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Infrared Photoelectric Photometry Program

What is Infrared Photometry?

Infrared astronomy is an exciting new area of observation and study for the amateur astronomer, and there is huge potential for amateur astronomers to break new ground and contribute important observations to this exciting field of research. The infrared region of the spectrum is typically defined as light with wavelengths greater than 1.1 micron. Human vision ends at about a wavelength of 0.75 micron. Members of the AAVSO and Optec, Incorporated have worked together to develop the SSP-4 infrared photometer. The SSP-4 photometer is designed to precisely measure light in the J (1.25 micron) and H (1.65 micron) bands. More information about the SSP-4 photometer can be found at the link above.

So why would the AAVSO want to measure variable stars in the J and H band? The infrared bands give information about variable stars that cannot be determined from the visual bands (CCDV or PEP). For example, a Mira type variable star measured in the infrared has a much smaller amplitude of variation. The infrared light curve relates more closely to the actual temperature and radius change of the star as it pulsates, unlike the visual light, which traces the opacity of the atmospheres. This gives theoretical astronomers a better understanding of the physical processes that occur in pulsating stars. (Mira variables also radiate the vast majority of their light at infrared wavelengths, and in infrared light, many of these stars are among the brightest in the sky, making their smaller amplitudes easy to detect.)

Observations of certain kinds of eclipsing binaries are also very useful because they can help us better determine the properties of binaries. When the stars in the system have very different temperatures, such as in the case of Algol, it is very important to be able to estimate the separate temperatures. In the ultraviolet, the secondary eclipse of Algol is barely detectable but in the IR, it is quite deep, this leads to a more accurate solution. Studies of binaries with spots -- such as the RS CVn stars -- benefit from IR observations because they enable us to better determine the temperatures of the spots.

Observation in the infrared region of the spectrum has a few advantages over photoelectric photometry in the visual bands. The atmospheric extinction is much less in the infrared when compared to the visual. As a result, differences in airmass between the comparison and target star don't introduce as much error as in the visual bands. In a light polluted city sky the infrared sky is much darker because most of the man made light pollution is in the visible band. And some stars are far, far brighter in the infrared, making it easier to perform high signal-to-noise photometry.

Current Status of AAVSO IR Photometry Group

A list of target and comparison stars for the Infrared Photoelectric Photometry Program may be found at this link: SSP-4 Targets and Comparison Stars.

The AAVSO Infrared Photometry is currently a small group of observers, but it has a lot of potential for breaking new ground and doing good science.  Hundreds of J and H band observations have already been submitted to the AAVSO database for archive. In 2010, IR-PEP observers submitted over 300 J and H observations of the following stars: epsilon Aurigae, beta Lyrae, U Aurigae, NO Aurigae, NSV 2537, rho Persei, zeta Aurigae, PU Aurigae, R Lyrae, UU Aurigae, lambda Andromedae, R Leporis, and miu Cephei. 

Many thanks to all of our IR PEP observers for participating in the AAVSO Infrared Photoelectric Photometry Program!

If you are interested in trying IR PEP, please let us know -- we have a waiting list of observers, and if one of the AAVSO's SSP-4 units becomes available, you can obtain one on loan for as long as you continue to make observations. If you are a researcher at a college or university with a campus telescope, or you belong to an Astronomy club with a private observatory, please contact us about collaborating on small research grant proposals to obtain a photometer.

Further reading

Return to the AAVSO Photoelectric Photometry Program

AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484