Notes and presentations at: www2.le.ac.uk/departments/physics/people/ academic-staff/slc25

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1 Department of Physics & Astronomy IR data reduction: Lecture 1 Sarah Casewell :slc25@le.ac.uk Notes and presentations at: www2.le.ac.uk/departments/physics/people/ academic-staff/slc25

2 Infrared

3 Why the IR

4 What this course will cover: Planning IR observations IR imaging reduction IR spectroscopy reduction Use of MOPEX Use of Gasgano Use of IRAF and XMOSAIC IR spectra reduction with Figaro

5 Imaging Spectroscopy Bias frame (optional) Flat field Dark Standards Bias frame Flat field Dark Arcs Standards

6 Bias Bias is the offset that is induced so that the ADC doesn t have to handle negative numbers. Images taken with shutter closed. Very short exposures Take ~10 and combine them all to make a master bias Normally taken in the daytime or before opening

7 Bias Bias is the offset that is induced so that the ADC doesn t have to handle negative numbers. Images taken with shutter closed. Very short exposures Take ~10 and combine them all to make a master bias Normally taken in the daytime or before opening

8 Flat field Normally fall into 2 types: Screen/Dome or Twilight Images taken with shortish exposures Take them in every filter you will use Take ~10 and combine them all to make a master flat Normally taken in the daytime or in twilight

9 Flat field Twilight flats: Need to not have stars in the image! Exposure times will increase as it gets daker Jitter the telescope Primarily for removing dust marks, defects on the detector

10 Flat field Twilight flats: Need to not have stars in the image! Exposure times will increase as it gets daker Jitter the telescope Primarily for removing dust marks, defects on the detector

11 Flat field Dome flats:more common for IR Light on a screen or inside the dome Some instruments : Gemini NIRI have an internal lamp Lamp on/lamp off use to make a bpm Primarily for removing dust marks, defects on the detector

12 Flat field Dome flats:more common for IR Light on a screen or inside the dome Some instruments : Gemini NIRI have an internal lamp Lamp on/lamp off use to make a bpm Primarily for removing dust marks, defects on the detector

13 Flat field Dome flats:more common for IR Light on a screen or inside the dome Some instruments : Gemini NIRI have an internal lamp Lamp on/lamp off use to make a bpm Primarily for removing dust marks, defects on the detector

14 Darks Use to remove dark current Must be same exposure time as exposures Particularly important for the IR

15 Darks Use to remove dark current Must be same exposure time as exposures Particularly important for the IR

16 Arcs Arc lamp usually inside the spectrograph (Ar, Ne, Xe) Used to calibrate the wavelength Important that it s taken in same grating and slit Important that it s taken at the SAME telescope position as the target unless instrument is stable Short and long exposures possible

17 Arcs Arc lamp usually inside the spectrograph (Ar, Ne, Xe) Used to calibrate the wavelength Important that it s taken in same grating and slit Important that it s taken at the SAME telescope position as the target unless instrument is stable Short and long exposures possible

18 Arcs Arc lamp usually inside the spectrograph (??) Used to calibrate the wavelength Important that it s taken in same grating and slit Important that it s taken at the SAME telescope position as the target unless instrument is stable Short and long exposures possible Can also use OH sky lines in the IR

19 Imaging

20 Jitter/Dither/Offset

21 Imaging 1. Sort out the frames according to their object types and exposure times: (hselect in IRAF, more in a non-resized terminal) 2. Subtract a bias frame (if you have one) from all other frames 3. Investigate what sort of flat you have and process accordingly 4. Divide all remaining frames (arc, std, object) by the flat 5. BPM subtract, Sky subtract, Mosaic

22 Imaging 6. Astrometry 7. Photometric calibration and ZP determination

23 To catalogue or to standard? Standard more accurate account of airmass BUT only one object. Easy to saturate May not be observed in your filter Need aperture correction Catalogue more objects BUT may be of wide range of spectral types Need a large field of view Eddington Bias Colour corrections easier

24 Imaging ORAC-DR GASGANO IRAF All will: Bias/Dark subtract, flat divide, Sky subtract and mosaic IRAF and XMOSAIC later in course

25 Spectroscopy

26 Spectroscopy 1. Sort out the frames according to their object types and exposure times: (hselect in IRAF, more in a non-resized terminal) 2. Subtract a bias frame (if you have one) from all other frames 3. Investigate what sort of flat you have and process accordingly 4. Divide all remaining frames (arc, std, object) by the flat 5. Locate the spectrum on the chip. Take a slice through it to verify it is the correct object.

27 Spectroscopy 6. Subtract in relevant pattern 7. Extract spectrum 8. Extract arc using same aperture as spectrum 9. Extract standard and its arc as above 10. Apply wavelength correction to std and data 11. Model/edit standard to account for H lines 12. Divide spectrum by std, then multiply by bbody

28 Spectroscopy

29 Next week: Workshop on Spitzer data reduction Will need to install Mopex on laptop or use system version Data available from here: /data/77/slc25/spitzer_workshop Workshop here:/data/77/slc25/spitzer_workshop Need to have mopex from spitzer installed

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