exoplanets

The SuperWASP
exoplanet transit survey
Alexis Smith
Nicolaus Copernicus Astronomical Centre, Warsaw
Summary
Introduction
Instrumentation
Observing strategy and
data reduction
Planet discovery process
Scientific yield
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Exoplanets
Other astrophysics
The future
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SuperWASP
related transit surveys
Some context
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First exoplanet, 51 Peg b, discovered 1995
First transiting exoplanet, HD 209458 b, discovered in
1999, but already known by radial velocities
Discovery was with small (10 cm) telescope
(Charbonneau et al. 2000)
Numerous projects set up to find more transiting
planets...
Transiting planet surveys
Transiting planet surveys
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Ground-based:
– Deep:
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Wide-field:
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Optical Gravitational Lensing Experiment (OGLE)
Wide Angle Search for Planets (WASP)
Hungarian Automated Telescope Network (HATNet)
Trans-Atlantic Exoplanet Survey (TrES)
XO
Others
Space-based:
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Convection Rotation & Transits (CoRoT)
Kepler
Sagitarius Window Eclipsing Extrasolar
Planet Search (SWEEPS)
* 70 of these published
** + 1000s of candidates
8
109*
49
5
5
17
23
> 100**
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The WASP project
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Consortium of UK universities
(Queen's Belfast, Keele, St Andrews,
Leicester, OU, Cambridge) and Isaac
Newton Group (ING) on La Palma
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PI: Don Pollacco (QUB → Warwick)
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SuperWASP-North (La Palma) 2004
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WASP-South (Sutherland) 2006
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Discovered a total of 109 planets to
date (~70 published)
Project described in Pollacco et al.
(2006)
www.superwasp.org
My involvement in SuperWASP
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Started in 2005 when I started my PhD at St.
Andrews:
– Analysing noise properties of data and predicting
planet yields
– Follow-up photometry
Keele (postdoc, 2009-12). Worked on WASP-South:
– Operations
– Raw data handling
– Maintenance / testing trip
– Planet discovery
Warsaw (postdoc, 2012-). Still involved in
– Some operations and raw-data handling
– Follow-up photometry
Enclosure & mount
Fibreglass enclosure with
slide-away roof
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Two rooms:
– mount + cameras
– computers, supplies
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Roof operated hydraulically,
with battery backup as
ultimate failsafe
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A single Torus fork mount
– 8 cameras
– 30'' RMS pointing error
– <0.01'' /s tracking error
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The cameras
8 Canon 200mm f/1.8 lenses (0.11 m aperture)
2048 x 2048 pixel CCD cameras (Andor, Belfast), Peltier
cooled to -50 ºC
Focus is temperature dependent – active focus control (S) /
heated lenses (N)
Field-of-view 7.8º x 7.8º
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1 exposure (8 cams) images ~1% of whole sky
The weather station
Detectors for:
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Rain
Cloud cover
Wind speed & direction
Webcam
Satellite feed for
lightning / storm info
Allows rapid automatic
closing of roof
Operations
Live 'status'
webpage:
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Weather
Webcams
Latest science
images
Instrument status
Weather info
regularly used by
other observers at
SAAO
Observing strategy
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~12 fields observed per night in a strip of declination
2 x 30 s exposures per pointing
Variable cadence, but typically ~10 minutes
Photometry for 9.5 < V < 13
Fields followed for ~5 months
Avoid galactic plane (over-crowded)
Greatest coverage is of equatorial region (observed
by both North and South)
A typical image
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Up to 100,000 stars per image
Big pixels! 13'' / pixel
Raw data back to Keele / QUB
A full night of data is up to 1000 images per camera
● Each image is ~ 8 Mb (compressed to ~5 Mb)
● ~40 Gb to transfer for each good night
● SuperWASP-N (La Palma) use internet
● Connection at Sutherland poor, so use data tapes / HDDs –
returned every 4 – 6 weeks
● Raw (and processed) data stored in archive at Leicester
(moving to Warwick this week!)
– 7.7 million raw images (from North and South)
– ~60 Tb of raw data in archive
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Data processing
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Data are read from
HDD and checked
Images are
calibrated
Astrometric solution
using USNO-B1.0
catalogue – V < 14
Aperture photometry
V < 13
Processed data sent
to archive...
The archive
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429 billion data points
31 million unique objects
Hunting for transits
Data de-trended using SysRem and TFA algorithms
(Tamuz et al. 2005, Kovács et al. 2005)
BLS transit search run on complete seasons of data
A webpage is automatically generated on each planet
candidate
Various metrics used to filter best candidates
Candidates 'eyeballed' by human(s)
Candidates may be:
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Rejected as junk – 'transit' obviously noise, or nonplanetary
Saved for later – more WASP data needed to decide
Sent for follow-up observations – RV and/or photometry
An example candidate page
An example candidate page
An example candidate page
Follow-up observations
Need radial velocities to confirm planetary mass
A single spectrum may rule out giant stars, fast
rotators, etc
Transit photometry with larger (~ 1 m) telescopes to
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determine which object is responsible for transit
give more precise system parameters for discovery
paper
WASP-36b Smith et al. (2012)
Follow-up observations
Need radial velocities to confirm planetary mass
A single spectrum may rule out giant stars, fast
rotators, etc
Transit photometry with larger (~ 1 m) telescopes to
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determine which object is responsible for transit
give more precise system parameters for discovery
paper
WASP-36b Smith et al. (2012)
Photometric follow-up
Use a range of telescopes, most commonly
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TRAPPIST – 0.6 m robotic @ La Silla
Euler – 1.2 m @ La Silla
Liverpool – 2 m robotic @ ORM, La Palma
Faulkes Telescope North – 2 m @ Haleakala, Maui
Faulkes Telescope South – 2 m @ Siding Springs
UK university telescopes
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Keele 0.6 m
James Gregory Telescope – 1 m @ St Andrews
Radial velocity follow-up
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CORALIE on 1.2-m Swiss Euler
HARPS on ESO 3.6-m
SOPHIE on OHP 1.93-m
Most candidates turn out to be lowmass / grazing / diluted Ebs
'Hit rate' is ~ 1 in 12 candidates →
planets
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This could be improved, but we
often send 'high risk, high reward'
candidates – small planets, etc
Combined MCMC data analysis:
e.g WASP-71b
Smith et al. (2013)
Scientific highlights: exoplanets
First planets: WASP-1b and WASP-2b (Collier Cameron et al.
2007)
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Total of 109 planets discovered, 70 are published (rest awaiting
data, papers in preparation)
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WASP-12b – a very hot Jupiter
– Hebb et al. (2009)
– 1.1 d orbit around a G0 dwarf
– atmosphere 'well' characterised
– first carbon-rich planet?
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K-band occultation (CFHT): Croll et al. (2011)
C-O ratio > 1:
Madhusudhan et al. (2011)
Scientific highlights: exoplanets
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WASP-17b – a huge planet, and the first
with a retrograde orbit (discovery:
Anderson et al. 2010)
– radius 2.0 RJ – far bigger than any
theory predicts
– Rossiter-McLaughlin effect reveals orbit
is retrograde w.r.t. stellar-spin axis
Anderson
et al. (2011)
Triaud et al. (2010)
Scientific highlights: exoplanets
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WASP-33 – first planet
discovered around an A-star
(Collier Cameron et al.
– confirmed (in retrograde orbit)
with line-profile tomography
– star is a δ Scuti pulsator
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hottest-known planet
(Smith et al. 2011)
Scientific highlights: other
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Variable stars and EBs
– Short-period EBs (Norton et al. 2011, Lohr et al. 2012, 2013)
– Variables coincident with ROSAT X-ray sources (Norton et al. 2007)
– Long timescale photometry of CVs (Thomas et al. 2010)
– Pulsations of Am stars (Smalley et al. 2011)
– Oscillations in roAp stars (Elkin et al. 2011)
SuperWASP data are available for you to use in your science!
– Unfortunately public archive no longer funded, but may re-appear
– In the meantime, you can contact a member of WASP to get data
Scientific highlights: other
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Variable stars and EBs
– Short-period EBs (Norton et al. 2011, Lohr et al. 2012, 2013)
– Variables coincident with ROSAT X-ray sources (Norton et al. 2007)
– Long timescale photometry of CVs (Thomas et al. 2010)
– Pulsations of Am stars (Smalley et al. 2011)
– Oscillations in roAp stars (Elkin et al. 2011)
The future: post-Kepler
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Kepler has discovered > 100 planets, with thousands more
candidates (Morton & Johnson 2011 estimate > 90% are
true planets)
– These include planets much smaller and with much
longer periods than found from the ground
– But, Kepler only observed a single field, and most
targets are faint (~14th – 15th mag)
The era of ground-based transit surveys is NOT over!
Wide-field surveys find intrinsically rare objects (WASP-17b)
There is a need for exoplanets for characterisation that:
– Orbit bright stars
– Are distributed across sky (e.g. southern objects for EELT)
The future of SuperWASP
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SuperWASP-N: trialling observing fewer fields per night,
with higher cadence
WASP-South: trialling wider-angle lenses to change
magnitude 'sweet spot' from 9.5 < V < 13 to 7 < V < 10
Motivation: planet host stars HD 209458 (V = 7.6) and
HD 189733 (V = 7.7) are both in Northern hemisphere.
These are best-studied transiting planets, almost all
new observing techniques tried on these objects first.
An 8th mag transiting HJ visible from VLT would be a
very valuable discovery!
Implementation: Canon 85 mm f/1.2 lenses: f.o.v. 18º x
18º, pixel scale 31'' / pixel.
1 year of data with 85 mm lenses: reduction in progress
The future of SuperWASP
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●
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SuperWASP-N: trialling observing fewer fields per night,
with higher cadence
WASP-South: trialling wider-angle lenses to change
magnitude 'sweet spot' from 9.5 < V < 13 to 7 < V < 10
Motivation: planet host stars HD 209458 (V = 7.6) and
HD 189733 (V = 7.7) are both in Northern hemisphere.
These are best-studied transiting planets, almost all
new observing techniques tried on these objects first.
An 8th mag transiting HJ visible from VLT would be a
very valuable discovery!
Implementation: Canon 85 mm f/1.2 lenses: f.o.v. 18º x
18º, pixel scale 31'' / pixel.
1 year of data with 85 mm lenses: reduction in progress
Future related surveys: QES
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SuperWASP expertise also feeding into other transit survey projects.
Qatar Exoplanet Survey (QES) operating 4 x 400 mm lenses (5º x 5º
f.o.v.) in New Mexico. Funding secured from Qatar National Research
Fund for additional stations.
Goal: to go fainter than SuperWASP, DIA photometry, longitude coverage
Uses WASP legacy in pipeline, archive, etc
Two exoplanets discovered to date: Qatar-1b (Alsubai et al. 2011),
Qatar-2b (Bryan et al. 2011)
Next Generation Transit Survey
(NGTS)
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See:
– Wheatley et al. 2013
– www.ngtransits.org
Thanks for listening!
Time lapse movie: Willie Koorts (SAAO)