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 750 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 HAT-P-37b in Draco depicted below is one of the latest transiting
exoplanets, having being announced in Apr/2012 along with three other exoplanet finds, and represents the thirty-seventh discovery by the
Hungarian-based HATNet Project team.
HAT-P-37b is characterized with a mass 1.169 times that of Jupiter while its radius is equivalent to 1.178 Jupiter radii, thus making this
exoplanet a typical "hot Jupiter". HAT-P-37b requires 139.8 minutes to transit its parent star at a depth of 18.1 millimag or 1.81% with a
period of 2.7974 days in a circular orbit.
The parent star, GSC 3553:0723, is an F- or G-type dwarf star estimated to have a mass of 0.929 solar masses, a radius equivalent to 0.877
solar radii, a temperature of 5,500° K and to lie at a distance of 1,341 light-years away with a visual magnitude of 13.23.
Further details regarding HAT-P-37 and HAT-P-37b are available in the paper published by the discovery
team led by Gaspar Bakos et al here.
Note: The C- and K-stars used for the purposes of the differential photometry measurements depicted below were
GSC 3553:0294 (mag 10.60) and GSC 3553:0844 (mag 10.87) respectively.
Parent Star: HAT-P-37 GSC/SAO Catalog: GSC 3553:0723 Constellation: Draco RA / Dec: 18h 57m 11.16s / +51° 16' 08.9" Magnitude: 13.23 Distance: 1,341 light-years Exoplanet: HAT-P-37b Period: 2.797436 + 0.000007 d Transit Duration: 139.8 mins Transit Depth: 18.1 mmag Minimum Mass: 1.169 MJup Radius: 1.178 RJup Pred Transit Details:
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Date: Jun 09-10, 2013 22:25:00 - 02:45:50 UT+3 Location: Athens, Greece Equipment: AP 305/f3.8 Riccardi-Honders AP 1200GTO GEM SBIG ST-10XME SBIG CFW10 SBIG LRGB filters Integrations:
Temperatures:
Software: CCDSoft V5.00.201 AIP4Win V2.4.0 Processing: Reduction Differential Photometry |