ENR CTIO 1.5-m 2025-02-21

Great to see Javier, the master! 

The first zpoint is done on Sirius in the beginnig of the night, but the first target is immediately off to the east by ~50 arcsec.

The pointing is acceptable for the first 9 targes but the pointing accuracy gradually degrades as the night goes on. By the 10th target or 3 hours after the first target, the pointing is about 3 arcmins. Here are the coordiante comparisons for star #10, #12, and #13. 

(#10 Telescope) RA=08:57:49.43, DEC= -38:19:33.1

(#10 Next target) RA= 08:57:43.94, DEC=-38:22:16.0

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(#12 Telescope) RA=09:46:07.16, DEC= -46:13:26.0

(#12 Next target) RA=09:45:59.34, DEC=-46:16:3.74

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(#13 Telescope) RA=09:48:42.13, DEC=-38:28:38.0

(#13 Next target) RA=09:48:36.04, DEC=-38:31:18.5

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It takes time to identify each target by using finder charts. Note that the 11th target (RA= 09:30:03, DEC=-46:34:53) is within the guider's FOV.

The second zpoint is done at 230am using a bright star close the zenith. After this zpoint, the next science target is off by ~50 arcsec to the east from (285, 243) pixel, just like the first science target of the night. Hence, the zpoint carries at least 50 arcsec error. All these above examples show the offset is at the N-E direction.  However, the RV standard star (RA=11 57 56, DEC=-27 42 25) and another science target have a 3 armins offset at the N-W direction. 

Like the 2nd zpointing, the third zpointing is executed at 530am. The first and second science star after this zpointing are off by ~50 arcsec in the east and 2.5 arcmins in the N-E (beyond the FOV), respectively.

Througout the night, three zpoints are executed to keep pointing inaccuracy within a managable range. In summary, with very limited data, I found

1. The zpoint carries a minimal 50 arcsec error right after the zpoint. 

2. The pointing accuracy degrades approximately with time, but for a few stars, their pointings seem acceptable.