The Copeland Septet (José Manuel López Arlandis)

The Copeland Septet

Ralph Copeland discovered the group of galaxies that today bears his name on February 9, 1874. The group is also known as Hickson 57, Arp 320 and VV 282. The septet is made up of faintly bright galaxies, with magnitudes between 13.6 and 15.2. The entire group measures 5' x 2', and is 400 million light-years away in the constellation Leo. Its members are NGC 3571, the lowest one, the central trio composed of NGC 3754 (above), NGC 3753 (center) and NGC 3750 (below), and a second trio at 2.4' above , composed of NGC 3748 (left), NGC 3754 (center) and NGC 3746 (right). To the south of NGC 3748 (below in the photo) there is an eighth galaxy, only 0.33' X 0.28' and magnitude 17.4, so it could not be seen by Copeland. However, Hickson did add it to his catalogue (#57). The proximity between galaxies produces deformations and tidal tails, most visible in NGC 3753. In addition, very weak bridges form between galaxies. The most prominent one forms between NGC 3754 and NGC3753. One of the spiral arms of NGC3754 heads south forming a tidal tail towards NGC 3753. I took LRGB and H shots on 7 nights in February and March, with a seeing between 4 and 6. On the clearest nights I got L shots (273 minutes). The RGB shots added no detail, and were used only for color composition. 260 minutes of HII shots did not improve color, noise, definition or obtain relevant details, so they were discarded. I tried to ensure that the contrast did not prevent us from appreciating the interactions between galaxies, preserving the bridges between them and the tidal tails. I also respected the north-south arrangement of the group, taking advantage of the arc of stars located to the west to balance the composition. The final crop is 11.8' x 8.02'. Lesson: if no one takes HII shots of a certain galaxy, it will be for a reason.

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