All for a.......clear picture

ASTRONOMY

All for a.......clear picture

I is something that would make sky watchers feel ecstatic. Give them a telescope and you will soon spot them at a vantage point training their instruments skywards. But even a cloudless sky with its inky black backdrop and sparkling stars will not serve as an ideal environment for telescopes on earth to get a clear picture of the planets and comets, thanks to  atmospheric impact.

For decades, astronomers have been using a technique known as Adaptive Optics (AO) to measure and compensate for the degrading effects of the atmosphere in real time to partially recover the image quality. Using a bright ‘guide’ star in the sky very close to the target of observation as a reference to determine detrimental atmospheric effect, commonly used in earlier times, has proven to be difficult as it is not possible to locate a bright enough star at every target position on the sky.

As Prof A N Ramaprakash of Pune-based Inter-University Centre for Astronomy and Astrophysics (IUCAA) explained in a note, the challenge could be overcome with lasers. However, firing laser beacons into the atmosphere or Laser Guided Stars (LGS) also posed their own challenges.

“Even while using LGS, it is still necessary to have a natural guide star to detect and correct the lowest order distortions introduced by the atmosphere,” Ramaprakash explained in a note he had written recently about the phenomena.

“Further, because laser beacons travel only to a limited height in the atmosphere and back, often it becomes necessary to have a set of several laser beacons to determine the atmospheric distortions with sufficient accuracy. Thus in a nutshell, practical adaptive optics systems are expensive to build and incur large operational overheads.

Therefore, only a handful of large observatories can usually afford to have adaptive optics. Even then, only a relatively small fraction of the available observing time is set aside for AO mode operation due to the large operating overheads.”
With a view to achieve improved observation results out of small and medium size telescopes and observatories, IUCAA and California Institute of technology (CalTech) have been involved in building Robo-AO, a low-cost, autonomous, Rayleigh Laser Guide Star AO system and science instrument. “(This is) being commissioned on the fully robotic P60 telescope at Palomar Observatory,” Ramaprakash said.

“By providing high-angular-resolution and high-sensitivity visible and near-infrared science with unprecedented observing efficiency, Robo-AO enables exploration of science parameter spaces inaccessible to large diameter telescope AO systems. On sky, Robo-AO serves as an archetype for a new class of affordable AO system deployable on one-three meter telescopes, bringing the benefit of adaptive optics to the large community of moderate-diameter telescopes around the world.”

The CalTech website dedicated to the Robo-AO said the system, which would be the first robotic laser guide star adaptive optics, is currently mid-way through its on-sky commissioning and is expected to start a month-long science demonstration period late in 2011 at Palomar Observatory 60-inch telescope.

Scientists said that Robo-AO development has also been used to pioneer lower-cost technologies in AO system development, including the use of micro-electromechanical systems (MEMS) deformable mirrors, and industrial guide star lasers. Its computer architecture is both robust and functions out of a simple PC, allowing fully automated operation and reduced lifecycle cost , while its aggressive open-shutter efficiency sets a standard for future large telescope LGS AO systems.

Ushering in a new era
“These capabilities of Robo-AO will usher in an era of new observational possibilities for small and medium class telescopes,” Dr Ramaprakash observed in its notes.

“These studies would cover the Solar system, extra-solar planets, the Milky Way galaxy, other galaxies, active galactic nuclei etc.” The Robo-AO capability will be particularly powerful for carrying out large surveys, rapid characterization of transients and time domain astronomy throwing open the possibility of covering several scientific cases under each of the categories. 

In August, IUCAA hosted a workshop on Robo-AO, providing an opportunity for scientific and engineering teams working on the project to “exchange information and plan in detail the programme for P-60 demonstration.” 

Scientists from United States and India interested in exploiting the capabilities of the new system worked on creative observational ideas. Experts from both the countries also explored ways of having a long-term collaboration.

LIKE A GUIDING STAR
* For decades, astronomers have been using a technique known as Adaptive Optics (AO) to measure and compensate for the degrading effects of the atmosphere in real time to partially recover the image quality.

* Using a bright ‘guide’ star in the sky very close to the target of observation as a reference to determine detrimental atmospheric effect, commonly used in earlier times, has proven to be difficult as it is not possible to locate a bright enough star at every target position on the sky.

*Scientists said that Robo-AO development has also been used to pioneer lower-cost technologies in AO system development

* In August, IUCAA hosted a workshop on Robo-AO, providing an opportunity for scientific and engineering teams working on the project to “exchange information and plan in detail the programme for P-60 demonstration.” 

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