Astrophotography by Anthony Ayiomamitis

Differential Photometry - Cepheus

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 GSC 04500-00083 is a fast pulsating variable star with a period of 122.50 minutes and which involves a delta mag of 0.25 (R) magnitudes during this brief time interval. GSC 04500-00083 is a high-amplitude delta-Scuti variable which was discovered by Shaw et al while mining the results of the Northern Sky Variability Survey (NSVS, Wozniak et al., 2004). Initially thought to be an eclipsing binary (W UMa type), a 2009 follow-up study by Sokolovsky revealed GSC 04500-00083 to be a delta-Scuti variable. Further details from the International Variable Star Index are available here.

Image Details
Light Curve for GSC 04500-00083
Imaging Details
Variable Star:
GSC 4500-0083

Other Designation:
NSVS 304708

RA / Dec:
00h 09m 49s /
+80° 21' 41"


Magnitude:
13.76 - 14.01 (R)

Period:
0.0850695 days

Variability:
HADS

Comparison Star:
GSC 4500:085

Check Star:
GSC 4500:411


Date:
Aug 06-07, 2012
21:45 - 04:30 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 :  182 x 120 sec
Dark :  010 x 120 sec
Flat :  ~ 25,200 ADU
Binning :  1x1

Temperatures:
Ambient : + 26.0 ° C
CCD Chip : - 10.0 ° C

Software:
CCDSoft V5.00.201
AIP4Win V2.4.0


Processing:
Reduction
Differential Photometry