We present simultaneous Hubble Space Telescope (HST) WFC3+Spitzer IRAC variability monitoring for the highly variable young (∼20 Myr) planetary-mass object PSO J318.5−22. Our simultaneous HST + Spitzer observations covered approximately two rotation periods with Spitzer and most of a rotation period with the HST. We derive a period of 8.6±0.1 hr from the Spitzer light curve. Combining this period with the measured v i sin for this object, we find an inclination of 56°.2±8°. 1. We measure peak-to-trough variability amplitudes of 3.4%±0.1% for Spitzer Channel 2 and 4.4%-5.8% (typical 68% confidence errors of ∼0.3%) in the near-IR bands (1.07-1.67 μm) covered by the WFC3 G141 prism-the mid-IR variability amplitude for PSO J318.5−22 is one of the highest variability amplitudes measured in the mid-IR for any brown dwarf or planetary-mass object. Additionally, we detect phase offsets ranging from 200°to 210°(typical error of ∼4°) between synthesized near-IR light curves and the Spitzer mid-IR light curve, likely indicating depth-dependent longitudinal atmospheric structure in this atmosphere. The detection of similar variability amplitudes in wide spectral bands relative to absorption features suggests that the driver of the variability may be inhomogeneous clouds (perhaps a patchy haze layer over thick clouds), as opposed to hot spots or compositional inhomogeneities at the top-of-atmosphere level.

We provide an overview of the design and capabilities of the near-infrared spectrograph (NIRSpec) onboard the James Webb Space Telescope. NIRSpec is designed to be capable of carrying out low-resolution (R = 30− 330) prism spectroscopy over the wavelength range 0.6 − 5.3µm and higher resolution (R = 500− 1340 or R = 1320− 3600) grating spectroscopy over 0.7 − 5.2µm, both in singleobject mode employing any one of five fixed slits, or a 3.1×3.2 arcsec 2 integral field unit, or in multiobject mode employing a novel programmable micro-shutter device covering a 3.6×3.4 arcmin 2 field of view. The all-reflective optical chain of NIRSpec and the performance of its different components are described, and some of the trade-offs made in designing the instrument are touched upon. The faint-end spectrophotometric sensitivity expected of NIRSpec, as well as its dependency on the energetic particle environment that its two detector arrays are likely to be subjected to in orbit are also discussed.

This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies.

As part of our ongoing NTT SoFI survey for variability in young free-floating planets and low mass brown dwarfs, we detect significant variability in the young, free-floating planetary mass object PSO J318.5-22, likely due to rotational modulation of inhomogeneous cloud cover. A member of the 23±3 Myr β Pic moving group, PSO J318.5-22 has T eff = 1160 +30 −40 K and a mass estimate of 8.3±0.5 M Jup for a 23±3 Myr age. PSO J318.5-22 is intermediate in mass between 51 Eri b and β Pic b, the two known exoplanet companions in the β Pic moving group. With variability amplitudes from 7-10% in J S at two separate epochs over 3-5 hour observations, we constrain the rotational period of this object to >5 hours. In K S , we marginally detect a variability trend of up to 3% over a 3 hour observation. This is the first detection of weather on an extrasolar planetary mass object. Among L dwarfs surveyed at high-photometric precision (<3%) this is the highest amplitude variability detection. Given the low surface gravity of this object, the high amplitude preliminarily suggests that such objects may be more variable than their high mass counterparts, although observations of a larger sample is necessary to confirm this. Measuring similar variability for directly imaged planetary companions is possible with instruments such as SPHERE and GPI and will provide important constraints on formation.Measuring variability at multiple wavelengths can help constrain cloud structure.1 Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 095.C-0590

We report the results of a J-band survey for photometric variability in a sample of young, low-gravity objects using the New Technology Telescope (NTT) and the United Kingdom InfraRed Telescope (UKIRT). Surface gravity is a key parameter in the atmospheric properties of brown dwarfs and this is the first large survey that aims to test the gravity dependence of variability properties. We do a full analysis of the spectral signatures of youth and assess the group membership probability of each target using membership tools from the literature. This results in a 30 object sample of young low-gravity brown dwarfs. Since we are lacking in objects with spectral types later than L9, we focus our statistical analysis on the L0-L8.5 objects. We find that the variability occurrence rate of L0-L8.5 low-gravity brown dwarfs in this survey is 30 +16 −8 %. We reanalyse the results of Radigan (2014) and find that the field dwarfs with spectral types L0-L8.5 have a variability occurrence rate of 11 +13 −4 %. We determine a probability of 98% that the samples are drawn from different distributions. This is the first quantitative indication that the low-gravity objects are more likely to be variable than the field dwarf population. Furthermore, we present follow-up J S and K S observations of the young, planetary-mass variable object PSO 318.5-22 over three consecutive nights. We find no evidence of phase shifts between the J S and K S bands and find higher J S amplitudes. We use the J S lightcurves to measure a rotational period of 8.45 ± 0.05 hr for PSO 318.5-22.