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 925 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 AX Tri is a pulsating variable star with a period
of 99.34 minutes and which involves a delta mag of 0.50 (R) magnitudes during this time interval. AX Tri is an Sx-Phe
variable star first identified by
A.V. Khruslov from Tula, Russia in 2008
following mining of the results of the
Northern Sky Variability Survey (NSVS; Wozniak et al.,
2004). AX Tri represents one of only a handful of Sx-Phe-type pulsating variables.
Further details from the International Variable Star Index are available
here.
Variable Star: AX Tri Other Designation: GSC 02301-01168 RA / Dec: 01h 31m 49s / +35° 13' 24" Magnitude: 14.5 - 15.1 (R) Period: 0.068983 days Variability: SXPHE Check Star: GSC 2301:0279 Comparison Star: GSC 2301:0312 |
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Date: Nov 02-03, 2013 19:45 - 01:45 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 |