AT2019zhd , Extragalactic Nova in M31
This nova in the Andromeda galaxy was detected by Zwicky Transient Facility on 14 Dec 2019. On discovery, its apparent visual magnitude, Vmag, was 14.9, and has since declined to Vmag = 15.6 on my photograph taken on 14 Feb 2020. Using the Distance Modulus equation, where the distance of the Andromeda galaxy, D, is 778,000 parsecs, we can calculate the absolute visual magnitude, Vabs, of the nova as follows:
Vmag - Vabs = 5 log ( D / 10 )
Vabs = Vmag - 5 log ( D / 10 ) = 14.9 - 5 log (77800)
Vabs = -9.55
From the distance of 10 parsecs, the nova's apparent magnitude on discovery would have been -9.55, or about 115 times brighter than the apparent magnitude of Venus at its brightest. Compare that to the mean maximum absolute magnitude of a type Ia supernova which is -19.5 +/-1.5, or nearly 10,000 times more luminous.
The nova is located in the SW spiral arms of the Andromeda galaxy, near the prominent OB Association NGC 206, which is an immense cluster of young, large, and very bright spectral type O and B stars.
The attached photograph is a stack of 2 x 120 sec unprocessed exposures taken with a Planewave CDK 610 x 4000mm telescope. The animation compares the current image with DSS2 sky survey plates taken at Palomar about 60 years ago. In addition to the nova, it shows several high proper motion stars belonging to our galaxy.