Transcript Detached WD/BD binaries as progenitors of CVs

Detached WD/BD binaries as
progenitors of CVs
Matt Burleigh
with Paul Steele, Francesca Faedi, Paul Dobbie (AAO) and Boris Gaensicke (Warwick)
Dr. Matt Burleigh
www.star.le.ac.uk/~mbu
Motivation
• Investigate 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 models
– Pinfield et al. (2006)
• 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
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)
Dr. Matt Burleigh
www.star.le.ac.uk/~mbu
Irradiation of WD0137-349B
Green - K
(+/-14%)
Red - H
(+/- 8%)
White - J
(+/- 3%)
• AAT + IRIS2 in July 2007
Dr. Matt Burleigh
www.star.le.ac.uk/~mbu
Post-CE binaries with BD
secondaries
• Constrain models of common
envelope evolution
• What is the lowest mass object
that can survive a CE?
• What fraction of CVs are born
with a BD secondary?
• Growing 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)
Dr. Matt Burleigh
www.star.le.ac.uk/~mbu
Known detached WD+BD binaries
• Rare: only three confirmed systems
• GD165
– 120AU separation, L4 secondary
– Becklin & Zuckerman (1988)
• WD0137-349
– P=116 mins, L8 secondary (0.053Msun)
– Maxted et al. (2006); Burleigh et al. (2006)
• GD1400
– P=9.98 hours, L6/7 secondary
– Farihi & Christopher (2004), Burleigh et al. (2009)
• 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 Spitzer
– PG1234+482 (Mullally et al. 2007; Steele et al. 2007)
• A handful of other WD + ultracool dwarf binaries
known
Dr. Matt Burleigh
www.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
Dr. Matt Burleigh
www.star.le.ac.uk/~mbu
Searching for unresolved WD+BD binaries in UKIDSS
• Cross-correlate UKIDSS LAS
DR4 release (1060 sq. deg)
with
– SDSS DR4 spectroscopically ided WDs (Eisenstein et al. 2006)
– McCook and Sion WDs
• J-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)
– Identify WDs with >3 sigma
excesses at H and K
Dr. Matt Burleigh
www.star.le.ac.uk/~mbu
Results
• 922 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 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) companions
• 5 candidate L dwarf companions
• 1 candidate T dwarf companion
Dr. Matt Burleigh
www.star.le.ac.uk/~mbu
WD+L4
WD+L6
WD+L8
Dr. Matt Burleigh
www.star.le.ac.uk/~mbu
PHL5038 = SDSS J222030.68-004107.3
K
• B=18, UKIDSS K=16.7
• Follow-up imaging and
spectroscopy with Gemini-North
+ NIRI
• Resolved at 0.92” (=55AU
projected)
• L8 companion (T~1600K,
M~0.055Msun @ 2-3Gyr)
• WD T=8000+/-100K, M=0.72+/0.15Msun, d=64+/-10pc
• 4th known WD+BD detached
system, 2nd wide
• Steele et al. 2009
Dr. Matt Burleigh
www.star.le.ac.uk/~mbu
Frequency of close, detached
WD+BD binaries
• PHL5038 is flagged as partially resolved in
UKIDSS
• 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)
• Single T dwarf candidate classed as “stellar” i.e.
more likely to be a close binary
Dr. Matt Burleigh
www.star.le.ac.uk/~mbu
• Sensitive 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 DAs
– Frequency of close T-dwarf companions is < 1%
• Caveat: this assumes all the unresolved candidate binaries
are real and are post-CE
Dr. Matt Burleigh
www.star.le.ac.uk/~mbu
Next stage
• Need to spectroscopically confirm remaining
substellar candidates
• Determine 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 releases
Dr. Matt Burleigh
www.star.le.ac.uk/~mbu
Magnetic WDs in UKIDSS
• 13 MWDs in list of Kawka et al. (2007) have UKIDSS
photometry
• One interesting system….
Dr. Matt Burleigh
www.star.le.ac.uk/~mbu
Eclipsing WD binaries in WASP
X-ray and observational Astronomy
● 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:
Average number of points per star
- 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
Dr. Matt Burleigh
www.star.le.ac.uk/~mbu
15 new transiting planets
discovered so far
V magnitude 12.8
WASP-1
Orbital Period = 2.52 days
X-ray and observational Astronomy
Simulated WASP light curve
of WD0137-349 (WD +
Simulations
0.053Msun BD, P=116 mins)white
if it was
noisean eclipsing binary
Dr. Matt Burleigh
www.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)
Dr. Matt Burleigh
www.star.le.ac.uk/~mbu