[Aavso-photometry] Questions about Z And Photometry

[Walt Cooney]

Oops.  I thought we had done Z And.  My mistake.

-Walt

Arne Henden 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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>>>
>>>
>>>       
>
>