NGC 6341 = Messier 92 field UBVRI sequence

Affiliation
American Association of Variable Star Observers (AAVSO)
Fri, 08/04/2023 - 19:13

     The list below shows several stars in a field on the southeast side of the globular cluster M92.  This is overhead at dusk just now, but because it is not far from the northern ecliptic pole, it is available much of the year for northern observers.  It is one of many situated in the field of some target you might observe anyway.  The stars are fairly isolated in the field, and the field-center is rigged for the 22'x22' useful field of the Lowell 1.1-m telescope.  I list only stars with fairly high-weight data; many more stars can be calibrated more reliably.  In observing, I try to maximize counts in any filter on the brightest star (HD 156821 on the east side of the cluster), and let the rest fall where they may.  The main data source in this case is Peter Stetson's 'homogeneous photometry' files at:

https://www.canfar.net/storage/list/STETSON/homogeneous/Latest_photometry_for_targets_with_at_least_BVI/

...with some added stars from Arne Henden and Mike Jerzykiewicz (world's best photometrist from the 1960s-90s that no one's ever heard of).

     The list shows a name, J2000 coords, the data, its source, the number of observations and (usually) mean errors on the values (the latter as a comma-delimited string).  Data from Arne's files give rms errors rather than mean errors.  The idea is that one weights the stars by including the observational errors and the uncertainties on the standard values themselves in a robust least-squares sense.  In most cases the errors are likely to be a lot smaller than your observational errors, so could be ignored.  A few of the stars are members of the cluster.

     The table columns line up with an equal-spaced font, but will look ragged with the proportional font used in the forum.

\Brian

 

---  NGC 6341-SE = Messier 92  field center:  17 17 52  +43 01  (J2000)
---  color ranges:  0.41 < B-V < 1.50;  -0.16 < U-B < 1.77
Name                 RA  (J2000)  Dec        V     B-V    U-B    V-R    R-I    V-I     source
TYC 3081-0200-1   17 16 56.78 +43 05 37.0  11.756  0.436 -0.051  0.242  0.227  0.469   Henden n=3 errors 0.006,0.020,0.060,0.004,0.007,0.008 (U-B uncer)
M92-S4279         17 17 13.90 +43 01 49.3  12.811  1.128  1.064  0.637  0.543  1.180   Stetson n~50 errors 0.0020,0.0028,0.0031,0.0081,0.0090,0.0049
M92-S4499         17 17 31.72 +43 05 41.5  12.767  1.043  0.478  0.615  0.594  1.209   Stetson n~25 errors 0.0027,0.0034,0.0038,0.0065,0.0075,0.0053
HD 156821         17 17 40.97 +43 08 58.2   9.773  0.411  0.028  0.246  0.235  0.481   Jerzykiewicz n=7 UBV/Henden n=3 VRI errors 0.007,0.007,0.007,0.006,0.002,0.006
M92-S5974         17 17 42.19 +42 51 35.3  13.487  0.677  0.136                0.751   Stetson n~25 errors 0.0024,0.0036,0.0036,,,0.0038
M92-S5563         17 17 47.05 +43 07 12.0  12.864  0.665  0.071  0.383  0.365  0.748   Stetson n~20 errors 0.0019,0.0028,0.0034,0.0071,0.0083,0.0051
M92-S4581         17 17 55.75 +42 57 14.3  11.704  0.619  0.119                0.694   Stetson n~20 errors 0.0038,0.0060,0.0056,,,0.0087
M92-S4588         17 18 01.65 +42 59 47.6  13.987  0.728  0.323  0.418  0.341  0.759   Stetson n~20 errors 0.0025,0.0041,0.0039,0.0046,0.0064,0.0057
TYC 3081-0438-1   17 18 06.23 +42 53 33.6  11.258  1.001  0.716                0.969   Stetson n~5 errors 0.0040,0.0042,0.0024,,,0.0129
M92-S4595         17 18 07.21 +43 02 55.5  14.265  0.510 -0.156                0.637   Stetson n~10 errors 0.0022,0.0038,0.0073,,,0.0049
M92-S6021         17 18 12.05 +42 55 02.5  11.949  1.499  1.771                        Stetson n=7 errors 0.0038,0.0068,0.0079