[Aavso-photometry] W Aur Comp Stars

[Richard Huziak]

On Oct 11, JJI questioned the seequence for W Aur.  Arne responded with 
the same answer most would give who have looked in detail at the 
sequences off of old charts - that the sequences are sometimes good and 
sometimes poor, based on photographic plates that may fall off at the 
lower end.  Often sequences also come from different sources and are 
mixed, so inconsistent.  But that is life until all stars in the sky are 
measured precisely on the same scale.  For visual observers, this may 
 or may not be an issue depending on how truly bad the sequence is, but 
since all visual observers are using the same charts, at least their 
data is consistent within itself (mostly).  For CCD people, as Jim 
pointed out, the choice of the comp star will produce different results 
for the measured stars and will introduce a zero-point offset (which is 
easily correctible if the comp star chosen is reported).  This may look 
poor on the LCG at times, but that is raw data, and anyone using it 
needs to understand the zero-point offset issues.  However, I ramble.....

After yacking with Jim on the AAVSO discussion group last eve, I 
remembered I promised him I'd post a sequence for W Aur, since it is a 
Suspect Field which I hit regularly.  This is a 1-night sequence 
linearly extended from the 9.5 comp star defined as 9.500.  Stars not 
measured are not in the frame, with the exception of the 131 and 132 
which are close together, and I didn't bother at this time to readjust 
the annulus to do these separately.  Differences in JJI and HUZ derived 
mags are due to different comp stars used.

At any rate - take it for what it is worth - it confirms Jim's result 
that some stars are out by a fair bit at the lower end, but you will 
find this on the majority of charts that did not get PEP or CCD 
sequences, and this currently just is life. :-)    An as a result, it 
may take several tries to find an ensemble set of comp stars that 'makes 
sense'.  I could write a book about this and associated issues!

Column 1 - AAVSO chart value, Column 2 CCDV rounded value (based on 9.5 
comp), Column 3 CCD value not rounded.  Column 4 - error (stdev of 5 
consecutive frames on 1 night).  Sorry for the alignment.

rick (HUZ)


W Aur PRELIM SEQUENCE           
Chart 050223   (Original HCO sequence 1944)           
Single star photometry based on 95 = 9.500           
One night, 5 frames, 4 Oct 2005           
Instumental mags - not all-sky           

AAVSO    CCDV     CCDV    Err (stdev)
    X.X    X.XXX   
9.0            not measured
9.3            not measured
9.5    9.5    9.500    Ref star defined as 9.500
9.6            not measured
9.9            not measured
10.0    9.9    9.869    0.007
10.5    10.4    10.374    0.007
10.7            not measured
10.9    10.9    10.887    0.005
11.4    11.3    11.325    0.006
11.6E    11.3    11.338    0.008
11.6SW    11.3    11.271    0.010
12.0    12.0    12.011    0.013
12.1    12.0    12.049    0.010
12.3    12.7    12.666    0.140
12.6    12.7    12.748    0.022
12.8    12.9    12.919    0.038
13.1            not measured
13.2            not measured
13.7    14.0    14.037    0.129
14.0    14.6    14.641    0.110
14.1    14.3    14.332    0.060
14.5    15.0    15.009    0.209
           
Nothing is known about variability in this field           
I have 7 nights on this field if a better reduction is wanted.
Rick Huziak (HUZ)

Jim Jones wrote:

> I have two nights of V data from W Aur that is driving me crazy.  The 
> measured magnitude will vary by several tenths of a magnitude 
> depending on which comp stars I use.  I finally concluded that 13.2, 
> 14.0, and 14.1 are in error (F chart dated 12/70).  Using 13.1, 11.4, 
> 12.1 in an ensemble, I measured as follows:
>
> 13.2          13.57 +/- 0.007
> 14.0          14.56 +/- 0.01
> 14.1           14.29 +/-0.01
>
> Both nights data are consistent.  I figured that such a thing isn't 
> likely so I must be doing something wrong. But the new values result 
> in consistent measurements of the variable.
>
> So is anyone else having problems with W Aur?
>
> Thanks
>
> Jim Jones, JJI
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-- 

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Richard Huziak
Manufacturing Engineering
SED Systems
Saskatoon, SK, Canada
tel. (306) 933-1676
<huziak at SEDSystems.ca>
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