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DEPARTMENT OF PHYSICS AND ASTRONOMY Direct detection of substellar and planetary companions to white dwarfs Matt Burleigh with thanks to: • Jay Farihi, Sarah Casewell, Martin Barstow, Richard Jameson, Katherine Lawrie (Leicester) • Paul Steele (MPA Garching) • Francesca Faedi (Belfast) • Paul Dobbie (AAO) • Fraser Clarke (Oxford), Emma Hogan (Gemini South) • Ted von Hippel, Fergal Mullally (Kepler) • Hans Zinnecker, Suzanne Friedrich Dr. Matt Burleigh www.star.le.ac.uk/~mbu Overview • IR searches for substellar companions – UKIDSS survey results • Direct imaging: into the planetary regime – Ground-based: DODO survey – Space-based: Spitzer survey • Latest results: a close WD+ Tdwarf binary in an open cluster • A transit survey of WDs with SuperWASP Dr. Matt Burleigh www.star.le.ac.uk/~mbu Direct imaging of planets around white dwarfs Burleigh, Clarke & Hodgkin 2002, MNRAS, 331, L41 • Ideal targets for direct imaging (and spectroscopy) of exoplanets: – Improve contrast problem: WDs up to ~104x fainter than their progenitors – Improve resolution problem through widening of orbits • M(MS) / M(WD) (Jeans 1924) – Indirectly study planetary systems around WD progenitors: early-type stars (B,A,F), intermediate masses (1.5<M<8Msun) – White dwarfs common in solar neighbourhood – White dwarf ages are well constrained • Planetary companions of WDs will be old, mature gas giants – – – – 200 < Teff < 600K > few x 108 years old Detectable at ages up to several Gyr Most direct imaging programmes target young stars Dr. Matt Burleigh www.star.le.ac.uk/~mbu The end of our solar system Dr. Matt Burleigh www.star.le.ac.uk/~mbu Evidence for old planetary systems 1. Planets have been found by radial velocity technique around evolved giant stars – – 2. 9% of stars 1.3<M<1.9Msun have planets (Johnson et al. 2007) >3% of stars M>1.8Msun have planets >5MJup (Lovis and Mayor 2007) White dwarfs have been identified as wide companions of planet-hosting stars – 3. eg CD-38 10980 (Mayor et al. 2004), eps Ret (Raghavan et al. 2006, Chauvin et al. 2006, Farihi et al. 2011) Growing number of brown dwarf companions in close and wide orbits – 4. eg Maxted et al. 2006, Steele et al. 2011, Girven et al. 2011, Debes et al. 2011 Metal-rich circumstellar dust and gas disks discovered around white dwarfs – See various papers by eg Jay Farihi & collaborators, Boris Gaensicke & friends Dr. Matt Burleigh www.star.le.ac.uk/~mbu Dust disks around white dwarfs • • • • A dozen WDs are known to be surrounded by dust disks Disks identified as near-IR and mid-IR excesses, 500oK < T < 1200oK Disks within a few solar radii of the WDs Material within the disks is being accreted onto the WD atmosphere – Finally explains WDs with metal-polluted atmospheres Dr. Matt Burleigh www.star.le.ac.uk/~mbu Dust disks around white dwarfs • • Disks dominated by silicates Disk forms from tidal disruption asteroid – Mass of GD362 disk suggests Mars-sized body • Suggests up to 20% of WDs may have rocky companions – If all polluted WDs have accreted terrestrial material at some point • But asteroids have to be moved by something: – Where are the perturbing giant planets? Dr. Matt Burleigh www.star.le.ac.uk/~mbu HR8799 as a white dwarf… • HR8799: A5V 1.2-1.8Mjup 39pc 30-160Myr old • Planets: 7Mjup @ 68AU, 10Mjup @ 38AU, 10Mjup @ 24AU • Will evolve after 1.75Gyr to a 0.58Msun white dwarf • Planet orbits expand by factor ~3 to ~200AU,~120AU & 75AU • Let WD cool to 10,000K over ~0.5Gyr….system age now 2.25Gyr… • 10Mjup planet will be J=23.8 @39pc, or J=22.4 @ 20pc – How common are HR8799-like systems? Dr. Matt Burleigh www.star.le.ac.uk/~mbu IR searches for substellar companions: UKIDSS survey results • Historical searches for brown dwarf companions to WDs going back to 1980s – eg Probst (1983), Zuckerman & Becklin (1987), Wachter et al. (2003), Farihi et al. (2005), Dobbie et al. (2005), Tremblay & Bergeron (2007) – GD165B (L4), GD1400B (L6/7), WD0137-349B (L8) • UKIDSS survey – ~dozen new BD candidates – Several confirmed (eg PHL5038, Steele et al. 2009, A&A, 500, 1207) – WD+L fraction >0.4+/-0.3% – WD+T fraction >0.2% – WD+BD fraction >0.5+/-0.3% – Steele et al. 2011, MNRAS, 416, 2768 – See also similar study by Girven et al. 2011, MNRAS, 417, 1210 – Parallel study for very wide binaries in UKIDSS discovered a WD+T4.5 (Day-Jones et al. 2009) Dr. Matt Burleigh www.star.le.ac.uk/~mbu Direct Imaging Searches Around White Dwarfs: The DODO project Degenerate Objects around Degenerate Objects With Emma Hogan (now Gemini South) and Fraser Clarke (Oxford) The idea: Burleigh et al. 2002, MNRAS, 331, L41 Results: Burleigh et al. 2008, MNRAS, 386, L5 and Hogan et al. 2009, MNRAS, 396, 2074 Dr. Matt Burleigh www.star.le.ac.uk/~mbu ^ ~90” V < ~120” > • ~40 white dwarfs within 20pc, ages <2-3Gyr • J band survey, depths J=23-24 Dr. Matt Burleigh www.star.le.ac.uk/~mbu Van Maanen’s Star (d=4.4pc) • DODO ground-based J-band imaging: – No companion found >7+/-1MJup (300+/-20K) at separations from 3”-45” / 15AU – 200AU – Separations around progenitor: 3 - 40AU • Spitzer mid-IR photometry: – No unresolved companions > 10+/-2 Mjup • Burleigh et al. 2008, MNRAS, 386, L5 – No resolved companions > 4MJup • Farihi et al. (2008) Dr. Matt Burleigh www.star.le.ac.uk/~mbu A candidate? WD • Candidate mass ~7MJup Dr. Matt Burleigh www.star.le.ac.uk/~mbu No candidate :( • 3rd epoch in 2008 refuted candidate Dr. Matt Burleigh www.star.le.ac.uk/~mbu Limits on giant planets at white dwarfs: mass – <5% of WDs have resolved substellar companions above deuterium burning limit (13MJup) – <7% of WDs have resolved substellar companions >10MJup – <1/3rd of WDs have resolved substellar companions >6MJup Dr. Matt Burleigh www.star.le.ac.uk/~mbu Limits on giant planets at white dwarfs: temperature – <4% of WDs have resolved substellar companions >500K – <7% of WDs have resolved substellar companions >400K Dr. Matt Burleigh www.star.le.ac.uk/~mbu Maximum and minimum orbital separations probed by DODO Dr. Matt Burleigh www.star.le.ac.uk/~mbu Comparison with Spitzer limits on unresolved companions (Farihi et al 2008, 34 targets) >13MJup DODO (resolved, >few 10s AUs) <5% Spitzer (unresolved, <few 10s AUs) <3% >10MJup <7% <4% >6MJup <1/3 <12% Dr. Matt Burleigh www.star.le.ac.uk/~mbu Spitzer warm mission programme • Repeat observations of ~90 white dwarfs originally observed 2004/5 – Prog ID: 60161 – Title: “Cool, spatially resolved substellar & exoplantary analogues at white dwarfs” – PI: Burleigh, co-Is Farihi, Steele, Mullally, von Hippel • Look for common proper motion companions – 4.5micron band only Dr. Matt Burleigh www.star.le.ac.uk/~mbu Spitzer 4.5micron image GJ3483 (LTT3059 / WD0806-661) 130” / 2500AU I maybe a planet… or a brown dwarf Dr. Matt Burleigh www.star.le.ac.uk/~mbu I am the white dwarf Dr. Matt Burleigh www.star.le.ac.uk/~mbu Dr. Matt Burleigh www.star.le.ac.uk/~mbu Proper motion WD Companion • PM error +/-25mas/yr Dr. Matt Burleigh www.star.le.ac.uk/~mbu Candidate parameters • WD – – – – 0.62Msun, Progenitor mass 1.8-2.4Msun Total age 1.2-2.0Gyr Distance 19.2pc • Candidate – 4.5micron mag = 16.75+/-0.08 – 6-10MJup – 310-380K • Binary – Projected separation 130” / 2500AU – Original separation 700AU Dr. Matt Burleigh www.star.le.ac.uk/~mbu Dr. Matt Burleigh www.star.le.ac.uk/~mbu Candidate parameters • WD – – – – 0.62Msun, Progenitor mass 1.8-2.4Msun Total age 1.2-2.0Gyr Distance 19.2pc • Candidate – 4.5micron mag = 16.75+/-0.08 – 6-10MJup – 310-380K • Binary – Projected separation 130” / 2500AU – Original separation 700AU Dr. Matt Burleigh www.star.le.ac.uk/~mbu Y band observation • AAT / IRIS2 2hours exposure on 25th March 2011 • No detection • Sensitivity – Recover 50% of injected fake stars at 21.1 Dr. Matt Burleigh www.star.le.ac.uk/~mbu J-band observations • Rodriguez et al. 2011,ApJ, 732, 1222; Luhman et al 2012, ApJ, 744, 135 • No detection to J=23.9 (3 sigma) – J-[4.5] > 7 – Redder than any known T dwarf – a Y dwarf? – Suggest mass 6-9MJup and 310K < Teff < 350K Dr. Matt Burleigh www.star.le.ac.uk/~mbu Planet or brown dwarf? • Is GJ3483B a brown dwarf or a planet? • Forget deuterium burning limit as the discriminator – can we classify by formation mechanism? • Original projected separation ~700AU – Too large for core accretion in a disk – Suggests disk fragmentation -> BD • Rodriguez et al. 2011 • But unstable, eccentric orbits expected in end states of stellar evolution – Debes & Sigurdsson 2002, Villaver & Livio 2007, Veras et al. 2011 – Disk of 2Msun star may be massive enough to make 6MJup companion – Progenitor could be an HR8799-like system • A5V+7MJup @68AU + 10MJup@38AU + 10MJup@24AU Dr. Matt Burleigh www.star.le.ac.uk/~mbu Spitzer survey completeness Dr. Matt Burleigh www.star.le.ac.uk/~mbu Spitzer survey completeness Dr. Matt Burleigh www.star.le.ac.uk/~mbu Spitzer survey completeness Black: Spitzer resolved Red: DODO resolved (Hogan et al. 2009) Green: Spitzer unresolved (Farihi et al. 2008) Dr. Matt Burleigh www.star.le.ac.uk/~mbu A WD+T dwarf close binary in Praesepe • RV & V band variability (4.2hr) in a WD in Praesepe cluster • M sin i > 25MJup • Non-detection in NIR and mid-IR (Spitzer IRAC) limits spectral type <T5 • At age of Praesepe (625Myr) M<30MJup • Strict age limit gives tight constraints on common envelope evolution parameters • Original orbit ~2AU (max extent of AGB envelope) • WD progenitor 3.5Msun/B9V • How did original binary form? • Most likely, capture early in cluster lifetime • Is this a significant method to populate the “brown dwarf desert”? For more details see poster by Sarah Casewell Dr. Matt Burleigh www.star.le.ac.uk/~mbu A search for eclipsing and transiting planets with SuperWASP • SuperWASP world’s most successful ground-based transit survey (>80 planets so far) • Has observed ~200 WDs since 2004 • 1% photometry to V=13, detection limit V~15 • No eclipsing or transiting companions detected • Placed (weak!) limits on incidence of such objects in close orbits around these white dwarfs • accounting for observing efficiency & co-variant noise in data • Limiting factors: • cadence: 8min for WASP v transit times of 1-few mins • unknown frequency of close planetary companions • Survivors of common envelope evolution? • 2nd generation planets? Faedi, West, Burleigh, Goad, & Hebb, (2011), MNRAS, 410, 899 and various conference proceedings since 2007 Please read the poster for more details Dr. Matt Burleigh www.star.le.ac.uk/~mbu Open questions, future directions • How common are GJ3483-like objects? – More direct imaging searches for wide companions – What are their formation mechanisms? • Disk fragmentation? • Core accretion and subsequent ejection ? • Where are the perturbers that help create dust disks around white dwarfs? – Mid-IR photometric searches; adaptive optics & HST • What is the lowest mass that can survive CE evolution intact? – Transit/eclipse searches • What is the orbital period distribution for substellar companions? – Are there “deserts”? • Can rocky planets exist in close orbits to WDs? – Transit searches • Can 2nd generation planets form? – Hot, young gas giants, metal-rich terrestrial planets? Dr. Matt Burleigh www.star.le.ac.uk/~mbu The lowest mass companions to WDs Name Mass (Mjup) Period a (AU) Evolutionary status Detection method Comment Reference GD66 b >2.4 ~7y >3AU WD Pulsation timing Retracted Mullally et al. 2008 GJ3483 b (WD0806-661 b) 6-9 2500 WD Direct imaging Y dwarf? 310K<T<350K Burleigh et al. 2012 Praesepe WD B 25-30 4.2hr 0.006 WD, Post-CE Radial velocity In Praesepe open cluster See Sarah Casewell’s poster WD0137-349 B 53 1.93hr 0.003 WD, Post-CE Radial velocity L8 dwarf, T~1300K Maxted et al. 2006 PHL5038 B 55 55 WD Direct imaging L8 dwarf, T~1400K Steele et al. 2009 GD1400 B 60 0.009 WD, Post-CE Radial velocity L6/7 dwarf, T~1500K Burleigh et al. 2012 LSPM 1459+0857 B 60-75 26500 WD Direct imaging T4.5 dwarf, T~1000K Day-Jones et al. 2011 NN Ser b NN Ser c 6.9 2.3 5.4 3.4 Pre-CV (WD+M) Eclipse timing 9.98hr 15.5y 7.7y Dr. Matt Burleigh www.star.le.ac.uk/~mbu Beuermann et al. 2010