| Summary: | Future spectroscopic observational programmes at Mount John University Observatory require the ability to acquire spectra with significantly higher spectrophotometric accuracy and geometrical stability than can currently be achieved. Therefore a solid-state linear-diode-array image detector system has been designed and developed for use with the MJUO échelle spectrograph.
A review of those electromechanical design techniques of significance to astronomical instrumentation is presented. Their application is exemplified with a complete electromechanical design for the detector, which is found to allow each electronic sub-system implemented within that design to achieve its theoretical level of performance.
The requirements for the video processing electronics of a solid-state image detector are explicitly developed, and are used to design the electronics for this detector. Subtle sources of electronic instability which can appear as noise or base-line shifts are identified and controlled in this design. In particular, differential non-linearity is identified in an existing preamplifier design, and so an alternative design is implemented.
The readout noise of the entire detector system is measured to be 200 e-/h pairs for a noiseless signal source of zero impedance to ground. This increases to 350 e-/h pairs when the impedance of this source is equal to that of the diode array, due to an additional noise contribution of 290 e-/h pairs. The net readout noise with the RL936F/30 diode array is 450 e-/h pairs, which is the quadratic sum of the detector system noise with the two 210 e-/h pair samples of diode capacitance thermodynamic noise. Thus the diode array is not found to contribute any noise in excess of its theoretical thermodynamic noise.
A temperature controller is developed for use with sensors which are cooled in cryogenic dewars. A short term control precision of 1.6 mK r.m.s. is achieved which is entirely due to the theoretical noise of the temperature sensor. The long term precision over all operating conditions is ±20 mK, which is dependent on the design of the dewar.
The hardware and software which provide interactive instrument control and data reduction are described. In particular, they provide for flexible control of the detector sub-systems during data acquisition and testing, and enable a high level of data reduction to be undertaken while the detector is integrating.
An observational programme has been carried out with this detector sys tern on the southern RS CVn sys tern HR4492. Radial velocity measurements with a precision of ±0.5 km s-¹ have enabled a new ephemeris for the binary motion to be determined, namely HJD = 2446317.5 ± 21.82E. It is used to interpret Hα line profile variations in terms of probable mass transfer within the system.
|
|---|
