A variable star, as its name suggests, is a star whose magnitude varies intrinsically, in contrast to eclipsing binaries whose magnitude
varies as a result of one star in the binary system eclipsing the other. True variables are one of five types, namely Mira stars, semiregular
stars, cepheids, eruptive variables and, finally, cataclysmic variables. Minimum to maximum magnitude can range from days to many months with
some variables displaying irregular periods.
A popular method for the study of variable stars, particularly short-term variables, is by the use of the technique known as "differential
photometry". Rather than measure the (variable) magnitude of a variable star on an absolute scale, measurements are made over time relative
to one or more non-variable star(s) and these differences are then plotted so as to study and illustrate the relative or differential change
in magnitude. Due to the very large number of variables stars, the field of differential photometry represents one of the key fields in
astronomy whereby the amateur astronomer can make a meaningful and long-lasting contribution to both science and astronomy.
More recently, the search for extrasolar planets (over 275 discovered so far) has identified yet another interesting application for the
practice of differential photometry whereby the minute drops in magnitude of a star hosting an exoplanet are studied. Further details for the
interested party are available here.
Note: The light curve for exoplanet WASP-10b in Pegasus depicted below is one of the latest (and most massive)
transitting exoplanets, having being announced in June/2008, and represents the tenth discovery by the WASP (Wide Angle Search for Planets)
team. WASP-10b is characterized with a whopping mass 3.06 times that of Jupiter while its radius is equivalent to 1.29 Jupiter radii, thus
making this exoplanet one of the densest discoveries to-date. WASP-10b requires 142 minutes to transit its parent star at a depth of 3.3%.
The parent star, GSC 2752:114, is a K5 star estimated to have a mass of 0.710 solar masses, a radius equivalent to 0.783 solar radii, a
temperature of 4,675° K and to lie at a distance of 294 light-years away with a visual magnitude of 12.7. Further details regarding WASP-10
and WASP-10b are available in the paper published by the discovery team led by D.J. Christian et al (click
here).
Note: The C- and K-stars used for the purposes of the differential photometry measurements depicted below were
GSC 2752:73 (mag 12.0) and GSC 2752:16 (mag 12.2) respectively. The light curve below is the first amateur
result of this newly discovered exoplanet in the constellation of Pegasus.
Parent Star: WASP-10 GSC/SAO Catalog: GSC 2752:114 Constellation: Pegasus RA / Dec: 23h 15m 58.23s / +31° 27' 47.1" Magnitude: 12.7 Distance: 294 light-years Exoplanet: WASP-10b Period: 3.0927616 + 0.0000182 d Transit Duration: 141.7 mins Transit Depth: 33 mmag Minimum Mass: 3.06 MJup Radius: 1.29 RJup Pred Transit Details:
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Date: Aug 28-29, 2008 21:40:02 - 01:59:58 UT+3 Location: Athens, Greece Equipment: AP 160 f/7.5 Starfire EDF AP 1200GTO GEM SBIG ST-2000XM SBIG CFW-10 SBIG LRGB + IR-block Integrations:
Temperatures:
Software: CCDSoft V5.00.188 AIP4Win V2.2 Processing: Reduction Differential Photometry |