Last update: 2018.02.19 by Wojtek Pych
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The Cluster AgeS Experiment (CASE).
Detecting Aperiodic Photometric Variability with the Friends of Friends Algorithm

Rozyczka, M.; Narloch, W.; Pietrukowicz, P.; Thompson, I. B.; Pych, W.; Poleski, R.

Abstract:
We adapt the friends of friends algorithm to the analysis of light curves, and show that it can be succesfully applied to searches for transient phenomena in large photometric databases. As a test case we search OGLE-III light curves for known dwarf novae. A single combination of control parameters allows us to narrow the search to 1% of the data while reaching a ≈90% detection efficiency. A search involving ≈2% of the data and three combinations of control parameters can be significantly more effective - in our case a 100% efficiency is reached. The method can also quite efficiently detect semi-regular variability. In particular, 28 new semi-regular variables have been found in the field of the globular cluster M22, which was examined earlier with the help of periodicity-searching algorithms.

DOWNLOADS:
Preprint (PDF) "The Cluster AgeS Experiment (CASE). Detecting Aperiodic Photometric Variability with the Friends of Friends Algorithm"
Rozyczka, M.; Narloch, W.; Pietrukowicz, P.; Thompson, I. B.; Pych, W.; Poleski, R.
Acta Astronomica, vol 68, no 1, p. 63-78
fof.f

fof.control
The source code implementing the FoF method
and
the control parameters file for the 'fof' program.


Table 1: Basic data of variables discovered in the field of M22 using the Friends of Friends method.
Star RA
[deg. J2000.0]
Decl.
[deg. J2000.0]
Vmean
[mag]
Δ V
[mag]
Bmean - Vmean
[mag]
PMa Statb νc δd
[%]
V light-curvee
V136 279.16521 -23.87854 13.93 0.02 1.07 Y V 0.34 2.73 V136.dat
U70f 278.98646 -23.90984 22.46
20.16
2.30 0.50
0.47
U V 0.89 0.04 U70.dat
N176 279.19779 -23.73977 15.05 0.28 1.84 N V 0.93 0.04 N176.dat
N177 279.21259 -23.83521 14.11 0.07 1.75 N V 0.93 0.04 N177.dat
N178 279.20565 -23.91109 14.11 0.13 1.76 N V 0.88 0.05 N178.dat
N179 279.19954 -23.89914 13.42 0.02 1.81 N S 0.42 0.98 N179.dat
N180 279.22549 -23.93757 16.66 0.42 1.87 N V 0.93 0.03 N180.dat
N181 279.20120 -24.05648 13.61 0.09 1.81 N V 0.87 0.06 N181.dat
N182 279.12222 -23.80253 14.69 0.03 1.65 N S 0.37 1.72 N182.dat
N183 279.13698 -23.88486 16.72 0.16 1.16 N V 0.63 0.16 N183.dat
N184 279.15103 -23.92146 14.76 0.39 1.81 N V 0.98 0.01 N184.dat
N185 279.14376 -23.96482 15.02 0.58 1.73 N V 0.96 0.02 N185.dat
N186 279.15241 -24.01048 13.92 0.12 1.73 N V 0.86 0.06 N186.dat
N187 279.11106 -23.75086 15.06 0.23 1.42 N V 0.79 0.08 N187.dat
N188 279.04501 -23.76959 14.44 0.06 1.82 N V 0.97 0.01 N188.dat
N189 279.09219 -23.81836 14.65 0.03 1.79 N V 0.69 0.12 N189.dat
N190 279.07769 -23.83870 15.35 0.21 1.71 N V 0.95 0.03 N190.dat
N191 279.07322 -23.83017 16.11 0.56 1.76 N V 0.95 0.02 N191.dat
N192 279.05198 -23.92851 15.41 0.25 1.58 N V 0.88 0.05 N192.dat
N193 279.08704 -23.97307 14.50 0.04 1.74 N V 0.61 0.18 N193.dat
N194 279.07205 -23.98484 13.67 0.15 1.70 N V 0.93 0.03 N194.dat
N195 279.07035 -24.09773 15.31 0.42 1.73 N V 0.95 0.02 N195.dat
N196 278.98961 -23.73304 16.00 0.61 1.78 N V 0.97 0.01 N196.dat
N197 279.00753 -23.79984 17.07 0.23 1.75 N V 0.89 0.04 N197.dat
N198 278.97410 -23.84254 13.92 0.31 1.75 N V 0.94 0.03 N198.dat
N199 279.01856 -23.86728 15.57 0.07 1.77 N V 0.94 0.03 N199.dat
N200 279.01240 -23.87550 15.80 0.37 1.80 N V 0.90 0.04 N200.dat
N201 279.01744 -23.98125 13.84 0.04 1.71 N V 0.92 0.04 N201.dat
N202 278.99578 -23.99937 14.41 0.04 1.20 N V 0.80 0.08 N202.dat
N203 278.97643 -24.05441 15.98 0.29 1.62 N V 0.70 0.11 N203.dat
#24 279.09078 -23.90371 13.42 0.65 0.9 Y V 0.93 0.04 24.dat
C1 279.08297 -23.86369 18.94 0.30 0.70 Y C 0.13 77.6 C1.dat
a Proper motion membership status: Y - member or likely member, N - field object, U - no data or data ambiguous.
b Variability status: V - variable, S - suspected variable, C - constant star.
c Variability index defined in Section 2, obtained for NM=5 and b=0.03.
d The percentage of light curves sorted over decreasing ν that has to be inspected before the star indicated in the first column is encountered.
e Data columns:
  1. HJD - 2 450 000.0
  2. magnitude
  3. error of magnitude (dummy points are maked with the error=9.999)
  4. photometric phase
f For U70, magnitude and color at low and high state are given.