MOIRCS field of view

Imaging mode

MOIRCS imaging field of view (FOV: 4' x 7') is sampled by two detectors, each of which has a 4' x 3.5' area. The long side of the FOV is the North-South direction on the sky for PA=0. Note that the raw FITS data from each detector is stored with the rotated layout by 90 degrees clockwise as shown in the middle panel of Figure 1. Therefore the Y-axis side on the raw FITS data will be the 4'-length side. The positive X-axis direction in the raw FITS data is to the North for PA=0, with the counterclockwise move of FOV on the sky being the positive move of the PA.

There is a ~30 arcsec-width area that is not used for imaging observation at a side of each detector (see Figure 1 middle). And also, there is a slight gap (a few arcseconds) between both channel images after mosaicking. The telescope pointing center just falls into the gap, so make sure to move the target to one of the channels if your target is a single compact object.

We note that the Hawaii-2RG detector has 4-pixel-wide "reference pixels" on each side. The sensitive pixel region is 2040 x 2040.

Figure 1: [Left] The field of view of MOIRCS at the Subaru Cassegrain focus. The cross symbol with the label "1" is the pointing center position (
Tokoku et al. 2002). We refer to Channels 1 and 2 the area each covered by detectors 1 and 2, respectively. [Middle] Vignetted and unused areas in the detectors of MOIRCS for imaging. Note that there is an additional smaller vignetted area at the bottom left of channel 1 for the data before July 2010 (see this figure). The crosses indicate the pointing position (center of the F.O.V.) of MOIRCS. [Right] The definition of the PA in OPE file. Note that the direction of the North in PA=0 corresponds to the positive X-axis direction in the RAW FITS image coordinate.




Spectroscopy mode

In spectroscopy mode, each the spatial and the dispersion direction of the spectra are each in y- and x-axis direction in the RAW image coordinate, respectively. Spectra are imaged also onto the ~30"-width "unused" area for the imaging mode. Please refer to the MOS page.


Figure 2: Spectra on the detectors for the spectroscopy mode. The crosses are the center of the FOV. of MOIRCS. Note that the RAW image format is rotated clockwise from the figure shown here (see the middle panel of Figure 1).


Updated 2022-07-28


Copyright © 2000-2022 Subaru Telescope, NAOJ. All rights reserved.