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

•  www.le.ac.uk

Department of Physics & Astronomy

Infrared

Why the IR

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

Imaging

•  Bias frame (optional)

•  Flat field

•  Dark

•  Standards

•  Bias frame

•  Flat field

•  Dark

•  Arcs

•  Standards

Spectroscopy

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

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

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

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

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

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

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

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

Darks

•  Use to remove dark current

•  Must be same exposure time as exposures

•  Particularly important for the IR

Darks

•  Use to remove dark current

•  Must be same exposure time as exposures

•  Particularly important for the IR

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

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

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

Imaging

Jitter/Dither/Offset

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

Imaging

6.  Astrometry

7. Photometric calibration and ZP determination

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

Imaging

•  ORAC-DR

•  GASGANO

•  IRAF

All will: Bias/Dark subtract, flat divide, Sky subtract and mosaic IRAF and XMOSAIC later in course

Spectroscopy

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.

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

Spectroscopy

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