(cba:news) BK Lyn comparison stars

[Joe Patterson]

Hi CBAers,

Coverage of BK Lyn has been very good, but this star's behavior is so 
regular that standardization of comparison stars has become an issue. 
(It's always *somewhat* of an issue, but for many stars I neutralize it 
by subtracting the mean from each nightly time series; this optimizes 
period search at most interesting frequencies, but blinds us to low 
frequency.)

Some of you list comparison stars, some not, and some change comparison 
stars.  For BK Lyn, it seems that popular choices have been
(1) GSC 2496-0893 (V=13.90) 9 20 23.45  +33 59 17.1
(2) GSC 2496-1453 (V=14.89) 9 20 13.21  +33 58 54.6

Some of you might want to re-send messages warning about variables in 
the field.  I took some notes on them, but am not certain I got it right.

So far, in analysis I've converted your observations to (1), with 
additive constants I've estimated.  In general this will go easier if 
you actually *use* (1) as your comparison star.`(2) is ok too.  Third 
best is any suitable comparison star in the field, assuming you always 
use the same comparison, OR measure the relevant additive constant for 
any new comparison star used.  (You have to measure it, not just use a 
catalogued value, because of the unfiltered magnitudes we generally use.)

I've been fussy about this because I can see that BK has a large 
low-frequency variation, which we need to measure carefully. It's just 
not our usual style, but it needs to be now.

Great target, by the way, and decently.  I can see that 2012 looms as 
the year of the negative superhump!

joe