Astronomical Data Astronomical Data Collection and Processing Collection and Processing

of LLPV’s in GGC’sof LLPV’s in GGC’s at the BGSU Observatory at the BGSU Observatory

J Leon WildeJ Leon Wilde

TAA Seminar, UT, February 2nd, 2007

IntroIntro

• Before observing…

• BGSU’s telescope

• CCD Imaging

• Typical observing night

• Image processing

• My Thesis Work

Before observing…Before observing…

• What to look at

• Where to look from

• What instruments?– 0.5 m Reflecting

telescope– CCD imager

The telescopeThe telescope

Incoming starlight

Secondary Mirror

Primary Mirror

Focus on optics

The CCD ImagerThe CCD Imager

• “Charge Coupled Device”

• Si diodes

• KAF-1000E– Specs .pdf for

KAF-1001E

Why use CCDs?Why use CCDs?

• High QE• High Linearity• Large dynamic

range• Uniform response• Low Noise• Digital

Our CCD’s QEOur CCD’s QE

Blue – KAF-1001EBlack – KAF-1401E

CCD Basic DesignCCD Basic Design

• Our CCD– 24x24 micron pixels– 1024x1024 array

Gate Structure/FunctionGate Structure/Function

• Voltage push

• Sends data to onboard amplifier and A/D converter

• Our CCD– Two phase push– Charge transfer

efficiency = 0.99997

CCD illuminationCCD illumination• Frontside

– Photons pass through phasing gates

– QE lower than Bs

• Backside– Etched back– High QE– Hard to make, thus... – More expensive

• Our CCD– Frontside

CCD DrawbacksCCD Drawbacks

• Noise!– Dark current– A/D conversion– CCD flaws– Worked out during processing

• Expensive!– Delicate manufacturing process– Better science means higher standards

Dark CurrentDark Current

• Thermal activity on CCD chip

CCD LinearityCCD LinearityP

ixel

val

ue (

AD

U’s

)

Integration time (seconds)

SBIG ST8Linearity Test

CCD CoatingsCCD Coatings

• CCDs naturally insensitive to blue

• Coatings used– Coronene & Lumogen phosphors– Lumogen better of the two– Lumogen commercially used in highlighters

• Our CCD– “Blue Plus Transparent Gate”

BloomingBlooming

• Our CCD– No anti-blooming

gates– We’re careful!

Typical NightTypical Night• Arrive an hour before sunset

• Get equipment ready

• Take bias frames / flat field frames

• Observe!

• Take more bias / flat fields

• Send images to Dr. Layden’s computer

• Shut equipment down

• Go home!

Image ProcessingImage Processing• Correct the images

– Optics aren’t perfect (dust donuts, vignetting)– CCDs aren’t perfect– Electronics aren’t perfect– Observers aren’t perfect

• “The problem exists between the chair and the computer.”

• “Garbage in, garbage out.”

• Get science from the data– Convert ‘relative’ values into ‘real’ values

• Programs:– IDL and IRAF

Processing…Processing…• Zero (Bias) frame

– Remove floor value– Subtract combined image from data

• Dark frame– Remove dark current– Subtract combined image from data

• Flat field– Remove non-uniformities arising from:

• CCD flaws• Optics flaws

– Divide combined image from data

Processing…Processing…

• Photometry– RR Lyrae Program, getting star magnitudes

versus time

• Pretty pictures– Combine images from different color filters

Pretty picturesPretty pictures

Ring Galaxy AM 0644-741 from Hubble

My Thesis Work:My Thesis Work:Why Study LPV’s?Why Study LPV’s?

• Variability provides distance calibrations

• LPV’s are understudied

• For SIM (Space Interferometry Mission)

BackgroundBackground

• What are they?

Why look in GGC’s?Why look in GGC’s?

• Stars are of the same age

• Stars are at the same distance

• Stars are similar in composition

DetectionDetection

• Acquire data over long enough time

• Process images

• Image subtraction– DAOPHOT, ISIS

GettingGettingthethe

DataData

NGC 6539NGC 6539

• 5 years of data

• [Fe/H] = -0.66

New GGC’sNew GGC’s

• “New” to us!

• Selected from Harris Catalogue– min Dec– max V_hb– Small:

• Core concentration• E(B-V) - Foreground reddening

– Span of [Fe/H]

PROMPT Images!PROMPT Images!

PROMPTPROMPT

• Back to Harris Catalogue

• Tracked down known LPV’s

• Corrected coordinates

PROMPTPROMPT

• NGC 288

PROMPTPROMPT

• NGC 1261

PROMPTPROMPT

• NGC 1851

Next steps…Next steps…

• Our data:– Finish processing / Photometery– Learn DAOPHOT– Perform DAOPHOT on recent data / NGC

6539

• PROMPT data:– Determine best collection method

ReferencesReferences• People

– Dr Andy Layden for his time, Dr John Laird for his books– Mike Smitka– Brian Pohl & Dr. Bruce Carney, UNC Chapel Hill

• Book– Steve B. Howell, 2000, Handbook of CCD Astronomy, Cambridge University Press

• Websites– http://physics.bgsu.edu/~layden/observatory.htm– http://zebu.uoregon.edu/ccd.html– http://www.ccd.com/ccdu.html– http://www.astro.virginia.edu/class/oconnell/astr511/lec11-f03.html– http://www.wildealien.com/ccd/

• PowerPoint file available online– http://physics.bgsu.edu/~jlwilde/taatalk-feb07.ppt

• Contacting me:

– jlwilde@bgsu.edu

Thanks for your attention!Thanks for your attention!