NGC 7242 in Lacerta
July 2018 - Galaxy of the Month
In terms of deep sky observing the month of July in the UK is not dissimilar to June in terms of observing opportunities, really a time to wash the telescope mirrors and sort out any niggles before Astronomical dark returns in August.
My target for this month is one therefore rather more of hope than expectation and is the elliptical galaxy NGC 7242 in Lacerta.
First discovered, although not reported, by Augustine Voigt in 1862 using the Foucault 80-cm silver on glass reflector at Marseilles observatory it was actually first reported by Stephan in 1873 using the same telescope. Voigt’s observations were not actually published until 1987!
NGC 7242 is a cD galaxy at the centre of a small group of galaxies catalogued as WBL 679, which seems to contain between 4 and 9 galaxies depending on the source used. The other galaxies in the group are NGC 7240 (discovered by Stephan in 1873), IC 1441 (discovered by Bigourdan in 1889) and UGC 11963 (Also known as IC 1591 discovered by Barnard in 1888.)
Barnard actually found three new nebulae in this field that have been assigned the numbers IC 5191, IC 5192 and IC 5193. Unfortunately, he did not send positions to Dreyer just a drawing so it was unclear which was which and the designations were only tied down recently after historical work.
There is another IC object here as well, IC 5195 found by Bigourdan which turns out to be a galaxy very close to NGC 7242. Barnard did not see this so it will be tough to find and require high power and steady seeing.
For those of a historical bent the original logbooks from Lick Observatory have been digitised and are available at The Lick Observatory Historical Collections. If you are interested in Barnard’s original observation of this group it was made on the 5th Dec 1888 with the 12” refractor and the drawing is there.
The group is going to be challenging because NGC 7242 itself is only about magnitude 13.9 and the rest are fainter, it does show however what a good observer Barnard was in that he saw six objects in this field with the 12” refractor, even though he was observing from Mt Hamilton at 4265'.
There was a supernova in NGC 7242 in 2001 which was independently discovered by Mark Armstrong and Ron Arbour in the UK (SN 2001ib). As expected from a supernova occurring in an elliptical galaxy it was a type Ia.
Most of the galaxies in the group are elliptical or lenticular with the exception of IC 1441 which is spiral. Even IC 5191 which looks like a spiral is actually a lenticular. The group would appear to be about 300 million light years from us.
NGC 7240 is also catalogued as VV 1936, and IC 1952 as VV 1935, so they were thought to be disturbed systems. I suspect these may be bad classifications as I suspect that what they thought were other galaxies were actually stars near the galaxies. Even Barnard was not able to resolve the stars from the nebula when he observed IC 5192. Note that because of the vagaries of software authors some charting software may show the Barnard IC numbers and some may not.
Luginbuhl and Skiff (L&S) suggest NGC 7242 and NGC 7240 can be seen with a 25cm telescope, but I suspect this is from altitude and at least 30-cm will be required from the UK. Probably 45-50-cm will be required to see any of the others.
Owen Brazell - Galaxy Section Director