Transcript FMOS mechanical review

Memorandam of the discussion on FMOS
observations and data
kicked off by Ian Lewis
Masayuki Akiyama
14 January 2004
FMOS Science Workshop
Memorandam Format
• Issues listed by Ian Lewis
– Detailed descriptions
– Questions raised
• Possible solution or answer
Observation Modes
• Standard star observations
– Do we need individual observation for a standard star ?
• Yes, potentially.
• Alternative is assign a few fibres to A,F-stars in FOV
• Stare mode
– 10-15 fibres on sky: determin mean sky with the fibres and
subtract the mean sky from object spectra
• Beam switching 1 (simple: obj-sky )
• Beam switching 2 (double-beam: pairs of fibres with objsky and sky-obj)
– What is the best timescale for the switching
• 15min? 30min? Check with the real sky during comissioning
• Out of focused bright star
Observation Data Types
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Normal (stare and beam switch)
Standard star observations
Calibration arcs
Flatfield image
Throughput mapping (on sky)
Slit dither with flat-field lamp illumination
– Purpose : Measure pixel-to-pixel sensitivity variation of detecter
Detector calibration
(Individual data frame preprocessing)
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Dark current
Flat-fielding
Hot/Dead pixels
Cosmic rays
Fringe ? How serious ?
Electrical cross-talk ?
– Especially, for a bright star for atm. Abs. Calibration.
• Linearity
• Memory from bright light source ?
Fibre Flat field Image
• Calibrate spectrum location (tramline mapping)
• Scattered light measurment
• Different illumination
– The light pass for the flat-field light is different from that of the
objects.
Dithered Flat field Image
• Different illumination
– The light pass for the flat-field light is different from that of the
objects.
Arc Calibration
• Wavelength
– OH lines are not uniform in wavelength direction, masked out
– Residual OH lines can be used...
• PSF difference between fibre to fibre
– Ar-lamp has different illumination from target light
Throughput mapping
• Must be done on sky (with fibres in correct configuration
due to spine tilt effects)
– 15% loss at edge of the field with maximum tilt
– flat field lamp : different illumination
• Sky lines missing (OH suppression)
– move slit unit to recover masked
• O2 line can be used at 1.7micron
• We need to take flat-field data for all configuration to
calibrate loss due to fibre entrance tilt
Data reduction
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Data extraction
Frame combination
Flux calibration
A,B beamswitch addition
Header information
– 2dF data pipeline.
Revision of 2dFdr
• FMOS specific issues
– IR-array
• large pixel-to-pixel variation : flat-field before extraction
• flat caribration in lab?
– beam-switching
– flux and absorption calibration
• Alternative software development in UK? Gavin
Implementation?
• Data analysis during observation
– Purpose : Quality control : feedback
– IR-array : Non-destructive read out during exposure ? CIRPASS
• Final data reduction
– No...Big survey
• Automated pipeline
• Semi-automated pipeline (e.g. 2dFDR)
• Independent tasks
Additional Issue
• Input Catalog Accuracy
– 0.2-0.3” is sufficient, and already achived ?
• Slit-gap between J and H band spectra