[Aavso-photometry] u crt sequence suspects!

[Richard Huziak]

Yenal, Arne, et al.

I've imaged the U Crt field over 6 evenings spanning the last month and 
once last fall, since someone had questioned the field in May 07.  The 
V-data below is untransformed and non-corrected for high airmass, but it 
clearly shows that this field is really screwy. (Many fields done in 
this era had strange 'photometry').  Besides 0.2 or 0.3 errors in the 
brighter stars, this field falls off at the low end, being a full 
magnitude out with fainter stars.  (Again, typical of some of the charts 
from then).  As Arne says - there will be a big 'adjustment' with his 
new calibration.  However, my worst star is indeed the old '12.7' star. 
Scatter is pretty severe over the 6 nights and there is a possibility 
the star is somewhat variable (around 0.1 mag), but further photometry 
is needed to confirm this.  Since the chart is so far off, I under 
estimated what exposures I needed at for the low end stars - those data 
have an SNR of around 20, so I can't conclude either way if the star is 
variable or not.  Maybe Arne's images will sort this out for sure.  The 
field is too far south for me, and with my brightening spring sky, I 
can't follow the field much longer.

rick HUZ

AAVSO Mag    HUZ mag    Err    # Nites    Notes

11.0    11.302    0.012    6   
11.4    11.355     --     --    Reference star  (Arne's improved value = 
11.358 (0.012)
11.9    12.036    0.004    1   
12.1    11.774    0.002    2   
12.3    12.770    0.008    2   
12.5    11.879    0.010    2   
12.7    14.305    0.069    6    was suspect 1107-06B; 14.349 if best 4 
nights used (Arne 14.274 (0.012))
13.0    14.058    0.027    5    Arne 14.038 (0.016)
*S UCrt    13.068    0.021    6    U Crt's companion to S


arne wrote:
> Yenal Ogmen wrote:
>   
>> Hi all,
>>
>> As you may know, one of U Crt sequence stars, "127
>> Comp S" is in the suspect list. A few hours ago, when
>> I tried to do photometry of U Crt with comp star 130
>> (GSC 4928:41) I got approx. 1 mag brighter result than
>> the expected value, observed from other observers' obs
>> at around the same time. Therefore I used 114 to get
>> reasonable estimate. Anyone know anything about this
>> star (GSC 4928:41)? It is neither in the suspect list
>> nor in VSX.
>>
>>     
> I've observed these stars multiple times in the process
> of calibrating this field from Sonoita Research Observatory.
> None of them are variable to the best of my knowledge.
> However, the chart photometry is far in error.  This is
> one of the fields that will change with the upcoming
> compDB/VSD update.  You can see this by clicking on
> the "Comparison Stars" link, where there are lots of
> comparison stars shown in the table, but with no
> accompanying photometry other than their label.
> Remember, the October 2007 update was only for those
> stars that did not change by more than 0.2mag from
> their labels - so you can be sure that most of the
> U Crt stars are going to change dramatically!
> The old photometry came from a preliminary chart from
> 1977, with a photometric sequence from WML and LEH.
> The new photometry for the three stars that Yenal
> mentions are:
>
> label  V      Verr
> 114  11.358  0.012
> 127  14.274  0.012
> 130  14.038  0.016
>
> This kind of error is exactly why we are updating the
> photometry, and why everyone has to pay attention when
> the update happens.
> Arne
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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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