1. Dr. Matt Burleighwww.star.le.ac.uk/~mbu Detached WD/BD binaries as progenitors of CVs Matt Burleigh with Paul Steele, Francesca Faedi, Paul Dobbie (AAO) and Boris Gaensicke (Warwick)

2. Dr. Matt Burleighwww.star.le.ac.uk/~mbu Motivation Investigate the known deficit of BD companions to main sequence starsInvestigate the known deficit of BD companions to main sequence stars –McCarthy & Zuckerman (2004), Grether & Lineweaver (2006) WD gives an age constraint: benchmark BDs for testing evolutionary and atmospheric modelsWD gives an age constraint: benchmark BDs for testing evolutionary and atmospheric models –Pinfield et al. (2006) In close systems, irradiated BD provides a laboratory for testing models of heated substellar atmospheres (hot Jupiters)In close systems, irradiated BD provides a laboratory for testing models of heated substellar atmospheres (hot Jupiters) –WD0137-349 Post-CE systems may provide another channel for CV evolutionPost-CE systems may provide another channel for CV evolution –Politano (2004) Previous searches by e.g. Probst (1983), Zuckerman & Becklin (1987), Green, Ali & Naperwotzki (2000), Farihi, Becklin & Zuckerman (2005), and using 2MASS: Wachter et al. (2003), Wellhouse et al. (2005), Holberg & Magargal (2005), Tremblay & Bergeron (2007) and Hoard et al. (2007)Previous searches by e.g. Probst (1983), Zuckerman & Becklin (1987), Green, Ali & Naperwotzki (2000), Farihi, Becklin & Zuckerman (2005), and using 2MASS: Wachter et al. (2003), Wellhouse et al. (2005), Holberg & Magargal (2005), Tremblay & Bergeron (2007) and Hoard et al. (2007)

3. Dr. Matt Burleighwww.star.le.ac.uk/~mbu Irradiation of WD0137-349B AAT + IRIS2 in July 2007AAT + IRIS2 in July 2007 Green - K (+/-14%) Red - H (+/- 8%) White - J (+/- 3%)

4. Dr. Matt Burleighwww.star.le.ac.uk/~mbu Post-CE binaries with BD secondaries Constrain models of common envelope evolutionConstrain models of common envelope evolution What is the lowest mass object that can survive a CE?What is the lowest mass object that can survive a CE? What fraction of CVs are born with a BD secondary?What fraction of CVs are born with a BD secondary? Growing number of CVs with confirmed BD secondariesGrowing number of CVs with confirmed BD secondaries –Including examples thought to have formed directly from a detached WD+BD progenitor –e.g. SDSS J150722.30+523039.8, Littlefair et al. (2007)

5. Dr. Matt Burleighwww.star.le.ac.uk/~mbu Known detached WD+BD binaries Rare: only three confirmed systemsRare: only three confirmed systems GD165GD165 –120AU separation, L4 secondary –Becklin & Zuckerman (1988) WD0137-349WD0137-349 –P=116 mins, L8 secondary (0.053Msun) –Maxted et al. (2006); Burleigh et al. (2006) GD1400GD1400 –P=9.98 hours, L6/7 secondary –Farihi & Christopher (2004), Burleigh et al. (2009) Fraction of L dwarf companions <0.5%Fraction of L dwarf companions <0.5% –(Farihi et al. 2005, survey of >300 WDs) One companion on M/L border found among ~150 WDs observed by SpitzerOne companion on M/L border found among ~150 WDs observed by Spitzer –PG1234+482 (Mullally et al. 2007; Steele et al. 2007) A handful of other WD + ultracool dwarf binaries knownA handful of other WD + ultracool dwarf binaries known

6. Dr. Matt Burleighwww.star.le.ac.uk/~mbu UKIDSS UKIRT Infrared Deep Sky Survey LAS (Large Area Survey) - 4000 sq. deg (~20% of northern sky, coincident with SDSS) Limiting magnitudes - Y=20.2, J=19.6, H=18.8 & K=18.2 (5 sigma) 2-3 mags deeper than 2MASS

7. Dr. Matt Burleighwww.star.le.ac.uk/~mbu Searching for unresolved WD+BD binaries in UKIDSS Cross-correlate UKIDSS LAS DR4 release (1060 sq. deg) withCross-correlate UKIDSS LAS DR4 release (1060 sq. deg) with –SDSS DR4 spectroscopically id- ed WDs (Eisenstein et al. 2006) –McCook and Sion WDs J-H v H-K plot provides an initial selectionJ-H v H-K plot provides an initial selection Better method: model each WD SED, first with BBs and finally with model atmospheres (DAs only)Better method: model each WD SED, first with BBs and finally with model atmospheres (DAs only) –Identify WDs with >3 sigma excesses at H and K

8. Dr. Matt Burleighwww.star.le.ac.uk/~mbu Results 922 SDSS WDs in UKIDSS DR4922 SDSS WDs in UKIDSS DR4 –+ a further 84 brighter WDs from McCook & Sion But DR4 incomplete: many stars missing photometry at one of J, H or KBut DR4 incomplete: many stars missing photometry at one of J, H or K After eliminating known WD+dMs, non-DAs and DAs missing photometry at H or K:After eliminating known WD+dMs, non-DAs and DAs missing photometry at H or K: –254 DAs with photometry at both H and K 8 with late M dwarf (M7-9) companions8 with late M dwarf (M7-9) companions 5 candidate L dwarf companions5 candidate L dwarf companions 1 candidate T dwarf companion1 candidate T dwarf companion

9. Dr. Matt Burleighwww.star.le.ac.uk/~mbu WD+L4 WD+L6 WD+L8

10. Dr. Matt Burleighwww.star.le.ac.uk/~mbu PHL5038 = SDSS J222030.68-004107.3 B=18, UKIDSS K=16.7B=18, UKIDSS K=16.7 Follow-up imaging and spectroscopy with Gemini-North + NIRIFollow-up imaging and spectroscopy with Gemini-North + NIRI Resolved at 0.92” (=55AU projected)Resolved at 0.92” (=55AU projected) L8 companion (T~1600K, M~0.055Msun @ 2-3Gyr)L8 companion (T~1600K, M~0.055Msun @ 2-3Gyr) WD T=8000+/-100K, M=0.72+/- 0.15Msun, d=64+/-10pcWD T=8000+/-100K, M=0.72+/- 0.15Msun, d=64+/-10pc 4th known WD+BD detached system, 2nd wide4th known WD+BD detached system, 2nd wide Steele et al. 2009Steele et al. 2009 K

11. Dr. Matt Burleighwww.star.le.ac.uk/~mbu Frequency of close, detached WD+BD binaries PHL5038 is flagged as partially resolved in UKIDSSPHL5038 is flagged as partially resolved in UKIDSS From evolutionary considerations, WD+BD binaries should either be wide (> few AU) or close (post-CE)From evolutionary considerations, WD+BD binaries should either be wide (> few AU) or close (post-CE) –Substellar companion either spirals inwards in CE, or orbit expands outwards as Red Giant loses mass –Farihi, Hoard & Wachter (2006) 2 of 5 L dwarf candidate companions classed as partially resolved (i.e. wide)2 of 5 L dwarf candidate companions classed as partially resolved (i.e. wide) Single T dwarf candidate classed as “stellar” i.e. more likely to be a close binarySingle T dwarf candidate classed as “stellar” i.e. more likely to be a close binary

12. Dr. Matt Burleighwww.star.le.ac.uk/~mbu Sensitive to companions L0 or later in 247 DAsSensitive to companions L0 or later in 247 DAs –Hence limit on frequency of close L-dwarf companions is < 1.2% –c.f. Farihi et al. (2005) <0.5%, at all separations…. Sensitive to companions T0 or later in 99 DAsSensitive to companions T0 or later in 99 DAs –Frequency of close T-dwarf companions is < 1% Caveat: this assumes all the unresolved candidate binaries are real and are post-CECaveat: this assumes all the unresolved candidate binaries are real and are post-CE

13. Dr. Matt Burleighwww.star.le.ac.uk/~mbu Next stage Need to spectroscopically confirm remaining substellar candidatesNeed to spectroscopically confirm remaining substellar candidates Determine periods and secondary masses for candidate close binariesDetermine periods and secondary masses for candidate close binaries –Optical/IR photometric variability c.f. WD0137-349 –Radial velocities of brown dwarfs from Halpha emission (WD0137-349) or near-IR spectroscopy (GD1400) Follow-up further candidates from future UKIDSS data releasesFollow-up further candidates from future UKIDSS data releases

14. Dr. Matt Burleighwww.star.le.ac.uk/~mbu Magnetic WDs in UKIDSS 13 MWDs in list of Kawka et al. (2007) have UKIDSS photometry13 MWDs in list of Kawka et al. (2007) have UKIDSS photometry One interesting system….One interesting system….

15. Dr. Matt Burleighwww.star.le.ac.uk/~mbu X-ray and observational Astronomy Eclipsing WD binaries in WASP ● Wide Angle Search for Planets Search for eclipses and transits of WDs by unseen very low mass companions (from BDs to Moon-size!) FoV 7.8 x 7.8 degrees Cadence 8 minutes Limit: V=13 (transiting planets) V=15 (eclipses of WDs) Instrument characteristics: - 8 Canon lenses 200mm f/1.8 - CCD 2048 x 2048 pixels - Field of View 7.8 x 7.8 degrees (61 sq. degrees) - magnitude limit =15 V mag. - photometric accuracy of 1% down to 1 Average number of points per star 15 new transiting planets discovered so far WASP-1 Orbital Period = 2.52 days V magnitude 12.8

16. Dr. Matt Burleighwww.star.le.ac.uk/~mbu X-ray and observational Astronomy Simulations white noise Simulated WASP light curve of WD0137-349 (WD + 0.053Msun BD, P=116 mins) if it was an eclipsing binary

17. Dr. Matt Burleighwww.star.le.ac.uk/~mbu 194 white dwarfs V<15 in WASP fields Searched for eclipsing systems with periods from 2hrs - 15 days No eclipsing binaries discovered After full consideration of detection limits, conclude <1% of WDs have undetected substellar companions P<3hrs (0.125 days)