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 large-amplitude pulsating star DY Peg is a pulsating variable star with a period
of 105.1 minutes and which involves a delta mag of 0.56 (v) magnitudes during this time interval. DY Peg is an Sx-Phe
variable star first identified by
O. Morgenroth in 1934
and has been studied intensely since then due to the fact it represents one of only a handful of Sx-Phe-type pulsating
variables.
Further details from the International Variable Star Index are available
here
whereas an AAVSO finder chart is available
here.
Variable Star: DY Peg Other Designation: HD 218549 RA / Dec: 23h 08m 51s / +17° 12' 56" Magnitude: 10.00 - 10.56 Period: 0.072926372 days Variability: SXPHE(B) Check Star: GSC 1712:1246 Comparison Star: GSC 1712:0542 |
|
Date: Sep 27-28, 2012 20:35 - 03:05 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 |