August 24, 2012
Astronomers Observe Type 1a Supernova Progenitor System
Lee Rannals for redOrbit.com - Your Universe Online
Previous evidence pointed to the merger of two white dwarf stars as the originators of other Type 1a supernovae. However, this new study led by Ben Dilday, a postdoctoral researcher in physics at UC Santa Barbara and at Las Cumbres Observatory Global Telescope Network (LCOGT), begs to differ.
The results are the first time astronomers have shown that at least some thermonuclear supernovae come from a recurrent nova.
The astronomers discovered supernova PTF 11kx in a galaxy 600 million light years away, which is actually pretty close in terms of astronomy.
The supernova was different, as its surrounding gas was moving too slowly to be from the supernova, but too fast to be a typical stellar wind.
Lars Bildsten, director of UCSB's Kavli Institute for Theoretical Physics, believed it was material shot out from a previous nova eruption. UCSB graduate student Kevin Moore performed calculations that proved Bildsten's hypothesis to be plausible, and would lead to gas moving at speeds seen in the observations. Also, the fact that the material moved at two different speeds added weight to the theory.
New observations showed that supernova ejecta was smashing into the interior shell of material.
"This was the most exciting supernova I've ever studied," Dilday said in a prepared statement. "For several months, almost every new observation showed something we'd never seen before."
Although a Type 1a supernova is considered rare, the team said that finding a Type 1a progenitor system like PTF 11kx is even more rare.
"You maybe find one of these systems in a sample of 1,000 Type 1a supernovae," said Peter Nugent, a senior scientist at the Lawrence Berkeley National Laboratory and a co-author on the paper.
The team used a robotic telescope mounted on the 48-inch Samuel Oschin Telescope at Palomar Observatory in southern California to scan the sky.
As observations were taken, the team detected the supernova and immediately followed up on the event with spectroscopy observations from the Shane telescope at the University of California's Lick Observatory.
The observations revealed a strong calcium signal in the gas and dust surrounding the supernova. The signal was so strong that they asked other astronomers to grab the Keck Telescope in Hawaii and have a look.
“We basically called up a fellow UC observer and interrupted their observations in order to get time critical spectra,” Nugent said.
In the months following the supernova, the team watched the calcium signal drop and then vanish. After 58 days the supernova went off, sending out a strong burst of calcium, indicating that the new supernova material had finally collided with the old material.
“Because we´ve looked at thousands of systems and PTF 11kx is the only one that we´ve found that looks exactly like this, we think it is probably a rare phenomenon. However, these systems could be somewhat more common, and nature is just hiding their signatures from us,” UC Berkeley postdoctoral researcher Jeffrey Silverman said.