Characterization of the commercial spectrograph system for astronomical observations: PIXIS 1300BX Camera and IsoPlane 320A Spectrograph

TL;DR

This work provides a comprehensive laboratory and on-sky evaluation of a commercial spectrograph system (PIXIS 1300BX + IsoPlane 320A) for the A-SPEC survey, detailing a gradient-correction approach for shutter-less CCD tests, a full photon-transfer analysis including gradient noise, and QE measurements showing high efficiency across the optical band. It demonstrates multi-object spectroscopy with $R$ in the range $600-2600$ when using different gratings, and validates on-sky performance at SAO with standard-star calibrations spanning $\sim390-900\mathrm{nm}$. The study also introduces robust methods for fiber-fed spectral tracing and Fourier-based resolution estimation, comparing to PSF+datasheet predictions, and provides open-source tools (EvalCCD, EvalSpec) to facilitate future instrument characterization. Overall, the PIXIS 1300BX with IsoPlane 320A constitutes a high-value, commissioning-ready platform for moderate-resolution MOS surveys, with practical guidelines for gradient handling, noise separation, and calibration applicable to larger, main-instrument deployments.

Abstract

We present the result from a comprehensive laboratory and on-sky characterization of the commercial spectrograph system consisting of a PIXIS 1300BX charge-coupled device (CCD) camera and an IsoPlane 320A spectrograph as part of the preparation of the forthcoming all-sky spectroscopic survey of nearby galaxies (A-SPEC). In the laboratory, we have quantified readout noise, dark current, gain, and full-well capacity via bias, dark, and photon transfer curve analysis at all acquisition modes. To do that, we have developed a gradient correction technique to address row-dependent signal gradients in the image, which are caused by the shutter-less condition of our CCD camera test setup. The technique successfully reproduces the values in the manufacturer specifications. We also have measured quantum efficiency exceeding 80% from 400--800 nm and $\gtrsim$ 90% between 450--750 nm, with sub-second persistence decay, making it ideal for rapid, multi-object spectroscopy. Using a set of diffraction gratings (150, 300, and 600 gr mm$^{-1}$), we have evaluated the spatial separability of multiple spectra and spectral resolution. We have conducted a test observation with this spectrograph system at the Seoul National University Astronomical Observatory (SAO) 1 m telescope and successfully demonstrated its capability of multi-object spectroscopy with moderate resolution of $R \approx 600 - 2600$. We release all Python codes for the test and recipes to facilitate further instrument evaluations.

Figures (27)

• Figure 1: Schematic of optical bench setup for testing CCD camera. (1) power supply, (2) arc lamp, (3) monochromator, (4) ND filter, (5) integrating sphere, (6) power meter, (7) CCD camera. The power meter is drawn along the same axis as the input port for clarity; in our actual setup, it is mounted on the integrating sphere at 90° to both the lamp input and the CCD illumination port.
• Figure 2: Attachment of PIXIS 1300BX onto IsoPlane 320A.
• Figure 3: Configuration for testing spectrograph. (1) camera (PIXIS 1300 BX), (2) spectrograph (IsoPlane 320A), (3) guide camera, (4) FIGU, (5) calibration source
• Figure 4: Schematic of the 7-core optical fiber bundle. Left panel depicts the slit end of the fiber, connected to the spectrograph. Right panel depicts the illumination end, connected to FIGU. The violet and black solid circles represent the individual fiber claddings and metal jackets, respectively.
• Figure 5: FIGU configuration for on-sky test (Config 1) and wavelength calibration (Config 2). FIGU mechanically switches the ray path by altering the mirror configuration with an electronic magnet.