CCD Imaging David Richards 2004 -04 -13 All

CCD Imaging David Richards 2004 -04 -13 All astronomical images taken by David Richards, 2001 -2004 (Meade 8” LX 200 SCT / SBIG ST-7 E )

CCD Imaging n Introduction n CCD Imaging Basics n n n CCD Chips and Cameras Considerations when choosing a CCD Camera Colour Imaging Comparison with Eyepiece View and Film CCD Images n n n Components of a raw CCD Image Reduction and Processing (Light, Dark and Flat Frames) CCD Cameras n n Example CCD Targets Typical CCD Results compared to Eyepiece View Moon, Planets Asteroids, Comets Stars, Clusters & Nebula Galaxies, Supernova Science with CCD Camera n n Astrometry Photometry

Example CCD Targets Planets and other Solar System Objects Nebulae Stars and Clusters Galaxies

Typical CCD result compared with Eyepiece View CCD (processed) Notebook Drawing, 1997 Eyepiece View M 51 (Ursa Major) 15 x 1 min exposures Simulated

Longer Exposure – Greater Magnitude Reach Consecutive CCD images (star field in Milky Way in Cygnus) 2003 -08 -05 5. 2 x 7. 6 arc mins (suburban site, Dorset, UK) The 10 sec exposure reaches to mag +12. 0 whilst the 40 sec exposure reaches to +13. 5

Deep Sky - Abell 744 Galaxy Cluster CCD Image, 3 x 60 sec exposure (summed) The image records distant galaxies down to magnitude +17

CCD Imaging – The Basics CCD Camera (CCD Chip, Circuit Board, Electronics, Shutter, Cooling Equipment, Housing) Object Telescope CCD Chip Focuser Attachment Photon Shutter Light Sensitive Area photons recorded as electrons in ‘square light buckets’ 0 0 0 0 1 5 7 67 2 8 0 0 0 1 3 1 0 0 0 Electronics USB or Parallel Cable 0 0 0 Computer Ram Hard Drive Software 0 0 1 5 7 67 2 8 0 0 0 1 3 1 0 0 0 Computer Screen

CCD Imaging involves some work Final Image Single Raw Image

Raw CCD Image Light from Sky / Aberdeen Satellite Or Aircraft Trail Light from Galaxies and Stars Defective Pixel(s) Noise Cosmic Ray Light Gradient Noise Single Raw Image Dark Current Read Out Noise Dust Shadows Vignetting Pixel to Pixel Variation in Sensitivity Let’s examine the components of this image

Stacking increases S/N Single Raw Image (realtime contrast) (summed, no alignment) 15 stacked frames (aligned and summed) Single Raw Image (adjusted contrast) 15 stacked frames (aligned & median combined)

Cross-Section through a CCD Image (1) Simulated image of light reaching camera in earth orbit Simulated image of light reaching camera at Sea Level Cross Section Light from 3 Objects

Cross-Section through a CCD (2) Light from 3 Objects (after dispersion through the atmosphere)

Cross-Section through a CCD Raw Image as recorded

Sky brightness

Cross-Section through a CCD (3) Addition of Sky Glow / Light Pollution

Effect of Vignetting and Dust and Pixel-to-Pixel Variation in Sensitivity Av. 40 x 0. 5 sec flat frames (tee-shirt flats)

Cross-Section through a CCD (4) Vignetting at edge of frame

Cross-Section through a CCD (5) Absorption of light from dust on lenses and CCD window / chip and Variation in Pixel to Pixel Sensitivity

Dark Current (electrons counted due to ‘heat’, even in the absence of light)

Cross-Section through a CCD (6) Addition of thermal electrons during exposure (includes noise)

Dark Current vs Time All Frames -25 deg C and identical white-black range 10 sec (Black = 0 ADU / White = 1000 ADU) 60 sec 120 sec 300 sec

Dark Current vs Temperature All Frames 60 s exposure and identical white/black range -5 deg C (Black = 150 ADU, White = 300 ADU) -15 deg C -25 deg C Colder Astronomical Cameras typically cool CCD chips to 30 deg C below ambient (using Peltier cooling)

Dark Current vs Camera Simulated 60 s exposures shown with identical white/black ranges Low Spec Camera -15 deg C Mid Spec Camera -15 deg C High Spec Cameras

Cosmic Rays Dark Frame Light Frame Dark Frame

Read Out Noise (Bias Frame – a 0 sec exposure) -15 deg C

Cross-Section through a CCD (7) Addition of Readout Noise (+/-)

Cross-Section through a CCD (9) Raw Image as recorded

Cross-Section through a CCD (10) Raw Image with Black Threshold applied Compare with light from 3 objects

Getting Good Images A principal aim during imaging (and subsequent reduction) is to maximise the Signal-To-Noise (S/N) in order to get the best image of the astronomical object. Techniques include : n n n n n Minimise noise from sky light by imaging from a dark site (if possible) Cool the CCD Chip as far as possible (temperature control important) Use longest exposure that telescope can track for without drifting, and without over-saturating the chip. Using on camera pixel binning (may decrease resolution – but not if seeing limited) Use camera with low read out noise / low dark current Reduce images to remove dark current, allow for the varying response of each CCD pixel and remove the impacts of vignettting and dust on CCD chips or telescope optics Minimise read-out and dark noise (using Median of multiple Dark Frames) Use average (or median) of multiple Flat Frames Use stacking to ‘add’ light from target, whilst cancelling noise – thereby increasing the S/N

Longer Exposure – Higher S/N

Reduction Steps (1) Raw Light Frame Dark Reduced Frame Dark Frame - = Removal of Dark Frame (an image with same exposure length but taken with closed shutter) Done in order to reduce read-out & thermal noise

Reduction & Processing Example Raw Light Frame (60 s) Dark Frame (median of 9) Final Image (15 frames stacked) Reduced Light Frame

Reduction Steps (2) Raw Flat Frame Even Light Flat Frame Dark Frame (same Raw Flat Frame (after dark subtraction) exposure as flat frame) - Creation of Flat Frame =

Flat Frame Av. 40 x 0. 5 sec flat frames (tee-shirt flats)

Reduction Steps (3) Flat Normalised Flat / Average Flat Field Value = Normalised Flat Dark Reduced Frame / Final Image

Final Processing Final Reduced Image Final Image (with Black Threshold Set) Wavelet Processed (Deconvolved) Image (assumed shape of atmospheric dispersion) Deconvolved with =

The challenge of recording very faint objects Attempt at imaging 2004 DW (a mag +19 Kuiper Belt Object). Star field in Hydra with the predicted position of Kuiper object marked by green circle. 2 x 5 min exposure (summed) Faintest visible objects are mag +17. 7

Reduction/Stacking Example IC 434 (Horsehead Nebula) 60 s Raw 11 aligned frames summed 60 s Reduced (dark subtract) Final Image

Reduction/Stacking Example NGC 2903 60 s Raw 60 s Reduced (dark subtract) Average 10 x 60 s

CCD Cameras SBIG (USA) e. g ST-7 e, $1995 (US) Starlight Express (UK) e. g HX-916 (Mono) £ 1395 Apogee (USA) Web. Cam eg Philip To. UCam Pro II, £ 75 Low Light Video e. g. Watec 120 N, £ 579 HX 7 -C (Colour) £ 995 e. g. Astrovid, $ 995 (US)

Example range of CCD Cameras n Cookbook CCD Cameras TC-211 (Mono) 13. 8 x 16 um, 192 x 164 px, 2. 6 x 2. 6 mm n Electronic Eyepieces Meade Electronic Eyepiece TV/VCR/Camcorder connection n Web. Cam Based Cameras Philips To. UCam Pro , Video 5. 6 x 5. 6 um, 640 x 480 px, 4. 6 x 4. 0 mm n Digital Cameras Various £ 200 - £ 400 n Long Exposure Video CCD Cameras Minitron Watec 120 N 8. 6 x 8. 6 um, 752 x 582 px, 6. 5 x 5. 0 mm, 0. 00002 lx , 0. 15 kg £ 299 £ 579 n Smaller CCD Cameras Starlight Express MX 5 (Mono) 9. 8 x 12. 6 um, 500 x 290 px, 4. 9 x 3. 6 mm, Starlight Express MX 5 C (Colour) £ 495 £ 620 n ‘Standard’ Size CCD Cameras Starlight Express MX 716 (Mono) 8. 6 x 8. 3 um, 752 x 580 px, 6. 47 x 4. 83 mm, 0. 2 kg, SBIG ST-7 XME, 9 x 9 um, 765 x 510 px, 6. 9 x 4. 9 mm, 0. 9 kg, £ 895 $1995 (US) n Large Format CCD Cameras Starlight Express HX 916 (Mono) SBIG ST-9 X SBIG ST-8 XME, £ 1345 $3195 (US) $5995 (US) n Very Large Format CCD Cameras Starlight Express SXV-M 25 (Col) 7. 8 x 7. 8 um, 3000 x 2000 px, 23. 4 x 15. 6 mm, SBIG STL-11000 CM 9 x 9 um, 4008 x 2745 px, 36 x 24. 7 mm (26 sec download) £ 50 -100 £ 90 £ 75 6. 7 x 6. 7 um, 1300 x 1030 px, 8. 71 x 6. 9 mm, 0. 25 kg, 20 x 20 um, 512 x 512 px , 10. 2 x 10. 2 mm 9 x 9 um, 1530 x 1020 px, 13. 8 x 9. 2 mm, 0. 9 kg, Spring 2004 $8995 (US)

Considerations when choosing a CCD Camera n n n n n Chip Size / Pixel Size / Number of Pixels / Pixel Shape Match with Telescope Focal Length Sensitivity of CCD Dark Current / Read Noise Cooling / Temperature Regulation / Shutter Digitisation (12 bit/ 16 bit) Linearity of CCD / Capacity of a pixel Anti-Blooming (ABG vs NABG) CCD Quality / Defective Pixels Camera Weight / Size Binning / Windowing Capabilities Download Speed, USB / Parallel Self Guiding Capabilities Single Shot Colour / Filter Wheel attachment Software Cost Reliability / Support

Example Spectral Response Curves

CCD Chip Sizes Compared with 35 mm Film TC 211 ST 7 ST 8 KAF 0400 KAF 1600 New Large Format Cameras SLR 35 mm film Camera

Matching CCD and Telescope (1) n Calculating Image Scale (arc secs per pixel) Image Scale = 206 x pixel size (in um) ----------focal_length (in mm) e. g for SBIG ST-7 and 8” f/10 SCT Pixel Size = 9 um Focal length = 25. 4 x 8 x 10 = 2032 mm Image Scale at 1 x 1 binning = 206 x 9 / 2032 Image Scale at 2 x 2 binning = 206 x 18/2032 = 0. 9 arc sec/pixel = 1. 8 arc sec /pixel Typical seeing is 2 -4 arc sec, so 2 x 2 binning (1. 8 arc sec/pixel) is about right (At 2 x 2, sensitivity is better and downloads are much faster, but images are only 382 x 255) 1 x 1 binning only really of benefit when imaging planets when there is benefit in sampling at <1 arc sec, and there is opportunity to benefit from brief moments of exceptional seeing With Focal Reducer (63%) 1 x 1 binning = 1. 3 arc sec/pixel, 2 x 2 binning = 2. 5 arc sec/pixel n General rule : chose CCD (or choose Telescope) that gives around 2 arc sec /pixel

Matching CCD and Telescope (2) n Calculating Field Of View Field (Horizontal) in arc mins Field (Vertical) in arc mins) = Image Scale x No. pixels (horizontal) / 60 = Image Scale x No. pixels (vertical) / 60 e. g for SBIG ST-7 and 8” f/10 SCT Pixel Size = 9 um, Focal length = 25. 4 x 8 x 10 = 2032 mm Image Scale at 1 x 1 binning = 206 x 9 / 2032 = 0. 9 arc sec/pixel (765 x 510) Field (Horizontal) = 0. 9 x 765/60 = 11. 4 arc min Field (Vertical) = 0. 9 x 510/60 = 7. 7 arc min With focal reducer (63%) Field (Horizontal) Field (Vertical) n Image Scale at 2 x 2 = 2. 5 arc sec/pixel (382 x 255) = 2. 5 x 382/60 = 15. 9 arc min = 2. 5 x 255/60 = 10. 6 arc min General rule : Dependant of proposed Targets chose a Camera with a larger dimension CCD to gives a larger FOV (price will be a limitation). Alternatively select a low focal ratio telescope (eg f/4) or use a focal reducer

CCD Cameras – with ordinary Camera Lens n CCD Cameras can also be used piggy-backed to a Telescope and fitted with ordinary camera lenses. This can provide wider fields of view Important to use Good Quality Lenses ST 7 e with 200 mm lens

Long Exposures / Guiding (1) n Unless a scope is perfectly polar aligned and has perfect tracking, stars will trail on long exposures (at focal length of 2000 mm this might be observed after only 2 mins exposure) Simulated unguided image of M 51 12 min exposure n Two main solutions to the problem - Take short (60 sec) exposures, then align & stack - Guide the telescope during the exposure

Long Exposures / Guiding (2) n CCD manufactures have developed several alternative guiding solutions : n n Track and Accumulate (SBIG) Expose Separate CCD Camera (e. g Meade) Guide Expose Guide Finder Expose Off-Axis Guide Camera Main Camera n Self Guided (SBIG) Telescope Guide CCD Main CCD n Star 2000 (Starlight Express) Guide Frames Camera Interline CCD Image Frame

Colour Imaging (1)– Single-Shot Cameras

Colour Imaging (2)– Using Filters Colour Filter Wheel SBIG CFW-8 A Red, Blue, Green, Clear Filters Option to take and image in other filter bands e. g UBRVI for photometry

Colour Imaging – with Filters Red (Av. 3 x 10 s) Green (Av. 3 x 10 s) Blue (Av. 3 x 20 s) Colour Image (LRGB) Luminance (Av. 6 x 10 s) M 42 (Orion)

CCD Imaging compared with Eyepiece Viewing +ve n n n n Can ‘see’ fainter objects (i. e. can ‘see’ objects impossible to see with the naked eye) Much easier to record and share what has been ‘seen’ Can generally ‘see’ more detail in objects (particularly nebula) Can find and locate objects more quickly (with appropriate software) Can even view from the leisure of indoors (with remote connection) Can playback /animate motion of slowly moving objects (eg Pluto) Can acquire the colour of faint objects (ones which look grey to naked eye) Can undertake more accurate (certainly easier) astrometry and photometry -ve n n Some objects more impressive with naked eye (eg red/blue double star , Jupiter + moons) Loose some of that ‘ 3 D’ effect & feelings of awe Difficulty of claiming one actually saw / observed the object Realtime CCD images are often very noisy

Typical realtime CCD image compared with Eyepiece View CCD (raw image on screen) Eyepiece View M 51 (Ursa Major) 1 min exposure

CCD – Comparisons with Film +ve n CCD Images immediately available (no waiting on film lab) n Digital (no need to scan in order to process further), Easier manipulation - ability to stack n Light record is linear (no recripicty) n With suitable software the image can be used to automatically locate telescope position or to guide the telescope. -ve n Smaller image area FOV (typically only ~ 20% that of 35 mm film)

Comparisons of CCD Images with Film and Eyepiece Observations Recording of naked eye observation Film CCD

Use and Sharing of CCD Images Astronomical Records World Wide Web Presentations Own records

CCD Images (2001 -2004)

Moon

Moon – Apollo 17 Landing Site

Planets Venus 2004 Uranus 2002 Mars 2003 Jupiter 2003 Neptune 2002 Saturn 2001 Pluto 2003

Jupiter / Saturn / Uranus Moons Six of Saturn's moons appear in this CCD Image (2 sec exposure)

Asteroids (Minor Planets) Animated Sequence of 10 CCD Images of Minor Planet Kleopatra (216) The animation records 58 arc sec motion of the minor planet over a period of 1 hr 56 min (= 30 arc sec/hour).

Near Earth Asteroid

Comets C/2002 T 7 (Linear) 2004 -Feb Comet C/2000 WM 1 (LINEAR) 2001 -Nov (passing through star field in Pegasus) (passing through star field in Aries)

Clusters in Gemini (CCD Mosaic) M 35 NGC 2158

M 45 Pleiades (CCD Mosaic)

Double Cluster In Perseus (7 x 6 CCD Mosaic, 20 s exposures)

Globular Cluster M 15 (Pegasus), 6 x 10 s

Extra-Solar Planets ? HD 209458 (Pegasus) has a transiting Jupiter mass short period extrasolar planet. (HD 209458 b). Every 3. 5 days, the planet produces a dimming of the star of 1. 7 % that lasts for about 3 hours. The dimming has been detected by Castellano and Laughlin using almost identical equipment to me (ie 8" telescope and ST-7 E CCD camera), which presents me the opportunity to also have a go at trying to detect a extra-solar planet lying at a distance of 1. 45 x 1015 km (153 light years) from Earth. .

Nebula M 57 Ring Nebula (Lyra) M 16 Eagle Nebula (Serpens Caput) M 27 Dumbbell Nebula (Vulpecula) NGC 2261 - Hubble's Variable Nebula (Monoceros)

NGC 4567 / 4568 (Virgo) Galaxies NGC 7331 (Pegasus) M 100 (Coma Berenices) M 105 (Leo) NGC 2903 (Leo) M 64 Black-eye Galaxy (Coma Berenices) NGC 2903 Spiral Galaxy

Galaxy Cluster NGC 7320 Galaxy Cluster (Stephan's Quintet, Andromeda) The 5 main galaxies range from magnitude +13. 6 to + 14. 8 Faintest galaxy in image is +16. 6 2002 -10 -02 21: 44 to 21: 51 h UT CCD Image, 2 x 2 min exposure (2 x 2 binning) 11. 4 x 7. 6 arc min (#28003 & 28005)

Supernova / Supernova Remnants M 1, Crab Nebula SN 2001 ib, 2001 -Dec

Colour Imaging - 2004 M 42 Orion NGC 2392 Planetary Nebula (Eskimo or Clown Face Cluster) NGC 2903 Spiral Galaxy, Leo NGC 1857, Auriga Saturn Jupiter

More Recent Images NGC 3628 Spiral Galaxy, Leo M 63 Spiral Galaxy (Sunflower Galaxy)

M 65 Area

Out-takes (1)

Out-takes (2)