[Aavso-photometry] Reporting Data, Guidelines for a new person?

[Richard Huziak]

Here you go, Ed :-)

rick

Jim Jones wrote:

>Hi Ed
>
>Welcome and glad to see you made it over here.
>
>Since Miras don't change very fast, I normally take enough images so 
>that after I get done stacking to get the SNR that I want, I have 5 
>stacked images to analyze.
>Then I report the average of the five as the magnitude (a single value) 
>and the standard deviation of the 5 as the error.  Just like reporting 
>double stars.  The 1/SNR error is probably one of the least accurate 
>methods to calculate error but sometimes that is all you have.  Having a 
>good SNR isn't a guarantee that a particular image might not have a 
>problem that gives you a flyer.
>
>As far as flyers are concerned, I always plot the check star.  If you 
>have a flyer, it usually will show up in the check star.  Sometimes you 
>get an observation that is out in left field even though the check star 
>looks good.  If it is really out in left field, I throw it away (talking 
>about Miras).  If it is just a little out, I include it in the average 
>and take a hit on the error.
>
>Many of the comps on the Mira Charts are not very accurate.  So I 
>sometimes also use a comp that another CCD observer has used (assuming I 
>am satisfied with the other observer's choice of comps).  Probably no 
>good reason except that it tends to make a "prettier" light curve ;>}.
>
>Time series error is more complicated.  I'm sure you will get lots of 
>comments and suggestions.  There is also a bunch of stuff in the 
>Aavso-photometry archives on this subject and it is probably worth going 
>back and reading it.  As I remember, you are using Canopus...doesn't it 
>calculate an error for you?
>
>Beware, variable stars are at least as addictive as double stars.  You 
>are you going to wind up observing all night and analyzing data all day.
>
>Jim Jones
>
>Ed Wiley wrote:
>
>  
>
>>I am just getting into variables. I am starting with CCD V-filter photometry
>>on some selected Miras that have recent observations that I can use to
>>compare my results. (So far, so good or at least reasonable!).
>>
>>My regular work is with neglected double stars, where I report the average
>>of four observations (position and angle) and the standard deviation.  
>>
>>However, I understand that (and why) the AAVSO needs single observations
>>with one comparison star for standardization. I am now taking a minimum of
>>3-4 images. So, a bit of advice would help me considerably.
>>
>>1. Consulting Quick Look I have not found a case of more than one
>>observation reported for the Miras I am following. Does this mean that the
>>usual protocol is a single CCD image? I would feel a bit strange if I was
>>the only person who was posting, say, say, three V magnitude estimates taken
>>at 5 minute intervals. But, I will not feel strange at all if this is the
>>correct protocol.
>>
>>2. If I have an obvious "outlier," perhaps due to a hot pixel or some such
>>thing, should I drop that measure, given that it does not agree with the
>>other 2-3 measures.  For example, of three measures I took of RCom, one
>>deviated considerable: 13.51, 13.50, 13.42, but since all have excellent
>>SNR, the "errors" were all small.
>>
>>3. Any standard way of measuring accuracy error for a series. For example,
>>computing standard deviation using pairs of companion stars?
>>
>>4. If so, should I put comments like "series of four images, SD +/-..." in
>>the comments section.
>>
>>5. I am taking a "monkey-see-monkey-do" attitude towards picking companion
>>stars. I have noted in playing around that V-mag estimate can vary
>>considerably by picking different comparison stars, even those close in
>>magnitude (no doubt due to color differences). So, I am going with what
>>seems to be what others have picked for the stars I am measuring. I assume
>>this is a good thing.
>>
>>Many thanks for any advice and answers!
>>
>>Ed Wiley
>>Remote Astronomical Society Observatory
>>http://www.remote-astronomical-society.org/
>>
>>
>> 
>>
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>>
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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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