X-ray and observational Astronomy

X-ray and observational Astronomy

Detection limits for close eclipsing and transiting sub-stellar and planetary companions to white dwarfs in the

WASP survey

Francesca Faedi

Richard West, Matt Burleigh, Mike Goad, Leslie Hebb

17th European White Dwarf Work Shop – 20/08/2010



1) Sub-stellar and Planetary companions to WDs

2) Monitoring WD variability with WASP

- Simulation - Detection algorithm- Results from the analysis of 194 WDs in WASP companion’s Frequency

- Photometric variability for our WD sample

Outline



The WASP survey

- 8 Canon lenses 200mm f/1.8 - CCD array 20482 13.5μm per pixel - Field of view 7.8 x 7.8 deg2 per camera - magnitude limit V ≈15 - photometric accuracy better than 1% down to V ≈12

42 confirmed transiting planets



All stars with mass ≤ 8M will evolve to white dwarfs

What is the fate of known planetary systems?

Motivation



Rwd ~ R

Deep transit signals2

WD

pl

R

R

3 < δ < 70 %

Terrestrial companions

δ =100%

BD/Gas Giant

Motivation


17th European White Dwarf Work Shop – 20/08/201017th European White Dwarf Work Shop – 20/08/2010

Parameters: Rpl , RWD , Porb MWD = 0.6M and RWD = 0.013R

Period range2 h – 15 d

WASP data: ~150 days per season 8 min sampling, 30 sec exposure

Companion size~ 0.3 – 12 R

Moon BD/Gas giants

Synthetic dataset

Simulations



Orbital Period = 2.52 days

White dwarf MS solar-type star

Gas giant companion



transit + Gaussian noise of standard deviation σ

real WASP data

Detection algorithm

Modified Box-Least Square (BLS) +

down weighting

Empirical criteria detection

S/Npeak > 6.3 SDE

PBLS within 0.003d of the corrected (inserted) period

White noise Red noise

Details in Faedi et al. 2010

Results

Our implementationClassic BLS



Results for V≈12 Results for V≈15

Results from simulations

Results

see Faedi et al. 2010 for detailed tables on detection limits



- Our WD sample consists of 194 stars - WASP multi-season light-curves (2004 - 2008)

€

f = f n 1− f( )N−n N!

n! N −n( )!

No evidence of transiting sub-stellar and planetary companions were found

We use our null result to estimate an upper limit to the frequency of companions to WDs

Data analysis



For a perfect survey

Combining the three magnitude-specific maps from simulations into a single averaged map by interpolating/extrapolating according to the magnitude of each object in the sample.

Using our simulations

Limits on companion frequency



conclusion

2) Our analysis of 194 WDs found no evidence of companion.

Constraints can only be put on Gas giants and sub-stellar objects in orbits with P< 0.1 − 0.2 days, similar to WD0137−349 (Maxted et al. 2006),

these objects must certainly be rare (∼ < 10%)

Future surveys such as NGTS, Pan-STARRS, LSST, Plato

• Increase sample size • Sampling rate (high cadence)• Baseline

1) My Key result is transits of terrestrial rocky bodies in short period orbits

are detectable in current ground-based photometric surveys such as WASP

none found as yet … !

~1100 WDs 15 <V< 17 McCook & Sion



Monitoring WDs variability with WASP



Interesting objects







Thank you!!

Documents

X-ray and observational Astronomy