Design and development of an optical-fibre-based Integral Field Unit (IFU) on the IUCAA 2-m telescope

Abstract

An optical-fibre-based Integral Field Unit (IFU) has been developed for the Inter-University Centre for Astronomy and Astrophysics (IUCAA) Faint Object Spectrometer and Camera (IFOSC), the main back-end instrument on the IUCAA 2-m telescope at Girawali, Pune, India. This IFU enables IFOSC to perform two-dimensional spectroscopy of extended astronomical objects and is being used as one of the modes of IFOSC. Based on the concept of coupling the telescope focal plane with the spectrograph slit using a fibre bundle, the IFU (named the Fibre-based Integral Field Unit for IFOSC, hereafter FIFUI) uses 100 optical fibres, each associated with a tiny lenslet on its tip, to sample the incoming field of view spatially. In addition, FIFUI uses some coupling optics to realize this two-dimensional interface. FIFUI offers three different spatial sampling scales of 0.8, 1.0 and 1.2 arcsec fibre−1. It is optimized for the visible spectrum and for a field of view of ∼13 × 6 arcsec2 on the sky for the nominal 1-arcsec sampling mode. FIFUI was commissioned on the IUCAA 2-m telescope during 2010 February–March after a series of sky tests and science-verification observations and a data-analysis pipeline was developed to extract the spectra and reconstruct the sky maps. Here we report on the development of FIFUI, including its opto-mechanical design and commissioning observations.