An HST/STIS optical transmission spectrum of warm Neptune GJ 436b. (2018)
Keywords :
planetary systems - planets and satellites atmospheres - planets and satellites: individual (GJ 436b) - stars: individual (GJ 436) - techniques: spectroscopic
Abstract:GJ 436b is a prime target for understanding warm Neptune exoplanet atmospheres and a target for multiple James Webb Space Telescope (JWST) Guaranteed Time Observation programs. Here, we report the first space-based optical transmission spectrum of the planet using two Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) transit observations from 0.53 to 1.03 {mu}m. We find no evidence for alkali absorption features, nor evidence of a scattering slope longward of 0.53 {mu}m. The spectrum is indicative of moderate to high metallicity (~100-1000x solar), while moderate-metallicity scenarios (~100x solar) require aerosol opacity. The optical spectrum also rules out some highly scattering haze models. We find an increase
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GJ 436 (M2.5V) has been monitored in Stroemgren b and y filters for
the past 14 years using the Tennessee State University's T12 0.8 m
Automatic Photoelectric Telescope (APT) at Fairborn Observatory in
southern Arizona (Henry 1999PASP..111..845H; Eaton et al.
2003ASSL..288..189E; Henry & Winn 2008AJ....135...68H) in order to
better characterize the star and how star spots may affect our transit
observations. In these observations, we nod the telescope between
GJ 436 and comparison stars of comparable or greater brightness; we
use these stars to remove extinction and seeing effects. Of the three
comparison stars analyzed, HD 102555 (hereafter C1) and HD 103676 (C2)
were the most constant, with very little variation between them over
the 14 years. The third star, HD 99518, showed a gradual brightening
throughout the 14 years of observations. Altogether we have obtained
1735 measurements, which we present in Table 1.
- J/A+A/471/L51 : Spitzer obs. of the hot Neptune GJ 436b (Gillon+, 2007)
- J/A+A/475/1125 : Characterization of the hot Neptune GJ 436b (Demory+, 2007)
- J/A+A/486/1039 : HST transit light curve for GJ436b (Bean+, 2008)
- J/ApJ/689/L149 : Parameter variations of Gliese 436b transits (Coughlin+, 2008)
- J/A+A/507/481 : GJ 436b and XO-1b transits (Caceres+, 2009)
- J/ApJ/694/1559 : Photometric follow-up observations of GJ 436b (Shporer+, 2009)
- J/ApJ/755/9 : Spitzer/IRAC light curves of GJ 436 system (Stevenson+, 2012)