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 short-period pulsating star RV UMa is a fast pulsating variable
star with a period of 11.23 hours and which involves a delta mag of 1.49 (CV) magnitudes during this brief time interval.
RV UMa is an RR-Lyrae variable with an asymmetric light curve and where the ascending branch is much steeper than the
descending branch and, hence, for its classification, namely "RRAB". The variable nature of RV UMa is attributed to
Cerasky (1907) with various studies from 1936 and thereafter confirming the presence of the Blazhko effect with a
secondary period of approximately 91-92 days (see, for example,
Kanyo, 1976).
Further details from the International Variable Star Index are available
here whereas an AAVSO finder chart is available
here.
Variable Star: RV UMa Other Designation: GSC 3850:0662, HIP 66122 RA / Dec: 13h 33m 18s / +53° 59' 15" Magnitude: 9.81 - 11.3 (V) Period: 0.46806 days Variability: RRAB Comparison Star: GSC 3850:0663 Check Star: GSC 3850:0346 |
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Date: Apr 30-May 1, 2013 21:22 - 04:01 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 |