NIRC2 Coronagraph Transmission Tests Using the Fiber
August 12, 2010

Objective:
The purpose of this experiment is to fully map the transmission of the coronagraph (coron600) in order to accurately obtaining relative astrometry. In addition, we want to check whether there are astrometric biases or offsets induced by the coronagraph/focal plane mask.

The maps below show the results of an experiment performed on July 10, 2010. Images of a binary star where taken with the primary on and off the coronagraph. The first map shows the reduction in flux of the primary as a function of the 9 probed locations. The values vary from a factor of ~30 to a factor of ~60.
Flux Ratio Variation, Coron600

The map on the left shows the offset of the astrometry as a function of position under the coronagraph. There appears to be roughly a constant offset of about ~0.5 pixels The map on the right shows the astrometry offset using vectors pointing from where the primary should be versus where it actually is.
Astrometric Offset
Coron600

Our plan is to use the fiber to map the coronagraph more fully to determine the flux attenuation across the coronagraph, and to look for the source of the astrometric bias by comparing the fiber centroid with and without the coronagraph/mask in place.

Plan:

  1. Set up camera
    • camera narrow
    • pupil largehex
    • filt brg
    • sampmode 2
    • tint 0.181
    • coadd 1

  2. Acquire Fiber
    • Randy will help you turn it on
    • Randy will help get AO going on fiber
    • Make sure fiber has been on for a few minutes before starting to take data (warm up)

  3. Test Fiber Brightness and Move to Coronagraph Center
    • goi
    • Adjust exposure time to ensure lt 10000 cnts
    • goi 10
    • Look at peak pixel, make sure variation is small
    • Find centroid: we want the center to be at 504, 429
    • Find pixel offset: xmeasured - 504, ymeasured - 429
    • movefiber offx offy
    • goi - test the move direction (positive = up/right; negative = down/left)

  4. Test subpixel jitter
    • corona coron600
    • goi
    • Adjust exposure time to ensure sufficient counts
    • fiber_jitter

  5. Begin coronagraph scan
    • corona coron600
    • goi
    • Adjust exposure time to ensure sufficient counts
    • Move to pixel 491,416: movefiber -13 -13
    • fiber_scan
    • This will map 100 positions across the 30x30 center of coron600

    6. Positions to be Probed

  6. Acquire "sky" frames
    • Turn off fiber
    • goi 5
    • corona clear
    • Adjust tint; goi 5

  7. Astrometry Test
    • Turn on fiber
    • goi 3
    • corona coron600
    • Adjust tint; goi 3
    • Move fiber - repeat

  8. Flats????
    • Is this possible?