[Aavso-photometry] HD37605 data request

[Jean-Luc]

Geir,

Thanks for your reply.. I usually report error using Stddev for each 
series, the way you describe.
But this time I chose to stack them , believing I would obtain a better 
precision and that I would be able to integrate Scintillation which was 
important factor.

If I do not stack, and get a stddev for each serie, how is scintillation 
taken into account  ? and how do I calculate the final error ?

Jean-luc




Geir Klingenberg wrote:

>Hi Jean-Luc,
>
>Yes, there has been quite a lot of error discussion on this list, I
>guess that's because it is not trivial and there's a lot of ways to do
>it.
>
>I believe reporting standard deviation in some form gives the best
>possible error estimate. So if you are satisfied with reporting a
>single error value for the data set you can simply use the standard
>deviation of the target star, which in your case is 0.009. Of course,
>this assumes that you where not fortunate enough to catch an
>ingress/egress and that trends from extinction has been removed.
>
>If the target star varies (as it usually does) the standard deviation
>will measure the stars inherit variations and not just error. In that
>case one can use the standard deviation of a comp star of similar
>brightness.
>
>However, many people prefer to get error estimates for each data point
>as this gives a more detailed view of the error throughout the series.
>There are many ways to do this as well, one being the method you and
>Radu mention. Another would be to use the standard deviation of the 10
>measurements you average (if you measure each frame instead of
>stacking them first).
>
>  
>




>Geir
>
>On Sat, 01 Jan 2005 19:58:49 +0100, Jean-Luc <jeanlucla at wanadoo.fr> wrote:
>  
>
>>Hi Aaron,
>>
>>I still have data to provide for HD 37605. Since I am not used to this
>>level of precision I would like to make sure I will submit data properly.
>>
>>Here is what I have done :
>>0/ I used AAVSO (e) chart,  86 (8.58) as comp star and 99 (9.89) as
>>check star
>>1/ I took a set of 10 exposures (20 sec + V filter) every 10-15 minutes
>>between Dec 28 - 21h00 UT and Dec 29 00h00 UT
>>2/ For each image of the set I substracted a master dark. I then
>>combined the 10 of them (with MIRA) in order to get an averaged (mean)
>>image.
>>3/ My SNR is good enough to have 2 millimag precision for HD 37605 and 3
>>millimag for the Check Star.
>>4/ At this point I got 17  Vmag values for HD 37605
>>5/ The average value of these 17 Vmag over 3 hours is 8,626 with Stdev
>>0,009.
>>5/ I calculated Airmass (between 1.51 and 1.36) and Scintillation (0,004
>>- 0,003) for each of the measures.
>>
>>Now my questions are :
>>
>>a) I don't know the Kv coefficient for my location, so I cannot correct
>>my data for first order extinction.
>>   Is it OK to report my data without applying the extinction
>>correction - and provide the uncorrected data with Airmass instead ?
>>
>>b) I am not sure how to calculate Scintillation error impact on my data.
>>I read in a previous thread that the err should be calculated as follows :
>>   err = SQRT(1/NetCountVar + 1/NetCountComp + 2*SQRT(Scintillation)).
>>    If  I do so, the err which was in the 0.002 range jumps to 0.3xx
>>... just because of the Scintillation factor.
>>    What does it mean ? Is Scintillation of 0,004 that bad ?
>>    Since it does not make any sense to try to detect a 0,02 gap with a
>>0,3x error...what error should I report  ?
>>    What is your recommendation to calculate / include scintillation
>>error ?
>>
>>c) A lot of things are told about about error reporting  and I am a bit
>>confused. Is there an AAVSO recommendation to calculate error ?
>>   The CCD Manual is giving SNR and Stdev as starting points but many
>>emails I read on this list tend to say that it is not enough.
>>    Is there a commonly agreed procedure/formula to calculate error
>>when submitting data ?
>>   (And especially for high precision measurement like for this campaign ?)
>>
>>Many thanks for your advices,
>>Best,
>>
>>Jean-Luc
>>
>>
>>Aaron Price wrote:
>>
>>    
>>
>>>I was wrong about Arto's data set, it does not include the estimate
>>>ingress time if Gary's event is indeed an egress. If anyone has
>>>observations of HD 37605 anywhere from JD 2453367.2 - 2453367.4 (16:48
>>>-  21:36: UT on December 27, 2004) please submit them as soon as you
>>>can as this is when the ingress should have occured. Thanks.
>>>
>>>
>>>
>>>      
>>>
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>>
>>    
>>
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