Stephan's Quintet

North is right (mirrored). 0.53"/pixel [17'x12' field]. FWHM=3.7"

Ok, this is a crazy one. Five tightly spaced galaxies with visible tidal interactions:

However, looking at redshift data, the blue spiral on the left is ten times closer than all the other objects: at z=0.0026 instead of z=0.022. This means it's not actually a member of the group, even though it's in the same part of of the sky.

The dim barred spiral below the cluster (NGC 7320C) is at a redshift of z=0.022, making it a proper member of the group. This interloper takes the total back to five, so there's no need to rename the cluster.

Speaking of names, this cluster is also known as Hickson Compact Group 92 and as Arp 319.

There's a weird double galaxy: NGC 7318. It looks like a barred spiral galaxy, but has two nuclei, so it's the result of a recent galaxy collision.

The NGC 7318 pair is also interacting with NGC 7320C, a true barred spiral, although heavly distorted: one of it's arms is stetched into massive tidal plume extending 2 arcminutes below it.

Total exposure time: 501 * 30 seconds = 4.2 hours.

Used in stack: 437 * 30 seconds = 3.6 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)

This object rises very late, so even when staying up till four in the morning, I still had to combine data from three nights to get good image. Otherwise, it's fairly unremarkable: no special processing or filters.

Related:

• ned.ipac.caltech.edu/level5/Arp/Figures/big_arp319.jpeg: Arp's image • /astro/h92/stacked.fits.fz: Raw stacks.