Amateurs Discover U Scorpii's Eruption
On the morning of January 28th, two amateur astronomers discovered the much-awaited outburst of the recurrent nova U Scorpii, as told here yesterday. See that article for comparison-star charts and other information. Here is more about the two discoverers and how they did it.
When the first image appeared on her computer, a huge, overexposed star was blazing right in the middle of the field. Barbara didn’t believe her eyes. Was something wrong with her gear? Just yesterday she had measured U Scorpii at photoelectric V magnitude 18.2. She quickly took another much shorter exposure, double-checked the position, “and,” she says, “that’s when I started to get excited.”
“Back in December I had gotten an email from Brad Schaefer, because I had obtained the first image of U Sco as it came out from behind the Sun” into morning visibility, explains Barbara. That image had helped astronomers determine that U Sco had not blown up while it was out of sight in conjunction with the Sun. “They were sure that it hadn’t gone into outburst,” she says, “so he emailed me and thanked me, and said, keep submitting your data to AAVSO, but here’s my home phone number. Call me right away if you get something!”
As soon as Barb sent her discovery observation to AAVSO, she looked up Brad’s phone number and then thought to herself, “Let me take one more image just to be sure. I don’t want to call him this early and wake him up if I’m not sure.” At this point it was about 5:30 a.m. EST. So she took another image, calibrated and measured it, removed all doubt from her mind, and called Schaefer.
Meanwhile In Clermont, Florida, near Orlando, Shawn Dvorak was waking up to go to the gym. His telescope had been running automatically all night, taking data on several variable stars that he was monitoring for the AAVSO. Shawn had also begun checking U Sco again in January as it emerged from behind the Sun. U Sco was usually his last observation before dawn.
“I almost didn't observe it this morning since I was planning to go to the gym. I'm glad I did!” Shawn still wasn’t quite awake, and when the first CCD image came up, he thought to himself, “Whoa, I'm pointing at the wrong field, there's no star that bright here.” As Shawn describes it, “Barbara Harris spotted the outburst about an hour earlier but I hadn't heard about it yet, so it was quite a surprise to me when I saw this ‘new’ star”. Thinking the telescope had somehow missed the target, he re-imaged the field to convince himself. He then took a series of shorter exposures so the erupting 8th magnitude star wouldn’t be saturated on the CCD, and he kept taking them for the next 15 minutes as dawn quickly advanced.
About this time the phone rang in Baton Rouge, Louisiana, and, half-awake, Brad Schaefer lifted the phone to his ear. It was Barbara Harris telling him U Scorpii was in outburst. “He let out a scream and said 'Thank you, thank you! I’ll start notifying everyone right away',” Barb recalls.
Schaefer has studied the 10 known recurrent novae for years and has collected a large database of observations of all their known eruptions including three previously unknown outbursts of U Sco that he found by searching archives of photographic sky-patrol plates going back to 1900. Based on this work, Schaefer made a bold prediction that U Sco, which last blew up in 1999, would erupt at 2009.3 plus or minus one year. This became the basis for the AAVSO's intensive monitoring campaign, and it was widely publicized in Sky & Telescope and in his recent book-length paper, "Comprehensive Photometric Histories of All Known Recurrent Novae."
But as U Sco approached conjunction with the Sun in late 2009 and still hadn’t gone into outburst, nova watchers everywhere started to get anxious.
Each time it erupts, U Sco leaps to maximum and then fades by a magnitude within just one day. It is, in fact, the fastest known nova. Its behavior this time is staying true to form. Its fast action made responding to the first sign of an outburst, and pointing large ground- and space-based telescopes in time to cover the early parts of an eruption, a daunting task. At 6 a.m. EST Schaefer was on the phone and emailing people to notify observatories and space-telescope control centers that the moment had finally come.
At 6:15 a.m., Matthew Templeton, observing-campaign coordinator for the AAVSO, was stepping out of the shower when he noticed a voicemail on his phone. It was news of the outburst. Matt swung into action, and by 6:45 the first "AAVSO Special Notice" had been sent, alerting subscribers around the world to begin observing the long-anticipated eruption.
The hope among astronomers is that, with all the advance preparation and fast notice, this will be the most thoroughly studied nova explosion in history.
At 1:30 p.m., six hours after Barbara Harris had first detected the outburst, the orbiting Rossi X-Ray Timing Explorer (RXTE) and the INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory) satellites were observing U Sco in X-rays and gamma rays. Observations from Hawaii and New Zealand were coming in, and the international campaign to observe U Sco in outburst worldwide had begun in earnest. Over the next several months, astronomers will be monitoring it at nearly all wavelengths from radio to X-rays.
Arne Henden, director of the AAVSO, comments, "This again shows the real advantage of the worldwide distribution of amateur astronomers for detecting transient events like this. Harris and Dvorak could watch U Sco rise over the Atlantic, hours before professional astronomers in the western U.S. would have a chance. Then, because of the winter weather for most U.S. professional observatories, amateurs continued monitoring U Sco from New Zealand and Australia, catching the important first hours of the outburst."
Astronomers might have missed the beginning of the eruption if Shawn had decided to go to the gym, and if Barb’s dog hadn’t barked. “My dog has been getting cookies and anything he wants all day,” said Barb.
Follow the progress of the U Scorpii outburst on the AAVSO's news page devoted to the event. Anyone can view magnitude measurements in real time as they are submitted to the AAVSO website. For more information on U Scorpii and the AAVSO campaign, see the news page or contact Matthew Templeton, matthewt(AT)aavso(DOT)org (617-354-0484).
Mike Simonsen, one of the world's leading variable star observers, is development director for the American Association of Variable Star Observers in Cambridge, Mass., and heads its Cataclysmic Variable Section, Chart Team, and Mentor Program. He writes the astronomy and variable star blog Simostronomy and is a cast member of the Slacker Astronomy podcast..