LYα TRANSIT SPECTROSCOPY AND THE NEUTRAL HYDROGEN TAIL OF THE HOT NEPTUNE GJ 436b

By Jennifer R. Kulow, K. France, J. Linsky, R. O. Parke Loyd. 2014

157 citations recorded by the source corpus.

To date, more than 750 planets have been discovered orbiting stars other than the Sun. Two sub-classes of these exoplanets, “hot Jupiters” and their less massive counterparts “hot Neptunes,” provide a unique opportunity to study the extended atmospheres of planets outside of our solar system. We describe here the first far-ultraviolet transit study of a hot Neptune, specifically GJ 436b, for which we use Hubble Space Telescope/Space Telescope Imaging Spectrograph Lyα spectra to measure stellar flux as a function of time, observing variations due to absorption from the planetary atmosphere during transit. This analysis permits us to derive information about atmospheric extent, mass-loss rate from the planet, and interactions between the star and planet. We observe an evolution of the Lyα lightcurve with a transit depth of GJ 436b from 8.8% ± 4.5% near mid-transit, to 22.9% ± 3.9% ∼2 hr after the nominal geometric egress of the planet. Using data from the time-tag mode and considering astrophysical noise from stellar variability, we calculate a post-egress occultation of 23.7% ± 4.5%, demonstrating that the signature is statistically significant and of greater amplitude than can be attributed to stellar fluctuations alone. The extended egress absorption indicates the probable existence of a comet-like tail trailing the exoplanet. We calculate a mass-loss rate for GJ 436b in the range of 3.7 × 106–1.1 × 109 g s−1, corresponding to an atmospheric lifetime of 4 × 1011–2 × 1014 yr.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/3ca21a744b4312d1915164bb9317bf7a88c4f6eb

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Citations in the corpus

Atmospheric Escape and the Evolution of Close-In Exoplanets (2018, background): “There is no doubt that GJ436b is undergoing atmospheric escape, and this result was confirmed by Lavie et al. (2017) who observed the Lyman-α transit over a wide range of phases.”
A New Window into Escaping Exoplanet Atmospheres: 10830 Å Line of Helium (2017, background): “Even greater transit depths in the wings of Lyα have been reported for a warm Neptune GJ 436b (Kulow et al. 2014; Ehrenreich et al. 2015; Lavie et al. 2017).”
THE MUSCLES TREASURY SURVEY. I. MOTIVATION AND OVERVIEW (2016, background): “GJ 436 does show signs of an active corona with log10LX = 27.16 erg s−1 (Poppenhaeger et al. 2010), and its chromospheric Lyα emission was previously observed by Ehrenreich et al. (2011) and Kulow et al. (2014).”
Exoplanetary Atmospheres: Key Insights, Challenges, and Prospects (2019, background): “On the other hand, the lowtemperature super-Earths and Neptunes have mostly shown flat spectra in the WFC3 bandpass (131, 124) with a few exceptions (85, 277), which indicate the predominance of clouds in low-temperature atmospheres.”
The Evaporation Valley in the Kepler Planets (2017, background): “…can be strongly evaporated by this irradiation (e.g. Yelle 2004; Tian et al. 2005; Murray-Clay et al. 2009; Owen & Jackson 2012; Johnstone et al. 2015; Erkaev et al. 2016), and indeed H/He evaporation has been observed from the low-mass planet GJ 436b (Kulow et al. 2014; Ehrenreich et al. 2015).”