ASSA imaging group DSLR Photometry Talk 27 Nov 2015

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Transcript of ASSA imaging group DSLR Photometry Talk 27 Nov 2015

DSLR Photometry

DSLR Photometryof Variable StarsDavid Benn, Nov 2015

OutlineBrief overview of variable starsThe varieties of variable star observingWhats the goal?Getting started with DSLR photometryMy setupProcedure

Introduction to Variables

Source: Society for popular astronomy

Introduction to Variables

Introduction to Variables

https://en.wikipedia.org/wiki/File:Eclipsing_binary_star_animation_2.gif

Introduction to Variables

http://www.citizensky.org

Introduction to Variables

http://www.astrosurf.com/aras/novae/Nova2013Del.html

Variable Star Observing VarietiesVisual variable star estimation since 2009Mostly binocularSimple (technique, equipment) & quickGreat for long period variables, novae~0.1 magnitude precisionWide-field DSLR photometry since late 2014~0.01 magnitude precisionCan quantify errorNot as precise as CCD or PEP but 10x lower costRepeatability; data re-use in future, e.g. for B, R

+ CHOICE courses

Whats the goal?

Whats the goal?

Whats the goal?

finder chart of W Sgr to describe technique

Visualhttp://www.citizensky.org, Southern Gems tutorial

DSLR Photometry: My SetupOverall motivationlow cost, timesuburban backyardCanon 1100D with 200mm lens on LX-90 or tripodCard table and light shield; light box for flats Free or readily available software IRIS (free; WINE on Mac), AstroImageJ, Muniwin, Spreadsheet (Excel, OpenOffice)Sky Safari Pro (telescope control, with SkyFi)

DSLR Photometry: My Setup

DSLR Photometry: My Setup

DSLR Photometry: My Setup

My Setup

DSLR Bayer Arrayhttps://en.wikipedia.org/wiki/Bayer_filter

Some ConsiderationsB, V, R possible from a single imageMay be more than one variable per imageISO 100 or 200 or 400 for high dynamic rangeExposure: depends upon tripod vs trackedTurn off auto featuresnoise reductionlens cleaning

ProcedureFinder chart & photometry tableLocate field, take test frame to verifyMake notes, e.g. of conditions!Deliberately under-focus for photometryConvert RAW to softwares format, e.g. FITSCalibration: lights, biases, flats, darks (maybe)Stellar registration, for automatic photometry

ProcedureExtract green (or blue or red) channelsDetermine photometry radiiLocal coordinates of target, reference starsSome software may automate via plate solvePhotometry on individual or stacked imagesLook at error, residuals; change one or more reference (comparison, check) stars if too highEnsemble-based transformation to V (or B or R)

Photometry Table from Finder

Have to consider:

Magnitude B-V

when choosing reference stars.

Deliberately under-focus

DSLR: Bayer Array

Calibration

CFA Conversion

Stellar Registration

Extract R, G, B channels

green channel: img-gN

Target Region

Target Region

Aperture Photometry

Aperture Photometry

Aperture Photometry

Aperture Photometry

Differential Photometry

Source: AAVSO DSLR manual

Linkshttps://aavso.orghttp://www.variablestarssouth.orghttps://en.wikipedia.org/wiki/Binary_star https://www.cfa.harvard.edu/news/2009-23http://astro.unl.edu/naap/ebs/animations/ebs.htmlhttp://www.popastro.com/news/newsdetail.php?id_nw=174https://www.aavso.org/observed-minima-timings-eclipsing-binarieshttps://en.wikipedia.org/wiki/Color_filter_array