V1280 Scorpii (Nova Scorpii 2007)
Published on Feb 18, 2007 at 6:27 am.
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Filed under observing, stars.
I recently got word that a nova recently discovered in Scorpius had become one of the brightest in several years. It was even reportedly naked eye bright! Novae tend to change quickly (they are variable stars, after all), so I really wanted to check it out first before posting anything. Naturally, these things can’t be in a convenient part of the sky. so, I set my alarm for 5am and got up to go look for the nova. I went outside, looked up, found Antares. From Antares, you just go down to ε Sco. The nova should be just up and to the left of that. Optimistic and enthusiastic reports from the web were suggesting that it might be 3rd magnitude this morning. That should be easy to spot. So, I looked. There was Antares. Then, down to the left to find epsilon, and … , oh. The neighbor’s house was in the way. No problem, go out in the front yard. I didn’t want to do that because many of my neighbors have these really bright lights on in the fronts of their houses all night. So, I found Antares, and epsilon, and saw no nova. OK, the sky was bright, but third magnitude should have been visible. I got binoculars, and there I found the nova. But, I put the magnitude at about 4.8 to 4.9 at 11:30 UT, based on comparisons to nearby stars. That is quite a bit dimmer than third magnitude, and is below the magnitude limit for these light polluted skies. I checked the latest data, and my estimate falls easily within the range that was being observed by others overnight. The nova seems to have peaked in brightness last evening, when it was still below the horizon from Texas. So, that means it will be even dimmer by the time that I meet my next class and can tell my intro astronomy students to go look for it. I doubt most of them would be able to find it. But, if you want to look for the nova, I’ve posted a finder chart from the American Association of Variable Star Observers (AAVSO) at the top of this post.
So, just what is a nova? The name comes from the Latin for “new” because most novae appear as new stars in a constellation (when viewed with the naked eye). The stars themselves are not new. Rather, they are originally stars that are too dim to be seen with the naked eye that suddenly brighten by a factor of a million or so, becoming visible for a while. Novae are part of binary star systems. One member of the system is a white dwarf, the end product of stellar evolution for a star like the Sun. Normally, textbooks portray a white dwarf as a stellar corpse, though that isn’t really accurate. They are very highly condensed objects. Normally, not much easily observable happens in a white dwarf.  But, in a binary system, if the other member of the system is close enough, it can dump mass onto the white dwarf. This often happens when the white dwarf’s companion begins to die, and it swells up. But, this mass being dumped onto the white dwarf is mostly hydrogen. The hydrogen accumulates on the surface of the white dwarf, compressed to very high density by the white dwarf’s gravity. Eventually, if enough hydrogen accumulates, then it begins to fuse to helium. Besides this fusion occuring on the surface of the white dwarf, instead of in the interior of a star, the normal checks and limits on the nuclear fusion don’t apply (at first), and so once it gets going, the fusion becomes a runaway process, and a massive burst of fusion results. It would be really tempting to call this an explosion (and it is often likened to a thermonuclear explosion in introductory textbooks, thought that isn’t quite accurate). But, little material is actually shed from the white dwarf. The accretion disk (the material falling onto the white dwarf from the companion star) is blown out into space, and it forms a pretty nebula eventually, but the white dwarf itself survives perfectly fine — able to repeat the process if the disk reforms and enough more material is deposited onto the white dwarf before the companion star itself collapses into its own white dwarf.
So, that is a nova: a runaway nuclear fusion reaction on the surface of a white dwarf. And, one is visible in Scorpius.  If you go look, and it has already faded, then you should at least look up and to the left of Antares. You can’t possibly miss Jupiter shining as the brightest thing in the sky at the moment.
-Astroprof
