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Exploring Dying Solar Systems: Planets Orbiting White Dwarfs

Discover the benefits of studying planets around white dwarfs and how it opens new opportunities for exoplanet research. Learn about imaging techniques and the potential of finding cool companions to white dwarfs. This survey aims to explore the frequency of planets around massive stars through direct imaging and proper motion studies.

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Exploring Dying Solar Systems: Planets Orbiting White Dwarfs

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  1. Searching for dying solar systems:Planets around White Dwarfs Matt Burleigh, Leicester Fraser Clarke, Oxford Emma Hogan, Leicester Simon Hodgkin, Cambridge

  2. 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 starlight (technology: AO, coronography, interferometry) • Remove the star (stellar evolution) Above: Gl229B – brown dwarf companion to nearby M dwarf Observe White Dwarfs!

  3. Surviving the RGB • Red Giant expands to maximum ~5AU • 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 • planets stay bound

  4. The Benefits of White Dwarfs • WD's are ~10,000 times fainter than their progenitors • => Huge contrast gain • Planets orbit increases • => Big resolution gain • And >120 WDs within 20pc

  5. 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

  6. 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

  7. 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

  8. Cool companions to WDs • Becklin & Zuckerman, Probst in the 1980s • 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)

  9. Strategy • Select young (<3Gyr), nearby (<20pc) white dwarfs • (0.2”yr < PM < few “/yr) • Sample ~40 stars • Progenitors mainly A/B stars (short main sequence lifetimes) • Obtain deep wide IR (J) images. • Total exp time ~1hr • Depth J~23.5 (GN) to ~24 (VLT) • 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

  10. Parameter space • For comparison with other planet search techniques; • Planet mass; >5 Mjup • Orbit; 5—1000 AU • Age; 0.5—3 Gyr • Star mass; 2—7 Msun (A and B stars) • Complimentary to other search techniques

  11. Not a discovery

  12. White dwarfs • Image depth J~24

  13. 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.

  14. ^ ~90” V • Two epochs • June 2002 GS+Flamingos-I • October 2003 VLT+ISAAC • WD motion ~1” between images • Image depth J~23.5 < ~120” >

  15. Motions in field • Arrows show direction and degree of motion x factor 20 • WD moved ~9 pixels in 15 months (~1”)

  16. A non-detection • Circles: 1s scatter on distribution of proper motions of background objects

  17. A detection? • Circles: 1s error on PMs • If associated, candidates are 7-10MJup • Would have originally orbited at ~65AU & ~75AU • First epoch June 2002, second June 2003

  18. Add third epoch (June 2004) • Candidates have gone away!

  19. 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

  20. Further work…. • Is a sample of 40 enough? • 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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