Star biometrics!

Subhra Priyadarshini

doi:10.1038/nindia.2009.150 Published online 5 June 2009

The National Optical Astronomy Observatory at Kitt Peak, Arizona.

They call it fingerprinting of stars.

Ranjan Gupta of the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune and Harinder Singh of University of Delhi, have been at it for 13 years now. They have compiled a mammoth digital spectral library of about 1273 stars along with US counterparts James Rose, Frank Valdes and Dave Bell1. And they aren't stopping at that – their next bet is to explore a French connection with Lyon University to go ahead and add more stars to this unique library.

In essence, it means the stargazers have analysed the spectrum of these stars. The spectrum provides information about the chemical composition and physical nature of the stars. Like fingerprints, no two spectra are the same.

The duo has been star-struck since 1997 collaborating with Rose from the University of Carolina, Chapel, and Valdes and Bell of National Optical Astronomy Observatory, Tucson. "We released the first data in 2003 and ever since the library has been the most quoted reference in recent conferences on stellar population studies," Gupta told Nature India.

All the spectra from this spectral library are available online at The astronomy community across the world has already started using it widely, he added.

Stars can be classified into seven broad types (O, B, A, F, G, K & M) with the O-type being the hottest and M-type the coolest. The spectra for the library were obtained by using the Coudé-Feed 0.9 meter telescope situated at Kitt Peak, Tucson, Arizona, USA and its spectrograph. The Coudé Feed is an auxiliary telescope (a 60" flat reflects the sky onto a 36" parabolic mirror, which directs a converging beam into the 2.1 m telescope Coudé optical train) that feeds a stellar image onto the slit of the Coudé spectrograph of the 2.1 m telescope.

Ranjan Gupta (left) and Harinder Singh.

Two spectrograph combinations were optimized for the red and blue portions of the spectra. For the blue the KPC10A grating (316 lines/mm) and blue corrector were used, while for the red the B&L181 grating (316 lines/mm) and red corrector were used.

"Altogether 6917 individual spectra have been obtained during the time period from 1995 June through 2003 April," Gupta said. The project involved many undergraduate and graduate students at the University of North Carolina.

Now, Gupta and Singh are trying to re-calibrate the first release of the library in 2003 with help from ELODIE, a French library released later in 2005. Singh is at the Lyon University in France to take the project ahead. "Re-calibrating would mean the spectra will be more calibrated to provide more information," Gupta said.

On how they plan to add more stars to their impressive library, he said they are looking at making more observations 'probably from the same telescope'.


  1. Valdes, F. et al. The Indo-US Library of Coudé Feed Stellar Spectra. Astrophys. J. Suppl. S. 152, 251-259 (2004) | Article |