First Astronomical Light with TIMMI2, ESO's 2nd-Generation Thermal Infrared Multimode Instrument at the La Silla 3.6-m Telescope
TIMMI, featuring a 64 × 64 gallium doped silicon array and mostly ger-manium refractive optics inside a solid-nitrogen/liquid-helium dewar, was in constant use until its decommission-ing in 1999 (cf. Stecklum et al. 1999). By then, the development of detectors had progressed so rapidly, that the instrument no longer appeared competitive. In fact, in 1993 ESO joined a consortium of French institutes to develop, based on the array used e.g. in TIMMI, a next-generation device (cf. e.g. Lucas et al. 1994). Already the format of this device (128 × 192 pixel) suggested that it would be desirable to build a new camera, rather than trying to use the new device in the existing setup. Even larger arrays were announced by US suppliers. To that end ESO had developed some basic ideas for the optics of a next-generation instrument for the La Silla 3.6-m telescope (cf. Käufl & De-labre, 1994). As a result of the La Silla 2000 questionnaire (see Anderson 1994) in The Messenger 78, ESO received a proposal from the A s t r o p h y s i k a l i s c h e s Institut und Sternwarte of the Friedrich-S c h i l l e r-Universität (FSU) in Jena, Germany, to build TIMMI2. This proposal , reflecting ESO's optical concept, was based on a modern cryostat cooled by a Closed Cycle Expansion Cooler Machine and was also featuring a polarimetric option (not available in TIMMI). Personnel cost and capital investments could largely be covered by funds raised by the Institute in Jena. The PI in Jena was Hans-Georg Reimann. After some negotiations , a Memorandum of Understanding was signed and the work began in early 1996. The design sketch of ESO (see above) was first transformed into a FEM 1 certified conceptual design, both for the optics and mechanics, by the company Jena-Optronik GmbH. Based on this work, the final design and the detail design of the instrument were done at the physics department of the FSU. To the extent that this was feasible, all mechanical parts were manufactured in the workshops of the FSU. In the course of the project, the group at the FSU could enlist a team from the Sternwarte der Universität Wien f o r
TIMMI, ESO’s new 10 μm camera/spectrometer☆
Abstract TIMMI stands for Thermal Infrared Multi Mode Instrument. TIMMI allows for imaging (at present 16 filters available) with variable magnifications as well as limited long-slit spectroscopy in the l0 μm atmospheric window. The instrument was built by the Service d'Astrophysique (SAP) according to ESO's specification in a period of 2 years. At the telescope the instrument is using the ƒ35 chopping configuration in conjunction with the special adaptor unit. TIMMI control and primary data-acquisition is performed by an VME-based computer (under OS9) while final data storage and online data processing with ESO's image processing system MIDAS is done using an UNIX workstation. While TIMMI will provide new observational possibilities for the ESO users community it is also supposed to become a test-bed to gain experience for similar instrumentation at the VLT.
Albedo, internal heat flux, and energy balance of Saturn
Full-disk and high-resolution measurements recorded during the Voyager 1 flyby of Saturn by the radiometer of the infrared instrument, IRIS, indicate a geometric albedo of 0.242 ± 0.012, which is lower than previous estimates. The given error is largely due to uncertainties in systematic corrections; random effects are small. Combining this measurement with the Pioneer-derived phase integral yields a Bond albedo of 0.342 ± 0.030. Infrared spectra recorded at the same time by the Michelson interferometer, along with a model extrapolation to wavenumbers not covered by the instrument, yield an effective temperature of 95.0 ± 0.4°K. As in the case of the radiometer, random instrumental errors are small, and the quoted error in the effective temperature reflects primarily uncertainties in systematic corrections. The rings of Saturn significantly affect both the short- and long-wavelength fluxes. From these measurements the internal heat flux of Saturn is 2.01 ± 0.14 10−4W cm−2, and the energy balance, defined as the ratio of total emitted to total absorbed energy, is 1.78 ± 0.09.