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

[Jim Jones]

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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