Re: GSC 540-84

[Arne Henden <aah@nofs.navy.mil>]

I looked at the email archive that Michael R. handles.  The original
email said:

 >Something peculiar is going on. Notice the two weird data points in the
 >V band at phase 1.15 or so. The images look perfectly good and don't
 >have errors or other indications of bad data. These points go up and
 >meet the other night of data. Both nights use the same comp star and
 >same everything else. The V band seems to have the same phenomena as
 >the Rc band in terms of the light curve being displaced a bit every so
 >often. The errors in the comp star magnitudes for the 8/22 data was
 >0.002. It was a very steady night. Those two points are way outside
 >even 3-sigma. Seen anything like that before?

 >It is far-fetched speculation at this point, but could this be an
 >eclipsing RR Lyr star?

My comments regarding eclipses were based on the phase 1.15 points,
which look like just photometric error to me.  Your statement that
the light curve is displaced a bit every so often did not say
anything about minimum, so I assumed you were talking about just
portions along the light curve such as on 08/22 around phase 1.10.
Certainly, the larger, global deviations such as exhibited for
07/29 are due to Blazhko effects.  Look at Smith's RR Lyr book
for more details, or look at Doug Welch/MACHO papers on their RR Lyrs.
Doug has a great time series example of an RR Lyr undergoing Blazhko
modulation on his web site.

On the other hand, your email of a day or so ago said:
 >The displacement I was talking about (and it wasn't clear to me if you
 >were talking about the same displacement) was how the minimum was
 >smooth on some cycles and rough on others. I'm pretty sure, and others
 >have seemed to agree, that this represents an additional fourier
 >component and not errors on my part.

Note that the displacement you are talking about is not "rough", but
is a general displacement towards brighter values when the star is
at minimum, and towards fainter values when the star is at maximum;
that is, an amplitude decrease.  I don't see any roughness.  If
it existed, it would not imply high-order Fourier terms unless there
was obvious sinusoidal variation.

I guess I have been reacting to your statements as if they were coming
from a professional working in the field and thereby misinterpreting
what you have been saying.  Sorry!  I will make an effort to ask
for clarifications before responding.
Arne

Michael Koppelman wrote:
> But some of the components may be on a longer period and not be evident 
> on every single cycle of a shorter component. That is what I *think* we 
> are seeing.
>