[Aavso-photometry] Possible new variable? (corrected)

[Dave Lane]

Hi Jeff,

Thanks for the long response. First of all, each measurement on my 
graphs is based on 5x60s exposures in V and 8x60s exposures in B, so 
aren't single exposures.

The exciting news is that a list member replied to me privately that he 
also noticed it varying last week and caught what looks like an EB eclipse!

With that aside, although I realize the variation is small, how does one 
explain the trend in both B and V while the other stars stay constant.

--- Dave

Jeff Hopkins wrote:
> Hi Dave,
>
> I have done a lot of photometry and typically my single channel photon 
> counting system approaches SD for three consecutive magnitudes of 
> 0.001. Now I have found it very difficult to see variation on the 
> order of 0.01 or 0.02, but when there are repeatable or continuous 
> trends I can easily see changes in the millimag region that track 
> well. This is with a C8 in the UBV bands.
>
> I have also done considerable BVRI CCD photometry with my 12" LX200, 
> but seldom can get SD for 3 reading better than 0.02 and usually worse.
>
> In both cases I determine extinction nightly. Even so I have found 
> extinction can vary on a short time scale and in different even close 
> locations in the sky. As such looking at your plots I do not see any 
> variation that I would call due to the stars. There may be some, but 
> until you can produce several repeatable cycles I think it is just 
> noise. Trying to get light curves on the order of 0.02 magnitudes max 
> is difficult. Something that is missed with CCD photometry is the 
> observation of what stars are doing real time, second by second. I see 
> great short term variations (great being 10 to 20% of the maximum 
> counts). Using at least three 10 second sets of data averages this out 
> and can produce good data, but just one short observation can easily 
> produce o.o2 magnitude variations over short periods. This seems to be 
> due to atmospheric scintillation. The higher the elevation of the 
> observatory the better and the closer to the zenith the better, but 
> even under ideal conditions (Earth bound)  there can be significant 
> short term variations.
>
> So again I think tracking variations in the 0.02 or smaller region is 
> very difficult and unless you can see repeatability it probably is 
> just noise.
>
> Jeff
>
>
> At 14:32 -0700 12/11/2007, Dave Lane wrote:
>> Corrected web links:
>>
>> http://www.davelane.ca/aro/images/lph058b.gif
>> http://www.davelane.ca/aro/images/lph058v.gif
>>
>> --- Dave
>>
>> Dave Lane wrote:
>>>  I was doing a time series on two stars last night for Gord Sarty and
>>>  Rick Huziak's campaign and my first choice of check star for the 
>>> LPH058
>>>  field seems to be variable. It was imaged in both B and V - see the 
>>> star
>>>  labeled "l" at:
>>>
>>>  http://www.davelane.ca/aro/images/*lph058b.gif
>>>  *http://www.davelane.ca/aro/images/*lph058v.gif
>>>
>>>  In both filters there is a general brightening trend of about 0.02 
>>> in V
>>>  and 0.03 in B. The airmass increases until the data gap (the meridian
>>>  flip) in the graph and then decreases towards the end **(ignore the 
>>> last
>>>  four points as the airmass was well over 2). **The star has a B-V of
>>>  about 0.36 and the comparison star about 0.34.
>>>
>>>  SIMBAD doesn't come up with anything other than identifying it as GSC
>>>  00154-00555 and as an A2V. Nothing in the NSV either. Another
>>>  interesting point is that in the subset of the Henden sequence chosen
>>>  for the finder chart, this star has the largest reported V error.
>>>
>>>  Being fairly new to this, is this the kind of thing that should be
>>>  reported some how or should I continue to observe it or are there just
>>>  too many unknown variables to bother with?
>>>
>>>  ... Dave