Astronomical Photometry

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Astronomical Photometry

• How to get from there
• to here

Stars, sky, observing, telescope, filters,
detector, noise, reduction, graphing
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Apparent magnitude of a star will depend
on Luminosity Distance (F is flux) Stuff
in between it and us (extinction reddening)
Stars
Definition of magnitude (visual wavelengths)
Definition of color of a star
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Getting the effective temperature of a star using
UBVRI FILTERS
Color of star will also depend slightly on
chemical composition (metal-rich vs metal-poor)
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Filters
B V R
B V R
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We always use filters. Original filter set was
for a photometer, not CCDs. Telescopes may have
different sets of filters (width and peak of band
passes may differ, response may differ) may need
to TRANSFORM magnitudes to a standard system.
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Reddening (de-bluing)
Antares/Rho Ophiuchus Region
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Color Excess
Slope of the reddening line for stars earlier
than A0
Find star here Extrapolate there
For cooler stars, must use spectroscopy.
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Sky
Bad, badder, baddest!
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Z
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Observations
CVs
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FIG. 1.Light curves are presented for the six
variable stars. Points represent observed data in
B (filled circles), V (asterisks), and I (open
circles). The dotted curves represent the
best-fitting template to the observed data. The
vertical axis in each panel spans 2 mag.