[Aavso-photometry] photometry of 27 virginis

[Jeff Hopkins]

My photometry technique, both singe channel and CCD photometry is to 
take three readings in a row in each filter (bracketed by the 
comparison star for single channel work). The resulting magnitudes in 
each filter are then averaged and a standard deviation computed as an 
indication of data spread (error).

Using the SNR to calculate error is fraught with problems. I know 
many do this, but the actual error can be  sum of many things. The 
SNR assumes no other errors. Using three readings gives a very good 
indication on how good the data is and by good I mean steady. The 
actual accuracy will be dependent on your transformation and 
extinction coefficients.

I'm currently working on a program that uses the FileMaker Pro 
database application to create it. It is designed for the SSP-3 and 
single channel BVRI observations. I am close to finished with it, but 
need to check it out good. If you are interested in a copy please 
contact me directly. I'm working on the program for Paul Beckmann who 
is helping with the epsilon Aurigae project and using an SSP-3. YOu 
may wish to contact him too at beckmannres at comcast.net.

Jeff

At 14:04 -0700 05/31/2007, trupti ranka wrote:
>hello everybody,
>   A month ago I started with photometry of a variable star named 27 
>virginis. i was using a 14" celestron telescope and SSP3-A 
>photometer. Sky map pro software said that the star magnitude varies 
>from 6.19 to 6.33 which we thought was good enough to be observed by 
>14" telescope. but after initial data reduction we found that star 
>magnitude varies only by 0.05 magnitude. we checked some IBVS papers 
>which confirmed are data. The papers (1975,1977,1980)reported a 
>magnitude differences of about 0.02 to 0.03.
>   Now the problem is that since we were using a 14" telescope for 
>such a small amplitide variation the data accuracy is poor. also the 
>star is multi periodic delta scuti star. Its period varies fro 0.5 
>hrs to 3 Hrs (according to IBVS papers). I would like to know if 
>there is a better and more relaible way to calculate error other 
>that 1/SNR or some special data reductoin tricks to improve 
>accuracy. also i would like to know if there is a specific software 
>for calcualting periods of short duration multi periodic stars(i 
>heard there is a FORTRAN based software but can't find it) . this 
>has turned into a tricky star for data reduction but i would like 
>have some help as i have spend lots of nights observing it and don't 
>want the data to go waste.
>
>   looking foward for you replies,
>   regards,
>   Trupti

-- 
Jeff Hopkins
HPO SOFT
Counting Photons
http://www.hposoft.com/Astro/astro.html
Hopkins Phoenix Observatory
7812 West Clayton Drive
Phoenix, Arizona 85033-2439 U.S.A.
(623)849-5889
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