NTT/SOFI Observing Procedures

Contents

  1. Prepare OBs
  2. Afternoon Calibrations
  3. Observing
  4. Night Time Calibrations
  5. Data Backup

1. Prepare OBs

  1. Get latest version of the P2PP program from this link.
  2. Examples of science OBs can be found in this tar file.
    Examples of calibration OBs can be found in this tar file.
    Download the .tgz file, and open it with
    %> tar xvzf SOFI_OBs_???.tgz
  3. Make OBs for the targets in the exposure time list.
  4. For each SN, add an OB for a telluric standard that has similar airmass to the SN.
    This tool can help you find a suitable standard. NOTE: there's been problems with the tool, so use it with care, especially at high airmasses.
  5. You may use the SOFI exposure time calculator from ESO.
    Remember the detector linearity limit is 10,000 counts.
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2. Afternoon Calibrations

  1. Darks:
    Use OB called SOFI_img_cal_Darks.
    Obtain darks using ALL the DITs (exposure times) you'll be using during the night.
    If you don't know all the DITs, you can add darks in the morning.
    Use the same NDITs as for science objects.
    Set Number of Exposures to 5.
  2. Dome flats:
    Use OB called SOFI_spec_cal_DomeFlats.
    Obtain Dome flats in blue and red, using all the slit widths used for science.
    Lamp-on and lamp-off flats are needed. The OB already takes care of this and obtains both.
    In general, these widths will be 0.6 and 2 arcsec.
    Set DIT=2s, NDIT=60, Number of Exposures=1 for all flats.
  3. Arc lamps:
    Use OB called SOFI_spec_cal_Arcs.
    Obtain one arc in blue and one in red, using the narrow slit (usually 0.6 arcsec).
    Set the following values in the OB:
    • List of DITs: 1.2 1.2 2 2
    • Lits of NDIT: 30
    • Number of Exposures: 4
    • Spectral Mode List: B B R R
    • Spectral Lamp List: N Xe
    The OBs yield one lamp-on arc and one lamp-off lamp for each channel.
    Check that the lamps look OK. This is an example of the blue arc. This is an example of the red arc.
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3. Observing

  1. For each SN, select the corresponding OB's to observe it through "blue" and "red" channels.
    Observe the SN in one channel, observe a std star in the same channel.
    Repeat this with the other channel, noting that the std star may not be the same as for the first channel.
  2. OB's should contain two templates: SOFI_img_acq_MoveToSlit, and SOFI_spec_obs_AutoNodOnSlit.
  3. The template SOFI_img_acq_MoveToSlit for SNe should have the following options:
    • DIT: 15 (blue);     10 (red)
    • NDIT: 1 (b&r)
    • Filter wheel 1: J;     Ks
    • Which Slit?: long_slit_0.6
    • Alpha offset: 10 arcsec
    • Delta offset: 10 arcsec
  4. The template SOFI_spec_obs_AutoNodOnSlit for SNe should have the following options:
    • Spectro Mode: LONG_SLIT_BLUE;     LONG_SLIT_RED
    • Which Slit?: long_slit_0.6
    • Jitter Box Width: 40 arcsec
    • Nod Throw: 60 arcsec
    • NINT: 1
    • Set DIT, NDIT and Number of AB or BA cycles as indicated in the exposure time list.
  5. For each SN observation, select a standard star with similar airmass.
    This tool can help you find a suitable standard.
    NOTE: there's been problems with the tool, so use it with care, especially at high airmasses.
    See below an alternative way of picking the standard.

    The tool is used like this:
    • Input RA and DEC of the SN.
    • Select "La Silla" under Location.
    • Fill approx. LST for SN and Std observations.
    • Leave Spectype range empty.
    • Select a magnitude range, if wanted.
    • Set dX=0.05, for instance.
    • Select "Hipparcos/2MASS G stars" as catalogue.
    • Click on SEARCH.
    • The result is a list of Hipparcos G stars which would have similar airmass --when observed-- to the SN observations.
    • Select a suitable star and make an OB with it, as described below.
  6. Alternative way of manually picking a suitable standard:
    • Take half of the time you'll spend on the SN (27 min for DIT=150s; 50 min for DIT=300s) plus half of the time you'll spend on the standard (5-7 min).
    • Pick a standard with similar DEC (within 2-3 degrees) to the SN, and RA equals the SN's RA plus the time computed above.
    • That will yield a standard spectrum which will have similar airmass to the SN spectrum.
  7. Once you selected the standard star, make an OB for it, including one SOFI_img_acq_MoveToSlit template,
    and two SOFI_spec_obs_AutoNodOnSlit templates.
  8. The template SOFI_img_acq_MoveToSlit for stds should have the following options:
    • DIT: 2 (blue and red)
    • NDIT: 2
    • Filter wheel 1: J;     Ks
    • Which Slit?: long_slit_0.6
    • Alpha offset: 10 arcsec
    • Delta offset: 10 arcsec
  9. The template SOFI_spec_obs_AutoNodOnSlit for stds should have the following options:
    • DIT: 5 (blue and red)
      Check you don't surpass 10,000 counts. Usually DIT=5 will work for stars at V~8, but you may use the SOFI ETC to be sure.
    • NDIT: 6
    • Spectro Mode: LONG_SLIT_BLUE;     LONG_SLIT_RED
    • Which Slit?: do one template with long_slit_0.6, and one with long_slit_2
    • Jitter Box Width: 20
    • Nod Throw: 60
    • NINT: 1
    • Number of AB or BA cycles?: 2
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4. Night Time Calibrations

  1. Take one set of arc lamps during the night or at the end of it.
    See how to take them in point "c" of Afternoon Calibrations.
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5. Data Backup

  1. Fill out Backup Request Form
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