Thirty Meter Telescope: Indian scientists develop tool for star catalogue

Bengaluru: A research team led by scientists at the Indian Institute of Astrophysics (IIA) has developed an online tool to create a catalogue of stars that can enable the upcoming Thirty Meter Telescope (TMT) in Hawaii to generate high-quality astronomical images. Findings from research anchored at the Bengaluru-based institute mark a significant contribution from India, a key partner, to the TMT project.

Ground-based telescopes, especially the ones with high light-collection capabilities like TMT, have to work around the challenge of atmospheric distortion to generate high-quality images. TMT is set to address these distortions with an adaptive optics system (AOS) that continuously senses and adjusts for changes in the atmosphere. An all-sky catalogue of near infrared (NIR) stars can significantly enhance the efficiency of this system.

Dr Sarang Shah from IIA said the AOS on TMT comes with a laser guide star facility that can project up to nine lasers into the sky to create artificial guide stars. “However, atmospheric turbulence affects these laser beams; so measuring atmospheric tip-tilt is uncertain. To correct these effects, the AOS requires feedback from three real stars, known as natural guide stars (NGS),” Shah, the lead researcher, said.

Simulations indicate that for the AOS to reach optimal performance, it requires at least three NGS within its field of view, each as bright as 22 magnitudes in the near-infrared J waveband. There is no comprehensive star catalogue that can provide NGS in all regions of the sky.

IIA researchers and their collaborators have developed an automated code that can be used as an online tool to create a catalogue of NIR stars. Smitha Subramanian, co-author and faculty at IIA, said this code can compute the expected near-infrared magnitudes of stellar sources identified in various optical sky surveys by using their optical magnitudes.

The team used multi-band optical photometry from the PAN-STARRS telescope in Hawaii to filter and identify the stars and predict their near-infrared magnitudes. Data from the UKIDSS survey of the United Kingdom Infrared Telescope were used to validate the approach which achieved over 85 per cent prediction accuracy.

The research was conducted at the IIA-headquartered India-TMT Coordination Centre. The findings were published in The Astronomical Journal.

TMT, planned on Mauna Kea in Hawaii, comes with a 30-meter diameter primary mirror made up of 492 precisely aligned individual segments. It is billed as one of the largest optical and NIR telescopes that can lead scientists to the makings of dark matter and facilitate closer studies of the evolution of galaxies.

The telescope is being jointly built by the California Institute of Technology, India’s Department of Science and Technology, the University of California, and institutions and observatories in Canada, China, and Japan.

IIA leads the Indian collaboration in the TMT project; the two other institutions involved in the project are the Inter-University Centre for Astronomy and Astrophysics, Pune, and the Aryabhatta Research Institute for Observational Sciences, Nainital.