PMAS :  Technical Overview


Principle of Operation
Telescope Data
Integral Field Units             New:    PPAK fiber bundle
Optical Fibers
Fiber Spectrograph, Gratings
Major Functional Units
Detectors
CCD Controllers
Field Acquisition and Guiding
Calibration Sources
Format of Fiber Spectra
Instrument Control Functionality
Instrument Control Software
Quick Look and Data Reduction Software
Planning Observations, S/N Estimates
Special Observing Modes        New:   nod-shuffle and PYTHEAS modes, mosaicking
 

Principle of Operation:
Integral Field Spectroscopy ( Fig. 1 ) with fiber-coupled lens array or fiber bundle IFU, and fiber spectrograph ( Fig. 2 )
 

Telescope Data:
f/10.0 RC focus station, f=35000mm, effective light-collecting area 8.153 m², aperture diameter 3500mm, diameter of central obscuration 1367mm, plate scale  5.89 arcsec/mm
 

Integral Field Units:
 
(1) Standard lens array IFU (recommended for high spatial resolution, small FOV, see Fig.3a) :
 
Standard - IFU

principle of operation :      square lens array with fore optics 
lens array :
16x16 square elements, 1mm pitch

( 32x32 array upgrade in preparation )
3 magnifications :
0.5 arcsec sampling, 8 x 8 arcsec^2 FOV

0.75 arcsec sampling, 12 x 12 arcsec^2 FOV

1.0 arcsec sampling, 16 x 16 arcsec^2 FOV
fiber configuration :
256 OH-doped fibers, 100um core diameter
acquisition & guiding :
Fig.3a-x

 
(2) Off-axis fiber bundle IFU (recommended for large FOV, low surface brightness objects, Fig.3b) :
       - see also AIP Highlight (10-May-2004) :
 
PPAK - IFU

principle of operation :     focal reducer + hexagonal packed fiber-bundle   
focal reducer lens
F10 to F/3.3,   platescale: 17.7"/mm
fiber configuration :
331 object + 36 sky + 15 calibration fibers
field-of-view :
74 x 65 arcsec^2, hexagonal, see Fig.3b-x
spatial sampling :
2.7 arcsec per fiber (diameter)
acquisition & guiding :
Fig.3b-y


Optical Fibers:
(1) Standard IFU fibers:
Polymicro FVP 100/110/140 (blue enhanced, high OH), core diameter 100um, fiber bundle in groups of 16, individual fiber length 1.8m ( Fig.4 ).
(2) PPAK IFU fibers:
Polymicro, (red response, low OH), core diameter 150um
 

Fiber Spectrograph,  Gratings :
Dedicated fiber spectrograph with nominal input focal ratio f/3, refractive collimator 150/450mm, pseudo-slit length 96mm, telecentric input, fiber coupling in immersion to first collimator lens.
Reflective diffraction grating 206 mm x 154 mm on grating rotator, angle position unrestricted from 0 to 360 degrees. Set of interchangeable gratings, stored in cartridges, manually inserted and removed. See Grating Table  .
Refractive f/1.5 camera 180/270mm, free of central obscuration, camera field-of-view 12 degrees corresponding to 4K x 4K / 15um pixel focal plane array ( Fig. 5Fig. 6 )
 

Major Functional Units  (  Fig. 7  ) :

  • Telescope Module (TELMOD)
  • Fiber Module (FIBMOD)
  • Fiber Spectrograph Module (FSPEC)
  • Electronics Module (ELRACK)
  • Main Frame (MAINFR)
  • Storage Support Carriage (MAINCAR)

  • Detectors:

  • Fiber Spectrograph CCD System (acronym spec) : SITe  ST002A with 2K x 4K / 15um pixels, thinned, blue-enhanced AR coating, upgrade to 4K x 4K mosaic in preparation, r.o.n. = 5.0 e, conversion factor 1.4 e/ADU, readout time: 2min12sec (2x2 binned) / 5min25sec(1x1 binned)
  • A&G Camera (acronym acq):  thinned SITe  TK1024 with 1K x 1K / 24um pixels, r.o.n. = 5.4 e, conversion factor 1.4 e/ADU

  • CCD Controllers:
    Dedicated ACE controllers for spec and acq CCD systems, exposure control and data acquisition with SPARC station "rike" (mounted in ELRACK).
     

    Field Acquisition and Guiding:

  • external 3.5m Telescope TV-Guider ("Spaltaufblick"), or, alternatively:
  • internal CCD Acquisition and Guiding Camera (A&G Camera), 0.2" per pixel, 1024x1024 pixels field-of-view, filter slider mechanism with 4 filter positions (for standard CAHA 50mm filters), internal focus

  • Calibration Sources:
    Internal flatfield exposures from integrating sphere, waveguide-coupled to various continuum and spectral line lamps, each lamp with individual shutter timing allowing for flexible combination of different light sources.

  • Lamp1: tungsten filament continuum lamp
  • Lamp2: Neon spectral line lamp, ORIEL pencil style type 6032
  • Lamp3: Neon spectral line lamp (spare for Lamp2, switched-in under remote control)
  • Lamp4: Hg(Ar)spectral line lamp, ORIEL pencil style type 6035
  • Lamp5: Hg(Ar) spectral line lamp (spare for Lamp4, switched-in under remote control)
  • Lamp6: ThAr hollow cathode spectral line lamp (for special applications)
  • Typical exposure times are 2sec for Lamp1 ... Lamp5,  and >120 sec  for Lamp6.
    Lamp6 (ThAr) has been provided as an option for simultaneous wavelength calibration for precision radial velocity spectroscopy (future upgrade).  It is only recommended for high dispersion work (1200 gr/mm) and calibrations at daytime.

    On special request, it is possible to replace pencil style lamps (Lamp2 ... Lamp5) by other line lamps of the same type, e.g. ORIEL  6034 (HgNe), 6033 (Xe), 6030 (Ar), 6031 (Kr). For calibrations at daytime, it is also possible to couple non-standard user-specific calibration sources to the Calibration Unit by use of a waveguide. Contact PMAS Team for special requests.


    Format of Fiber Spectra 

    (1) Standard lens array IFU ( Fig. 8 ) :
    256 spectra, dispersion along CCD rows, spacing from spectrum to spectrum perpendicular to the direction of dispersion: 14 pixels . Scale: 100um fiber core projecting onto 60um on the CCD, i.e. 4x4 pixels. Corresponding width of spectra perpendicular to dispersion with  ~ 4 pixels FWHM. Typical crosstalk from nearest neighbour: 1% of peak intensity (corrected for by data reduction).
    >> Because of oversampling, 2x2 pixel binning of spec CCD is highly recommended for this mode.<<

    (2) PPAK IFU


    Data format of raw data:
    standard FITS (~17MB for single full frame, unbinned)
     

    Instrument Control Functionality:

  • FSPEC Collimator Focus
  • FSPEC Camera Focus
  • Grating Rotator Angle
  • read Grating ID
  • spec CCD  wipe/bias/dark/exposure control
  • acq CCD  wipe/bias/dark/exposure control
  • Calibration Lamp1 ... Lamp6 on/off
  • Shutter Lamp1 ... Lamp6 open/close
  • move Calibration Unit (Integrating Sphere) in or out of beam
  • select external TV Guider / internal A&G Camera
  • internal A&G camera focus
  • select internal  A&G Camera Filter1 ... 4

  • Instrument Control Software:

  • pics_gui (PMAS Instrument Control Software): exposures/observing (GUI, see   Fig. 9  ,  Fig. 9a )
  • pics_ag : target acquisition and guiding with internal A&G camera (GUI, see   Fig. 10  )
  • various IDL command line programmes, mixed operation with PICS software possible
  • low level EPICS command line operation (maintenance mode)
  • status window (GUI, see   Fig. 11  )

  • Quick Look and Data Reduction Software:

  • P3d_online : online data reduction software for standard IFU and nod-shuffle observations
  • P3d_ppak : online data reduction software for PPAK observations
  • full P3d package : contact PMAS Team for support
  • various IDL utilities
  • DS9 / saoimage

  • Planning Observations, S/N Estimates:

  • each single spectrum is fed from SPAXEL of  0.5" x  0.5" on the sky (default magnification)
  • with recommended 2x2 pixel binning, each fiber projects onto 2x2 = 4 super-pixels
  • CCD readout noise: 5.0 electrons per super-pixel
  • effective dispersion per super-pixel: multiply grating table values by factor of 2
  • total efficiency estimates (including atmosphere and CCD):

  •  
    360 nm 440 nm 550 nm 700 nm 900 nm
    3.8 % 12.7 % 18.7 % 16.9 % 7.7 %

    Remarks:

    1. Listed values are expected performance and, given the early status of the instrument, have not fully been verified yet.
    2. Throughput estimates are based on new aluminized telescope mirrors. For reflectance data of dust contaminated surfaces as a function of time after re-aluminization, consult CAHA Reflectance webpage .
    3. Mean Calar Alto extinction coefficients according to Hopp & Fernandez, CAHA Newsletter 4/2002 , have been applied. Notice that, particularily in early summer and after Sahara desert sand storms, extinction may become considerably worse(especially in the blue).
    4. Grating efficiencies of 60% near blaze have been assumed.


    Special Observing Modes:
    PMAS has a number of special observing modes, which are available on request and on a shared risk basis.
    Please contact PMAS team for details.

  • nod-shuffle 3D spectroscopy for very accurate sky subtraction
  • PYTHEAS mode with scanning Fabry-Perot etalon, see Fig.14 and Fig.15 for demo (commissioning run August 2004)
  • Mosaicking for larger FOV coverage, see Fig.12



  • PMAS Overview page designed by  M. Roth
    Last update January 17, 2006 by  M. Roth