[vsnet-chat 3111] LMC V1341 prelim sequence

[Brian Skiff <bas@lowell.edu>]

     My thanks to John for extracting the magnitudes from the UCAC catalogue
for the field near LMC V1341.  I have done what was suggested in my earlier
post, by finding the mean offset of the UCAC magnitudes compared to V and then
applying that offset to stars closer to the variable.  As John points out this
is not necessarily going to be perfect.  However, because the four-fold
overlap of the UCAC frames will yield some averaging, and because northern
Chile is practically cloudfree for several months centered right in "LMC
season" (austral summer), it is near-certain that the LMC images were taken in
photometric conditions and that the internal consistency is likely to be high.
     The two sequences show the following wrt UCAC:

1)  a mean offset wrt V for the eight stars of ordinary color of -0.34 +/- 0.03
    mag. (UCAC too bright as expected), the scatter gratifyingly small;
2)  a color term, not at all surprising, between UCAC 'r' and V evident on the
    two redder stars;
3)  however, in the color range 0.28 < B-V < 0.69 no obvious color term
    is present;
4)  a star of R mag. 14.8 is missing from UCAC---this catalogue will not be
    _complete_ to the limit stated.

I looked up each of the sequence stars and those John found close to V1341 in
USNO-A2.0 to look at their relative colors (and add the final decimals to the
coords for the new ones).  None of the new stars is especially red, so I have
simply added 0.34 to the UCAC values to get a reasonable 'mv', which I show in
the second table below.  If Peter or others can make a visual check to confirm
that this sequence appears reasonable, I'd suggest using it until someone can
do the photometry properly.

\Brian

=============================================

Name              1UCAC     V/B-V    V offset

Martin LMC II-1   11.86  12.17/0.58  -0.31
Martin LMC II-2   12.92  13.26/0.55  -0.36
Martin LMC II-3   13.12  13.50/0.69  -0.38
Martin LMC II-4   13.75  14.37/1.45  -0.62
Martin LMC II-6                             NOT a 1UCAC star (R ~14.8)
S056-C            10.55  10.86/0.55  -0.33
S056-D            10.91  11.21/0.41  -0.30
S056-E            11.29  11.66/0.57  -0.37
S056-F            12.73  13.03/0.28  -0.30
S056-G            13.57  13.90/0.62  -0.33

>>  mean offset -0.34 +/- 0.03


LMC V1341 Field Stars
                       (2000)         UCAC(r)   mv    color
GSC 9169-1555   5 09 04.9  -71 43 01   10.16   10.5   blue
GSC 9169-1568   5 09 45.9  -71 37 47   12.01   12.3   med
GSC 9169-1064   5 09 42.6  -71 47 16   12.86   13.2   med
1UCAC           5 11 51.4  -71 38 50   14.19   14.5   med
1UCAC           5 09 51.1  -71 34 00   15.13   15.5   blue

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