PROCEDURE : -
TITLE : Coronagraph Performance
CATEGORY : Calibration.
The main goal is to acquire a comprehensive dataset of HRC coronagraphic RAS/HOMS PSFs to assess the PSF suppression capabilities of the two spots (1.8 and 3.0 arcseconds in diameter) and of the Fastie finger. The PSF will be centered and moved under the spots and finger to characterize its off-center characteristics. We will also verify centration of the pupil mask using the M1 tip/tilt to steer the pupil image and examine the residual spider diffraction.
Execute this procedure once.
Flight build detectors HRC#1 (amp C) and WFC#4 (amps ABCD).
The optimal focus and tip-tilt position of the M1 corrector mirror should first be determined using the HRC focus and tip/tilt SMSs (see Item 1 : Image Quality vs Field Position).
A rudimentary version of this procedure was performed with the non-flight build detectors HRC#1 and WFC#3 in June 2000 with RAS/HOMS (see HRC Coronagraph). The agreement with the models was found to be generally good. For this test, the optimal focus and M1 mirror position used were : focus = 2291, inner cylinder = 56931, outer cylinder = 10308.
HARDWARE REQUIREMENTS :
RAS/HOMS is in its normal configuration with the RAS source plate and pupil mask in position. The illumination is provided by the central fiber (A1) at HeNe 6328 Ang. A suitable complement of ND filters is available and ready to be positioned in front of the laser. The coronagraphic arm is in place. An operator is suited in the clean room to adjust the micrometer stage and move the ND filters. All images are acquired through the F625W filter.
SOFTWARE REQUIREMENTS :
IDL to view the images and J. Krist's software for data analysis and model comparison.
COMMAND MODE : Real time.
We will acquire a significantly more comprehensive and deeper dataset than was obtained in the June 2000 campaign. As a reference, we show in Fig. 1 an HRC flat field acquired in June 2000 at BATC with HRC Build 1 and with the illumination provided by RAS/HOMS (6328 Ang) through the F606W filter. The central 1.8 arcsec-diameter spot, the bottom 3.0 arcsec-diameter spot, and the 0.8 arcsecond-wide Fastie finger are clearly demarcated. No attempt had been made to align the end of the finger with the center of the bottom spot; it was simply assembled in the front of the detector, knowing that the detector would be replaced in the near future.
Cuts across the spots and the finger are shown in Figs. 2, 3, and 4. In coronagraphic mode, the HRC plate scale is 0.027 arcsec/pixel. The "true" width of the central spot is ~110 pixels or 3.0 arcseconds and the width of the bottom spot is ~180 pixels or 4.9 arcseconds. Similarly, the width of the Fastie finger is ~55 pixels or 1".5. The centre of the central spot is at (595,469) and the bottom spot is at (694,141). The Fastie finger makes an angle of 72.5 degrees with the bottom horizontal edge of the chip.
The program is divided into two parts. In the first part, the PSF-suppression capabilities of the occulting spots and Fastie finger will be studied for centered and offset positions of the PSFs. In the second part, the M1 corrector mirror will be tip-tilted symmetrically about its nominal position to evaluate the residual strength of the vertical and horizontal spiders.
Part I : PSF Suppression : Spots + Fastie finger
Part II : Verification of Pupil Mask Centration
If time allows, repeat the entire procedure at a different wavelength.
The setup prior to the actual test will require ~15 full HRC frames. Part I will generate at least 60 full HRC frames as well as a few bias frames. Part II will produce ~15 frames. We then estimate a total of ~100 full HRC frames.
TOTAL TIME :
Assuming 2 minutes per HRC frame, the total estimated time for Part I is at least 2 hours, but more realistically twice this amount if overhead is included, such as positioning the fiber. In the June 2000 campaign, Part II took 1.2 hours. Including setup images and overhead, the total estimated time for this procedure is then ~8 hours.
The analysis will be performed by J. Krist using his own software routines.