Text Size:
Smaller Text Normal Text Larger Text

Facebook page

Twitter profile

YouTube channel

How to run spectroscopy OBs manually

As you know the NOTCam spectroscopy mode does not have a complete OB compiler. PIs can prepare their observations using the OB generator, and the compiled script simply sets all the FITS header keywords and does the pointing. When the telescope is tracking and guiding, the script tells you to start doing the actual observations in a separate sequencer window and when finished coming back and press return (this leaves the OB execution time counting).

You may wish to stop the BleepLoop with the command alert.killBleepLoop

Up to now I have added all the steps you need to take as an observer as comments in each single OB. This is quite time-demanding, though, and in some cases I have not done it recently. So when observing NOTCam spec OBs keep a couple of things in mind:

  • Target spectra are always taken together with a telluric standard (in the same OB-group), as close as possible in time, and either right before or right after, such that it best matches the airmass.
  • Always take lamps while still tracking on target, use the script notcam.easy-calib.

There are 4 main steps to take (slit acquisition, data acquisition, potential change of wavelength region, and lamp calibrations, examples are in green):

  1. Slit acquisition:
    notcam.acquisition -c -q camera slit filter expt
    notcam.acquisition -c -q wf 128 208 3 (WF-camera, 0.6'' wide slit = 128 micron slit, K-band = #208, 3 sec)
    notcam.acquisition -c -q hr 44 203 20 (HR-camera, 0.2'' wide slit = 44 micron slit, H-band = #203, 20 sec)

    You need to check in the OB which camera, slit and wavelength region is needed. If the target is faint (> 12 mag), and you are going to observe in several wavelength regions, for instance JHK, select the wavelength where the target is the brightest, for optimal slit acquisition, and for the following bands you just change setup. You need to decide acquisition exptime based on target magnitude. Note that if the backgrounds are low, as for the Y-band, you need longer exposures to be able to measure the slit position.

    The script will ask you to first measure the slit position at a given X, select X=374, as this is a good location for spectrum A with very few bad pixels. If you saturate the target in the acquisition images, clean the array with a few dark 0 before starting to take spectra, otherwise it will cause memory effects in spectra.

    It is similar to alfosc.acquisition except for:
    1. measuring slit position (due to flexure),
    2. potentially doing sky subtraction for faint targets, and
    3. the need to put in a NB filter from wheel 1 if the object is brighter than 6-7th mag.

  2. Taking the spectra (dither modes: ABBA or AB3):
    notcam.abba t N objname x-offset
    notcam.ab3 t N objname x-offset
    notcam.abba 5 10 star1 22.2 (takes 4 exposures of 50s)
    notcam.ab3 30 10 star2 22.2 (takes 6 exposures of 300s)

    You need to find the t and N input parameters in the OB sequence of each target and standard. It is given as frame t N. Note that the last parameter, x-offset, the offset step for the B position, is given in arcseconds from position A (WF-cam: 0.234''/pixel), and typically a good B location is found both with the x-offset = 22.2.

  3. If more wavelength regions than only one are needed, then:
    notcam.setup-spec camera filter slit grism
    notcam.setup-spec wf 201 128 1 (J-band WF spectroscopy)

    Note that this script does not move neither slit nor grism in order to guarantee the target stays in the slit! It changes the filter and the internal focus. When ready, start your observation as in the point above.

  4. Take lamp calibrations before leaving target (the script checks which camera/slit is in use and applies default exptimes):
    notcam.easy-calib fid1 [fid2] [fid3] [fid4]
    notcam.easycalib 208 (only the K-band)
    notcam.easycalib 236 201 203 208 (Y, J, H, and K bands)

  5. Press return in the first sequencer window to stop the OB execution-time counter.

For details consult the spectroscopy sections in:
NOTCam Cookbook
list of NOTCam template scripts