The RApid Temporal Survey (RATS)
Gavin Ramsay (Armagh Observatory), Tom Barclay (NASA Ames Research Center, Armagh Observatory), Pasi Hakala (FINCA),
Adam Brooks (Armagh Observatory), Ralf Napiwotzki (Univ Hertfordshire), Stephen Potter (SAAO), Gijs Nelemans (Radboud University, Nijmegen)
Inspiration: More than ten years ago, two sources, RX
Strategy: We took a series of 30 sec exposures in white
light of the same field for 2-2.5 hrs. Our initial fields
were biased away from the Galactic plane but since
then they have been concentrated within ~10 degrees
of the plane.
J0806+15 and RX J1914+24, were identified as ultracompact binaries with an orbital period of 321 sec and
569 sec respectively. They were interesting for many
reasons, one of which was that they were predicted to
be strong sources of gravitational radiation. Indeed,
there were the some of the few known sources which
LISA would be expected to detect.
The 2.5m Isaac Newton Telescope on La Palma in the Canary Island where the bulk
of our data has been obtained.
The location of our pointings in Galactic co-ordinates in the first
five years of our observations.
An artists impression of an ultra-compact binary
As seen in the Figure on the upper right, in the optical
(and indeed at X-ray energies too) the signature of the
orbital period is detected as a modulation of the flux.
We set out to detect sources with short period variability. In particular, we aimed to determine the space
density of ultra-compact binaries and test theoretical
predictions.
The results of the first five years of our survey
(INT1-5+ESO1) have been published in Barclay
et al (2011). The results from the last year will
be published next year. We will make the products of our survey publically available.
Software: We used existing tools and software suites
and built wrap-arounds to make a pipeline.
Since many of our fields are moderately crowded we
have used `Difference Imaging’ techniques. Until recently we have used Dandia (Bramich 2008). Our favoured DI software is now
diapl users.camk.edu.pl/pych/DIAPL
We also use the astrometry package
astrometry.net and
Topcat: www.star.bris.ac.uk/~mbt/topcat/
Stilts: www.star.bristol.ac.uk/~mbt/stilts/
Space Density of UltraCompact Binaries: At this stage the implied space density of
these objects is consistent with the predictions of Nelemans et al (2001, 2004). However, we will not be in a position to make a definitive conclusion regarding this question until we have fully analysed the final 16 square degrees of data and obtained the
essential follow-up spectroscopy of candidate systems.
Short Period A stars: We have identified a number of short period variable A stars.
One possibility is that they are long period examples of rapidly oscillating, chemically
peculiar A stars which have typical pulsation periods of 10 min - though longer periods – up to 21 min – have been seen. Alternatively they could be low amplitude delta
Scuti stars with a pulsation period at the very short period end of the delta Scuti period distribution.
W UMa stars: An analysis of the light curves of these contact binaries is shown in a
separate poster by Pasi Hakala et al.
Light curves of nine blue sources which show periods shorter than 25 mins (Barclay et al 2011).
RAT J0455+1305: This is an sdB star with a dominant pulsation period of 374
sec which has the second highest amplitude of any sdB star. Further observations show it to be a rare hybrid systems showing g and p modes allowing a
sensitive test of stellar structure models (Ramsay et al 2006).
SX Phe stars: These are the low metalicity and shorter period analogues of RR Lyrae
stars. Several tens are these stars have been identified in our survey. Since they follow the Period-Luminosity relationship their period allows their distance to be determined.
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RAT J0455
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Follow up observations of RAT J0455 using the
Nordic Optical Telescope (Ramsay et al(2006).
The location of RAT J0455 in the log g, T plane
(Baran & Fox-Macado (2009).
Pulsating White Dwarfs: We have identified at least three pulsating white
dwarfs, including one (RAT J2059) which shows a pulsation period of 15.3
mins appears to have a hot companion. Its medium resolution optical spectrum and its broad band photometry - which extends into the UV - is consistant only if the companion star has a temperature >25000K. Such an object is
interesting for binary evolution models (Barclay et al in prep).
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The left hand panel show the colours of the SX Phe stars in our survey together with
the colours of all the stars from fields which have low optical extinction. The right
hand panel shows followup photometry made using the NOT of one star which is located in the Galactic anti-center and 30kpc distant from the Galactic center - beyond
the usual limits of the spiral arms (Ramsay et al 2011).
RATS-Kepler: This summer we commenced a deep, high cadence, photometric
survey of the Kepler field using the INT. We take a series of 20 sec exposures
in the g band lasting one hour. We are sensitive to objects in the range
13.5<g<21 and variability on timescale of 2 mins to one hour. Unlike other surveys, we aim to cover the whole of the Kepler field. Currently we have covered
more than 1/4 of the field with further observations expected in the summer of
2012. Initial results suggest our existing data contains nearly 1000 sources
which have variability timescales less than 40 mins. Our ultimate goal is to obtain photometry of our most astrophysically interesting sources using Kepler in
Short Cadence mode. Our data has already led to one object, a PG1159 star,
being scheduled for SC mode observations. We will make the results of our
survey public.
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1928+4040
1931+4147
1928+4041
1940+4647
1944+4431
1953+4158
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Left Hand Panel: The optical light curve and power
spctrum of RAT J2059. Right Panel: The broad band
photometric spectrum showing a single temperature
model does not well describe the data.The UV data
were obtained using the Swift satellite.
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Gavin Ramsay ([email protected])