Download Direct Imaging Searches Around White Dwarfs - X

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