Astrophotography by Anthony Ayiomamitis

Differential Photometry - Lacerta

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 pulsating star KZ Lac is a pulsating variable star with a period of 150.36 minutes and which involves a delta mag of 0.60 (p) magnitudes during this time interval. KZ Lac is a delta-Scuti variable star first identified by Miller and Wachmann in 1973 following a widefield study of the Cepheus-Lacerta section of the Milky Way. Further details from the International Variable Star Index are available here whereas an AAVSO finder chart is available here.

Image Details
Light Curve for KZ Lac
Imaging Details
Variable Star:
KZ Lac

Other Designation:
VV 363

RA / Dec:
22h 18m 47s /
+50° 31' 48"


Magnitude:
14.6 - 15.2 (p)

Period:
0.10441604 days

Variability:
DSCT

Comparison Star:
GSC 3615:1638

Check Star:
GSC 3615:1224


Date:
Sep 26-27, 2012
20:50 - 04:02 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 :  134 x 180 sec
Dark :  010 x 180 sec
Flat :  ~ 23,800 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