[Aavso-photometry] Questions about Z And Photometry

[Arne Henden]

I would be happy to release such data, if it were available.
To the best of my knowledge we have not observed Z And from
Sonoita.  However, it does have good Tycho2 data, along with
some other sources, which will be used in the upcoming release.
We probably ought to put Z And on the LPV calibration project
with short exposures to calibrate this star properly at all wavelengths.
Arne

On Jan 1, 2008 8:28 PM, Walt Cooney <waltc at cox.net> wrote:
> Arne,
>
> Since Z And is getting attention, would you mind releasing the SRO BVRI
> photometry of the "92" star in an email to the list?  I'm shooting BVRI
> of Z And tonight.  I'd like to use the "92" star as my comp star since
> it is similar in brightness to Z And at the moment.  Otherwise, I'll
> wait until the improved photometry is released later this month before
> submitting my measurements.
>
> Thanks,
> Walt
> (CWT)
>
>
> arne wrote:
> > Barbara G. Harris wrote:
> >
> >> I submitted a CCDV observation of Z And taken on 12/30/2007 @ 01:52 UT.  I
> >> use MaximDL for photometry.  I used the 9.2 star as my reference star (9.165
> >> from field photometry).  Using that as a reference, I go a Mag of 9.25 for Z
> >> And.  I submitted this to AAVSO.   Later after looking at other observations
> >> around that time I noticed that the 9.25 was not consistent with the other
> >> observations around that time (9.7226 CCDV, 9.6 Vis).  I then went back to
> >> my image and used the 11.2 star as a reference (11.194 field photometry).
> >> With that star as a reference I got a mag of 9.56 for Z And which is more in
> >> line with the other observations at that time.  When I selected the 11.2
> >> star as my reference and then selected the 9.2 star as a check star, the mag
> >> that I got as a check for the 9.2  star was 9.49.   If I use them both as
> >> reference then I get a mag of 9.40 for Z And.  I have gone back and modified
> >> my observation in AAVSO.
> >>
> >>
> >>
> >> So that teaches me that I should always use a check star.  My question is:
> >> Why was there such a disparity in my 9.2 star?  I consider myself still new
> >> at CCD photometry so any other advice or recommendations would be
> >> appreciated.
> >>
> >>
> > If you look at the photometry table for Z And, you will notice
> > that the 92 star (AUID 000-BCR-684) has very large errors, while
> > the 112 star errors are ten times smaller.  You ran into one of the
> > problems that happened with automatic population of the photometry table
> > in October.  These stars are from Henden and Munari, as Z And is
> > a symbiotic star and we calibrated the fields of about 100 such
> > stars.  In this case, the 92 star is saturated, which is why it has
> > large errors.  Your 9.49 value for that star is probably much closer
> > to the truth.  As you indicate, using a check star is always a good
> > idea, and with CCD images, be sure you save the images as well so that
> > you can go back and find other stars if necessary at a later time.
> >
> > Thank you for pointing this out - I'll revise the 92 star's photometry
> > for the January release of the comparison star database.
> > Arne
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> >
>