NIR Spectrograph

Table 43 SOXS NIR Spectrograph/Array Characteristics

Parameter

Value

Detector

Teledyne H2RG

Pixel-Size

18 \(\mu\)m

Array-Size

2048 \(\times\) 2048 px

Array-Scale

0.25 arcsec/px

Read noise (RMS)

Double correlated: \(< 20 e^{-}\)
16 Fowler pairs \(< 7 e^{-}\)

Dark current @ 45K

\(< 0.005 {e^{-}/s/px}\)

Resolution \((R)\)

\(\simeq\) 5000 (1 arcsec slit)

Wavelength Range

800-2000 nm

Slit Widths

0.5, 1.0, 1.5, 5.0 arcsec

Slit Height

12 arcsec

Grating Blaze Angle

44\(\degree\)

Detector Operating Temp

45K

Spectrograph Operating Temp

140K

Orders

15

Penrays

Ar-Ne-Xe-Hg

As described in Vitali et al. [VAC18], the SOXS NIR spectrograph is a near-infrared, cross-dispersed echelle spectrograph, with \(R=5000\) (for a one-arcsec slit). It employs ‘4C’ (Collimator Correction of Camera Chromatism) to cover a wavelength range from 800 to 2050nm over 15 orders. This wavelength range provides a 50nm overlap with the SOXS UV-VIS arm for cross-calibration.

As with the UV-VIS, four slits options (\(0.5\), \(1\), \(1.5\) and \(5\) arcsec) are provided, which will project a FWHM for an unresolved spectral line onto four detector pixels. A slit height of 12 arcsecs is employed. The detector is a \(2k\times2k\) 18-micron pixel Teledyne H2RG TM array. As atmosphere dispersion is less severe in the NIR regime, unlike the UV-VIS arm, the NIR arm does include an atmosphere dispersion corrector (ADC). The SOXS NIR spectral arm achieves a resolution \(R > 6000\), for a 1 arcsec slit, across all dispersion orders (as seen in Fig. 27).

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Fig. 25 A SOXS flat-lamp calibration image.

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Fig. 26 The SOXS NIR spectral format, Figure 5 of Vitali et al. [VAC18]. The inter-order gap is always >10px.

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Fig. 27 The spectral resolution of the SOXS NIR spectral arm. This plot is generated during the execution of the soxs_spatial_solution recipe. For selected lines resulting from Ar-Ne-Hg-Xe penray lamps, imaged through a 1 arcsec slit, the FWHM is measured at nine locations along the length of the slit. In the top panel, the measured FWHMs are displayed with respect to the wavelengths of the lines. The different coloured circles represent the unique dispersion orders of the spectrograph, and the black circles (with error bars) represent the mean FWHM for the order (and standard deviation). In the bottom panel, the measured pixel scale from the dispersion solution is used to convert FWHM to spectra resolution \(R\). For a 1 arcsec slit, the SOXS NIR detector achieves a resolution \(R > 6000\) across all orders. The wavelengths of the arc-lines detected range from \(795-1995 \mathrm{nm}\).

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Fig. 28 The NIR slit-height as measured between the edges of each dispersion order on an d NIR through-slit flat frame. Each colour in the plot represents an individual dispersion order. The slit height is measured at \(\sim\)12 arcsecs across all orders, as expected.

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Fig. 29 The NIR inter-order gaps as measured between the edges of adjacent dispersion orders on an NIR through-slit flat frame. Each colour in the plot represents an individual dispersion order. The minimum inter-order gap is \(\sim\)6 arcsecs.