Characterization of the ASTRONIRCAM Spectral Mode
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acterization of the ASTRONIRCAM Spectral Mode S. G. Zheltoukhov1 , A. M. Tatarnikov1* , and N. I. Shatsky1 1
Sternberg Astronomical Institute, Moscow State University (SAI MSU), Universitetskii pr. 13, Moscow, 119992 Russia Received December 2, 2019; revised December 2, 2019; accepted December 5, 2019
Abstract—The algorithm for the reduction of spectroscopic observations with the ASTRONIRCAM camera-spectrograph installed at the 2.5-m telescope of the Sternberg Astronomical Institute of the Moscow State University is described. The instrument allows spectra of astronomical objects with long (280 ) and short (10 ) slits to be taken in the wavelength range from 1 to 2.5 μm. The measured resolution reaches R = 1270 for a 0 . 9 slit; the light efficiency of the system changes from 6 to 14% in the working wavelength range in the long-slit mode and from 1 to 2% in the cross-dispersion mode. The transmission is limited by the quality of the grisms used. We have estimated the fraction of scattered light and studied the mechanical flexures and temperature drifts of the structure. DOI: 10.1134/S106377372002005X Keywords: infrared range: general questions, instruments: spectrographs, methods: spectroscopy, methods: data reduction.
INTRODUCTION ASTRONIRCAM (ASTROnomical NearInfraRed CAMera) is an infrared instrument installed at the 2.5-m telescope of the Caucasus Mountain Observatory of the Sternberg Astronomical Institute of the Moscow State University (SAI MSU) (Sadovnichii and Cherepashchuk 2015). The camera operates in the wavelength range from 1 to 2.5 μm in two modes: photometric (direct sky imaging in the JHK filters of the MKO photometric system and several narrowband filters) and spectral (taking low-resolution spectra with a long or short slit). The design of the camera, its optical layout, and the detector and recording system parameters are described in Nadjip et al. (2017). The main element of the camera is a HAWAII2RG 2048 × 2048 HgCdTe array with a 18-μm pixel size. The detector quantum efficiency in the working wavelength range is ∼94%, the readout noise is 12e− , and the pixel capacity is ∼120 000e− . The image on the detector is formed by an optical system consisting of an entrance window, a focal turret with an entrance diaphragm and a set of ten spectral slits, a collimator, two filter turrets, and a camera lens. Three diagonal mirrors “folding” the optical system are used to reduce the volume occupied by the camera. Diaphragms are installed between the optical elements to reduce the amount of scattered light. All *
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elements are in a cryostat on a liquid-nitrogen-cooled optical bench. The signal is digitized and recorded by an ARC Gen III controller (Leach and Low 2000). A calibration unit containing an incandescent lamp and an argon lamp with a line spectrum is used for calibration in the spectral mode. The camera operates in the pixel-by-pixel nondestructive readout mode. This allows the data to be repeatedly read out from the detector during signal accumulation, but places a c
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