During the first-light run of the Gemini Planet Imager we obtained K-band spectra of exoplanets HR 8799 c and d. Analysis of the spectra indicates that planet d may be warmer than planet c. Comparisons to recent patchy cloud models and previously obtained observations over multiple wavelengths confirm that thick clouds combined with horizontal variation in the cloud cover generally reproduce the planets' spectral energy distributions. When combined with the 3 to 4 μm photometric data points, the observations provide strong constraints on the atmospheric methane content for both planets. The data also provide further evidence that future modeling efforts must include cloud opacity, possibly including cloud holes, disequilibrium chemistry, and super-solar metallicity.
The master set of the BCRA–NPL Ceramic Colour Standards, Series II, has been calibrated by NPL in the specular excluded, specular included and 0/45 geometries at a temperature of 25C. Tables of spectral reflectance and colorimetric data are presented. The thermochromism of the standards in the specular excluded geometry was also measured by NPL and the changes in spectral reflectance for a 10 degC change in temperature are given. The corresponding changes in colour data for the specular excluded geometry were calculated by NPL. Following a request from the Colour Measurement Committee of the Society of Dyers and Colourists, the corresponding changes in colour data for the specular included geometry were calculated by the Scottish College of Textiles on the assumption that the changes in spectral reflectance are the same for both geometries. Thus changes of colour data are presented for the specular excluded and specular included geometries. It has been shown by Ceram Research that it is possible to use these thermochromism data to correct colour data measured at an arbitrary laboratory temperature to a standard temperature.
The NPL hemispherical reflectometer /transmissometer can be used to measure a complete set of spectral radiometric properties from 2.5 to 56 micrometres for any kind of sample, whether or not it has a regular component of reflectance or transmittance. A rotatable hemispherical copper mirror focusses radiation from a cylindrical source on to the sample. Systematic errors are caused by radiometric non -linearity from interreflection effects and by temperature changes of the source arising from interreflection and from the necessary purging air current. A custom -built power supply is operated in a constant -load -resistance mode to maintain the source at a constant temperature to within 0.1 K. This allows simplification of the correction procedures, but the use of standard reference samples is still required for calibration service work.A new method of use for absolute measurements employs a supplementary mirror for additional measurements to let the monochromator optics view the source directly, without and with the sample present. The ratio of these readings then provides a simple correction factor for the reflectometer value, allowing immediate calculation of absolute spectral reflectance. Experimental tests show that the method is valid from 2.5 to 36 micrometres with a grating spectrophotometer, but becomes impracticable at longer wavelengths. A Fourier transform instrument has been modified radically to accommodate the hemisphere reflectometer for further tests.
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