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The TMT Infrared Guide Star Catalog

Overview of the TMT Infrared Guide Star Catalog (TMT-IRGSC)

To support the operations of TMT near-infrared instruments (e.g. IRIS), it is essential to provide all users with an access to a near-infrared guide stars catalog with limiting magnitude as faint as 22 mag in JVega i-band. Such a faint catalog does not presently exist but TMT has developed a method (based on the optical magnitude of stellar sources), which has been successfully validated and will lead to providing a near-IR catalog of guide stars with near-infrared magnitudes in the [16th-22nd] magnitude range in J, H and K bands.

Development of the TMT-IRGSC

As no catalog of stars exists that reaches the required faintness levels in the infrared, groups within the TMT partnership are actively developing methods to generate a suitable catalog. At present, the expected NIR magnitudes of stellar sources are computed from their optical magnitudes using stellar atmospheric models. The method has been verified for stars with temperatures above 3500K using test fields (at galactic latitudes of ~ 45 degrees) which have deep optical (CFHTLS g,r,i data) and NIR (UKIDSS DXS data) observations. Final developments of the method is taking place to improve the accuracy for stars with temperatures less than 3500K and improve the identification of galaxies from stars.

The full catalog will be computed using the Pan-STARRS data set, whose observations cover the entire northern sky of interest for TMT. The Pan-STARRS catalog reaches g-r-i-z-y band magnitudes sufficiently faint to support the generation of TMT's near-IR catalog catalog, reaching 22nd  J-band magnitudes with sufficient astrometric accuracy.

The development of the TMT-IRGSC is being led from the Indian Institute of Astrophysics by the India-TMT team.