These are the slides for a talk I gave to the imaging group of the Astronomical Society of South Australia about DSLR photometry of variable stars on November 27 2015.
2. Outline
Brief overview of variable stars
The varieties of variable star observing
What’s the goal?
Getting started with DSLR photometry
My setup
Procedure
8. Variable Star Observing Varieties
Visual variable star estimation since 2009
Mostly binocular
Simple (technique, equipment) & quick
Great for long period variables, novae
~0.1 magnitude precision
Wide-field DSLR photometry since late 2014
~0.01 magnitude precision
Can quantify error
Not as precise as CCD or PEP but 10x lower cost
Repeatability; data re-use in future, e.g. for B, R
20. Some Considerations
B, V, R possible from a single image
May be more than one variable per image
ISO 100 or 200 or 400 for high dynamic range
Exposure: depends upon tripod vs tracked
Turn off auto features
noise reduction
lens cleaning
21. Procedure
Finder chart & photometry table
Locate field, take test frame to verify
Make notes, e.g. of conditions!
Deliberately under-focus for photometry
Convert RAW to software’s format, e.g. FITS
Calibration: lights, biases, flats, darks (maybe)
Stellar registration, for automatic photometry
22. Procedure
Extract green (or blue or red) channels
Determine photometry radii
Local coordinates of target, reference stars
Some software may automate via plate solve
Photometry on individual or stacked images
Look at error, residuals; change one or more reference
(comparison, check) stars if too high
Ensemble-based transformation to V (or B or R)
24. Photometry Table from Finder
Have to consider:
• Magnitude
• B-V
when choosing reference stars.