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

2. Dr. Matt BurleighRAS November 2004 Improving Contrast To understand extrasolar planets, we need their light!To understand extrasolar planets, we need their light! None of the radial velocity planets can be imaged with current technologyNone of the radial velocity planets can be imaged with current technology Planet is too faint and too close to the starPlanet is too faint and too close to the star Two solutions;Two solutions; –Remove the starlight (technology: AO, coronography, interferometry) –Remove the star (stellar evolution) Observe White Dwarfs! Above: Gl229B – brown dwarf companion to nearby M dwarf

3. Dr. Matt BurleighRAS November 2004 Surviving the RGB Red Giant expands to maximum ~5AURed Giant expands to maximum ~5AU Planets inside 5AU are destroyed by Red GiantPlanets inside 5AU are destroyed by Red Giant Planets outside ~5AU will migrate outward due to mass loss and survivePlanets 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. Dr. Matt BurleighRAS November 2004 The Benefits of White Dwarfs WD's are ~10,000 times fainter than their progenitorsWD's are ~10,000 times fainter than their progenitors => Huge contrast gain=> Huge contrast gain Planets orbit increasesPlanets orbit increases => Big resolution gain=> Big resolution gain And >120 WDs within 20pcAnd >120 WDs within 20pc

5. Dr. Matt BurleighRAS November 2004 The Benefits of White Dwarfs PLUS the WD progenitors are more massive than solar-type starsPLUS 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 starsSo by targeting WDs we are probing frequency of planets around massive stars

6. Dr. Matt BurleighRAS 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

7. Dr. Matt BurleighRAS November 2004 Imaging planets around white dwarfs Large format NIR cameras on 8m-class telescopesLarge 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 AONo immediate need for AO –Searching outside star’s PSF

8. Dr. Matt BurleighRAS November 2004 Cool companions to WDs Becklin & Zuckerman, Probst in the 1980sBecklin & 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 WDsBut 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 >10M Jup found among Hyades WDsNo companions >10M Jup found among Hyades WDs –Zinnecker & Friedrich, in prep. (HST/NICMOS)

9. Dr. Matt BurleighRAS November 2004 Strategy Select young (<3Gyr), nearby (<20pc) white dwarfsSelect 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.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…Wait 1—2 years… –Obtain 2 nd epoch images of all systems to check for common proper motion companions

10. Dr. Matt BurleighRAS November 2004 Parameter space For comparison with other planet search techniques;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 techniquesComplimentary to other search techniques

11. Dr. Matt BurleighRAS November 2004 Not a discovery

12. Dr. Matt BurleighRAS November 2004 White dwarfsWhite dwarfs –Image depth J~24

13. Dr. Matt BurleighRAS November 2004 Two epochs for Proper Motion One epoch in One colour tells us nothing.One epoch in One colour tells us nothing. Faint objects could be faint companions, or they could simply be far away…Faint objects could be faint companions, or they could simply be far away… Any object in the field could be a companion!! (orbital expansion)Any object in the field could be a companion!! (orbital expansion) 2 nd epoch observations are needed to confirm companions via proper motion.2 nd epoch observations are needed to confirm companions via proper motion.

14. Dr. Matt BurleighRAS November 2004 Two epochsTwo epochs –June 2002 GS+Flamingos-I –October 2003 VLT+ISAAC –WD motion ~1” between images –Image depth J~23.5 ^ ~90” V

15. Dr. Matt BurleighRAS November 2004 Motions in field Arrows show direction and degree of motion x factor 20Arrows show direction and degree of motion x factor 20 WD moved ~9 pixels in 15 months (~1”)WD moved ~9 pixels in 15 months (~1”)

16. Dr. Matt BurleighRAS November 2004 A non-detection Circles: 1  scatter on distribution of proper motions of background objectsCircles: 1  scatter on distribution of proper motions of background objects

17. Dr. Matt BurleighRAS November 2004 A detection? Circles: 1  error on PMs If associated, candidates are 7- 10M Jup Would have originally orbited at ~65AU & ~75AU First epoch June 2002, second June 2003

18. Dr. Matt BurleighRAS November 2004 Add third epoch (June 2004) Candidates have gone away!

19. Dr. Matt BurleighRAS November 2004Summary White dwarfs open up more parameter space for planet surveysWhite dwarfs open up more parameter space for planet surveys –Direct imaging of planets >5M Jup –Probing frequency of planets around massive stars (>2M Sun ) Sensitivity required is achievable with 8m telescopes in near-IRSensitivity required is achievable with 8m telescopes in near-IR Our survey is beginning to reach maturityOur survey is beginning to reach maturity –2 epochs for 12 systems –40 systems by 2006

20. Dr. Matt BurleighRAS November 2004 Further work…. Is a sample of 40 enough?Is a sample of 40 enough? –Coronographic searches of nearby young stars indicate frequency of companions >5M Jup beyond 75AU is 5M Jup beyond 75AU is <3% (McCarthy & Zuckerman 2004) Plus want to probe to lower masses (<5M Jup )Plus want to probe to lower masses (<5M Jup ) –Spitzer mid-IR observations for photometric excesses (several programmes in progress)