Arp 90

North is up (mirrored, exact). 0.53"/px [15' x 9.2' field]. FWHM = 3.9"

Arp 90 is the two interacting galaxies in the east.

The west of the image has a wierd distorted galaxy (?), with a similar redshift to the interacting pair. This means it could be a tidal fragment, or a gravitationally bound irregular galaxy... I really don't know.

Total exposure time: 314 * 30 seconds = 2.6 hours.

Used in stack: 276 * 30 seconds = 2.3 hours.

Telescope: C9.25 (230mm, f/10, fl=2300mm) + 0.63 Starizona reducer

Camera: IMX533 (16mm diagonal, square, color)

Processing:

1. Callibration (dark + flat)

2. Stacking (average w/ outlier rejection)

3. White balance and background subtraction (no gradient removal)

4. Asinh stretch (color preserving)

5. Rotation + crop

6. Tone curve

Taken during one night, with typical (ML-free) processing... except I rotated the image before cropping to align it to north. This should make it easier to cross reference.

Related:

• ned.ipac.caltech.edu/level5/Arp/Figures/big_arp90.jpeg: Arp's image.

• /astro/arp90/stack.fits.fz: Raw stacks.