Astrophotography by Anthony Ayiomamitis

Differential Photometry - Triangulum

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 925 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 AX Tri is a pulsating variable star with a period of 99.34 minutes and which involves a delta mag of 0.50 (R) magnitudes during this time interval. AX Tri is an Sx-Phe variable star first identified by A.V. Khruslov from Tula, Russia in 2008 following mining of the results of the Northern Sky Variability Survey (NSVS; Wozniak et al., 2004). AX Tri represents one of only a handful of Sx-Phe-type pulsating variables. Further details from the International Variable Star Index are available here.

Image Details
Light Curve for AX Tri
Imaging Details
Variable Star:
AX Tri

Other Designation:
GSC 02301-01168

RA / Dec:
01h 31m 49s /
+35° 13' 24"


Magnitude:
14.5 - 15.1 (R)

Period:
0.068983 days

Variability:
SXPHE

Check Star:
GSC 2301:0279

Comparison Star:
GSC 2301:0312


Date:
Oct 25-26, 2013
19:50 - 04:24 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 :  231 x 120 sec
Dark :  010 x 120 sec
Flat :  ~ 24,000 ADU
Binning :  1x1

Temperatures:
Ambient : + 22.0 ° C
CCD Chip : - 12.5 ° C

Software:
CCDSoft V5.00.201
AIP4Win V2.4.0


Processing:
Reduction
Differential Photometry