[Aavso-photometry] Questions on Henden sequences

[arne]

Michel Bonnardeau wrote:

>I try to use the Henden sequences and I have the following questions:
>
>Most of the files have columns for V, B-V, U-B, V-R, R-I but sometimes 
>there is a 6th column for apparently another magnitude differential. 
>Is it I-J or something else?
>Example: doher.dat.
>
>The errors on the magnitudes may be negative. What is the meaning?
>Example: 3c279.dat.
>
>
Michel,
  The 6th column is (V-Ic).  This is a new format that will be used starting
next year.  There are two reasons:  you get more accuracy for (V-Ic) by 
solving
for it directly, which is the case in these 6-column files, than by 
forming it
from
  (V-Ic) = (V-Rc) + (Rc-Ic)
Second, there are a number of stars that do not have (B-V) in my datasets,
but which do have (V-Ic).  Therefore, my current transformations permit 
solving
for V vs. (V-Ic) in addition to V vs. (B-V) so that I can add these stars to
the final dataset.
  The negative errors mean the observations came from a single night, so 
that
the errors are purely Poisson rather than night-to-night scatter.  This was
the simple "flag" that I implemented to handle this case.
Arne