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 03986-01266 is a fast pulsating variable star with a period of 213.96 minutes and which involves a delta mag of 0.15 (R) magnitudes during this brief time interval. GSC 03986-01266 is a delta-Scuti variable which was discovered by Martin Lehky and Miroslav Broz from the Czech Republic in 2005 and which happens to lie in the same field of view as the Algol-type eclipsing binary star NW Cep. Further details from the International Variable Star Index are available here.

Image Details
Light Curve for GSC 03986-01266
Imaging Details
Variable Star:
GSC 3986-1266

Other Designation:
NSVS 3434670

RA / Dec:
22h 13m 37s /
+55° 44' 28"


Magnitude:
11.2 - 11.35 (R)

Period:
0.148585 days

Variability:
DSCT

Comparison Star:
GSC 3973:0467

Check Star:
GSC 3973:1365


Date:
Sep 03-04, 2012
21:00 - 02:00 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 :  243 x 60 sec
Dark :  010 x 60 sec
Flat :  ~ 24,100 ADU
Binning :  1x1

Temperatures:
Ambient : + 22.0 ° C
CCD Chip : - 10.0 ° C

Software:
CCDSoft V5.00.201
AIP4Win V2.4.0


Processing:
Reduction
Differential Photometry