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Digitized photographic plate photometry with VaST software Kirill - - PowerPoint PPT Presentation
Digitized photographic plate photometry with VaST software Kirill - - PowerPoint PPT Presentation
Digitized photographic plate photometry with VaST software Kirill Sokolovsky Michigan State University and Sternberg Astronomical Instjtute How to fjnd a variable star? One way is image subtractjon... Example of image subtractjon: discovery
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How to fjnd a variable star?
Construct lightcurves of all sources, fjnd which stand out:
- smooth
- high scatuer
- periodic
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How to fjnd a variable star?
Construct lightcurves of all sources, fjnd which stand out:
- smooth
- high scatuer
- periodic
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How to fjnd a variable star?
Construct lightcurves of all sources, fjnd which stand out:
- smooth
- high scatuer
- periodic
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Variability Search Toolkit (VaST)
Original design goals
- Find variable sources in a series of sky images
- Support photgraphic and CCD images
- Can be used interactjvely or as pipeline
- Modest hardware requirements = lots of big images
Open source - comments and contributjons welcome! htups://github.com/kirxkirx/vast htup://scan.sai.msu.ru/vast/
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VaST workfmow
Input: FITS images with obs. date/tjme (plate cutouts)
- Source detectjon/aperture photometry with SExtractor
- Triangle matching -> star matching -> lightcurves
- Plate-solve reference image with Astrometry.net code
- Fix astrometry - TPV/SIP problem
- Match to external catalogs: UCAC5 (μ), APASS B, PS1
- Magnitude scale calibratjon
- Local astrometric correctjons
Result: calibrated lightcurves + source ID
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TPV vs SIP convention problem
Two alternatjve FITS header conventjons to approximate distortjons with polynomials
- SIP supported by Astrometry.net code
- TPV supported by SExtractor & Co
Ignore? There are bigger issues with astrometry... Workaround 1: fjx (R.A.,Dec.) in SExtractor catalog with xy2sky from WCStools Workaround 2: wcs-addpv.py by Evert Rol htups://github.com/evertrol/sippv
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TPV vs SIP: illustration
Cutouts from 10 plates median-stacked with SWarp ignore the problem apply wcs-addpv.py
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Flatbed scanner vs. astrometry
Mitjgated with local correctjons, no hope for science, just ID The “hacksaw” patuern and stjtches
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Flatbed scanner vs. astrometry
The stjtch is hard to see (its in the marked area)
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Magnitude calibration
plate-to-plate plate-to-catalog We use the fjttjng relatjon suggested for DSS by Bacher, Kimeswenger & Teutsch (2005 MNRAS, 362, 542)
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Filtering SExtractor detections
To remove blended and extended sources (that will have bad photometry) reject outliers in mag-size curve
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VaST -> lightcurves of all sources
The lightcurves may be (non)interactjvely earched for variability using “variability index”-mag. plots or processed with external sofuware like VARTools (period search, etc.)
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VaST testing
- Automated testjng
- VMs with various Linux & FreeBSD versions
- Profjling with Valrind
- Memory debugging: Valgrind & AdressSanitjzer
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Image access
We are testjng web interface providing cutouts from Moscow “A” series plates:
- 40cm astrograph
- 10x10 deg, 30x30cm plates
- limit B<17
- fjve fjelds digitjzed so far
- 169 to 413 plates/fjeld
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Image access
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Image access
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Image access
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Photometry of known variables
Exotjc example: Radio galaxy 3C 282 = 1833+326 most are eclipsing binaries and red irregular variables >2000 known variables passed automated scatuer/smoothness-based variability selectjon. Photometry available at htup://scan.sai.msu.ru/pl/
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Summary
- VaST is an open code that constructs lightcurves from
a series of photographic (or CCD) images
- Can be used interactjvely or as a pipeline
- We use it for variable star studies with digitjzed
Moscow collectjon plates
- Test access to the images of fjve 10x10 deg fjelds and