Troubleshooting guide

• Make certain the PA is correct.
• Set M_RPTPAT to the number of times to repeat the pattern.
• Set M_THROW, the distance in arcseconds between the A & B beams (which are symmetrically offset
about the telescope zero point). For MOS observations we use 4".
• If USEMNUDG = 1, the ABBA pattern will be offset along the slit by M_NDGSZ (in arcseconds) on
pattern repeats. For MOS observations we use M_NDGSZ = 0.3. Alternatively, one can execute the
dither sequence with one ABBA pattern at a time, and use relative.offset.kpno.pl and
clear.offsets.kpno.pl before repeating the ABBA pattern. Just keep track of the size and number of
offsets.
7. Start spectral dither sequence, dither.mos.kp4m.pl. Repeat as necessary.
8. Take one or more sets of quartz or dome flats at end of spectral dither sequence (cf. § V. E. Taking
Spectra with FLAMINGOS: Taking Flats and Wavelength Calibrations).
9. Take a long slit spectrum of a telluric standard at a similar airmass to that at the middle of the dither
sequence. Use a bright star with spectral type G5-6 V.
10.Some observers also take a long slit spectrum of an A0 V star.
F. Taking Flats and Wavelength Calibrations
There are two types of calibrations required for long slit and MOS spectra: wavelength calibration and flat
fields. The 4-m guider/rotator above FLAMINGOS provides a set of quartz and arc lamps for these
calibrations.
NOTE: The 4-m calibration projection unit was designed for the RC spectrograph, whose field is smaller than
10 arcmin. Therefore, this does not provide uniform coverage of the entire FLAMINGOS field of view, and
flats/arcs will be significantly weaker at the ends of the mask or slit. In addition, the quartz optics within the
projector have absorption bands near 2.3 μm which will show up in the flatfield spectra. Therefore, an
alternative approach to obtaining flats is to observe the inside of the dome using the flatfield lights mounted at
the end of the telescope.
Usually only one set of wavelength calibrations is needed per target; alternatively the OH sky lines may be used
for wavelength calibration, if they are not saturated.
Flat fields should be taken contemporaneously with the target observations: there may be flexure between the
slit and the detector which is dependent on telescope hour angle (HA) and zenith distance (ZD). Additionally, if
one tries to take them at a later time it may not be possible to precisely insert the slit and grism in exactly the
same way as they were when set up on the target. More than one flat field data set may be required if the
observation spans a large enough range of hour angles ( 1 hour, possibly).
We recommend the following:
• If the target is a bright standard star, then the observation time probably is short and a single set of
calibrations, taken after the target, should suffice.
• If the target is faint, and the time on source is long, take more than one set of flats at several different
hour angles that lie within the same range of hour angles as covered by the science target, but take
them all after finishing the target observations. For example, if the science target is taken over the
hour angle range from -2:30 to +1:00, take a set of flats at the final hour angle, then move the
telescope back to an hour angle similar to the initial hour angle, and take another set of flats (the
telescope does not need to be tracking). Or, if you only have time for one set of flats, consider moving
the telescope to the midpoint of the track in hour angle.
The following procedure is used for taking quartz flats with the rotator/guider calibration projector after taking
FLAMINGOS@4-m, Ver. 2.39, 2013 April 23 Page 31 of 47