searching for dying solar systems: planets around white dwarfs

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Searching for dying solar systems: Planets around White Dwarfs. Matt Burleigh, Leicester Fraser Clarke, Oxford Emma Hogan, Leicester Simon Hodgkin, Cambridge. Improving Contrast. To understand extrasolar planets, we need their light! - PowerPoint PPT Presentation

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Imaging Planets around White DwarfsPlanets around White Dwarfs
Improving Contrast
To understand extrasolar planets, we need their light!
None of the radial velocity planets can be imaged with current technology
Planet is too faint and too close to the star
Two solutions;
Remove the star (stellar evolution)
Observe White Dwarfs!
Dr. Matt Burleigh RAS November 2004
Surviving the RGB
Planets inside 5AU are destroyed by Red Giant
Planets outside ~5AU will migrate outward due to mass loss and survive
Dynamical time ~10-30 yr
mass loss time ~1000-10000yr
The Benefits of White Dwarfs
WD's are ~10,000 times fainter than their progenitors
=> Huge contrast gain
Planets orbit increases
=> Big resolution gain
Dr. Matt Burleigh RAS November 2004
The Benefits of White Dwarfs
PLUS the WD progenitors are more massive than solar-type stars
Mainly A and B stars
Not generally being targeted by radial velocity programmes
So by targeting WDs we are probing frequency of planets around massive stars
Dr. Matt Burleigh RAS November 2004
Planet brightness v age
Solid lines Burrows 1997 models, dashed lines Burrows 2002 models
Models assume evolution in isolation: no addition heating source or reflection component
Dr. Matt Burleigh RAS November 2004
Imaging planets around white dwarfs
Large format NIR cameras on 8m-class telescopes
Typically reach J~24 in 1 hour (e.g. VLT+ISAAC, Gemini+NIRI)
Comparable with predicted magnitudes of planets around nearby white dwarfs
No immediate need for AO
Searching outside star’s PSF
Dr. Matt Burleigh RAS November 2004
Cool companions to WDs
IR excess in WDs may indicate cool companion
First L dwarf discovered is a companion to a WD, GD165
But brown dwarfs are not common companions to WDs
Only one more found so far (GD1400B, L6/7, Farihi et al. 2004)
Confirms brown dwarf desert at wide separations
No companions >10MJup found among Hyades WDs
Zinnecker & Friedrich, in prep. (HST/NICMOS)
Dr. Matt Burleigh RAS November 2004
Strategy
(0.2”yr < PM < few “/yr)
Sample ~40 stars
Obtain deep wide IR (J) images.
Total exp time ~1hr
Image quality typically 0.4”-0.6”
Wait 1—2 years…
Obtain 2nd epoch images of all systems to check for common proper motion companions
Dr. Matt Burleigh RAS November 2004
Parameter space
Planet mass; >5 Mjup
Orbit; 5—1000 AU
Age; 0.5—3 Gyr
Complimentary to other search techniques
Dr. Matt Burleigh RAS November 2004
Not a discovery
White dwarfs
Two epochs for Proper Motion
One epoch in One colour tells us nothing.
Faint objects could be faint companions, or they could simply be far away…
Any object in the field could be a companion!! (orbital expansion)
2nd epoch observations are needed to confirm companions via proper motion.
Dr. Matt Burleigh RAS November 2004
Two epochs
Image depth J~23.5
Motions in field
Arrows show direction and degree of motion x factor 20
WD moved ~9 pixels in 15 months (~1”)
Dr. Matt Burleigh RAS November 2004
A non-detection
Circles: 1s scatter on distribution of proper motions of background objects
Dr. Matt Burleigh RAS November 2004
A detection?
Would have originally orbited at ~65AU & ~75AU
First epoch June 2002, second June 2003
Dr. Matt Burleigh RAS November 2004
Add third epoch (June 2004)
Candidates have gone away!
Summary
White dwarfs open up more parameter space for planet surveys
Direct imaging of planets >5MJup
Probing frequency of planets around massive stars (>2MSun)
Sensitivity required is achievable with 8m telescopes in near-IR
Our survey is beginning to reach maturity
2 epochs for 12 systems
40 systems by 2006
Further work….
Coronographic searches of nearby young stars indicate frequency of companions >5MJup beyond 75AU is <3% (McCarthy & Zuckerman 2004)
Plus want to probe to lower masses (<5MJup)
Spitzer mid-IR observations for photometric excesses (several programmes in progress)

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