Astrophotography by Anthony Ayiomamitis

Differential Photometry - Leo Minor

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 02996-00677 is a quick eclipsing binary variable star with a period of 0.3609 days and which involves a delta mag of approximately 0.34 (C) magnitudes during this brief time interval. The variable nature of GSC 02996-00677 was first reported by Anthony Ayiomamitis in 2014 following inspection of the field of view for the exoplanet host star KELT-3 in Leo Minor. GSC 02996-00677 is an W Ursae Majoris-type eclipsing system where the binary components involve main sequence stars with ellipsoidal components virtually in contact with each other and, hence, for its classification, namely "EW/KW". The characteristics of the phase light curve based on 38.9 hours of total data suggests that a W-subtype system is involved using Binnendijk's criteria between A- and W-type subtypes. Further details from the International Variable Star Index are available here.

Image Details
Light Curve for GSC 2996-0677
Imaging Details
Variable Star:
GSC 2996-0677

Other Designation:
N/A

RA / Dec:
09h 53m 12s /
+40° 08' 19"


Magnitude:
13.47 - 13.81 (C)

Period:
0.3609 days

Variability:
EW

Comparison Star:
GSC 2996:0618

Check Star:
GSC 2996:0799


Date:
Mar 09-10, 2013
21:50 - 03:50 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 :  293 x 60 sec
Dark :  010 x 60 sec
Flat :  ~ 22,400 ADU
Binning :  1x1

Temperatures:
Ambient : + 12.0 ° C
CCD Chip : - 15.0 ° C

Software:
CCDSoft V5.00.201
AIP4Win V2.4.0


Processing:
Reduction
Differential Photometry