Astrophotography by Anthony Ayiomamitis

Differential Photometry - Aquarius

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 300 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 CY Aqr is one of the fastest variables known with a period of 87.9 minutes and which involves a delta mag ranging from 0.74 (V) to 0.88 (B) magnitudes during this very brief time interval. Further details from the General Variable Star Search Gateway are available here whereas an AAVSO finder chart is available here.

Image Details
Light Curve for CY Aqr
Imaging Details
Variable Star:
CY Aqr

Other Designation:
HIP 111719

RA / Dec:
22h 37m 48s /
+01° 32' 04"


Magnitude:
10.42 - 11.16

Period:
0.061038328 days

Variability:
SXPHE

Check Star:
GSC 567:2036

Comparison Star:
GSC 567:1944


Date:
Aug 25-26, 2010
22:15 - 03:57 UT+3


Location:
Athens, Greece

Equipment:
AP 160 f/7.5 Starfire EDF
AP 1200GTO GEM
SBIG ST-10XME
SBIG CFW10
Baader IR Pass filter


Integrations:
Infrared :  310 x 60 sec
Dark :  010 x 60 sec
Flat :  ~ 18,000 ADU
Binning :  2x2

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

Software:
CCDSoft V5.00.201
AIP4Win V2.2


Processing:
Reduction
Differential Photometry