Two Novae in Scorpius

Looking south-southeast before dawn's first light
Jupiter, Antares, and the familiar constellation pattern of Scorpius guide the way to Nova Scorpii 2007 Number 1. This is the view above the south-southeast horizon just before dawn at latitude 40° north. Stars are plotted to magnitude 5.5.
Sky & Telescope diagram.

Nova Scorpii 2007 wasn't a big deal when two Japanese nova hunters, Yuji Nakamura and Yukio Sakurai, independently discovered it at 9th magnitude on February 4th. But it brightened and brightened, peaking at magnitude 3.8 on Friday the 16th. As February the 27th it was down to about 5.4 and by March 1st it was about 6.0, but then it started dropping fast: to 10th magnitude as of March 6th.

Scorpius is up in the south-southeast before the first light of dawn. You can't miss brilliant Jupiter shining near it, as shown here. The nova (also named V1280 Scorpii) is 9° southeast of Antares and a couple degrees northeast of Epsilon Scorpii; at declination –32° 21', right ascension 16h 57.7m.

Be out and looking just as morning twilight begins at your site. To find when this occurs, make sure you've entered your location and correct time zone into our online almanac. Bundle up, and make it an early-morning adventure!

Nova from Iran
From the Varzaneh Desert at Isfahan, Iran, Mohammad Rahimi took this picture on Nova Scorpii #1's date of peak brightness, Febuary 16th. He used a Canon 350D digital camera set for ISO 1600 and a 30-second exposure at f/ 5.6. Click image for larger view.

Here are the most recent observations submitted to the American Association of Variable Star Observers (AAVSO), which has also put up a comparison-star chart

And a second nova right nearby!

On February 21st came surprise news: another nova had gone off in Scorpius, a mere 3° south of the first!

Yuji Nakamura, codiscoverer of the first one, found the new object at magnitude 9.3 on two CCD images taken at February 19.86 Universal Time. A day later, at February 20.85 UT, K. Itagaki confirmed the new star; it's at right ascension 16h 56m 59s, declination –35° 21.8' (2000.0 coordinates). He judged it to be magnitude 8.8. Nova Scorpii 2007 #2 (also named V1281 Sco) was also independently discovered by Hideo Nishimura on the morning of the 20th Japanese time; he called it magnitude 9.2. See the AAVSO Alert Notice.

No brightening was in store for this one, however. As of March 7th it was down to magnitude 11. It is probably much farther away than the first nova; its spectrum shows sharp absorption lines due to interstellar gas, a sign that its light is probably dimmed a great deal by intervening interstellar gas and dust.

So, what is a nova?

A classical nova occurs when fresh hydrogen from a donor star builds up on the surface of a hot white dwarf. Eventually the bottom of the hydrogen layer becomes hot and dense enough to ignite the hydrogen-fusion reaction, and the entire layer enshrouding the white dwarf suddenly explodes as a hydrogen bomb.

Scorpius with new addition
Nova Scorpii #1 was at its peak brightness around magnitude 3.9 — and still very white — on the morning of February 16, 2007, when Sky & Telescope contributing editor Gary Seronik took this picture from Costa Rica. The brightest objects are Jupiter and Antares. Click on image for larger view.
Gary Seronik.

In its first days a nova is essentially an expanding, opaque photosphere, like the surface of a hot star growing larger. Eventually the outward-flying layer thins, cools, reddens, and becomes transparent.

The change was evident in the nova's evolving spectrum. On February 20th, Italian astronomers at the Padova Astronomical Observatory reported (in IAU Electronic Telegram No. 852) that "the nova has concluded the pre-maximum phase, characterized by a pure-absorption spectrum. . . . The spectrum is now completely dominated by a rich forest of strong permitted emission lines that display deep P-Cyg profiles," a shape indicating that the light was coming from an expanding shell of gas that was at least semitransparent. Measurement of the spectral lines' profile showed that the shell was expanding at a speed of about 600 kilometers per second.