Overheads

Direct links to instruments on UT1 , UT2, UT3, UT4, VLTI, VISTA, VST.

Telescope Instrument Action Time (seconds)
UT1   Preset + GS acquisition + active optics
 360
UT1   Preset  + GS acquisition + active optics (2nd OB and following in a concatenation)
 (40+target separation in deg)+60
  NACO see User Manual ---
  FORS2 Acquisition IMG/IPOL/LSS/HIT (1 loop)
 90
  FORS2 Acquisition MOS/MXU/PMOS (1 loop) 120
  FORS2 Through Slit Image (2 loops w/o exp. times)[1] 240
  FORS2 Instrument Setup 30
  FORS2
 Collimator exchange
 270
  FORS2 Retarder Plate Setup per PMOS/IPOL OB 60
  FORS2 E2V Read-out 100kHz binned (spectroscopy) 39
  FORS2 E2V Read-out 200kHz binned (imaging) 28
  FORS2
 E2V Read-out 200kHz unbinned (imaging)
 78
  FORS2 MIT Read-out 100kHz binned (spectroscopy) 41
  FORS2 MIT Read-out 200kHz binned (imaging) 31
  FORS2 MIT Read-out 200kHz unbinned (imaging) 62
  KMOS Acquisition, MOSAIC setup 0
  KMOS Acquisition, non-MOSAIC setup, without exposure time, per cycle (2 cycles usually necessary):  
  KMOS - : read-out + writing image to disk 6
  KMOS - : interaction + image reconstruction 35
  KMOS Acquisition (2nd OB in a concatenation, MOSAIC and non-MOSAIC setups): arms parking and deployment 240
  KMOS Read-out + writing image to disk 6
  KMOS Image reconstruction 20
  KMOS Offset (dither, i.e. within individual IFUs) 9
  KMOS Offset to sky 45
UT2   Preset + GS acquisition + active optics
 360
UT2   Preset  + GS acquisition + active optics (2nd OB and following in a concatenation)
 (40+target separation in deg)+60
  FLAMES Acquisition[2] 420
  FLAMES Instr. Setup GIRAFFE 60
  FLAMES Instr. Setup UVES 60
  FLAMES CCD read-out GIRAFFE 60
  FLAMES CCD read-out UVES 60
  FLAMES Screen Flatfields 420
  FLAMES Plate Configuration[3] 0-1200
  XSHOOTER Target acquisition (3 loops, incl. telescope offset and AG readout time; excl. AG integration time): direct/blind 49/65
  XSHOOTER Telescope offsetting 15
  XSHOOTER Instrument setup Slit 30
  XSHOOTER Instrument setup IFU 60
  XSHOOTER Delay before start of exposure: UVB 0
  XSHOOTER Delay before start of exposure: VIS 5
  XSHOOTER Delay before start of exposure: NIR 10
  XSHOOTER UVB Read-out[4], 1x1, Slow/Fast 68/16
  XSHOOTER UVB Read-out[4], 1x2, Slow/Fast 34/8
  XSHOOTER UVB Read-out[4], 2x2, Slow/Fast 17/4
  XSHOOTER VIS Read-out[4], 1x1, Slow/Fast 89/21
  XSHOOTER VIS Read-out[4], 1x2, Slow/Fast 45/11
  XSHOOTER VIS Read-out[4], 2x2, Slow/Fast 22/5
  XSHOOTER NIR Read-out (per DIT) 1.46
  XSHOOTER AG camera detector Read-out 1
  UVES Instrument Setup 60
  UVES Acquisition. Bright Point Source 120
  UVES Acquisition. Faint, Extended or Crowded Field 300
  UVES Read-out[5], 1x1, Fast 40
  UVES Read-out[5], 2x2, Slow 45
  UVES Read-out[5], 1x1, Ultra-fast (VM only)
 10
  UVES Dead-time between shutter closing and re-opening Ultra-fast mode only: red arm only/dichroic 25/32
  UVES Attached ThAr, Night time; set-up dependent, see User Manual Table 4.2
 41 to 89
  UVES Attached Flat, Night time; set-up dependent, see User Manual Table 4.2
 44 to 190
UT3   Preset + GS acquisition + active optics
 360
UT3   Preset  + GS acquisition + active optics (2nd OB and following in a concatenation)
 (40+target separation in deg)+60
  SPHERE Acquisition without coronagraph centering
 600
  SPHERE Acquisition with coronagraph centering
 900
  SPHERE Flux measurement (incl. exposure)
 210
  SPHERE Centering measurement (incl. exposure)
 210
  SPHERE IFS observations, per exposure
 NDIT*1.7+10
  SPHERE IFS observations, per dithering position
 4
  SPHERE IRDIS observations, per exposure
 NDIT*0.85+10
  SPHERE IRDIS observations, per dithering position
 4
  SPHERE IRDIS_LSS observations, attached wavelength calibration
 210
  SPHERE ZIMPOL observations, per exposure, StandardImaging readout mode
 NDIT*0.1+3
  SPHERE ZIMPO observations, per exposure, FastPolarimetry readout mode
 NDIT*0.1+3
  SPHERE ZIMPOL observations, per exposure, SlowPolarimetry readout mode NDIT*0.1+13
  SPHERE ZIMPOL observations, per polarimetric cycle 2*5
  SPHERE ZIMPOL observations, per dithering position 5
  SPHERE ZIMPOL observations, per number of field angle values 5
  VISIR Target acquisition: imaging, direct (>1 Jy source), 1 loop, incl. exposure 300
  VISIR Target acquisition: imaging, blind 120
  VISIR Target acquisition: spectroscopy (>1 Jy source) 900
  VISIR Target acquisition: spectroscopy (0.2 to 1 Jy source) 1800
  VISIR Chopping and nodding duty cycle losses 50% of exposure time
  VIMOS IMG acquisition + Instrument setup 180
  VIMOS MOS acquisition + Instrument setup 900
  VIMOS IFU acquisition + Instrument setup 600
  VIMOS Read-out IMG,MOS,IFU (4 quadrants) 60
  VIMOS Change of Filter (IMG) 180
  VIMOS Attached screen flat+arc (IFU, MOS)[6] 300-480
  VIMOS Attached arc (MOS) 240
UT4   Preset + GS acquisition + active optics
 360
UT4   Preset  + GS acquisition + active optics (2nd OB and following in a concatenation)
 (40+target separation in deg)+60
  HAWK-I Blind acquisition and Instrument Setup 60
  HAWK-I Acquisition (Move to Pixel) and Instrument Setup 180
  HAWK-I Telescope offset (large) 45
  HAWK-I Telescope offset (small) 9
  HAWK-I Read Out (per DIT), normal observation
 1.8
  HAWK-I Read Out (per DIT), FastPhot/Burst NXxNYx1.e-06
  HAWK-I Filter Change 21
  HAWK-I Header merging 15
  HAWK-I After exposure overhead 8
  SINFONI Acquisition no AO 180
  SINFONI Acquisition AO (NGS) 120+ 240*(DIT*NDIT)[7]
  SINFONI Acquisition AO (LGS) 660 + 240*(DIT*NDIT)[7]
  SINFONI Centering of target (AO and no AO) 240 + 240*(DIT*NDIT)
  SINFONI Instrument setup (per grating change) 220
  SINFONI Science exposure read-out (per DIT) 4.2
  SINFONI Detector setup (per DIT x NDIT) 18
  MUSE Interactive acquisition loop 18
  MUSE Acquisition: Slow Guiding System loop closure 20
  MUSE Detector setup 15
  MUSE Detector readout + file merging 60
  MUSE Intra-exposure detector delay (for multiple exposures) 5
  MUSE Small telescope offset < 2 arcmin 15
  MUSE Large telescope offset > 2 arcmin 45
  MUSE Slow Guiding System closure after offset 10
  MUSE Derotator offset 5+0.11/deg
  MUSE Attached calibration: 5 Flat-Fields 240+106/flat-field
  MUSE Attached calibrations: 3 wavelength calibrations 180+112/arc lamp exposure (1 exposure per lamp)
  MUSE Return to origin (no offset/small offset/large offset) 0/15/45
VISTA   Preset 120
VISTA   Preset (2nd OB and following in concatenation) 20+ target separation in deg
  VIRCAM Guide star handling 3
  VIRCAM Autoguiding start 5
  VIRCAM Active Optics start 45
  VIRCAM Filter change 21-40
  VIRCAM Detector readout 2 per DIT
  VIRCAM Writing FITS to disk 4
  VIRCAM Pawpring change 15
  VIRCAM Jitter offset 8
  VIRCAM Micro step 4
VST   Preset 120
VST   Offset at template start 15
VST   Set rotator position angle (PA) (abs(PA) < 180) PA/2
VST   2nd OB and following in concatenation  
VST   - Preset 30+(target separation in deg)/1.5
VST   - Set Rotator PA (abs(PA_n)+abs(PA_n+1))/2 [8]
  OmegaCAM Guide Star (GS) aquisition 60
  OmegaCAM Acquisition of new Guide Star after offset 60
  OmegaCAM Re-acquisition of same Guide Star after offset [9] 5
  OmegaCAM Pick object for Move to Gap acquisition 45
  OmegaCAM Filter exchange between acquisition and 1st science templates:  
  OmegaCAM - different magazine 65
  OmegaCAM - same magazine 115
  OmegaCAM Filter exchange between science templates:  
  OmegaCAM - different magazine 35
  OmegaCAM - same magazine 85
  OmegaCAM Detector readout and data writing to disk, last exposure of an OB 0
  OmegaCAM Detector readout and data writing to disk, other exposures 40
  OmegaCAM Start Active Optics/Image Analysis 180

Direct links to instruments on UT1 , UT2, UT3, UT4, VLTI, VISTA, VST.

[1] Through-slit exposures are mandatory for all spectroscopic OBs. Two cycles are typically enough to center the target on the slit (exposure time of the through slit image not included). MXU,MOS,PMOS,LSS,ECH 2.0 min (per cycle), IMG and IPOL none.

[2] Includes configuration of UVES fibres, homing the rotator to zero degrees, swapping of the plates, and the acquisition of field. For ARGUS fast acquisition (VM only), the acquisition overhead is 2 minutes and is calculated assuming that plate 2 is already attached to the telescope.

[3] Plate configuration takes 20 minutes at most (Medusa fibres). This does not translate into additional overheads if the running exposure on the other plate is at least 20 minutes long. Plate configuration overheads have to be added if the exposure time is shorter than 20 minutes.

[4] Detectors are read sequentially.

[5] In a dichroic exposure the CCDs are read out in parallel.

[6] Attached flats and arcs are mandatory for all IFU and MOS modes.

[7] Here: DIT and NDIT as required for the AO natural guide star (NGS).

[8] When switching from OBn to OBn+1 in a concatenation, the overhead for repositioning the rotator is (abs(PA(OBn)) + abs(PA(OBn+1)))/(2 deg/s). I.e. for an OB sequence with PA=90 degrees, the overhead per OB is 90s. PAs > 180 or < -180 are interpreted as modulu 360. E.g. PA=270 implies motion to PA=-90.

[9] The default dither sequence 'diagonal' with N=5 exposures will not require to change the guide star. A larger offset sequence increases the overhead due to the reaquisition of a new guide star. For exposures shorter than 1-2 minutes, observations can be performed without guiding.