MUSE observations of comet 67P/Churyumov-Gerasimenko

Aims. Observations of comet 67P/Churyumov-Gerasimenko were performed with MUSE at large heliocentric distances post-perihelion between 3 and 7 March 2016. These observations are part of a simultaneous ground-based campaign aimed at providing broad-scale information about comet 67P to complement the ESA/Rosetta mission. Methods. We obtained a total of 38 datacubes over five nights. We took advantage of the integral field unit nature of the instrument to carry out a simultaneous study of the spectrum of 67P’s dust and its spatial distribution in the coma. We also looked for evidence of gas emission in the coma. Results. We produced a high-quality spectrum of the dust coma over the optical range that could be used as a reference for future comet observations with this instrument. The slope of the dust reflectivity is of 10%∕100 nm over the 480–900 nm interval, with a shallower slope towards redder wavelengths. We used the Afρ to quantify the dust production and measure values of 65 ± 4 cm, 75 ± 4 cm, and 82 ± 4 cm in the V, R, and I bands, respectively. We detected several jets in the coma as well as the dust trail. Finally, using a novel method combining spectral and spatial information, we detected the forbidden oxygen emission line at 630 nm. Using this line, we derived a water production rate of 1.5 ± 0.6 × 1026 molec. s−1, assuming all oxygen atoms come from the photo-dissociation of water.

Development of a Planar Array Infrared Reflection Spectrograph for Reflection—Absorption Spectroscopy of Thin Films at Metal and Water Surfaces

Planar array infrared (PA-IR) spectroscopy offers several advantages over Fourier transform infrared (FT-IR) methods, including ultrafast speed (< 100 μs temporal resolution) and excellent sensitivity. However, obtaining spectra in the range of 1800 to 1000 cm−1 of films at the air–water interface remains difficult due to the poor IR reflectivity of water, the extremely low concentration of the thin film on the water subphase, and the interference of water bands. In this study, we report a new planar array infrared reflection spectrograph (PA-IRRS), which has several advantages over conventional approaches. This instrument can record sample and reference spectra simultaneously with an instrumental setup that is the same as that of a single-beam instrument by splitting the incident infrared beam into two sections on a plane mirror (H) or a water trough. With this design, the instrument can accommodate large infrared accessories, such as a water trough, without a loss of infrared beam intensity. Water bands can be subtracted to obtain a high-quality spectrum for poly(L-lactic acid) Langmuir film on the water subphase with a resolution of about 6 cm−1 in 10.8 s. Hence, this PA-IRRS system has great potential for investigating the time-resolved dynamics of a broad range of Langmuir films, such as cellular membranes or biopolymers, on the water subphase.

Bayerite, Al(OH)3, from Raoul Island, Kermadec Group, South Pacific

Bayerite forms a cascading, travertine-like deposit over volcanic tuffs on Raoul Island in the South Pacific where it is produced from episodic discharge of spent, caustic aluminate solutions from a hydrogen generator. Textural evidence indicates microbial activity has possibly been involved in formation of the hydroxide, as well as sodium carbonate aluminate, present in minor amounts. X-ray powder diffraction and infrared spectral studies failed to give confident identification of the bayerite, the identity being confirmed by laser Raman spectroscopy. A high quality spectrum was obtained extending from 3280 to 3680 cm−1 and from 100 to 1000 cm−1.