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 obj-sky 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• 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)

• 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

• 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