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

[Jeff Hopkins]

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
-- 
Jeff Hopkins
HPO SOFT
Counting Photons
http://www.hposoft.com/Astro/astro.html
Hopkins Phoenix Observatory
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Phoenix, Arizona 85033-2439 U.S.A.
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