MOIRCS Information for Spectroscopy Mode

How To Make an OPE File for Spectroscopy Observation

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_012508.ope (Caution!! UNIX or Linux only! Assuming NDUM=2 mode.)
  
  The appearance will become curious under Windows browser -- it looks as if there is no line break. It should look fine in unix editor.
  

Flat Fielding/Comparison

We usually use the "topscreen-illuminated" dome flats for spectroscopy. You can also use the calibration lamp ("cal-lamp": slit-illumination halogen lamp) for flat fielding of the MOS data. The cal-lamp scans the entire field of view of MOIRCS just after the target observation without changing the position of the telescope. It will take about 7-15 minutes to scan the entire area of the FOV to produce a set of frames for flat fielding. This "cal-lamp" flat is sometimes difficult to use for the actual data reduction. One reason is because its spectral shape is strongly skewed to longer wavelengths and difficult to achieve good count across the entire spectra. The other reason is because the flatness across the spatial direction is poor. The repeatability of mask position is good, as we go to zenith during the mask move. Mask will anyway moves due to the gravitational flexure. Even if we use the calflat, the gain in the accuracy is expected to be not much.

In usual observation we use the backsurface of the top screen illuminated by domelamp as the dome flat source. Dome flat data will be taken before and after the observation. Usually we just take light-on dome data as well as darks under the same exposure. If you need the additional lamp-off data also, please explicitly request it before the observation.

Th-Ar comparison lamp is available for the wavelength calibration. We take the comparison data by scanning the entire MOS field of view (5 exposure is at least necessary). Usually, in NIR window there are much OH night sky lines so we do not need to take comparison. But there are some wavelength region where the OH line is relatively poor (e.g. red side of K window). We can take comparison on request.

Autoguider Issue

As the MOIRCS FOV is relatively large within the Cassegrain focal area, the position we can choose an Autoguider star without vignetting is very limited. A star with visual magnitude of 8 to 15 magnitudes are necessary for Autoguider, but sometimes it is difficult to find such star without vignetting. We may ask about putting AG probe inside the MOIRCS FOV. In this case, you may have to decide which slits you can accept to be abondoned by vignetting. Quick on-site decisition may be necessary. Observers who plan to go to high Galactic latitude shoud prepare enough for the quick on-site decision.

The diameter of the shadow by the Autoguider has 72 arcseconds. We can choose a star for AG from the circular region with 4.6 arcminutes radius from the FOV center (Schematic view is available here). If you can consider about the existence of the good AG star before you decide the coordinates of the MOS preimage, it will be the best to avoid such problem.

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.

Bad Data During Oct 30th to Nov 2nd 2007

Some data taken during Oct 30th to Nov 2nd may have suffered from the affection of trouble in channel-1 filter turret. Please do not use the channel-1 data during the period.

Stray Light on Spectroscopy Data

Before September 2006 the spectroscopic data affected by a significant amount of stray light. That is mechanically fixed and now the effect is minor, though under the observation without the order-sorting filter for zJ500 and under the use of the old 1.3um order-sotring filter the effect remains slightly.

All the related information about the previous updates for the stray light problem have been collected into the MOIRCS Stray Light Information Page

Created by Yuka Katsuno Uchimoto (Apr 2006)
Revised by Ichi Tanaka (2008-07-31)