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

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:

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

Filters B V R B V R

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.

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

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

Sky Bad, badder, baddest!

Z ADVANTAGES OF DIFFERENTIAL PHOTOMETRY

Observations CV’s Cataclysmic variables

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC, 114: 645-649, 2002 June ｩ 2002. 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.