Infrared photometry is yet another area where amateurs are encroaching on what used to be the sole domain of professionals. Two amateurs, in particular, have been collecting an amazing near-IR light curve of epsilon Aurigae.
Below is the J and H-band light curve of epsilon Aurigae over the last 1000 days, with the V band light curve also plotted for comparison. Most of the J and H-band data comes from Brian McCandless (MBE) or Tom Rutherford (RTH). They are using SSP-4 Infrared photometers. Recognizing the scientific need, the AAVSO entered into an agreement with Optec in 2001 to develop the detector and distributed many to experienced PEP observers around the world. Since then, many have gone on to purchase their own from Optec.
So why would amateurs 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. 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.)
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. Also, lunar glare interference is less in the infrared. And some stars are far, far brighter in the infrared, making it easier to perform high signal-to-noise photometry. Some stars can even be seen in the IR during the daytime. Brian and Dr. Bob have been doing daytime IR observations of epsilon Aurigae during the summer months, when the star is lost to the glare of the Sun for most of us using eyeballs and regular PEP equipment.
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.
For more information, check out the following:
- AAVSO PEP IR Program
- Preliminary Results from the AAVSO Infrared Photometry Group (3.3 MB, pdf) - by M.R. Templeton, J.D. West (AAVSO), D. Terrel (SWRI), W.D. Hodgson, M.D. Koppelman, K.D. Luedeke, J.E. Wood, and A.A. Henden (AAVSO); Poster paper presented at the January 2006 AAS Meeting
- Henden, A. (2002) JKH Standards for Small Telescopes (pdf). Journal of the AAVSO, 31, 1.
AAVSO Science Director Matt Templeton contributed to this post.