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DC DFT Amplitude - or is it Semiamplitude?

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arx
arx's picture
DC DFT Amplitude - or is it Semiamplitude?

In the DC DFT Amplitude versus Frequency (or Period), plot, is the y axis the full amplitude or semiamplitude?

Roy

David Benn
David Benn's picture
Semi-amplitude

Hi Roy

It's semi-amplitude.

The y-axis title should be revised accordingly for clarity. I've created a ticket for this:

    https://sourceforge.net/p/vstar/bugs-and-features/685/

In some sources, amplitude and semi-amplitude are used interchangeably. Grant Foster's light curve analysis book provides context (p 130).

In any case, I've verified that the y-axis in VStar's amplitude vs period/frequency plot represents semi-amplitude. You can verify this for yourself by running DCDFT against a signal with a sem-amplitude of 1 such as the one attached.

David

File upload: 
arx
arx's picture
Semi-amplitude

Thanks David,

I thought so, but wanted to check.

The question was prompted by light curves and analysis of an unusual star which varied between ~7.1 and 7.5 for a few days, then between ~7.5 and 7.9 for another few days. True range therefore about 0.8 mag. DC DFT in VStar shows an amplitude of about 0.35.

Couldn't check using a true sinusoid - away from home without a computer.

Cheers,

Roy

David Benn
David Benn's picture
Semi-amplitude

Hi Roy

I've made the change to the code and user manual so it will be in the next release.

David

arx
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Semi-amplitude

Thanks David

Best wishes for the New Year.

Roy

David Benn
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New Year

Best wishes to you for the New Year too Roy.

David

arx
arx's picture
DC DFT Amplitude etc. - not an active Forum topic

I am wondering why 'DC DFT amplitude - or is it semi amplitude?' still displays intermittently as an active topic when it is not.

Roy

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