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 (453 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-14b in Bootes depicted below is one of the
latest (and most massive) transitting exoplanets, having being announced in June/2008, and represents the fourteenth
discovery by the WASP (Wide Angle Search for Planets) team. WASP-14b is characterized with a whopping mass 7.725 times
that of Jupiter while its radius is equivalent to 1.259 Jupiter radii, thus making this exoplanet one of the densest
discoveries to-date. WASP-14b requires 183.6 minutes to transit its parent star at a depth of 10.2 mmag or 1.02%.
The parent star, GSC 1482:882, is an F5V star estimated to have a mass of 1.319 solar masses, a radius equivalent
to 1.297 solar radii, a temperature of 6,475° K and to lie at a distance of 570 light-years away with a visual magnitude
of 9.75. Further details regarding WASP-14 and WASP-14b are available in the paper published by the discovery team
led by Y.C. Joshi et al here.
Note: The C- and K-stars used for the purposes of the differential photometry measurements
depicted below were GSC 1482:261 (mag 9.78) and GSC 1482:83 (mag 10.39) respectively.
Parent Star: USNO-B1 11118-0262485 GSC/SAO Catalog: GSC 1482:882 Constellation: Bootes RA / Dec: 14h 33m 06.35s / +21° 53' 40.9" Magnitude: 9.745 Distance: 570 light-years Exoplanet: WASP-14b Period: 2.243752 + 0.000010 d Transit Duration: 183.6 mins Transit Depth: 10.2 mmag Minimum Mass: 7.725 MJup Radius: 1.259 RJup Pred Transit Details:
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Date: May 01-02, 2010 23:00:00 - 04:30:58 UT+3 Location: Athens, Greece Equipment: AP 160 f/7.5 Starfire EDF AP 1200GTO GEM SBIG ST-10XME SBIG CFW-10 SBIG Lum filter Integrations:
Temperatures:
Software: CCDSoft V5.00.195 AIP4Win V2.2 Processing: Reduction Differential Photometry |