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Greet Decin

A study of the occurrence and time evolution of circumstellar debris disks and their relation with planetary systems. Greet Decin. 1. 2. 1. 2. 4. 3. 3. 4. Star formation and evolution of circumstellar material. Formation of low-mass stars.  Star Formation and Disk Evolution

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Greet Decin

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  1. A study of the occurrence and time evolution of circumstellar debris disks and their relation with planetary systems Greet Decin

  2. 1 2 1 2 4 3 3 4 Star formation and evolution of circumstellar material • Formation of low-mass stars  Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  3. 3 • Circumstellar material around young stellar objects • Detection of compact mm-emission • Frequency of occurrence  Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars 4

  4. Disk dispersal around young stars • Planet formation • Other disk removal processes Bulk of the disk removes in < 107 yr  Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  5. Proto-type: Vega • Vega phenomenon: disks around MS stars  Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  6. Grain lifetime < stellar lifetime • How? Collisions and thermal fragmentation of asteroids and comets need of larger bodies e.g. planets • Destruction and removal of dust grains in Vega-type disks due to e.g. • Radiation pressure • Poynting-Robertson drag • Grain collisions • …  Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars • Solution? Dust replenishment

  7. The Vega phenomenon linked with Solar system  Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  8. and HD10647? • Vega phenomenon linked with planet formation?  Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  9. Scope of this thesis • Frequency of the Vega phenomenon? • The Vega phenomenon after the main sequence? • Age dependence of the Vega phenomenon? • Different abundance for planetary systems versus Vega-type systems?  Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  10. ISO - PHOT • The Infrared Space Observatory - ISO • Star Formation and Disk Evolution ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  11. The photo-polarimeter ISOPHOT • PHT-P detectors • PHT-C camera • PHT-S spectrophotometer • Star Formation and Disk Evolution ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  12. ISOPHOT accuracies and limitations:most important aspect for our proposals • Chopped observations are not scientifically validated • Star Formation and Disk Evolution  ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars • Attention with the reduction of the PHT-S data • Use good reference SEDs

  13. • Star Formation and Disk Evolution ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  14. ISOPHOT accuracies and limitations:most important aspect for our proposals • Chopped observations are not scientifically validated • Attention with the reduction of the PHT-S data • Use good reference SEDs • Mispointing >3”: bad pointing correction • Star Formation and Disk Evolution ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  15. • Star Formation and Disk Evolution ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  16. ISOPHOT accuracies and limitations:most important aspect for our proposals • Chopped observations are not scientifically validated • Star Formation and Disk Evolution  ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars • Attention with the reduction of the PHT-S data • Use good reference SEDs • Mispointing >3”: bad pointing correction • Weight for dynamic calibration: not the errors but flux ratio

  17. • Star Formation and Disk Evolution ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  18. Sample selection G dwarfs from CORALIE planet-search programme Visible with ISO Less background 34 ISOPHOT observations 4 by bad observation mode, 30 by PHT-C100 maps Vega phenomenon around G dwarfs • Star Formation and Disk Evolution • ISO – PHOT  Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  19. Reliability of the reduction 5 excess stars from 30 good observations (=17%) • Star Formation and Disk Evolution •ISO – PHOT  Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  20. Results: 17% excess stars (~ H. Plets, 1997) • Survival of the remnant dust disk Old stars with “massive” disk • Star Formation and Disk Evolution • ISO – PHOT  Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars • Co-existence of a planet with a dust disk? Too less data

  21. Vega Phenomenon around K Giant Background and open problems dropped ~ Mira stars from regions above photosphere constraints on origin of (still unknown) mechanism triggering stellar mass loss and/or pulsations • PHT-P 60 µm • PHT-C 90 µm and 160 µm chopped • Sample selection: 30 K Giants with IR excess from IRAS database • Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs  Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars • Observations: • PHT-S spectrum: Origin of the strong CO and/or H2O absorption feature around HD129456?

  22. Analysis of the data Only 5 stars with 60 µm and 90 µm ISO excess and 6 stars with only 90 µm excess BUT IRAS excess fluxes ~ 2 * ISO excess fluxes Extended sources? • Omit 3 stars as candidate • Vega-like successor • Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs  Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars • True nature of IR excess? 2. extensiveness

  23. Disk Shell Cirrus • Star Formation and Disk Evolution •ISO – PHOT • Vega Phenomenon around G Dwarfs  Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars Rough method of Kim et al. 2001: flux central pixel/flux boundary pixels

  24. Analysis of the data Only 5 stars with 60 µm and 90 µm ISO excess And 6 stars with only 90 µm excess BUT IRAS excess fluxes ~ 2 * ISO excess fluxes True nature of IR excess? Extended sources? • Omit 3 stars as candidate • Vega-like successor Omit still 5 stars • Star Formation and Disk Evolution •ISO – PHOT • Vega Phenomenon around G Dwarfs  Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars 2. extensiveness 3. Control with HIRAS maps

  25. • Star Formation and Disk Evolution •ISO – PHOT • Vega Phenomenon around G Dwarfs  Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  26. • Star Formation and Disk Evolution •ISO – PHOT • Vega Phenomenon around G Dwarfs  Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  27. Kuiper Belt disk model: too large distance of dust grains around HD164712 photosphere at 2.5σ • HD3627, HD82421 and HD164712: genuine debris disk candidates? • HD3627 in Local Bubble • Star Formation and Disk Evolution •ISO – PHOT • Vega Phenomenon around G Dwarfs  Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars • Comparison of dust features of HD3627 and HD82421 with those of Vega-type stars: • somewhat hotter • little closer • fd in same range • slightly more massive • Submm observations of HD3627

  28. Discussion • Fraction of Vega-type successors < Vega-type MS stars • Older • Only most massive debris disks around K giants detected due to lower contrast (= flux density disk/photospheric flux density) • Evolution to the RGB of a debris disk star • L* T gr efficiency grain removal processes small dust away fdbut higher observed dust masses observed fd ≈ fd Vega-type stars • Increase L* have NO influence on lifetime disk because no affect on outer larger planets which stir the KBOs in collisional encounters • Star Formation and Disk Evolution •ISO – PHOT • Vega Phenomenon around G Dwarfs  Vega Phenomenon around K Giants • Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  29. Age Dependence of the Vega Phenomenon Background • Star Formation and Disk Evolution •ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants  Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars fd~ t-2?

  30. Sample selection: Vega-type stars observed with ISOPHOT Habing et al. 1999, 2001 Decin et al. 2000 Silverstone et al. 2000 Spangler et al. 2001 K giant HD3627 Parameter determination Age determination Cluster method Moving group Isochrones Metallicity Rotation Ca emission lines kinematics Most reliable methods B9-G5 Late-type stars • Star Formation and Disk Evolution •ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants  Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  31. Fractional luminosity fd≡ Fexc /F photosph =Ldust/Lbol • Accepted sources have S/N excess ≥ 2 • 2 different methods for all stars same method used • Remarks • No small number statistics • Exclude pre-main-sequence stars • Check whether IR excess is due to Vega phenomenon • Exclude ‘negative’ excesses • Star Formation and Disk Evolution •ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants  Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  32. Relationship between lifetime and fractional luminosity • Star Formation and Disk Evolution •ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants  Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  33. 60 µm HIRAS 100 µm HIRAS • Observed properties • Upper cut-off fd ≈ 10 –3 : true limit • Lower cut-off fd ≈ 10 –5 : sensitivity limit of ISOPHOT • Few young stars with small amounts of dust? • Star Formation and Disk Evolution •ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants  Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  34. Dependence of visible dust on different parameters Standard model with • disk mass = 10 M • mean distance star-disk = 43 AU • collision velocity/ keplerian velocity ~ 0.1 • start radius comet = 1 km • around an A0 star • Collisional model derive the amount of dust produced by a collisional cascade of large bodies, and its evolution with time • Star Formation and Disk Evolution •ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants  Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars • Remark dust removal is collisionally dominated in large disks (disks now observed, slope -1) and Poynting- Robertson drag dominated in small disks (slope -2) (transition at disk mass of ~10-3 M )

  35. • Star Formation and Disk Evolution •ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants  Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  36. Explain the observed features: The initial decrease for young stars remark: slope steeper than -1?? increase the collision velocity • The upper limit self-accelerating avalanche effect • Independence of upper limit of age stirring of disk starts after certain time • Absence of young stars with low fd-values 3 ways to populate this region: • Low inititial disk masses below 10 M • High collision velocities very early on • Collisional cascade at large distance from star • Star Formation and Disk Evolution •ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants  Age Dependence of Vega Phenomenon • Abundance Analysis of Vega-type Stars

  37. Abundance Analysis of Vega-type Stars Background Star-formation remnants • Overlap between stars surrounded with a planet and Vega-type stars is at this moment very small •Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants •Age Dependence of Vega Phenomenon Abundance Analysis of Vega-type Stars • Stars surrounded with inner giant planets are on the average metal-rich. Origin? • Initial conditions which favours what kind of star-formation remnants are formed? • Sample selection • 2 stars surrounded with planet(s) and a disk • 2 planet-harbouring stars • 6 Vega-type stars • 5 field stars

  38. Observations: CORALIE, 1.2 m Leonard Euler telescope, La Silla, λ/Δλ= 50000, 3800 to 6800 A Atomic data Determination of stellar parameters Comparison with other studies Abundance analysis •Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants •Age Dependence of Vega Phenomenon Abundance Analysis of Vega-type Stars

  39. Results • Fe abundance •Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants •Age Dependence of Vega Phenomenon Abundance Analysis of Vega-type Stars Planet-harbouring stars can have low metallicity • Comparison in the [X/Fe] versus [Fe/H] plane

  40. Vega-type stars, stars with planet, + field stars •Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants •Age Dependence of Vega Phenomenon Abundance Analysis of Vega-type Stars

  41. Volatile versus refactory elements no signs of accretion of chemically fractionated solid materials • Results • Fe abundance •Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants •Age Dependence of Vega Phenomenon Abundance Analysis of Vega-type Stars Planet-harbouring stars can have low metallicity • Comparison in the [X/Fe] versus [Fe/H] plane the normal galactic trend

  42. Discussion Maximum mass in a Kuiper Belt • Infall of KBO occur, but no signs found in chemical abundance • When 40 M of Halley-dust material is accreted by Sun, mean increase of 0.09 dex for volatiles and refractories • 20% of dust produced by KBO spirals onto the Sun • Maximum of 200 M can be present in KBOs •Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants •Age Dependence of Vega Phenomenon Abundance Analysis of Vega-type Stars

  43. Confrontation with different models • Difference between inner planet and disk-harbouring stars = difference between inner and outer planet-host stars = different timescale of planet formation • Timescale is dependent of e.g. eccentricity, mass density, tensile strength, total mass of planetesimals, metallicity? • Rapid formation = inward migration of planet and accretion onto star of ‘inside’ pristine planetesimals • Slow formation = ‘no’ gaseous envelope around planet and outward migration of planet which increases the collision rate of planetesimals in resonance positions delayed onset of collisional cascades • Normal or low metal content may favour debris disks observable at large ages •Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants •Age Dependence of Vega Phenomenon Abundance Analysis of Vega-type Stars

  44. Conclusions and Outlook • Conclusions • ISO (-PHOT): carefull analyis • 30 G dwarfs: • 17% Vega-type stars • old stars with relatively high fractional luminosity • 30 K giants: • 2 candidate Vega-type successors (point sources) • Dusty debris disks are less common because older and more difficult to detect • Disk is somewhat more massive • Dust grains are larger, warmer, further away • HD129456: remarkable absorption feature around 2.5 µm •Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants •Age Dependence of Vega Phenomenon Abundance Analysis of Vega-type Stars

  45. Age dependence of Vega phenomenon: • Vega-like excess is more common in young than in old stars but ... • No global power law in the age-fd diagram • Collisionally dominated: power law of -1, steeper with continuous stirring • Poynting-Robertson dominated: power law of -2 • Maximum excess at fd ≈10-3 at all ages delayed stirring • Absence of young stars with small excesses planet forming not active • Abundance analysis of Vega-type stars and planet stars • Inner planet harbouring stars: higher metallicity • Other elements follow galactic trend • No signs of accretion of refractory elements • Vega-type disk: maximum 200 M • High metallicity: positive influence on inner planet formation • Normal or low metal content may favour debris disks observable at large ages •Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants •Age Dependence of Vega Phenomenon Abundance Analysis of Vega-type Stars

  46. Future prospects Coronographic measurements of HD10647 and HD3627 High resolution spectrum of HD129456 (2.5 µm) SIRTF (launched August, 25th 2003) More accurate measurements of Vega-type disks SIRTF, AMBER and MIDI Transition between HAeBe and Vega-type systems CORALIE … More low-mass and long-period planets •Star Formation and Disk Evolution • ISO – PHOT • Vega Phenomenon around G Dwarfs • Vega Phenomenon around K Giants •Age Dependence of Vega Phenomenon Abundance Analysis of Vega-type Stars • …Future holds promising results…

  47. A study of the occurrence and time evolution of circumstellar debris disks and their relation with planetary systems Greet Decin

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