Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.eso.org/~rsiebenm/FTP/PR14/NIHrep.pdf Дата изменения: Mon Apr 14 00:52:46 2014 Дата индексирования: Sun Apr 10 19:59:06 2016 Кодировка:

Summary of SPHERE performance at NIH

Ralf Siebenmorgen (PS) and Markus Kasper (PM)



SPHERE performs in the NIH similar to what was achieved in Grenoble. Most of the measurements are template driven and analysed by the pipeline. The Consortium has provided a detailed report1. The main findings are summarised below.

IRDIS The IR and V filters are well mounted and the positioning accuracy is within a 1% pixel tolerance. The IRDIS wheel positioning error is below 0.1pixel. The IRDIS detectors have a read-out noise 9.4 e-, a gain of 2e-/ADU and the dark current is <0.5e-/pixel/s. The instrumental background is still high. The higher temperature in the NIH causes this. The variation between flats separated by 15min is below 1%. In deep staring images filters at a level of 0.1% be calibrated out in the ADC control law for the some ghosts are identified in narrow band from the brightest spot. Such ghosts will reduction process. The software of the detectors needs improvements. Any

Figure 1: H band PSF at high flux regime provides a SR of 97% (left). Such high SR performance cannot be achieved for both detectors simultaneously at the same time. The image with coronagraph under turbulent conditions is shown right. 1 see: https://bfs.ujf-grenoble.fr/files/b83999e


c8a7e3ce28583f6c8fcbc9839/SPHERE_UT3_TRR_Meeting.zip

Ralf Siebenmorgen, Markus Kasper

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change of a coronagraph requires verification of the focus settings. It is demonstrated that such a new setting can be obtained by an iterative procedure during execution of the acquisition template. Centering of the pupil is achieved at an accuracy of 0.1% of the pupil diameter. The field distortion is below 0.2 pixels. The 1-contrast achieved in coronagraphic imaging (DBI) with filter B_H at a distance from the star of 0.1" - 0.2" is ~100ppm and further out at 0.6" - 0.8" it improves down to ~10ppm. Using DPI in the same filter the contrast goes up 40±1 ppm. The turbulence

Figure 2: (Top) Coronagraphic images in broadband filters: H2 (left), H3 (middle) and the difference H2-H3 (right). Contrast curves as labelled (bottom).
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simulator likely causes this larger value. In coronagraphic observations the achieved 1-contrast at 1.61µm is for 0.5" separation form the star <300 ± 8 ppm and at 1.3" separation 70 ± 1ppm (Fig.3). IRDIS absolute wavelength accuracy is <4.9nm (LRS) and <0.5nm (MRS). The spectral resolution in the LRS mode at 988nm is R ~30 m and at 1450nm it is R~50, and for MRS and at same wavelengths it is R = 340 and 365, respectively.

Figure 3 IRDIS contrast curve (5) in LRS mode with coronagraph (curves as labelled).

IFS The IFS detector has a read-out noise of 9.4 e-, gain of 2e-/ADU and the dark current is 10.7 e-/pixel/s. The variation between flats separated by 5min is below 1%. The best focus is within 3% of its nominal position stable and so is the wavelength calibration. Centering of the pupil is achieved at an accuracy of 0.3% of the pupil diameter. The centering of the star is achieved without
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saturating the clearly visible waffles. The distortion is nominal, and below 0.2 pix across the field. In images of the data cube no strong ghosts are visible. The achieved contrast is at separation between 0.25" and 0.75" flat and after spectral de-convolution close to the photon noise limit of ~1.2ppm (1). ZIMPOL Bias frames are at a level of 1000 ADU and for all detector modes free of spurious patterns. The readout noise < 5 ADU/pix and the dark current < 3 ADU/s/pix. Flatfields for imaging and fast polarimetry do not reveal unexpected features. The pupil appears well aligned and shifts between the Lyot stop w.r.t. the HODIM pupil plane are along the horizontal axis -2.23pix and the vertical axis -1.85 pix. The dithering accuracy is < 0.15 pix (rms). All these measurements are well within specs. Imaging of AO corrected, coronagraphic and non-coronagraphic PSFs for different filers were obtained without detection of spurious features. The polarimetric efficiency is for fast pol mode ~0.8 (spec: >0.75) for slow pol ~0.9 (sepc: >0.85). The instrument polarization range between 1.8 - 2.7 % and this can be compensated to a residual of less than 0.3% (specs: < 1 %). The 1 contrast between 160 and 350 mas is in double difference mode for fast pol about 1ppm and for slow pol 60ppm.

Figure 4: Sequence of coronagraphic ZIMPOL PSFs in simulated 0.85" seeing conditions (from left to right in filters V, NR, NI, VBB).



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