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ESPaDOnS: control software and user interface http://webast.ast.obs-mip.fr/magnetisme/espadons_new/control.html © Jean-François Donati, last update May 18 2004 2 of 2 08/07/04 11:31 PM
ESPaDOnS: viewing, guiding and exposure meter facilities http://webast.ast.obs-mip.fr/magnetisme/espadons_new/guiding.html ESPaDOnS viewing, guiding and exposure meter facilities Viewing The instrument aperture of ESPaDOnS consists of two pinholes drilled within a small tilted mirror. The central pinhole (of diameter 0.22mm or 1.6") is used for collecting the stellar light in all three observing modes, ensuring that 90% of the stellar light enters the instrument in median seeing conditions (0.7" seeing). The second pinhole (located at a distance of 1.1mm or 7.9" to the south of the central pinhole) is used to collect the background light from the sky in the ’object+sky’ spectroscopic mode only. The tilted mirror (of diameter 100") is used to reflect off the light to a viewing camera, so that the observer can easily focus the telescope on the central instrument pinhole, identify the star of interest and make sure that it fits optimally within this pinhole. The camera we selected is model CM2-1 of the MaxCam series, developped by Finger Lake Instrumentation (implementing an eev ccd of type CCD47-10 with 1kx1k 0.013mm square pixels). Along with reimaging optics, the viewing channel includes a filter (of schott type bg38, to select visible light only) and a density wheel (to adapt the stellar brightness to the camera sensitivity). The control software includes a viewing agent that can display in real time the image from this camera as observations are carried out. When the star of interest is fitted into the central pinhole (as on the image above), the observer can see no more than the light from the far wings of the stellar image at Cassegrain focus. When the star is properly centred into this pinhole, this light should draw a bright ring around the central hole, as in the above example image. Guiding The viewing agent also include guiding facilities specifically developped for ESPaDOnS. This tool uses the residual light from the edges of the stellar image to evaluate any potential image decentring and remove it by interacting with the telescope control system. If a second star is also present in the camera field of view, the observer can also choose to offset guide on this second star. This is obtained by simply moving the guiding zone (depicted with a dashed circle on the above image) to the star from which guiding must be performed, and the guider ensures that the star within the guiding zone remains at the centre of this circular area. The sensitivity of the camera is such that guiding can be performed with a star as faint as a V magnitude of about 17 (when guiding on the central star), and of about 19 (when offset guiding). The guiding algorithm used for ESPaDOnS implements a 2d gaussian fitting (following Levenberg Marquard technique for chi square minimisation) with two predefined null sensitivity circular area modelling the two mirror pinholes (from which no flux is redirected to the camera). The algorithm has proved to be rather robust when used with fake stars (obtained by reimaging a fibre core onto the instrument aperture). 1 of 2 08/07/04 11:32 PM
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Page 59 and 60: CFHT’s Web page for ESPaDOnS http
Page 61 and 62: Home Page of ESPaDOnS project http:
Page 63 and 64: ESPaDOnS: instrument details and co
Page 65 and 66: ESPaDOnS: spectral domain and resol
Page 67 and 68: ESPaDOnS: spectral response and glo
Page 69 and 70: ESPaDOnS: thermal response and spec
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Page 73 and 74: ESPaDOnS: ccd readout modes and cha
Page 75: ESPaDOnS: control software and user
Page 79 and 80: ESPaDOnS: temperature and pressure
Page 81 and 82: ESPaDOnS: observing procedures http
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Page 85 and 86: ESPaDOnS: instrument status http://
Page 87 and 88: ESPaDOnS: description of critical i
Page 89 and 90: ESPaDOnS: examples of frames http:/
Page 91 and 92: ESPaDOnS: examples of spectra http:
Page 93 and 94: ESPaDOnS: picture gallery http://we
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Page 101: ObservatoryManual - Maps http://www
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