[Cmunipack] New version released (1.1.1)

[cmunipack at amper.ped.muni.cz]

Hi David,

thank you for your answer. When putting the question about photometry I 
didn't keep in mind that the programm computes relations and does not work 
with PSF in connection with a star catalogue like Astrometrica.
What about detecting and measuring moving objects (Lightcurves of minor 
bodies)?

Best wishes
    Jörg!


----- Original Message ----- 
From: <cmunipack at amper.ped.muni.cz>
To: <cmunipack at amper.ped.muni.cz>
Sent: Saturday, May 27, 2006 11:24 AM
Subject: Re: [Cmunipack] New version released (1.1.1)


>> Hi David,
>>
>> thank you for your new version. I tested the SNR-feature and wondered why 
>> the output is in mag and negative (Barnard's star: -10 mag). Isn't it a 
>> datum without a dimension?
>
> Yes, it is. But the magnitude is also a unit without dimension. It means 
> logarithm of luminosity of a measured star with respect to some agreed 
> value. So I thought what representation is suitable for displaying SNR. 
> For it is also the ratio - signal of a star and a sky noise (both in ADU). 
> If I had use simple ratio, it would result in very great numbers (-10 
> magnitudes correspond to 100,000 in linear scale). In technics, decibels 
> (dB) are used for this value, but in astronomy, there is one unit, which 
> suits better - it is logarithm-based and well known - magnitudes. So when 
> Muniwin displays SNR = -5 mag, it means, that the star is 100 times 
> brighter than the sky signal.
>
>> When doing photometry on Barnard's star the program gives me an 
>> instrumental value of 13.66 mag which is really too low.
>> My photometry settings:
>>            readout noise 15 e
>>            gain: 24 e/ADU         (full well capacity: 100 000 e)
>>            low good datum: 5 sigma
>>            high good datum: 4096 ADU
>>            FWHM: 3 pix
>>            threshold: 3 sigma
>>
>> When I measure the same frames with Astrometrica I receive a value of 
>> about 9.1 mag for this star. Astrometrica uses the USNO-B1 star 
>> catalogue.
>
> I think it is no good idea to rely on instrumental magnitudes and compare 
> them with star atlas, for example Tycho-2. To do so, you had to count in 
> many conditions, which are not always constant and predictable - 
> extinction for example. The Muniwin program is designed to produce 
> relative magnitudes - to use one star as comparison star, which is 
> believed to be constant and with well known brightness, and to derive 
> brightness of some another star in neighbourhood. Their distance should be 
> small enough to disregard the difference in extinction. I've done listing 
> of instrumental magnitudes for users, which need raw data to perform their 
> own further corrections and processing, it wasn't intended as final 
> product.
>
> Best regards,
>
> David
>
> _______________________________________________
> Cmunipack mailing list
> Cmunipack at amper.ped.muni.cz
> http://amper.ped.muni.cz/mailman/listinfo/cmunipack
>