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IRCS

  Information for S25B applicants

  • The Nasmyth Beam Switcher (NBS) is planned to be installed in early S25B

    Due to the installation work of the Nasmyth Beam Switcher (NBS), all instruments except for IRD on the NsIR focus - including IRCS+AO188 - will be unavailable for 2-3 months from August.
    Please see the poster presentation in Subaru UM2023 for the design, performance, and status of the NBS. Possible impacts to IRCS observations are:

    • 10-20% increase of the background emission in K, L, M-band (to be confirmed)
    • Recalibration of polarization efficiency and instrument polarization are required
    • Large impacts on the imaging performance and distortion are not expected (to be confirmed)

  • Deformable mirror upgrade and AO188-modes

    The deformable mirror (DM) in Subaru Telescope's facility AO system (AO188) has been upgraded from a 188-element bimorph mirror to a 3228-actuator magnetic mirror. The following AO modes are available:

    • NGS-AO188 mode: Uses 188-element WFS + 3k-element DM
    • LGS-AO188 mode: Uses 188-element WFS + 3k-element DM
    • NIR WFS-AO3k mode: Uses NIR WFS + 3k-element DM

    The new AO3k-mode is available with the near-infrared wavefront sensor (NIR WFS) only. NGS/LGS observations still use the visible wavefront sensing, therefore, the performance remains unchanged. Please carefully read the IRCS + NIR WFS webpage and the AO3k + NIR WFS webpage for the available modes, sensitivities, and restrictions. Users planning to submit a proposal MUST contact Dr. Julien Lozi (lozi_at_naoj.org; the PI of the NIR WFS) and include him in the proposal as a Co-I.

    An increase in thermal background up to a factor of 2 in K- and L-bands was found after the new DM installation. The reason for this is currently under investigation.

  • LGS mode operating with TBAD (Shared-risk)

    The new laser guide star (LGS) system for AO188 is now operated with TBAD (Transponder Based Aircraft Detector) with a shared-risk policy. It is recommended that all proposals requesting LGS mode observation describe a backup plan with NGS mode. Please carefully read the AO188 webpage for additional information of the new laser system.

  • Other general informations

    Please see the general information of IRCS + AO188 before preparing your proposal.
    Also, please check the current status of IRCS.

Introduction

The Infrared Camera and Spectrograph (IRCS) is installed at the Infrared Nasmyth focus of Subaru Telescope and incorporates two 10242 ALADDIN III arrays which are sensitive from 0.9βˆ’5.6 ΞΌm. IRCS is designed to deliver diffraction limited images from 2 ΞΌm and up, as well as providing spectroscopy with grisms and a cross-dispersed echelle. The camera can also be used as a slit viewer for the echelle spectroscopy.

IRCS is always operated with Adaptive Optics (AO188) attached regardless of using adaptive optics, and relies on AO188 for guiding without a separate autoguider.

Imaging

The imaging mode of IRCS provides two plate scales, of 20 and 52 mas per pixel, producing fields of view of 21'' and 54'', respectively. The camera is equipped with a range of broad and narrow-band filters in its three filter wheels.

Grism spectroscopy

The camera section of IRCS provides a number of grisms which provide a low resolution (R = 100-2000) spectroscopic capability. Slit widths of 0.1-0.9'' are available.

Echelle spectroscopy

IRCS has a cross-dispersed echelle spectrograph, providing spectral resolution up to 20 000. The IRCS echelle provides a pixel scale of 55 mas along the slit and slit widths of 0.14'', 0.27'' (providing half the spectral resolution), or 0.54'' (providing one-quarter the spectral resolution). The camera-side detector is used as a slit viewer.

Note: The NH3 gas absorption cell, provided by Andreas Seifahrt (University of Chicago) in collaboration with colleagues at the University of Goettingen (Germany) and Lund Observatory (Sweden), will be decommissioned and is no longer available for high-precision radial velocity measurements.

Polarimetry

IRCS provides several linear polarimetry modes in 0.95βˆ’4.80 ΞΌm as 'Shared-Risk' mode. Imaging polarimetry is available for Y-, J-, H-, K(K')-, L'-, and M'-bands. Spectropolarimetry is available with zJH-, HK-, K-, and L-grisms in 52 mas mode only. Please be advised that circular polarimetry is not available. Users must contact Dr. Tamura (motohide.tamura_at_nao.ac.jp) and the primary support astronomer if they are planning to submit any kind of proposal with polarimetry mode observation.

Observation Preparation

Citations

When referring to IRCS in a paper, please use the following citation. The papers can be downloaded from links below.

Further information

Contacts

Questions regarding IRCS should be directed to the support astronomer (Vera Maria Passegger, vmpas__at__naoj.org).

Please note that all numbers on these pages are subject to change as the performance of IRCS is better determined.

updated on Jul 07 2025