[Aavso-photometry] Questions about Z And Photometry

[Arne Henden]

Further to my comment below:  I *did* do short exposure calibration
of the 92 star during the 2004 outburst using the 1.0m telescope
at NOFS, so the proper calibration information
exists - I just have to use the proper frames and reprocess.  I'll
see if I can take care of it this week.  I also note that I did quite a
bit of time series photometry of Z And that is described in
Arne's Projects #31.  So plenty of data exists, just not from SRO.
Arne

On Jan 1, 2008 10:24 PM, Arne Henden <arne at aavso.org> wrote:
> 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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> > >
> > >
> >
>