Flare Recognition
Algorithm was developed by Marcin Sokolowski
The purpose of this algorithm is to find events when existing object
suddenly increased its brightness. The algorithm is executed off-line
and acts on data reduced and cataloged to the star catalog database.
Generally program inspects many light curves of stars in the database
looking for signature of brightness increase. Due to instrumental
effects there is a lot of background sources for such kind of events .
The main steps of the algorithm are as follows :
selection of stars which have significant brightness variations,
by requiring | Mmax- Mmin | > Δm
with at least Nmin number of measurements
determine the range of magnitude (Mstart , Mend ) where
85% of measurement points reside
find measurements which are brighter then Mend which
form a chain of measurements with at least Nflare points
require brightness increase between the peak and normal brightness level
to be | Mflare- Mnon-flare | >= Δmflare
The above cuts select all events when object increased its brightness.
There is still a lot of background events in the resulting list,
the background events are rejected by the following cuts :
check if the flare is not the artificial effect due to change of
star position on the CCD chip
check if it is not due to high value of sky background ( Moon light ) or clouds
check if it is not due to very close bright objects, variations
of bright stars PSF can cause variations of fainter stars located in
the PSF of very bright stars
if data was collected with permanently opened shutter additional check for
bright stars above the flare candidate is applied
check if object is not on the list of known hot or damaged pixels
Event candidates satisfying all the above criteria are saved to the
database. The algorithm is executed on the remote computer in LCO, so
results are finally synchronized to the database on local server in Warsaw and
can be inspected by the WWW interface. The final verification of every
event candidate is done by a men, but the number of events found by the
algorithm every night is small enough.
The algorithm is working since Jule 2006 and it has already detected
one sure and confirmed event of astrophysical origin. It was a
detection of outburst of flare star GJ 3331A / GJ 3332
(RA = 5h06m50s, Dec = -21o35'),
observed on 2006-11-28. More details on this particular observation can
be found here.
In several cases algorithm has detected known variable stars with quite
big brightness variations. The algorithm is still developed and several new
improvements in background rejection cuts will be introduced
Marcin Sokolowski
05.03.2007