[comment to another CCD photometrist]
FYI, here is a list of "best" values for the M67 dipper stars. Although it's not clear in your JAAVSO paper, using the Schild magnitudes/colors for these stars will put you off the Landolt system by about 0.04 in V, and his results are really noisy generally. The Joner & Taylor 1990 analysis is the best published so far, since they are tied directly to Landolt, and take into account all other results using a conservative statistical approach. The Chevalier & Ilovaisky (CI91 in the list below) used their results for calibration. When mixed with high-weight Landolt standards, these values come out quite consistently.
The "sig" columns below are means errors of means, not per-observation sigmas.
Here is the M67 dipper standards table amended with mean errors of the mean added in as available. The units are millimags. These are explicit or readily derived from JT90 and CI91, but given only generically in MMJ93. The latter say the data for these stars (the standards list they produced) had to have at least two sources other than their own data whose averaged values had per-observation sigma less than 0.015 mag. This implies equal-weight mean errors of means less than 9 mmag, but no account was taken of errors on a per-star basis, as JT90 have. For what it's worth, in V two of the three MMJ93 stars are in common with CI91, and the differences are only 3 mmag or less, but the MMJ means include the CI91 results. For the moment, you might arbitrarily assign all the remaining errors to be something like 5 or 7 mmag.
version 4 November 1996
nominal field center is: 8 51 21 +11 46.3, very close to star F130, which
conveniently is at the joint between "bowl" and "handle" of "dipper" asterism.
Star RA (2000) Dec V B-V U-B V-R R-I sigV sigBV sigVR sigRI
F81 8 51 11.7 +11 45 23 10.027 -0.086 -0.385 -0.032 -0.036 3.3 2.0 1.2
I-242 8 51 14.4 +11 45 01 10.884 0.268 0.265 3.2 2.5 3.0
I-12 8 51 14.8 +11 47 24 (12.821) 0.556 (0.329) (0.322) 4.6 5.8
F95 8 51 15.4 +11 47 31 (12.668) 0.507 (0.293) (0.304) 4.6 5.8
F108 8 51 17.4 +11 45 24 9.701 1.373 1.539 0.715 0.636 5.2 2.7 3.2
F111 8 51 18.0 +11 45 54 12.730 0.564 0.065 0.328 0.326 4.9 3.3 4.5
F117 8 51 18.7 +11 47 03 12.630 0.787 0.467 0.434 4.9 3.7 6.6
F124 8 51 19.9 +11 47 00 12.118 0.459 0.021 0.280 0.280 4.9 3.7 6.6
F127 8 51 20.1 +11 46 42 12.769 0.559 0.036 0.330 0.321 4.0 2.9 4.2
I-198 8 51 20.4 +11 45 53 13.152 0.574 0.049 0.333 0.295 4.5 3.6 7.3
I-199 8 51 20.6 +11 46 05 13.152 0.577 0.068 0.333 0.328 6.9 3.1 5.5
F130 8 51 20.6 +11 46 16 12.869 0.454 0.007 0.289 0.291 5.4 3.4 5.9
F132 8 51 20.8 +11 45 02 13.091 0.609 0.080 0.350 0.355 4.0 3.0 4.0
F134 8 51 21.2 +11 45 53 12.256 0.584 0.337 0.332 4.5 2.9 3.0
F135 8 51 21.6 +11 46 06 11.436 1.066 0.556 0.497 3.5 2.7 3.0
I-9 8 51 22.1 +11 46 41 13.194 (0.584) 0.326 0.326 4.0 5.8 3.4 4.7
I-51 8 51 25.0 +11 45 43 14.200 0.337 0.282 6.9 5.0 8.8
F149 8 51 25.4 +11 47 34 12.55 (0.593) 0.342 0.331 11. 5.8 7.9 6.9
F170 8 51 29.9 +11 47 17 9.663 1.357 1.464 0.702 0.625 5.9 3.8 3.2
F176 8 51 31.2 +11 45 51 (12.649) 0.577
F81 GSC 0814-1795. B8V.
I-242 GSC 0814-1931. F3; close (~2") pair, data is for combined light.
I-12 GSC 0814-1491.
F95 GSC 0814-1647.
F108 GSC 0814-2331. K4III.
F111 GSC 0814-1827.
F117 GSC 0814-1803.
F124 GSC 0814-1937.
F127 GSC 0814-1997.
I-198 GSC 0814-1975.
I-199 GSC 0814-1811.
F130 GSC 0814-2137.
F132 GSC 0814-1775.
F134 GSC 0814-1913.
F135 GSC 0814-2231. K2III:.
I-9 GSC 0814-1863.
I-51 GSC 0814-1903.
F149 GSC 0814-1715.
F170 GSC 0814-1515 = BD+12 1926 (sic: the BD name applies to the whole
cluster). K3III.
F176 GSC 0814-2387. V-I = 0.700 (MMJ).
sources:
V from JT90 except in parens from MMJ93.
B-V from MMJ93 except in parens from CI91.
U-B from MMJ93.
V-R from JT90 except in parens from CI91.
R-I from JT90 except in parens from CI91.
CI91 = Chevalier & Ilovaisky 1991, A&AS 90, 225.
JT90 = Joner & Taylor 1990, PASP 102, 1004.
MMJ93 = Montgomery, Marschall, & Janes 1993, AJ 106, 181.
Here's another short list, containing stars near NGC 1275 in the Perseus cluster. Here the authors published no chart, but only offsets in arcsec from the center of the galaxy (in a system which was not quite orthogonal to the sky). These positions were extracted from A1.0. I've sent this list to the SIMBAD folks, so when the paper gets indexed for SIMBAD, they will include the stars and their positions explicitly (without the positions the stars would have been ignored by SIMBAD).
Prestwich et al. stars near NGC 1275 = Table 1 from Prestwich et al. 1997, ApJ 477, 144. (star 13 omitted) no. RA (2000) Dec V V-I 1 3 20 10.8 +41 29 22 16.66 0.92 2 3 19 48.6 +41 28 09 14.43 0.67 = GSC 2856-1758 3 3 19 50.9 +41 27 53 16.77 1.24 4 3 19 58.0 +41 27 03 16.78 1.64 5 3 20 07.6 +41 26 55 15.40 0.68 6 3 20 02.7 +41 26 50 15.37 0.97 7 3 20 04.2 +41 26 46 15.23 0.78 8 3 19 57.5 +41 26 41 15.35 0.97 9 3 19 56.2 +41 26 35 16.14 1.05 10 3 20 06.1 +41 26 23 16.19 1.69 11 3 20 07.9 +41 26 01 15.24 0.90 12 3 19 56.3 +41 25 57 16.37 0.74 14 3 19 52.3 +41 25 49 16.34 0.79 15 3 19 59.5 +41 25 46 14.45 0.87 16 3 20 12.7 +41 25 22 15.45 0.90