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 eclipsing binary star KW Peg is a quick eclipsing binary variable star with a period of 0.81640194
days and which involves a delta mag of 0.31 (v) magnitudes during this brief time interval. The variable nature of KW Peg was discovered
by James A. DeYoung of the US Naval Observatory in 1991
and which lies in the same field of view as BX Peg.
KW Peg is an Algol-type eclipsing system with spherical or slightly ellipsoidal components and, hence, for its classification, namely "EA".
Further details from the International Variable Star Index are available
here whereas an AAVSO finder chart is available
here.
Note: The minimum observed below represents the secondary minimum. The small hump at the beginning of the time
series suggests a possible flare.
Variable Star: KW Peg Other Designation: GSC 2197-1412 RA / Dec: 21h 39m 11s / +26° 42' 34" Magnitude: 10.95 - 11.25 (v) Period: 0.81640194 days Variability: EA Comparison Star: GSC 2197:1871 Check Star: GSC 2197:1485 |
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Date: Sep 25-26, 2012 20:55 - 02:55 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 |