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Phase II Checklist

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Checklist for GMOS Phase II (OT) programs


  • General
    • Have you selected appropriate templates from the GMOS OT library? Have you gone through the checklist in the Top-level Program Overview note and included relevant standardized notes? Add notes with information about the program and acquisition that will make it easier for the observer. Try to use the standardized notes provided in the OT Library.

    • In the GMOS component, check that readout, translation stage, and ROI are correctly defined for the observation type. If in doubt, see the relevant examples in the GMOS OT library. Make sure that nighttime science observations have the Translation Stage set to Follow and daytime calibrations set to "Do Not Follow" or "Follow in Z Only" (GMOS-S). Check also that the Region of Interest that will be read out is appropriate for the observation type and that the read mode is set to Fast Read/Low Gain for acquisitions, daytime calibrations etc, and to Slow Read/Low Gain for science observations (or Fast Read/High Gain for bright targets). The CCD readout must be set to Use 12 amplifiers for the Hamamatsu GMOS-N and GMOS-S CCDs.

    • Is the binning set appropriately for the instrument configuration and requested observing conditions? Basically, make sure your are optimizing the pixel sampling of the spatial resolution (GN/GS) and/or the spectral resolution.

    • Are the integration times reasonable? Individual imaging observations should not be longer than 10-15min, individual spectroscopy observations should not be longer than 20min (GMOS-S and GMOS-N Hamamatsu CCDs, due to the high rate of cosmic rays). Short exposures result in large overheads from the readout of the detectors, and may give data dominated by the read-noise.

    • GMOS observation sequences that take longer than ~3 hours to execute will likely not be executed all on one night, and you must allow adequate time for re-acquisitions on subsequent nights when filling the allocated time. Have you read the details about the overhead calculations? Have you added a note explaining how many reacquisitions you have assumed for the calculation of the overheads? Taking the correct overheads into account, do your defined observations fit within the allocated observing time? Is there an appropriate mix of science exposures and baseline calibrations in the sequence? Spectral flats at redder wavelengths should be taken about once per hour, while flats at bluer wavelengths can be taken in the daytime.

    • Have you checked Baseline Calibrations to see what is offered/required.

    • Baseline arcs and flats should be set up using smartcals now. Choosing a flat (as observe element) within a science sequence will automatically set up a baseline nighttime partner calibration with an optimal exposure time. Choosing an arc within a science sequence will automatically set up the correct exposure time but these must be set to nighttime program calibration. Within a daytime arc sequence, this will be set up as daytime partner calibration. If you feel you need a different exposure time (e.g., because the desired grating/filter/wavelength/slit width combo is not known by the smart cal library), please contact your Gemini program Contact Scientist, or file a helpdesk ticket. As of 2012B, arcs and flats configured manually will no longer be checked by either the NGO or Contact Scientist. Any time lost will be charged to the PI.
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    • Have all observation classes been set correctly?

    • Have you considered the effects of differential atmospheric refraction on your data? The default position angle has been set to 90deg in the GMOS-N and GMOS-S Libraries, as for most science targets this will minimize the slit losses. However, if your target Declination differs from the observatory latitude by more than ~ 25-30 deg (for targets observed with GMOS-N Dec > +50 or Dec < -10, for targets observed with GMOS-S Dec > 0 or Dec < -60), at a minimum the position angle should be changed to 0 deg if possible. More information is available on why target Dec influences the choice of default position angle. If desired, take longslit observations at the parallactic angle. To do so, please include a note with the title


      in the program. If this is not possible, the hour angle/airmass constraints can be chosen to ensure that the target is observed closer to transit. These will need to be approved by the appropriate head of sci ops.

  • Guide stars
    • Are guide stars selected for the GMOS OIWFS? The PWFSs are not used for observing sidereal targets with GMOS in most cases. First, select the position angle mode (Fixed, Allow 180deg flip, Average parallactic) in the GMOS component as appropriate. The automatic guide star selection service will select an appropriate guide star for the specified observing conditions. Alternatively, the PI can still choose a guide star using the Manual GS button on the OT position editor. For manual guide stars, ensure that the guide star can be reached for the selected position angle, that the guide star is within the magnitude limits for the OIWFS, and that all guided offset positions can be reached. Check that the probe arm is visible and falls within the green box in the position editor. Fix any red offset positions. The UCAC4 catalog should be used whenever possible for choosing guide stars as the magnitudes are usually reliable.

    • Ensure guide stars are stars and not galaxies.

  • Calibrations
    • Check that appropriate calibrations are included in the program. To see which baseline calibrations/standards are recommended, see Baseline Calibrations.

    • For baseline spectrophotometric standards or twilight flats, make sure that the target component is left blank or excluded.

    • If the PI requires calibrating standards beyond what is offered in the standard baseline calibrations, these must be defined, including a specific target, and time will be charged against the program for the observation. Observing class should be set to Nighttime Program Calibration. Baseline standards are set to partner calibration.

  • Imaging
    • Note that binning is recommended for imaging observations in IQ70 conditions or worse.

    • Have you considered spatial dithers for imaging? There are gaps between the three detectors in GMOS, illustrated on the GMOS imaging page and whose approximate positions are indicated in the OT position editor.

    • If imaging in the i, z, Z, and Y-filters, have you considered how to handle the fringing? In GMOS-N and GMOS-S the fringing becomes apparent redward of about ~800 nm and is about ~2% of the background level in the Y-band (GMOS-N and GMOS-S), and ~1% (GMOS-N)/less than 0.5% (GMOS-S) in the z'-band. A minimum of 5 exposures is recommended in order to generate a good fringe frame.

    • Baseline photometric standards should not be defined within the program. These baseline standards are already taken on each photometric night that imaging data is obtained. If the PI wishes to have more than one taken, or insists on having one taken with a program defined for CC70 conditions, then a program standard with target component will have to be defined in the program by the PI.

  • Spectroscopy
    • Have you considered spectral dithers for spectroscopy? There are gaps between the three detectors in GMOS, illustrated on the GMOS long-slit spectroscopy page. If complete wavelength coverage is essential, then two sets of observations with slightly different wavelengths are needed. The recommended minimum shifts are ~20nm for the R150 grating, ~7.5nm for the R400 grating, and ~5nm for all other gratings.

    • At long wavelengths, fringing becomes a problem. If not using N&S to correct for the sky background, it is best to use spatial dithers from which fringe frames can be generated.

    • Ensure that all the appropriate baseline calibrations (nighttime GCAL flats, twilight flats, daytime CuAr, mask image obs [for MOS], and spectrophotometric [flux response] standards) and acquisition observations are included.

    • For spectroscopy at wavelengths longer than about 850 nm, the wavelength calibration can be improved by including 2nd-order CuAr lines in the wavelength calibration. In this case, it may be beneficial to take additional CuAr exposures without any order-blocking filter. An example line list can be found here.

    • Have you included the appropriate acquisition observations?

    • If an observation includes an unusual or non-standard acquisition (eg. off-axis long-slit or IFU where the guide star cannot be accessed with the science target on-axis, blind offset acquisitions, MOS acquisitions with large initial offsets, etc), include the appropriate OT Library standardized note in the program. The text of the note can either describe the acquisition or point to other notes within the program. Using these standardized notes should minimize acquisition errors and observers won't be surprised. See the OT library for examples of non-standard acquisitions. See COMPLETE EXAMPLE: Longslit (extended/double/off-axis source), for cases where the science object is either extended by more than 15", a double source where the targets are separated by more than 20", or a target which is more than 20" off-axis in the q-direction.
    • BLIND OFFSETS: Use when targets are too faint to be acquired within 5 min of imaging.
      • Make sure that a User1 target is defined with coordinates on the same astrometric system as the science
      • Make sure the blind offset User1 star has a name, preferably something like 'Reference Star' or 'Blind offset star'
      • Offset star should preferably be within 20 arcsec of the science target. The accuracy of blind offsetting is better than 0.1 arcsec for offsets less than 20 arcsec.
      • For the blind offsetting to work, it is essential that the same guide star can be reached for the bright object and the science target.
      • Include a note in the program to warn the observer of the non-standard acquisition.
    • If your longslit or IFU spectroscopic observations involve complicated alignments, crowded fields, or targets fainter than about R=18 (eg. if the target is not obvious in the OT position editor with the Digitized sky survey 2 image loaded), you need to prepare finding charts. Such a finding chart should indicate the target/s and display the orientation (preferably North up and East to the left) and scale. Finding charts should be uploaded through the OT.

    • Have you included the observation for the flux (spectral-response) standard? For MOS, standard star observations should be taken at 2-3 central wavelengths in order to span the full wavelength range over the mask (see the Description in the MOS Baseline Calibration Examples in the OT LIbrary). Otherwise, if spectral dithers are used in the science, only one central wavelength will be observed for the flux standard. Do not include a target component (or if included, please leave the target blank) for baseline standards. The observer will choose one appropriate for the time of the observation.

    • Have you considered using Nod&Shuffle for spectroscopy in the red?
      • If using N&S, check that electronic offsetting is chosen if small offsets (< 2.0arcsec) have been defined (this will reduce overheads significantly).
      • Recommended exposure times are 60s for CC50/70 and 30s for more variable and thick cloud conditions.
      • The nod should be less than half the length of the slit if the observation intention is to keep the object within the slit for both nods. For large nods, if the guide star cannot be reached at the sky position, make sure the OIWFS is set to freeze.
      • Ensure that the shuffle distance defined in the Nod & Shuffle tab makes sense. For microshuffling, the distance should be the same as the slit length (but must be an even number of rows if binning by 2).
      • Check that a N&S dark is defined in order to correct for charge traps. For deep observations it is also recommended to translate the detector a few pixels in the y-direction between N&S observations. Check that the observations have been split into multiple dithered exposures, with the translation of the detector set by the DTA-X offset. For GMOS-S new detectors, charge traps are not present therefore N&S darks and DTA-X offsets is no longer necessary, but if these are defined the minimum allowed value for DTA-X offset is -2 
    • For IFU observations, make sure that the guide star can be reached in both the acquisition and science observation. If it is not possible, choose a guide star appropriate for the science observation and include a standardized note in the program warning of this.
      • Binning: check that the Y-direction is left unbinned since the width of each IFU fiber is only 5 unbinned pixels. Since the spectral resolution in the IFU is equivalent to 4.26 unbinned pixels, binning in the spectral direction for very faint objects may be useful.
      • If you are using the IFU in two-slit mode, you will have to use one of the color filters to avoid overlap between the spectra. For IFU observations in one-slit mode, IFU-R should be chosen over IFU-B (IFU-R is recommended over IFU-B for both GMOS-N and S)..
    • If your program is a MOS program, have you defined any pre-imaging along with mask observations? You will get the chance to modify the MOS observations once you design your mask. However, the pointing and PA of your target cannot be changed between the pre-imaging and the MOS observations.
      • If taking pre-imaging, make sure the MOS pre-imaging option on the OT GMOS component is indicated.
      • If no pre-imaging was taken, make sure the acquisition starts with a mask out of the beam step for coarse alignment.
      • For MOS programs, have you included the required daytime calibration mask image(s) .
      • If your program is a MOS program, prepare yourself for the mask design by reading the MOS instructions in detail and installing the required software.
      • Mask names must be in the correct format: ie for program GN-2003B-Q-27, the mask names should be GN2003BQ027-01 and GN2003BQ027-02 for the first and second mask, respectively.
      • If a mask was designed from a catalog, make sure the RA, Dec, and position angle entered in the OT are the same values used for making the mask. You can extract the RA and Dec information from the MDF file or pseudo image (eg by using "thselect {maskfile.fits} RA_IMAG,DEC_IMAG" or "hselect {psuedo_image} RA,DEC in pyraf). Check the PA by comparing the pseudo image orientation (after inverting y and rotating to the PA listed in the OT) with eg. a DSS image in the OT position editor.