Unique sky survey brings new objects into focus

BY DR EMILY BALDWIN

ASTRONOMY NOW

Posted: 16 June, 2009

The Palomar Transient Factory (PTF) has begun returning images that will be used to detect unprecedented numbers of supernovae in distant galaxies, variable stars in our own Galaxy and possible new near-Earth asteroids.

The Samuel Oschin Telescope at Palomar Observatory Image: Palomar Observatory/ Caltech.

The innovative PTF combines the power of a wide-field telescope, a high-resolution camera and high-performance networking and computing with rapid follow-up by telescopes around the globe, to open a new era of discovery for astronomers. First light was achieved in December last year and already the survey has detected 40 supernovae. It is currently gearing up to switch to a robotic mode of operation that will allow objects to be discovered without the need for human intervention.

The PTF operates using an automated wide-angle 48-inch Samuel Oschin Telescope at Caltech’s Palomar Observatory, which scans the skies using a 100-megapixel camera. More than 100 gigabytes of data is acquired every night, which is beamed off the mountain via the High Performance Wireless Research and Education Network and then to the Lawrence Berkeley National Laboratory (LBNL)’s National Energy Scientific Computing Center. There, computers analyse the data and compare it to images previously obtained at Palomar in order to identify sources that vary in brightness or position. Once detected, the system sends the object’s coordinates and instructions for follow-up observations using the Palomar 60-inch telescope and other instruments.

The Andromeda galaxy, as seen with the new PTF camera on the Samuel Oschin Telescope at Palomar Observatory. This image covers 3 square degrees of sky, more than 15 times the size of the full moon. Image: Nugent & Poznanski (LBNL), PTF collaboration.

If follow-up observations indicate that something interesting is occurring, the system will generate a list of priority targets for an astronomer to look at. At this stage, the astronomer will perform detailed observations of the object in question, using telescopes such as Palomar’s 200-inch Hale Telescope, a Keck Telescope in Hawaii, or other partner telescopes around the world.

“By looking at the sky in a new way, we are ushering in a new era of astronomical discovery,” says PTF principal investigator Shrinivas Kulkarni, MacArthur Professor of Astronomy and Planetary Science at Caltech and director of the Caltech Optical Observatories. “Nimble automated telescopes and impressive computing power make this possible.”

The PTF will search for a variety of transient sources with timescales ranging from minutes to months, giving astronomers one of their deepest and most comprehensive explorations of the Universe in the time domain. “No one has looked on these timescales with this sensitivity before,” says Nicholas Law of Caltech, the project scientist for PTF. “It’s entirely possible that we will find new astronomical objects never before seen by humans.”

PTF astronomers uncovered supernova SN2009av-1 in the act of exploding. At left, the image was created by layering observations taken by the PTF camera from February 23-27. Second from left is the image captured by the PTF camera on February 28. Next, using the NERSC pipeline to digitally subtract the earlier image from the new one, scientists exposed this cosmic transient, a supernova. At right, subtracting the previous images from one taken March 2 showed the source getting brighter. Image: Palomar Transient Factory/Dovi Poznanski, Berkeley Lab.

The PTF will look for anything that shows change, meaning it will uncover a wide variety of objects from exploding stars – supernovae – to near-Earth asteroids and possible planets around other stars. So far the survey has been on the look out for so-called Type Ia supernovae, which are formed from the explosion of a class of dead star known as a white dwarf. Identifying these dramatic explosions can help establish distances across the Universe, allowing astronomers to build models on the origin and evolution of our Universe. To date, the survey has uncovered 32 Type Ia supernovae, eight Type II supernovae, and four cataclysmic variable stars, as well as several intriguing objects with characteristics that do not appear to exactly match any other objects seen before. PTF astronomers are eagerly watching these objects to see how they change, and to determine what they might be.

The quality of data and speed at which it is being acquired has impressed astronomers working on the project. On one recent night, PTF patrolled a section of the sky about five times the size of the Big Dipper and found 11 new objects. “Today I found five new supernovae before breakfast,” says Caltech’s Robert Quimby, a postdoctoral scholar and leader of the PTF software team. “In the previous survey I worked on, I found 30 in two years.”

The Palomar Transient Factory is a collaboration of scientists and engineers from institutions around the world, including the California Institute of Technology (Caltech); the University of California, Berkeley, and the Lawrence Berkeley National Laboratory (LBNL); Columbia University; Las Cumbres Observatory; the Weizmann Institute of Science in Israel; and Oxford University.