MOIRCS Spectroscopy Mode: Information

How To Make an OPE File for Spectroscopy Observation

Please read the OPE file manual for Imaging first. Then go to the following documents.
    Manual and sample OPE files (for spetroscopic observation):
  • Description of an OPE file: Guide to MOS Observation with MOIRCS [Under Construction]
  • Sample OPE file for spectroscopy observation: template_spec_20180622.ope (Caution!! UNIX or Linux only-- Last update: 2018-06-22)
      The appearance may become curious under Windows browser -- it looks as if there is no line break. It should look fine in unix editor.
  • The list of the current filter and grism configuration alias can be found here (Last update: 2016-11-15)
  • Preparing the Observing Time Table beforehand would be useful for better understanding of your plan among the observing staff. It is advised to try filling it and send back to the Support Staff by a few days before your observing run.
  • Recent dome flat setting log can be found here (internal only).

Flat Fielding/Comparison

We usually use the bare aluminum backsurface of the top screen which is illuminated by domelamp as the spectroscopic dome-flat source. Dome flat data will be taken before and after the observation. Usually we do not take the dome data with the dome light off. Instead the dark data under the same exposure may be used for subtraction. If you need the additional data, like the lamp-off data too, please explicitly request it before the observation.

There is also the other light source for flatfielding of spectroscopic data. The halogen lamp on the calibration probe may work as a light source, though it only illuminate a part of the field of view. We take the flat data at least on 5 cal-probe position in order to illuminate the whole MOS area.

The ThAr comparison lamp is available for the wavelength calibration. We take the comparison data with scanning the entire MOS field of view (exposures at the 4-5 position). As there are much OH night sky lines in NIR window so we may not need to use the comparison data for wavelength calibration. But there are some wavelength region where the OH line is relatively poor (e.g. red side of K window). The night lines may also be blended in the low-dispersion grism data under wider slit width in zY window. Therefore we take the ThAr data for the R500 observation. For more detail, see the Wavelength calibration page.

Autoguider Issue

As the MOIRCS FOV occupies a large fraction of the Cassegrain field of view, the area we can choose the Auto Guider (AG) star without vignetting is fairly limited. A star with visual magnitude of 9 to 16 in R-band (650 nm) is necessary as the AG star. Such bright stars are relatively sparse in high Galactic latitude, and sometimes it is difficult to find such a star in the non-vignetting area. If the AG vignetting occurs in the imaging data, it would pretty much complicates the data reduction. In MOS mode you may lose the data from some slitlets by vignetting. To avoid such troubles, all MOS or NB imaging observers shoud check the availability of an AG star in the "safe" area before the observation to avoid the possible loss of important targets.

The diameter of the shadow by the Autoguider has 72 arcseconds. You can choose any bright star within 4.6'-radius area from the FOV center in the Cassegrain focal area (See figure below). But if you want to avoid vignetting by the shadow of the AG probe, the area you can choose is limited to at least 72" away from the edge of the MOIRCS f.o.v. or any of your slitlets. The blue-colored area in the bottom figure indcates the "safe" region, where the shadow of the AG probe will never cause vignetting on the area you may put slitlets. For imaging, only the left- and the rignt-side of the blue areas can be used for the AG.

The ds9 region file for the AG availability check is available here . It is prepared for the DSS image only.

Another issue is the affection of the Moon, cloud, or twilight onto the AG. As is written in the Imaging Information page, the AG may not work properly if the Moon is close to your target less than 20 degrees. If cirrus/clouds come into the field of view during the observation, the autoguider may quickly lose the star, which will lead the loss of the MOS alignment. As the MOS acquisition takes long time, it is not recommended to push the spectroscopic observation under cloudy condition. The twilight in morning time will also change the background level very quickly and the AG will become unavailable. Usually we ask to take preimaging data during the morning time.

Troubled Data Information

The list below is not complete. The use of any archived data should be with enough caution. The date is in HST.

  • Feb 2017 to March 2018
      The time-related FITS header keywords (HST*, UT*, MJD) are still in problem. HST-END, UT-END, MJD-END, HST, UT, MJD are totally wrong. "HST" is approximately "HST-STR" + ((N-1)*NDR)/2 + 5. HST-END is approximately HST-STR" + (N-1)*NDR + 5. It may still have the uncertainty of +-30 sec. We are sorry about this.

  • 11 August, 2017
      There are no channel-2 data due to the hardware trouble (MCSA00241250 -- MCSA00241452, except 241254 and 241256).

  • July 2016 to Feb 2017
      The time-related FITS header keywords (HST*, UT*, proably MJD too) are still inaccurate. Sometimes values are inconsistent with each other. Error ranges from a few minutest to sometimes a few 10s minutes, depending on the exposure parameter.

  • June-July, 2016
      The time-related FITS header keywords (HST*, UT*, proably MJD too) are inaccurate by 20-40 seconds.

Before the MOIRCS Upgrade

MOS Spectroscopic Data Reduction Software

Note that the program and the document were prepared for the OLD MOIRCS before 2016.

If you are developing your own software and want to put the link to your software website here, please contact to the SA. We greatly appreciate your contribution.

Please note that all data on these pages are subject to change. Any questions/comments should be directed to the SA (Ichi Tanaka: ichi [at] ; change " [at] " to @).

Updated 2018-06-22

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