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 300 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 large-amplitude short-period pulsating star XX Cyg is a fast pulsating variable star with a period of
194.2 minutes and which involves a delta mag of 0.85 (V) magnitudes during this brief time interval. XX Cygni was discovered in 1904 by
Mme. Lydie Ceraski and has been studied fairly intensely with indications suggesting of a slight increase in its period over time.
Further details from the General Variable Star Search Gateway are available
here
whereas an AAVSO finder chart is available
here.
Variable Star: XX Cyg Other Designation: HIP 98737 RA / Dec: 20h 03m 16s / +58° 57' 17" Magnitude: 11.28 - 12.13 Period: 0.134865113 days Variability: SXPHE Check Star: GSC 3948:2431 Comparison Star: GSC 3948:1552 |
|
Date: Aug 28-29, 2010 21:50 - 05:37 UT+3 Location: Athens, Greece Equipment: AP 160 f/7.5 Starfire EDF AP 1200GTO GEM SBIG ST-10XME SBIG CFW10 SBIG LRGB filters Integrations:
Temperatures:
Software: CCDSoft V5.00.201 AIP4Win V2.2 Processing: Reduction Differential Photometry |