Development of Spectrograph in FUV region for a possible ISRO flight

Abstract

The FUV (900-1800 Å) is the richest part of the spectrum in terms of emission lines – O VI (1032/1038 Å) and C IV (1548/1550 Å) from hot gas, C III (977 Å) and N III (1750 Å) from warm gas, and the Lyman and Werner bands of molecular hydrogen from cold gas. We plan a proposal-driven mission of emission line spectroscopy of extended sources in the FUV with a spectral resolution, sufficient to separate the O VI doublet and to resolve the molecular hydrogen bands. Our long-slit spectrograph will take simultaneous spectra of multiple locations to track different phases of the gas in extended regions from nebulae to galaxy clusters. The proposed spectral range necessitates a windowless detector for which we have begun a collaboration with the Institute of Astronomy and Astrophysics (IAAT) at the University of Tubingen. They will provide a 40 mm X 40 mm GaN detector with a peak efficiency of 70%. The name of this mission has hence been chosen to be Tubingen-IIA Nebular Investigator (TINI). Here, I present two designs for the telescope system viz., the off-axis and on-axis design.