Astrophotography by Anthony Ayiomamitis

Differential Photometry - Bootes

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 (275 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 TZ Boo is a type W UMa variable with a period of just over six hours and involving a change of 0.59 magnitudes during this 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 TZ Boo
Imaging Details
Variable Star:
TZ Boo

Other Designation:
BD +40 2857

RA / Dec:
15h 08m 09s /
+39° 58' 13"


Magnitude:
10.41 - 11.00 v

Period:
0.2971620 days

Variability:
EW/KW

Spectrum:
G2V

Check Star:
GSC 3045:1118

Comparison Star:
GSC 3045:959

Lunar Phase:
N/A
Date:
May 27-28, 2008
22:50 - 03:05 UT+3


Location:
Athens, Greece

Equipment:
AP 160 f/7.5 Starfire EDF
AP 1200GTO GEM
SBIG ST-2000XM
SBIG CFW10
SBIG LRGB + IR-block


Integrations:
Green :  645 x 20 sec
Dark :  015 x 20 sec
Flat :  ~ 20,500 ADU
Binning :  2x2

Temperatures:
Ambient : + 24.0 ° C
CCD Chip : - 07.5 ° C

Software:
CCDSoft V5.00.188
AIP4Win V2.2


Processing:
Reduction
Differential Photometry