SING: an Instrument for spectroscopic investigation of nebulae gas

One of the most exciting parts of the astrophysical spectrum is the ultraviolet (900 – 3000 Å),

with a greater density of absorption and emission lines than any other part of the electromagnetic

spectrum. Understanding the astrophysics – the physical conditions, temperatures, densities, and

radiation fields – requires UV spectra of the atomic emission lines which will complement the imaging

observations. We propose here to build an imaging spectrograph (SING) to track emission lines over

the entire spatial extent of a nebula.

Our payload is a 6U spectrograph designed for operation in the spectral range between 1300 -

2300 Å (NUV). The field of view is 0.25°×0.24` with a spatial resolution of 10􀀅and a spectral

resolution of 1 Å (R ~ 2000) at the central wavelength. Imaging surveys (GALEX and UVIT) have

mapped the sky with high spatial resolution but without the spectral diagnostics necessary to probe

local physical conditions. Our long-slit spectrograph (SING) will take simultaneous spectra of

multiple locations to track different phases of the gas in extended regions from nebulae to galaxy

clusters. The spectrograph will be assembled, calibrated and tested at MGKML located at the CREST

campus of Indian Institute of Astrophysics. This facility was used for the integration, characterization

and calibration of the UVIT instrument on board ASTROSAT (Kumar et al., 2012, Proc. SPIE, 8443,

84431N). Through this mission, we will probe physical conditions of the interstellar medium over a

number of different phases, from the cold molecular clouds to the hot halo.