; Linsky et al. 2010), while archival searches for X-ray detections (Kashyap et al. 2008) and more recent observations of planet-hosting stars with…”
• Estimation of the XUV radiation onto close planets and their evaporation (2011, unknown): “Current age is marked with solid circles. the authors as hydrogen escaping the planet atmosphere, and with the calculation of∼ 8 × 1010 g s−1 extrapolated from Cii line absorption by Linsky et al. (2010).”
• DISEQUILIBRIUM CARBON, OXYGEN, AND NITROGEN CHEMISTRY IN THE ATMOSPHERES OF HD 189733b AND HD 209458b (2011, background): “…2007, 2008; Ballester et al. 2007; Snellen et al. 2008; Redfield et al. 2008; Sing et al. 2008a; Ehrenreich et al. 2008; Langland-Shula et al. 2009; Linsky et al. 2010; Ben-Jaffel 2010; Lecavelier des Etangs et al. 2010), (2) the identification of molecular species such as H2O, CH4, CO2, and CO…”
• Hubble Space Telescope transmission spectroscopy of the exoplanet HD 189733b: high‐altitude atmospheric haze in the optical and near‐ultraviolet with STIS (2011, background): “HD 209458b also shows evaporation of atomic H, C, O, and Si (Vidal-Madjar et al. 2003, 2004; Linsky et al. 2010) through ultraviolet observations.”