[vsnet-chat 5964] Re: [AAVSO-DIS] CCD-V Vs visual observations = U ORIONIS

["Sebastian Otero" <varsao@fullzero.com.ar>]

Dear Gary,

> Since we know
> that Comp 5 was actually 13.991,  we can fix the observation of 6.97 and
it
> becomes 7.31.

I'm glad that some of the problems could be fixed by correcting comp. stars
values.
However,

> B-V of 3.69---actually I reported
> B of 10.66.
> I gave the B observation two different days of scrutiny, and
> could find nothing obvious.  The comps are in the right places and are the
> same ones used in the V observation.  The 10.66 is the average of 3
> observations which gave 10.18, 10.73, and 11.09 for comps 5, 4 and 3.

and

> B = 8.83, 9.01, 10.66, 9.17, & 8.66 from the same observers at the
> same time.  Not as  good as the V, but B is tougher with a CCD.

Well, I think I have been wrong all the time by thinking that one could get
accurate results when using photometric equipment...
I don't understand how one can get so different results depending on the
comparison stars used and how it can be right to make an average.
The only thing that comes to mind is that if the results are this wrong,
some comparison star values must have wrong B values... If so, theyse stars
should be removed and the results shouldn't be averaged.
But since I am only a visual guy I am speaking without knowing the rules of
CCD photometry...


> So lets summarize at this point, with the correction, we have from the
> beginning V = 7.31, 7.26, 7.31, 7.38 and 7.13.  This is for 3 different
> observers, over 14 days, on 4 different nites.  The max peak to peak is
.25
> mags.  I wish it were better, but this is about typical, I believe.

What I mean is: if this is typical, what are the advantages of the use of a
CCD over visual observations?
I can get 0.1 mag. accuracy and much more consistency than the presented
observations
Maybe the use of a B filter to derive a color, but I don't know if it's
worth the effort.
At least some of the B "blue" magnitudes of U Ori were just a processing
error but the rest are still too poor...


> 2452667 from the above.  These V observations were 7.13, 8.01, 8.11, 8.17
and
> 7.26.  By ploting this on the Light Curve Generator, I can see a dip in my
> observations, which might at first seem like an error.  There is however,
> only one other obervation on 2452655 which is a Visual one that lists 7.7.
> This is about a half a mag lower that the other Visual observations the
> preceed and follow this observed dip.  If anyone has additional
observations,
> it would be interesting to see if this dip is real.  This is not the only
> time that short term variations have been observed in the CCD data.

Luckily I was observing the star by the dates of the "dip" and there was no
dip.
Actually, the maximum was some day near your 7.13 observation but all the
flickering observed I don't think it is real.
One magnitude dip is too big and could be used to make false interpretations
on the star's behaviour.


2452630.699     7.4
2452634.692     7.4
---- 2452635.8165       7.22  KMP
---- 2452638.7993     7.31-7.26 PDO
2452641.572     7.3
2452642.535     7.3
2452644.539     7.3
2452645.580     7.3
----- 2452647.5259      7.31 WGR
----- 2452648.515        7.38 MTK
----- 2452651.5975      7.13 WGR
----- 2452652.5634      8.01 WGR
2452652.568     7.2
----- 2452654.5285      8.11 WGR
----- 2452655.5459      8.17 WGR
2452658.587     7.4
----- 2452661.5404      7.26 WGR
----- 2452661.577        7.65 MTK
2452663.555     7.5
----- 2452665.5004      7.47 WGR
2452667.525     7.5


> Moral:  This is the world of UNEVALUATED DATA.  This is why the discalmer
at
> the top reads "Do not use for Publication".  EVALUATED data scrubs this
out
> of the data base.  We need to work towards eliminating these errors.  The
> electronic submission has helped greatly.  We need to do more.

Well, although some of the errors mentioned can be recognized at first sight
as software errors or typos, I am focused on accuracy in general.
I would prefer my visual U Ori data a million times.... ;-))

Best wishes,
Sebastian.



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