Dwarf Nova V392 Persei Goes Big — It's Now Binocular Bright

By: Bob King May 1, 2018 14

In a rare move, a sleepy cataclysmic variable blows its top and suddenly becomes a nova.

Outrageous outburst — Although low in the sky at nightfall, there's still time to observe the nova outburst. V392 Per is located near the junction of Auriga, Perseus, and Camelopardalis about 5° west of bright Capella. A more detailed AAVSO chart is below.
*Stellarium*

The dwarf nova V392 Persei, which only gets as bright as magnitude 14 during outburst, appears to have undergone a rare nova outburst. The sudden and steep brightening was discovered photographically on April 29th by Yuji Nakamura of Japan, who recorded the star at magnitude 6.2. Spectra obtained shortly thereafter with the 2.4-meter Hiltner telescope on Kitt Peak confirm the explosion as a nova.

Had the Moon not brightened the sky, the outburst would have been visible with the naked eye from a dark site.

New to the crew — There's a new luminary in the neighborhood. The nova stands out plainly in this short time exposure taken from Somerset in the UK last night. North is at upper right.
***Will Gater***

As of this morning, May 1st, V392 Per has faded a magnitude to 7 and remains an easy catch in binoculars. There's no telling whether it will brighten further, continue to fade, or hit a standstill. One thing is certain: dwarf novae rarely explode as novae. This is something very special, and I encourage you to grab your binoculars for a look.

Rude Awakening — This AAVSO light curve compiled from observations made by amateur astronomers reveals that V392 Per normally shines at magnitude 15 (with occasional minor outbursts). This remained true until the end of April, when it skyrocketed to magnitude 6.2 (right).
*AAVSO*

Dwarf novae are binary stars where the more massive star, a white dwarf, robs matter from a closely-orbiting lower mass companion. As the material spins into an accretion disk around the dwarf, variations in its flow and temperature cause the disk to periodically heat up and brighten. Through a telescope, the star swells 2 to 6 magnitudes in just a day or two. Catching one on the rise after seeing it at minimum for weeks is one of the more exciting sights in amateur astronomy.Two of the most famous dwarf novae are U Geminorum in the winter sky and SS Cygni in the summer.

Two to tango — In a typical dwarf nova, a Sun-like star orbits a planet-sized but massive white dwarf. The white dwarf draws material from the orbiting star into a spinning accretion disk.
*NASA*

Only once in the history of dwarf novae observations has a star (V1213 Cen) transitioned to a nova. In a nova, material from the disk gets dumped onto the surface of the white dwarf, where it's compressed and heated to ignite in a much more powerful (and brighter) explosion. V392 Per shot up nearly 9 magnitudes and may brighten even more. Eruptions like this are predicted to recur on timescales of 10,000 to 1 million years.

Print out this AAVSO chart of V392 Persei. North is up, and the 5.7-magnitude star shown here (decimal omitted) is the same as the one marked on the wide-field map at the top of the page. Field of view here is about 7.5°. The nova is located at RA 04h 43′ 21″, Dec. +47° 21′ 26″.
*AAVSO*

You can stay in touch with the nova's daily behavior by going to the AAVSO website and typing in the star's name in the Pick a Star box. Then, select a link to either review recent observations, make a new light curve, or create a chart.

Use the accompanying AAVSO chart (and/or this more detailed chart) to find the star and estimate its brightness. Start at Epsilon (ε) Aurigae, the star at the apex of the skinny triangle that forms "The Kids" asterism near Capella, then star-hop to the northwest past the "star pair" on the map to the nova.

In both charts, you'll notice a 9.3 magnitude star close to and nearly due east of the nova. It's a nice comparison star to help in seeing the nova's changing brightness over the coming nights. Click to enlarge, download, and print each. North is up in both. Clear skies!

** Update: I estimated V392 Per at magnitude 8.3 on May 2.12 UT. Several people have asked me how far away the nova is. Using the star's parallax from the most recent GAIA data release, it's about 12,700 light years away.

Comments

Tom-Reiland

May 1, 2018 at 3:26 pm

Bob, I observed it Sunday night and estimated it at 6.5 magnitude. I tried it again last night, but I only got brief glimpses of it from my light polluted neighborhood, plus the Moon was a problem both nights. I "guessed" that it was close to 7.5 mag last night with my 10 X 5o binocs. John Bortle wrote in the AAVSO page that this was the first time he ever remembered seeing a Dwarf Nova become a classic Nova. This is why many of us love observational Astronomy. The surprises and unusual events.