searching for dying solar systems: planets around white dwarfs
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Searching for dying solar systems: Planets around White Dwarfs. Matt Burleigh, Leicester Fraser Clarke, Oxford Emma Hogan, Leicester Simon Hodgkin, Cambridge. Improving Contrast. To understand extrasolar planets, we need their light! - PowerPoint PPT PresentationTRANSCRIPT
DEPARTMENT OF PHYSICS AND ASTRONOMY
Searching for dying solar systems:Searching for dying solar systems:Planets around White DwarfsPlanets around White Dwarfs
Matt Burleigh, LeicesterMatt Burleigh, LeicesterFraser Clarke, OxfordFraser Clarke, Oxford
Emma Hogan, LeicesterEmma Hogan, LeicesterSimon Hodgkin, CambridgeSimon Hodgkin, Cambridge
Dr. Matt Burleigh RAS November 2004
Improving ContrastImproving Contrast
• To understand extrasolar planets, we need To understand extrasolar planets, we need their light!their light!
• None of the radial velocity planets can be None of the radial velocity planets can be imaged with current technologyimaged 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, Remove the starlight (technology: AO, coronography, interferometry)coronography, interferometry)
– Remove the star (stellar evolution)Remove the star (stellar evolution)
Observe White Dwarfs!Observe White Dwarfs!
Above: Gl229B – brown dwarf companion to nearby M dwarf
Dr. Matt Burleigh RAS November 2004
Surviving the RGBSurviving the RGB
• Red Giant expands to maximum ~5AURed Giant expands to maximum ~5AU• Planets inside 5AU are destroyed by Planets inside 5AU are destroyed by
Red GiantRed Giant• Planets outside ~5AU will migrate Planets outside ~5AU will migrate
outward due to mass loss and surviveoutward due to mass loss and survive– Dynamical time ~10-30 yrDynamical time ~10-30 yr– mass loss time ~1000-10000yrmass loss time ~1000-10000yr– planets planets stay boundstay bound
Dr. Matt Burleigh RAS November 2004
The Benefits of White DwarfsThe Benefits of White Dwarfs
• WD's are ~10,000 times fainter than WD's are ~10,000 times fainter than their progenitorstheir progenitors
• => Huge => Huge contrast gaincontrast gain
• Planets orbit increasesPlanets orbit increases
• => Big => Big resolution gainresolution gain
• And >120 WDs within 20pcAnd >120 WDs within 20pc
Dr. Matt Burleigh RAS November 2004
The Benefits of White DwarfsThe Benefits of White Dwarfs
• PLUS the WD progenitors are more PLUS the WD progenitors are more massive than solar-type starsmassive than solar-type stars– Mainly A and B starsMainly A and B stars– Not generally being targeted by radial velocity Not generally being targeted by radial velocity
programmesprogrammes
• So by targeting WDs we are probing So by targeting WDs we are probing frequency of planets around massive stars frequency of planets around massive stars
Dr. Matt Burleigh RAS November 2004
Planet brightness v agePlanet 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
Dr. Matt Burleigh RAS November 2004
Imaging planets around white dwarfsImaging planets around white dwarfs
• Large format NIR cameras on 8m-class Large format NIR cameras on 8m-class telescopestelescopes– Typically reach Typically reach J~24 in 1 hourJ~24 in 1 hour
(e.g. VLT+ISAAC, Gemini+NIRI)(e.g. VLT+ISAAC, Gemini+NIRI)– Comparable with predicted magnitudes of Comparable with predicted magnitudes of
planets around nearby white dwarfsplanets around nearby white dwarfs
• No immediate need for AONo immediate need for AO– Searching outside star’s PSFSearching outside star’s PSF
Dr. Matt Burleigh RAS November 2004
Cool companions to WDsCool companions to WDs
• Becklin & Zuckerman, Probst in the 1980sBecklin & Zuckerman, Probst in the 1980s– IR excess in WDs may indicate cool companionIR excess in WDs may indicate cool companion– First L dwarf discovered is a companion to a WD, GD165First 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) Only one more found so far (GD1400B, L6/7, Farihi et al. 2004) – Confirms brown dwarf desert at wide separationsConfirms brown dwarf desert at wide separations
• No companions >10MNo companions >10MJupJup found among Hyades WDs found among Hyades WDs– Zinnecker & Friedrich, in prep. (HST/NICMOS)Zinnecker & Friedrich, in prep. (HST/NICMOS)
Dr. Matt Burleigh RAS November 2004
StrategyStrategy• Select young (<3Gyr), nearby (<20pc) white Select young (<3Gyr), nearby (<20pc) white
dwarfs dwarfs – (0.2”yr < PM < few “/yr)(0.2”yr < PM < few “/yr)– Sample ~40 starsSample ~40 stars– Progenitors mainly A/B stars (short main Progenitors mainly A/B stars (short main
sequence lifetimes)sequence lifetimes)• Obtain deep wide IR (J) images.Obtain deep wide IR (J) images.
– Total exp time ~1hrTotal exp time ~1hr– Depth J~23.5 (GN) to ~24 (VLT) Depth J~23.5 (GN) to ~24 (VLT) – Image quality typically 0.4”-0.6”Image quality typically 0.4”-0.6”
• Wait 1—2 years…Wait 1—2 years…– Obtain 2Obtain 2ndnd epoch images of epoch images of allall systems to systems to
check for common proper motion companionscheck for common proper motion companions
Dr. Matt Burleigh RAS November 2004
Parameter spaceParameter space
• For comparison with For comparison with other planet search other planet search techniques;techniques;– Planet mass; >5 MjupPlanet mass; >5 Mjup– Orbit; 5—1000 AUOrbit; 5—1000 AU– Age; 0.5—3 GyrAge; 0.5—3 Gyr– Star mass; 2—7 Msun Star mass; 2—7 Msun
(A and B stars) (A and B stars)• Complimentary to Complimentary to
other search other search techniquestechniques
Dr. Matt Burleigh RAS November 2004
Not a Not a discoverydiscovery
Dr. Matt Burleigh RAS November 2004
• White dwarfsWhite dwarfs– Image depth J~24Image depth J~24
Dr. Matt Burleigh RAS November 2004
Two epochs for Proper MotionTwo epochs for Proper Motion
• One epoch in One colour tells us nothing.One epoch in One colour tells us nothing.
• Faint objects Faint objects couldcould be faint companions, be faint companions, or they could simply be far away…or they could simply be far away…
• AnyAny object in the field could be a object in the field could be a companion!! (orbital expansion)companion!! (orbital expansion)
• 22ndnd epoch observations are needed to epoch observations are needed to confirm companions via proper motion.confirm companions via proper motion.
Dr. Matt Burleigh RAS November 2004
• Two epochsTwo epochs– June 2002 GS+Flamingos-IJune 2002 GS+Flamingos-I– October 2003 VLT+ISAACOctober 2003 VLT+ISAAC– WD motion ~1” between imagesWD motion ~1” between images– Image depth J~23.5Image depth J~23.5
^~90”
V
< ~120” >
Dr. Matt Burleigh RAS November 2004
Motions in fieldMotions in field
• Arrows show direction Arrows show direction and degree of motion x and degree of motion x factor 20factor 20
• WD moved ~9 pixels in WD moved ~9 pixels in 15 months (~1”)15 months (~1”)
Dr. Matt Burleigh RAS November 2004
A non-detectionA non-detection
• Circles: Circles: 11scatter on scatter on distribution of distribution of proper motions of proper motions of background background objectsobjects
Dr. Matt Burleigh RAS November 2004
A detection?A detection?
• Circles: 1 error on PMs
• If associated, candidates are 7-10MJup
• Would have originally orbited at ~65AU & ~75AU
• First epoch June 2002, second June 2003
Dr. Matt Burleigh RAS November 2004
Add third epoch (June 2004)Add third epoch (June 2004)
• Candidates have gone away!
Dr. Matt Burleigh RAS November 2004
SummarySummary
• White dwarfs open up more parameter White dwarfs open up more parameter space for planet surveysspace for planet surveys– Direct imaging of planets >5MDirect imaging of planets >5MJupJup
– Probing frequency of planets around massive Probing frequency of planets around massive stars (>2Mstars (>2MSunSun))
• Sensitivity required is achievable with 8m Sensitivity required is achievable with 8m telescopes in near-IRtelescopes in near-IR
• Our survey is beginning to reach maturityOur survey is beginning to reach maturity– 2 epochs for 12 systems 2 epochs for 12 systems – 40 systems by 200640 systems by 2006
Dr. Matt Burleigh RAS November 2004
Further work….Further work….
• Is a sample of 40 enough? Is a sample of 40 enough? – Coronographic searches of nearby young stars Coronographic searches of nearby young stars
indicate frequency of companions indicate frequency of companions >5M>5MJupJup beyond 75AU is <3% beyond 75AU is <3%
(McCarthy & Zuckerman 2004)(McCarthy & Zuckerman 2004)
• Plus want to probe to lower masses (<5MPlus want to probe to lower masses (<5MJupJup))
– Spitzer mid-IR observations for photometric Spitzer mid-IR observations for photometric excesses (several programmes in progress)excesses (several programmes in progress)