Astrophotography by Anthony Ayiomamitis

Differential Photometry - Hercules

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 V1267 Her is a fast pulsating variable star with a period of 0.4687883 days and which involves a delta mag of 0.90 (v) magnitudes during this brief time interval. V1267 Her is an RRAB-type variable star first reported by Akerlof et al. in 2000 during inspection of the Robotic Optical Transient Search Experiment I (ROTSE-I) database involving the entire northern sky. Further details from the International Variable Star Index are available here whereas an AAVSO finder chart is available here.

Image Details
Light Curve for V1267 Her
Imaging Details
Variable Star:
V1267 Her

Other Designation:
GSC 02083-00720

RA / Dec:
17h 29m 07s /
+27° 49' 21"


Magnitude:
12.4 - 13.3 (v)

Period:
0.4687883 days

Variability:
RRAB

Comparison Star:
GSC 2083:1087

Check Star:
GSC 2083:0143


Date:
Jun 15-16, 2013
22:30 - 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 :  160 x 120 sec
Dark :  010 x 120 sec
Flat :  ~ 22,400 ADU
Binning :  1x1

Temperatures:
Ambient : + 21.0 ° C
CCD Chip : - 15.0 ° C

Software:
CCDSoft V5.00.201
AIP4Win V2.4.0


Processing:
Reduction
Differential Photometry