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mercredi 20 juin 2012, par Françoise Roques

MIOSOTYS (ex MEFOS) consists of a multi-objects fibre system and a high speed EMCCD camera. It has be implemented at the cassegrain focus of the 193 cm telescope at the Observatoire de Haute-Provence (OHP), France. The fibre positioner moves 29 arms to the targets within a field of view of 25 arc-minute. Each arm is equipped with an individual viewing system for accurate setting and carries one individual fibre that intercept 12’’ arc-sec on the sky. All the 29 fibre images are projected onto a EMCCD camera for fast photometry acquisition.

  • Fibre Positioner

There are 30 positioning arms arranged in a circle of 200 mm diameter of at the edge of the field. One of the arm is used solely for guiding system, and rest of 29 arms are for observing targets. Each arm sweeps a triangular zone by 2 motions : translation by 130mm and rotation by +/- 7 degrees. The image fibre is fixed on the arm tip which is electrically insulated. The image fibre is a glass fibre bundle of 900 mm long, the diameter of the elementary fibre is 18microns. Its transmission efficiency is about 40-45%. The viewing surface is 1.9X1.9 mm. The output end of the 29 image fibres are projected on to a CCD camera through the optics of AGIS with a reduction factor.

  • EMCCD camera

We chose the ProEM camera manufactured by Princeton Instruments as the imaging sensor for the instrument. The sensor of e2v CCD201B is a back-illuminated, frame-transfer EMCCD with 1024X1024 image pixels (or active area 13.3X13.3 mm). The large image area can cover all of 29 fibre images. The peak Q.E. at 530 nm is 95%. The air cooling system maintains the operating temperature at -55 degrees C or lower. At the temperature the typical dark current is less than 0.008 electron/pixel/second. The readout noise then depends on the readout modes : electron-multiplying (EM) or low-noise (LN).

The EMCCD has dual readout amplifiers (or ports), one is a traditional series register for LN mode. The other, for EM mode, is an extended multiplication register which provide 1 to 1000 times multiplication which can be controlled in linear, absolute step. The dual ports design means that the camera can be optimised to perform different type of observations. For example, EM mode is suitable for low-light, high speed conditions, and LN mode is for more conventional observation (i.e., long exposure). The readout noise in EM mode is significant greater (50 electron rms at readout rate 10 MHz), but is effectively reduced to less than 1 electron rms when multiplication gain is sufficiently applied.

You can see a diagram to explain the MIOSOTYS data scheme here :

Diagramme miosotys Diagramme miosotys

Science Case :

  • Stellar occultations by external solar system objects
  • Monitoring of variable sources
  • pre-project for UltraPhot

Laboratories/Institutes :

  • Observatoire de Paris : LESIA
  • National Tsing Hua University, Taïwan
  • Observatoire de Haute-Provence

Financing :

Co funding by ANR (France) and NSC (Taïwan)