Source-Sky-Tnn

[CraigNZ]

A quick question, in the measurements table for two stars I see the values:

  10.818625 (9th mag star)
    0.586212 (13th mag star)

What units are these numbers in?  How would I convert them back to electrons?

[CraigNZ]

I'm assuming this is normalized to the ccd sensor max ADU, entered in the aperture setup.

Craig

[karenacollins]

Hi,

Source-Sky_Txx is the actual number of ADU (after background subtraction) within the photometric aperture. There is no normalization in those values.

See Appendix D in the expanded AIJ paper for a description of all of the data columns in the measurements table:

https://arxiv.org/abs/1701.04817

I'm not sure why those values are so low. They look more like rel_flux_Txx values. I suppose if your exposure time is really short, they could be correct.

Karen

On 4/28/2018 4:37 PM, CraigNZ [via AstroImageJ] wrote:

A quick question, in the measurements table for two stars I see the values:

  10.818625 (9th mag star)
    0.586212 (13th mag star)

What units are these numbers in?  How would I convert them back to electrons?

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[karenacollins]

No data values are affected by the linearity and saturation settings in the aperture setup panel. Those only affect the background colors in the reference star panel.

On 4/28/2018 5:11 PM, CraigNZ [via AstroImageJ] wrote:

I'm assuming this is normalized to the ccd sensor max ADU, entered in the aperture setup.

Craig

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[CraigNZ]

Hi Karen,

I think I know the problem.  The FITS images I am processing are in 32 bit FP.  When I hover the mouse over a star it shows very small values for Int counts.  But if I load a 16 bit raw image and do the same I get a large int count.  I'll do some more research on this and report back, but I think it is due to the data type.

Craig

[CraigNZ]

Just confirmed that a 16 bit unsigned integer image shows Source-Sky ADU counts.  But the same image as a 32 bit real shows very small numbers.  I can put one of the images on a FTP server for you to download if you would like to look at it.

Craig

[CraigNZ]

Found the problem, Pixinsight is used to calibrate the images because of its ease of use (Batch PreProcessing).  Apparently, in the Flat Frame division, the output has been normalized to very small numbers.  I'm sure if I fix this, everything will work okay.  I apologize for the confusion.

Craig

[karenacollins]

Yes, that sounds like a reasonable explanation. Good sleuthing.
Karen

On 4/29/2018 5:22 AM, CraigNZ [via AstroImageJ] wrote:

Found the problem, Pixinsight is used to calibrate the images because of its ease of use (Batch PreProcessing).  Apparently, in the Flat Frame division, the output has been normalized to very small numbers.  I'm sure if I fix this, everything will work okay.  I apologize for the confusion.

Craig

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NAML