Japanese astronomer Koichi Itagaki noticed a ‘new’ star in an image that he took on the 14th of Aug. How did he know it was new? The star wasn’t there the day before. It didn’t take long after the discovery notice was posted on the Central Bureau of Astronomical Telegrams (CBAT) web page that confirmation images started flowing in. The initial magnitude measurement put the star at 6.3 making it just under naked-eye visible. Over the next couple of days the nova continued to brighten and by the 16th it had peaked just a bit brighter than 4.5 making it naked-eye visible and a very easy binocular target.
Nova Del 2013
A nova is the result of a nuclear explosion on the surface of a white dwarf star. By itself, a white dwarf will not cause a nova. On the other hand, if it orbits another star and gets close enough, the white dwarf’s immense gravity may pull material off of the partner star. Over time that material, mostly hydrogen and helium, collects on the surface of the white dwarf. As the depth of the material increases so do pressures and temperatures. Eventually, the pressures and temperatures rise enough that fusion occurs and the explosion produces a very bright flash. Roughly 5 percent of the collected material fuses and the remaining collected material is blown back into space, leaving the white dwarf, for the most part, unharmed. From there the process starts over.
Sky&Telescope magazine reports the star is normally magnitude 17.0. That means the stars brightness increased about 100,000 times by the time it peaked. The star at magnitude 17.0 would be slightly dimmer than the reference star in the following image cropped from the full frame.
Nova Del 2013 (detail)
My image was taken on the 20th of Aug and by then the brightness had dropped a bit to 5.14. The image is a stack of thirty 5 second exposures. At 5 seconds the star was bright enough that it was blooming and I needed to drop the exposure to 0.01 seconds to make the brightness measurement.