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The second source of photometric standards available at the WHT are the unpublished cluster sequences of L. Davis (NOAO). These are sequences of 20-30 stars near galactic clusters, with typically 15 tex2html_wrap_inline6217 V tex2html_wrap_inline6217 20 and 0.5 tex2html_wrap_inline6217 (B-V) tex2html_wrap_inline6217 1.5, taken at the 0.9m Kitt Peak telescope. These fields are approximately 4.6 x 7 arcmin in size, and will thus fit within the 7.2 arcmin field of the TEK2 chip at prime focus. Since the stars in these fields are generally fainter than the Landolt standards, they can be used with longer exposure times. However, observers should restrict themselves to stars brighter than V tex2html_wrap_inline5557 18.5, as the photometric errors increase rapidly for stars fainter than this. Observers are reminded that these are unpublished data and are available on a user-risk basis. Because of the limited color coverage and small number of repeat observations for some field/filter combinations, observers should not rely solely on these standards, but should supplement with other standards, e.g. the Landolt standards described above (in particular, there are few blue stars [(B-V) tex2html_wrap_inline6217 0.5] in these cluster sequences). Finder charts and data for these sequences are given in the next section below, and may also be found in the above-mentioned green binders.

manuals store
Wed Sep 17 12:36:20 BST 1997