Re: Error was GSC 748-1618 period

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

Zeropoint offset and large scatter do not bother me.  Difference
in light curve shape does bother me.  Michael K., your measures
were with a V filter, right?  And can you quote the TASS (V-I)
for both the variable and for your comp stars?  I don't trust
Tycho2 at V=11.5.
Arne

Tom Droege wrote:
> Michael worries why he can't match up the two curves more precisely.
> 
> To determine whether the miss-match is expected or not, we have to 
> consider the errors.
> 
> I now know a little about the tass error.  At 11.5 the internal tass 
> error is of order 0.05 mag for this data.  This is just the rms scatter 
> of points taken in V and run through the pipeline.  We don't not know 
> about the tass error when compared to standards.  I would be surprised 
> if it were zero (with some error attached).
> 
> We need also to know something about the Koppelman error.  One can tell 
> a little about the internal error by looking at the scatter of the 
> measured points.  We know nothing about the Koppelman error when 
> compared to standards?  I would again be surprised if it were zero 
> (again with some error attached).
> 
> Just for tass the 0.05 mag number is just a "most of the time" number.  
> You can be unlucky and see 3 or even more times this error.
> 
> So thinking about the known errors, the match looks OK to me.  I would 
> be more suspicious if it were closer to zero.
> 
> Tom Droege
>