Sorry for the delay, I had to put back the same setup together to test again with 1.9.1. And that did it. No more space character (see below).
Thanks for your support, Jasem.
Sébastien
FITS HEADER
SIMPLE = T / file does conform to FITS standard
BITPIX = 16 / number of bits per data pixel
NAXIS = 2 / number of data axes
NAXIS1 = 5184 / length of data axis 1
NAXIS2 = 3456 / length of data axis 2
EXTEND = T / FITS dataset may contain extensions
COMMENT FITS (Flexible Image Transport System) format is defined in 'Astronomy
COMMENT and Astrophysics', volume 376, page 359; bibcode: 2001A&A...376..359H
BZERO = 32768 / offset data range to that of unsigned short
BSCALE = 1 / default scaling factor
DATAMIN = 1751. / Minimum value
DATAMAX = 4523. / Maximum value
MIN1 = 1751. / Min Channel 1
MAX1 = 4523. / Max Channel 1
MEAN1 = 2048.74838785841 / Mean Channel 1
MEDIAN1 = 2049. / Median Channel 1
STDDEV1 = 14.9475417720419 / Standard Deviation Channel 1
ROWORDER= 'TOP-DOWN' / ROWORDER
INSTRUME= 'Canon DSLR EOS 650D' / INSTRUME
TELESCOP= 'Celestron AVX' / Celestron AVX
OBSERVER= 'Sebastien Seb@stro' / Sebastien Seb@stro
OBJECT = 'NGC_2238' / OBJECT
EXPTIME = 0.1 / Total Exposure Time (s)
CCD-TEMP= 23. / CCD Temperature (Celsius)
PIXSIZE1= 4.3 / Pixel Size 1 (microns)
PIXSIZE2= 4.3 / Pixel Size 2 (microns)
XBINNING= 1 / Binning factor in width
YBINNING= 1 / Binning factor in height
XPIXSZ = 4.3 / X binned pixel size in microns
YPIXSZ = 4.3 / Y binned pixel size in microns
FRAME = 'Light ' / FRAME
IMAGETYP= 'Light Frame' / IMAGETYP
XBAYROFF= 0 / X offset of Bayer array
YBAYROFF= 0 / Y offset of Bayer array
BAYERPAT= 'RGGB ' / Bayer color pattern
FOCALLEN= 2032. / Focal Length (mm)
APTDIA = 203.2 / Telescope diameter (mm)
SCALE = 0.4365601 / arcsecs per pixel
SITELAT = 46.91556 / Latitude of the imaging site in degrees
SITELONG= -71.55139 / Longitude of the imaging site in degrees
AIRMASS = 4.916825 / AIRMASS
OBJCTAZ = 264.9341 / Azimuth of center of image in Degrees
OBJCTALT= 11.55105 / Altitude of center of image in Degrees
OBJCTRA = '6 30 38.39' / Object J2000 RA in Hours
OBJCTDEC= '5 00 49.73' / Object J2000 DEC in Degrees
RA = 97.65996 / Object J2000 RA in Degrees
DEC = 5.013815 / Object J2000 DEC in Degrees
EQUINOX = 2000 / EQUINOX
DATE-OBS= '2021-08-29T17:59:01.192' / UTC start date of observation
COMMENT = ' ' / Generated by INDI
ISOSPEED= 800 / ISOSPEED
END = ' '