[vsnet-chat 5595] Re: [AAVSO-DIS] BD+59 224 V, Rc, and H alpha Photometry

[Brian Skiff <Brian.Skiff@lowell.edu>]

     Thanks for the new observations, Doug.  Yes, H-alpha emission would
not be so surprising in a big close binary like this from either the hot
star (if it were a Be-type star) or the cool giant/supergiant (a lot of
Miras show Balmer emission near maximum, though another mechanism might
be at work here).  
     How sensitive is the H-alpha wide/narrow passband differencing to
the spectral type of the star?  It would seem as though if your standards
are, say, mostly B-type stars with/without emission, that you could run
into trouble when comparing these on an M star.  The proximate cause for
concern is a big TiO bandhead at 6544A---just 20A short of H-alpha---which
would put a funny gradient across even your narrow filter.  I don't know
anything about what sorts of systematic effects might occur, but perhaps
someone on the lists can chime in on this subject.  It could be that you
could deal with temperature effects simply by adding a color term like
V-R to the reductions for the H-alpha width.

\Brian

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