Subject: GRIM II plate scale

From: Alan Watson

Submitted: Tue, 11 Feb 1997 18:29:09 -0700

Message number: 37 (previous: 36, next: 38 up: Index)

On 29 January 1997 I observed the dipper asterism in M67 in J, H, and
Ks to determine the scale of the f/5, f/10, and f/20 cameras of GRIM
II. I used the astrometry of Montgomery et al. (1993, AJ, 106, 181,
although stars 23 and 28 are mislabelled in their finding chart).

I find no evidence for any wavelength dependence. I find the scales
are 0.473, 0.236, and 0.113 arcsec/pixel. I estimate uncertainties of
order 0.001 arcsec/pixel from an assumed uncertainty in the reference
positions of order 0.1 arcsec and a span of order 200 pixels.

My values differ by about 2% from the values quoted on the APO
detectors WWW page (0.482, 0.238, and 0.111 arcsec/pixel); I have no
idea where these values come from or what their likely uncertainties
might be.

Alan Watson

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