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IRSIS : an IFU prototype in fluoride glass David HORVILLE 1 , Jean Michel KRIEG 1 , Thibaut LE BERTRE 1 , Louis D'HENDECOURT 2 , Emmanuel DARTOIS 2 1 Observatoire de Paris 2 Institut d’Astrophysique Spatiale Abstract: IRSIS (Infra-Red Spectroscopic Imaging Survey) is a project of a Small Satellite for Astronomy & Astrophysics developed by several indian laboratories under the leadership of Prof. S.K. Gosh from the Tata Institute of Fundamental Research (Mumbai/Bombay). This scientific experiment will carry out unique infrared spectro-imaging observations in the 1 to 6 μm wavelength range. The payload consists of a 30 cm telescope and of a two-channel spectrograph (SW : 1 to 3 μm and LW : 3 to 6 μm) equipped with two 1024x1024 array detectors. The spectral resolution is ~ 100, and the spatial resolution ~ 18 arcseconds. The field-of-view covered by the instrument is 10 arcminutes by 10 arcminutes. A key element of the instrument is a fiber bundle that converts a two-dimension image in the focal plane of the telescope into several parallel slits located at the spectrograph entrance (IRSIS anamorphoser, or Integral Field Unit –IFU-). In the present concept, one-thousand optical fibers are coupled to a micro-lens array at one end (focal plane), and at the other end are arranged in four slits. Both the microlens array and the fibers are made of a fluoride glass that transmits light efficiently in the 1 to 6 μm range. In this poster, we present the first phase of development of the IRSIS anamorphoser. In cooperation with LeVerreFluoré, a company based in Rennes, we have developed a prototype consisting of a 10x10 micro-lens array coupled to a bundle of 100 fibers. This study was supported by CNES (Centre National d’Etudes Spatiales). In orbit, the IFU will be exposed to high energy radiations. The amount of radiations expected for a 4 years mission in a low altitude polar orbit (h=800km) has been estimated (OMERE simulations) and an equivalent glass (AFG450) has been exposed at the accelerator of Orsay to the same quantity of radiations (2 ×10 14 protons of 1 MeV/cm 2 ). No effect has been detected (see figure on the left). Infrared spectra before and after ion irradiation (left panel) and the transmittance at low temperature (right panel, 77 and 17K) with respect to ambient (296K) were measured using an FTIR spectrometer coupled to a high vacuum chamber at IAS. The hexagonal shape of the microlenses is well respected, the measurements are in accordance with the specifications. The edges of the microlenses are well defined. Only the central 10x10 microlenses are coupled to a fiber. 259μm 296μm 120.5° 118.99° Low FRD : the input beam F-ratio is 3.4 and the average output of the fiber beam F-ratio is 3.3 )LHOG RI DUFPLQ [ DUPLQ DURXQG 0LUD 7KLV PDVV ORVLQJ $*% VWDU LV PRYLQJ VRXWK ZLWK D VSDFH YHORFLW\ RI DERXW NPV $ ERZ VKRFN VRXWK DQG D WXUEXOHQW ZDNH QRUWK DUH GHWHFWHG E\ *$/(; LQ WKH )DU 89 EDQG FHQWHUHG DW ¶ EDFNJURXQJ LPDJH LQ IDOVHFRORU 7KH )89 HPLVVLRQ LV DVVXPHG WR FRPH IURP FROOLVLRQDOO\ H[FLWHG PROHFXOHV RI K\GURJHQ LQ WKH WDLO RI 0LUD 7 KH WDLO LV DOVR GHWHFWHG LQ DWRPLF K\GURJHQ DW FP ZLWK WKH 9/$ FRQWRXUV 7KH VWDU V\PERO PDUNV WKH SRVLWLRQ RI 0LUD 0DWWKHZV HW DO $S- Summary: An Integral Field Unit prototype has been developed for IRSIS. The present phase-A study has proven the concept of an infrared IFU in fluoride glass. The manufacturer (Le Verre Fluoré) has demonstrated its competence and its ability to develop an adequate product for IRSIS. IRSIS preliminary concept IFU input with microlens array The 100 fibers are rearranged in one exit slit. Scientific Objectives: IRSIS will cover large areas of the sky in spectro-imagery, with a goal of 50%. In this survey mode it will detect all point sources down to magnitude K ~ 14 (L ~ 13). It will provide spectra from 1.6 to 5.5 μm, at a resolution of 100, that will allow us to characterize all detected sources directly without necessity of a follow-up. Deeper integrations by repeated observations in selected areas will also be possible. In addition, it will provide images in narrow spectral bands of extended sources, for instance in the PAH band at 3.3 μm or in the hydrogen Brackett and Paschen lines. Thanks to the low level of background emission which can be reached in Space, extended structures around AGB stars have recently been revealed by satellites such as Spitzer, Herschel and GALEX (e.g. see GALEX image of Mira's tail on the left). In the near-infrared range WISE is expected to reveal also such structures, with a spatial resolution of 6 arcsec, in the broad bands centered at 3.4 and 4.6 μm. By resolving them spectrally, IRSIS will allow us to investigate in details these extended emissions. IRSIS will thus be capable of addressing a wide variety of astrophysical topis. It will help to understand the processes at work in the interstellar medium and in circumstellar environments. It will allow us to classify stars of different types, in particular of late-type (AGB stars in the Galaxy and in the Magellanic Clouds, M-dwarfs in the Solar Neighborhood, etc.), and emission-line stars. Short Wavelength (SW) channel The curvature of the spectra has been minimized by curving the IFU exit slit. Long Wavelength (LW) channel
