1. Astronomical Photometry
How to get from there
to here
Stars, sky, observing, telescope, filters, detector,
noise, reduction, graphing

2. Stars 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):
Star A == Vega or standard star
Magnitudes and colors are calibrated in terms of standard stars
Vega chosen so that magnitudes are 0 at all wavelengths
Definition of “color” of a star:

3. 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)
BUT, IT IS MORE complicated than just that

4. Filters
B V R
B V R

5. We have research-grade UBVRI Bessell filters
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.

7. Reddening
(“de-bluing”)
Antares/Rho Ophiuchus Region

8. Slope of the reddening line for stars earlier than A0: Find star here
Color Excess
Slope of the reddening line for stars earlier than A0:
Find star here
Extrapolate there
For cooler stars, must use spectroscopy.
EXTINCTION VARIES WITH WAVELENGTH

9. Sky
Bad, badder, baddest!

10. Z
ADVANTAGES OF DIFFERENTIAL PHOTOMETRY

11. Observations
CV’s
Cataclysmic variables

13. PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC, 114: , 2002 June ｩ The Astronomical Society of the Pacific. All rights reserved. Printed in U.S.A
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.