How to fit a single PSF (fits image format) on an image?

[dsluse]

I am a newbee wit SE++. So apologize if this is obvious.
I want to fit galaxy-like models on a Euclid VIS image. To simplify, let's say that I have a VIS image, a RMS file and a PSF fits image for the small region that I want to fit (100 x 100 pixels).
According to the documentation (https://astrorama.github.io/SourceXtractorPlusPlus/Input.html), it seems possible to use a constant PSF as a fits image for fitting a model on that image. However, this does not seem to work. As soon as I provide a fits image as PSF, it is identified as a stacked PSF ...
Specifically:
If I create a PSF with a single extension fits file (i.e. only PRIMARY), I get as an error message:
Error loading PSF file: FITS Error: Cannot read HDU in FITS file: No HDU with index 1
If I create a multi-extension PSF, with aprimary extension without data, and a first extension with my PSF data, then the code identifies that I have a stacked PSF and complains about missing extensions. If I fill those with the same PSF model, the code complains that the 'STMPSIZE' keyword is missing (which is correct but I do not need it).
Can someone help me? I could not find an example of a fit with a single image.

[mkuemmel]

Hi @dsluse,

this is kind of strange, since I know this should work and has been working. However also I was not able to find an example as well now when quickly browsing through my data.
I'll try to make one and get back here.

Martin

[mkuemmel]

Okay, maybe you need to provide the image extension in the python configuration file such as:

image_files.append(MeasurementImage(fits_file='jw02736-o001_t001_nircam_clear-f444w_i2d_cut.fits',
                                    weight_file='jw02736-o001_t001_nircam_clear-f444w_i2d_cut.fits',
                                    image_hdu=1, weight_hdu=4,
                                    weight_type='weight',
                                    psf_file='psfs/psf_f444w.fits',
                                    weight_absolute=0, weight_threshold=1.e-06))

Since you provide an explicit image extension via "image_hdu" SE++ assumes the PSF to be in the same extension in the PSF file. However if the PSF data is in a different extensions you need to provide that number via "psf_hdu":

image_files.append(MeasurementImage(fits_file='jw02736-o001_t001_nircam_clear-f444w_i2d_cut.fits',
                                    weight_file='jw02736-o001_t001_nircam_clear-f444w_i2d_cut.fits',
                                    image_hdu=1, weight_hdu=4,
                                    weight_type='weight',
                                    psf_file='psfs/psf_f444w.fits',psf_hdu=0,
                                    weight_absolute=0, weight_threshold=1.e-06))

With this python configuration I was able to run the ADASS example 01_basics with an image PSF in the 0th (primary) extension.

Hope this helps.

[dsluse]

Thank you so much! I did not know about the argument psf_hdu and implicit formatting assumptions (which make sense). That works well now.