Astrophotography by Anthony Ayiomamitis

Differential Photometry - Ursa Major

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 GSC 04145-00930 is a quick eclipsing binary variable star with a period of 0.33801 days and which involves a delta mag of 0.422 (r) magnitudes during this brief time interval. The variable nature of GSC 4145-093 was first reported by Hoffman et al in 2009 following identification while mining the results of the Northern Sky Variability Survey (NSVS; Wozniak et al., 2004). GSC 4145-0930 is an W Ursae Majoris-type eclipsing system where the ellipsoidal components are virtually in contact with each other and, hence, for its classification, namely "EW". Further details from the International Variable Star Index are available here.

Note: The minimum observed below represents the secondary minimum.

Image Details
Light Curve for GSC 04145-00930
Imaging Details
Variable Star:
GSC 4145-0930

Other Designation:
NSVS 2578605

RA / Dec:
10h 57m 23s /
+61° 43' 02"


Magnitude:
11.583 - 11.405 (R)

Period:
0.33801 days

Variability:
EW

Comparison Star:
GSC 4145:1011

Check Star:
GSC 4145:0757


Date:
Apr 25-26, 2013
21:10 - 04:10 UT+3


Location:
Athens, Greece

Equipment:
AP 305/f3.8 Riccardi-Honders
AP 1200GTO GEM
SBIG ST-10XME
SBIG CFW10
SBIG LRGB filters


Integrations:
Lum :  337 x 60 sec
Dark :  010 x 60 sec
Flat :  ~ 23,100 ADU
Binning :  1x1

Temperatures:
Ambient : + 12.0 ° C
CCD Chip : - 17.5 ° C

Software:
CCDSoft V5.00.201
AIP4Win V2.4.0


Processing:
Reduction
Differential Photometry