Astronomical Observation Templates (AOTs)

• standard observing modes for routine observations

• designed to accomplish particular tasks:
  • SWS01: full scan of the SWS wavelength range
  • SWS02: single line scans
  • SWS06: wavelength range scans
  • SWS07: high resolution Fabry-Pérot scans

• observer has to specify astronomical input parameters:
  target position, wavelengths, flux density, S/N ratio

• AOT logic translates input into instrument commands:
  => S/C pointing, scan mode, reset interval, amplifier gains

• observational result is suitable for pipeline processing

• standard products with fixed formats are generated

Restrictions:

• observational details depend on observer input:
  • pointing:  target position has to be accurate to 1"
  • scanning: good radial velocity, rest wavelengths (FP!)
  • settings:  proper flux density estimates and S/N ratio

• fundamental detector reset intervals tr = 1, 2 or 4 sec and
  amplifier gains 1x, 4x, 16x (saturation problem)

• fixed relation between wavelength ranges and aperture sizes

• orientation of the aperture can not be specified by observer
  (achieved orientation is supplied in the product headers)

• no chopping mode for subtraction of diffuse background
  (zodiacal light, galactic background), use off-position

SWS01: full scan of the SWS wavelength range

• quick full scan at reduced spectral resolution

• 2.38-45.2 µm spectrum of bright sources

• three long up/down scans, one for each aperture
  (up/down in scanner position = down/up in wavelength)

• inherent merging: SW and LW section are done simultaneously

• four scan speeds 1-4 <=> integration time 13, 25, 50, 100 mins

• low(er) spectral resolution, depending on scan speed:
  reduced absolutely by a factor of 1/2 to 1/7 compared to SWS02
  and relatively by a factor of 0.6 to 0.3 refered to SWS01 speed 4

• artificial blurring:
  • scans performed too fast, to obtain nominal resolution
  • to avoid undersampling and/or imperfect flat fielding,
    the grating scanners step 8 or 16 times per reset time
  • integration in time translates into a smoothing of the
    spectrum, which prevents from aliasing problems =>
  • each detector produces a sufficiently sampled spectrum

• high resolution mode for SWS01 observations,
  by replacing 2s resets by a pair of 1s integrations

• dark currents measured before and after each scan

• photometric check done at the end of an observation,
  for slower speeds also between the scans

• observer input:
  • target position
  • speed value
  • expected peak flux densities for band 1-4

SWS02: single line scans

• high quality grating scans of individual spectral lines

• line fluxes and profiles (FWHM > 300-150 km/s) and
  detection of faint, not too narrow lines on strong continuum

• scans with minimum stepwidth 1 LVDT (band 4: 2 LVDTs)

• full nominal SWS grating resolution (R=1,000-2,000)

• fixed scan range of typically 10 resolution elements
  or about 3,000-1,500 km/s (40-50 steps/scan)

• one (or more) up/down scan(s) for each line
  (up/down in scanner position = down/up in wavelength)

• each detector of an array provides a well-sampled spectrum

• combined data are oversampled:
  => smoothing/rebinning to instrument resolution is necessary!
  redundancy can help in case of faulty detectors, memory effects

• AOT logic optimises for merging:
  simultaneous observations in SW and LW section

• possible reset intervals tr = 1 or 2 sec (for band 1 also 4 sec)

• dark current measurements done before and after each scan

• photometric checks at regular intervals (every 3,600 secs),
  or at least once at the end of an observation

• observer input: (up to 64 lines)

  • target position
  • heliocentric radial velocity
  • vacuum wavelengths
  • expected flux densities
  • required S/N ratios

SWS06: wavelength range scans

• scans of wavelength ranges broader than SWS02 line scans
  up to scans of full SWS AOT bands

• broad lines and spectral features (FWHM > 1,000 km/s)

• coarser sampling compared to SWS02 line scans:
  minimal stepwidth 1-2 LVDT only for the slowest possible mode,
  stepwidth 4-6 LVDTs (one resolution element) for the quickest

• (nearly) nominal SWS resolution:
  for quick modes single detector spectra might be undersampled
  => flatfielding and combining of all 12 detectors is necessary

• one (or more) up and down scan(s) for each range,
  long scans are possibly splitted up into parts
  (up/down in scanner position = down/up in wavelength)

• scan length up to a whole AOT band:
  SWS06 scans must not cross AOT band limits
  (band definition for SWS06 includes some overlaps)

• AOT logic optimises for merging:
  simultaneous observations in SW and LW section

• reference scans before, between and after long range scans
  (dropped after revolution ..., not used in data reduction)

• dark currents recorded before and after a range is scanned

• photometric checks at regular intervals (every 3,600 secs),
  or at least once at the end of an observation

• observer input: (up to 64 ranges)

  • target position
  • heliocentric radial velocity
  • wavelength ranges
  • reference wavelengths
  • expected flux densities at reference wavelengths
  • expected peak flux densities in the wavelength ranges
  • required S/N ratios at reference wavelengths

SWS07: high resolution Fabry-Pérot scans

• high resolution scans of individual lines or line groups

• close line groups or line profiles (FWHM > 10 km/s) and
  detection of very narrow faint lines on strong continuum

• high spectral resolution (R=20000-350000)
  at reduced sensitivity (lower transmission)
  => very time-consuming

• single or repetitive up scans for each line
  (up scan in FP position = down scan in wavelength)
  no down scans due to the hysteresis in the FP drive

• the FP scan length must be between 50-1,000 km/sec,
  the spectrum is sampled at intervals of 1/4 resolution element

• only one detector (49 and 51) of the FP detector pairs is used!
  the second one is spare

• LW section is used as order pre-selector for the Fabry-Pérot
  FP scan is performed by increasing the FP gap

• LW grating is kept in tune with the FP wavelength, to minimize
  leakage from the adjacent FP orders (tracking noise!)

• SW section can perform SWS06-like scans (2.4-3/3-7 µm)
  simultaneously with FP1 observations (11.4-16/16-26 µm)

• SW and FP1 section can operate rather independently, but
  scans might be interupted because of needs of the other section

• due to a slight aperture mis-alignment between SW and FP2,
  merging is not possible for FP2 observations ("aperture 4"),
  scheduled pairs of SW/FP2 observations were done separately

• observer input (for SW ranges see SWS06):

  • target position
  • heliocentric radial velocity
  • vacuum rest wavelengths
  • velocity range to be covered
  • expected flux densities
  • required S/N ratios