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[vsnet-chat 5412] Some very red standard stars

     We went over the "very red" standard stars business last winter on the
AAVSO discussion list.  At that time, I cobbled together a list of fairly
reliable red standards that might be suitable for observation of Miras and
carbon stars with photoelectric/CCD instruments---and more generally for seeing
how one's system behaves in this regime.  These are well observed on the
Johnson-Cousins UBVRI system and have reasonably small uncertainties,
suggesting they are not greatly variable.
     Most of the stars are selected from the various Landolt standards papers,
and for the most part are fainter than V mag. 7 and redder than B-V = 1.75,
or V-R = 1.0.  Although there are additional Landolt red stars, none are
well-observed, and the errors on the figures makes them unsuitable as
standards.  None of the Cousins E-region standards is quite as red as these.
     Arne Henden noted that since the stars are bright toward the red, one
might end up using the fainter stars here when observing in VRI colors, but
using the brighter stars when doing U-B in order to get enough signal.
Because of the slight variability, another suggestion is to observe as many of
these stars as possible in hopes of being able to average out the scatter that
will inevitably occur in fitting the data.
     Many of the of stars are designated or suspected variables, and are at
least slightly variable in V (0.03-0.05 mag. range).  Except for U-B, however,
the _colors_ should be fairly stable.  An odd exception is HD 172829 = HK Aql,
which is certainly constant.  A comparable star in the northern winter sky is
HD 27482, which is another strongly reddened ordinary K-giant star.  If you can
observe stars as bright as these, I recommend you consider them as very red
"friends".
     Few photometric systems are linear in this color regime.  If red stars
are on the menu, a suggestion is do two separate solutions:  one for stars
with B-V < 1.5, and another for stars with B-V > 1.2 (yes, some overlap) that
will be used to reduce the red stars only.  Arne Henden noted that since the
stars are bright toward the red, one might end up using the fainter stars here
when observing in VRI colors, but using the brighter stars when doing U-B in
order to get enough signal.  Because of the slight variability, another
suggestion is to observe as many of these stars as possible in hopes of being
able to average out the scatter that will inevitably occur in fitting the data.

\Brian

-------------------------------------------------------------------------------

Some "very red" standard stars
version:  30 Jan 2002

Name            RA (2000) Dec      V     B-V    U-B    V-R    R-I    V-I
SA 95-330     3 54 31 +00 29.1  12.174  1.999  2.233  1.166  1.100  2.268  L92
SA 95-275     3 54 44 +00 27.3  13.479  1.763  1.740  1.011  0.931  1.944  L92
HD 27482      4 21 15 +27 21.0   7.30   2.05   2.49                        L67
SA 97-75      5 57 55 -00 09.5  11.483  1.872  2.100  1.047  0.952  1.899  L92
SA 98-618     6 51 50 -00 21.3  12.723  2.192  2.144  1.254  1.151  2.407  L92
SA 98-674     6 52 13 -00 19.7  13.398  1.909  1.936  1.082  1.002  2.085  L92
HD 57884      7 23 07 -04 12.8   9.135  2.299         1.264  1.019  2.283  L83a
HD 79097      9 11 51 -06 58.8   7.601  1.628  1.933  0.990  1.100  2.087  L83a
HD 140850    15 45 58 -01 26.7   8.816  1.670  2.078  0.948  0.947  1.895  L83a
BD-14 4395   16 18 37 -15 08.8  10.84   1.81   2.10   1.26   1.47   2.27   L83b
HD 160471    17 40 12 -02 09.1   6.18   1.67   1.87                        C65
BD+04 3508   17 47 33 +04 50.4   9.326  1.753  2.077  0.974  0.900  1.874  L83a
SA 110-229   18 40 46 +00 01.8  13.649  1.910  1.391  1.198  1.155  2.356  L92
HD 172829    18 42 18 +00 09.3   8.447  2.002  2.292  1.186  1.120  2.306  L83a
SA 110-365   18 42 57 +00 07.4  13.470  2.261  1.895  1.360  1.270  2.631  L92
SA 110-280   18 43 07 -00 03.7  12.996  2.151  2.133  1.235  1.148  2.384  L92
SA 110-502   18 43 10 +00 27.7  12.330  2.326  2.326  1.373  1.250  2.625  L92
SA 110-446   18 43 39 +00 19.6  13.95   2.89          2.06   2.01   4.07   AAH
SA 110-516   18 43 40 +00 33.0  11.23   2.47          1.47   1.32   2.79   AAH
SA 110-315   18 43 52 +00 00.8  13.637                1.206  1.133  2.338  L92
SA 111-775   19 37 16 +00 12.1  10.744  1.738  2.029  0.965  0.896  1.862  L92
SA 111-1969  19 37 43 +00 25.8  10.382  1.959  2.306  1.177  1.222  2.400  L92


sources
AAH    Arne Henden photometry files
C65    Cousins 1965MNSSA..24..120C
L67    Landolt 1967AJ.....72.1012L
L83a   Landolt 1983AJ.....88..439L
L83b   Landolt 1983AJ.....88..853L
L92    Landolt 1992AJ....104..340L

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