[Aavso-photometry] CCD 'fainter-than' question

[Michael Newberry]

There's no straightforward way unless you do it starting with the 
theoretical values from the Error(T) results in the table. Even then, I 
could imagine this getting complicated for any kind of reliable "autiomatic" 
calculation. I think your best bet is to do it manually, at least for now. 
How often do you have "fainter than" reports to submit?

Michael

----- Original Message ----- 
From: "Wolfgang Renz" <w_renz at onlinehome.de>
To: "Michael Newberry" <mnewberry at mirametrics.com>
Cc: "AAVSO-PHOTOMETRY" <aavso-photometry at mira.aavso.org>
Sent: Wednesday, May 28, 2008 1:16 PM
Subject: Re: [Aavso-photometry] CCD 'fainter-than' question


> Hi Michael
>
> They make sense.
>
> I already thought about doing it that way too (how do you think I
> have selected those faint background fluctations), but it is really
> time consuming doing it by trial and error and find the right ones.
> There might be also not always the right ones available in every
> light frame (e.g. due to a small  or depopulated FOV).
>
> I actually hoped that you could give a general simplified / appro-
> ximation formula that could do the job to dmag accuracy.
>
> Clear skies
> Wolfgang
>
> -- 
> Wolfgang Renz, Karlsruhe, Germany
> Rz.BAV = WRe.vsnet = RWG.AAVSO
>
>
>
> ----- Original Message ----- 
> From: "Michael Newberry"
> To: "Wolfgang Renz"
> Cc: "AAVSO-PHOTOMETRY" <aavso-photometry at mira.aavso.org>
> Sent: Wednesday, May 28, 2008 7:22 PM
> Subject: Re: [Aavso-photometry] CCD 'fainter-than' question
>
>
>> You are using Mira Pro. So suppose that the readout noise, exposure time,
>> and gain values are present so that Error(T) can be computed. Then can't 
>> you
>> just pick a star for which Error(T) is 0.36 magnitudes (which corresponds 
>> to
>> S/N=3, or whatever other criterion you want). That tells you what 
>> magnitude
>> to use for the "fainter than" value. But what star would you use? There 
>> are
>> 2 ways to do this:
>>
>> 1) From the photometry toolbar, switch to "move" mode and move the marker
>> from point to point on faint stars and find one that gives Error(T)=0.36.
>>
>> 2) Measure a bunch of stars in the field. You might find 2 who's errors
>> bracket the value 0.36 mag, and then interpolate the magnitude between 
>> them.
>> Alternatively, you could make a scatter plot of Error(T) vs Magnitude (or
>> vice versa) from the table.
>>
>> Do those short descriptions make sense?
>>
>> Michael
>>
>>
>>
>> ----- Original Message ----- 
>> From: "Wolfgang Renz" <w_renz at onlinehome.de>
>> To: "Michael Newberry" <mnewberry at mirametrics.com>
>> Cc: "AAVSO-PHOTOMETRY" <aavso-photometry at mira.aavso.org>
>> Sent: Wednesday, May 28, 2008 10:09 AM
>> Subject: Re: [Aavso-photometry] CCD 'fainter-than' question
>>
>>>>> If its a less than a 3 sigma detection, it should be probably reported
>>>>> as a 'fainter than' with the value of the background + 3 sigma as mag
>>>>> But this mag value is unfortunatly nothing that is available with 
>>>>> usual
>>>>> photometry software. So maybe someone of the experts can recom-
>>>>> mend how it can be fast and easily determined.
>>>>
>>>> I am not sure what you mean.
>>>> Can;t you get that number out of _any_ software that does photometry?
>>>
>>> Not necessarily, some simple ones hide everything except the mag or
>>> delta mag values.
>>>
>>> But I meant the mag value to use for the 'fainter as' to be reported
>>>
>>> I've just made a Mira photometry with some measurements below SNR
>>> 3 down to SNR 0.2 (which is of course just noise):
>>> #,Image,Obj,Magn,Std?,Error,Error(T),X,Y,Col,Row,Bagkgr,S/N,Resid.,Net
>>> Count,Filter,Date,Time,JD - 2453000,Airmass,Exp 
>>> Time,Weight,Object,Object
>>> 1,HV_Vir.fts,1,14.1000,*,0.0133,0.0134,609.615,654.057,609.615,654.057,108,81.1,0.0000,15067.4,V,2008-05-24,04:21:01,1610.681262,1.1673,90.000,1.000,HV
>>> Vir,HV Vir
>>> 2,HV_Vir.fts,22,18.3602,
>>> ,0.5877,0.5944,732.713,723.969,732.713,723.969,107,1.8,0,297.827,V,2008-05-24,04:21:01,1610.681262,1.1673,90.000,1.000,HV
>>> Vir,HV Vir
>>> 3,HV_Vir.fts,23,20.8089,
>>> ,5.6841,5.6727,964.941,433.693,964.941,433.693,108,0.2,0,31.2236,V,2008-05-24,04:21:01,1610.681262,1.1673,90.000,1.000,HV
>>> Vir,HV Vir
>>> 4,HV_Vir.fts,24,19.0179,
>>> ,1.1263,1.0913,858.000,128.000,858.000,128.000,108,1.0,0,162.512,V,2008-05-24,04:21:01,1610.681262,1.1673,90.000,1.000,HV
>>> Vir,HV Vir
>>> 5,HV_Vir.fts,26,18.2622,
>>> ,0.6146,0.5450,992.553,141.438,992.553,141.438,108,2.0,0,325.948,V,2008-05-24,04:21:01,1610.681262,1.1673,90.000,1.000,HV
>>> Vir,HV Vir
>>> 6,HV_Vir.fts,27,18.1889,
>>> ,0.5030,0.5079,546.208,821.348,546.208,821.348,107,2.1,0,348.735,V,2008-05-24,04:21:01,1610.681262,1.1673,90.000,1.000,HV
>>> Vir,HV Vir
>>> 7,HV_Vir.fts,33,18.8217,
>>> ,0.9170,0.9112,324.052,752.881,324.052,752.881,108,1.2,0,194.689,V,2008-05-24,04:21:01,1610.681262,1.1673,90.000,1.000,HV
>>> Vir,HV Vir
>>> 8,HV_Vir.fts,35,19.4107,
>>> ,1.5484,1.5663,301.009,425.941,301.009,425.941,108,0.7,0,113.175,V,2008-05-24,04:21:01,1610.681262,1.1673,90.000,1.000,HV
>>> Vir,HV Vir
>>> 9,HV_Vir.fts,39,18.4497,
>>> ,0.6835,0.6474,448.693,62.319,448.693,62.319,108,1.7,0,274.263,V,2008-05-24,04:21:01,1610.681262,1.1673,90.000,1.000,HV
>>> Vir,HV Vir
>>> Aperture Photometry Calibration Results
>>> Zero Point Calculation for 'HV_Vir.fts'
>>> Calibration Summary:
>>> Zero point: 20.356
>>> Rms Error : 0.000 mag
>>> Standards : 1
>>> Aperture Summary:
>>> R1=10.00, R2=20.00, R3=30.00, E=0.000, Theta=313.00
>>>
>>> How would you report them as < x mag ?
>>> How would you determine x ?
>>>
>>> Clear skies
>>> Wolfgang
>>>
>>> -- 
>>> Wolfgang Renz, Karlsruhe, Germany
>>> Rz.BAV = WRe.vsnet = RWG.AAVSO
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