[Aavso-photometry] variable comp star in field of TT Ari?

[Arne Henden]

On 10/31/07, Jim Roe <jroe at jamesroe.com> wrote:
>
>
> Denis Denisenko wrote:
> > Hello Jim and all!
> >
> > Jim Roe writes:
> >
> >> It looks to me like the 111(11.075) star brightened substantially in
> >> one day.
> >> Comments, questions?
> >
> > Looks like BD+14 339 = TYC 1207-1550-1 is variable indeed.  Is it 111 comp?
> >
>
> No, the star in question is (from AAVSO chart 071025) 000-BBD-456 at
> 02:06:38.06, +15:19:59.5.
>
> I've gone over my images from the last three nights to get the following
> results.  First some orientation.
>
> 000-BBD-456 02:06:38.06 +15:19:59.5 V=11.075 (0.049) Target Star
> 000-BBD-478 02:07:19.46 +15:17:51.03 V=12.494 (0.012) Reference Star
> 000-BBD-473 02:07:14.08 +15:19:41.3 V=11.829 (0.015) Check Star
> 000-BBD-471 02:07:11.42 +15:14:47.7 V+13.064 (0.017) Check Star
> 000-BBD-458 02:06:47.74 +15:22:22.5 V=13.849 (0.006) Check Star
>
> The Check Stars more-or-less surround TT Ari and the Target Star.  Data
> was taken with a V filter on an STL-1001 camera and a 32-inch f/4.5
> Newtonian. Values are averages (stdev). (I hope the formatting survives.)
>
> Date           456      478     473    471    458
>
> 20071029      11.004   12.494  11.834  13.076  13.858
> (283 points)  (0.011)  (0)     (0.010) (0.016) (0.023)
>
> 20071030      10.856   12,494  11.900  13.136  13.850
> (62 points)   (0.039)  (0)     (0.004) (0.007) (0.009)
>
> 20071031      11.004   12.494  11.846  13.071  13.865
> (43 points    (0.050)  (0)     (0.014) (0.015) (0.034)
>
> Delta (my values - chart photometry)
>
> 20071029      -0.071   0       0.005   0.012   0.009
>                (0.050)          (0.018) (0.023) (0.024)
>
> 20071030      -0.219   0       0.071   0.072   0.001
>                (0.063)          (0.016) (0.018) (0.011)
>
> 20071031      -0.071   0       0.007   0.007   0.016
>                (0.051)          (0,021) (0.023) (0.035)
>
> The check stars match the chart photometry on all three nights to well
> within the uncertainties.  The target star does so too on 210071029 and
> 20071031.  The target star is clearly 0.2 mag brighter on 20071030 (the
> larger stdev is NOT measurement uncertainty, but variability over the
> measurement period).
>
My reading of your data is that 20071030 was significantly
different for all of your stars, not just the target.  That always
worries me.  What are your exposure times - are you running
into saturation with the 10th magnitude star (it is the brightest
of the set)?  What is different about 20071030 - worse seeing,
clouds, what?  Why are 471 and 473 brighter than normal
on that date?  I'd also be suspicious of your flatfielding on that
night.
Arne