Protoplanetary disk evolution and clearing Paola D’Alessio (CRYA) J. Muzerolle (Steward) C. Briceno (CIDA) A. Sicilia-Aguilar (MPI) L. Adame (UNAM) IRS disk modeling team L. Allen (SAO) D. Wilner (SAO) C. Qi (SAO) R. Franco-Hernandez (SAO) K. Luhman (PennState) T. Megeath (Toledo) Michigan: T. Bergin L. Hartmann J. Hernandez C. Espaillat Z. Zhu L. Ingleby J. Tobin Nuria Calvet (Michigan)

Disks evolve from optically thick dust+gas configurations to mostly solids debris disks Disk evolution and Clearing HK Tau, Stapelfeldt et al. 1998

optically thick dust+gas configurations, formed in the collapse of rotating molecular cores dust/gas ~ 0.01 heated by stellar radiation captured by dust (and viscous dissipation) dust reprocesses heat and emits at IR collisions transfer heat to gas, determines scale height accreting mass onto the star Optically thick disks (T Tauri phase) Furlan et al 2006Photosphere

Optically thin disks (debris disk) Chen et al 2006 dust/gas ~ 0.99 small secondary dust, from collisions of large bodies large inner holes, tens of AUs no gas accretion

Questions How does gas evolve – dissipate? How does dust evolve – formation of large bodies? Characteristic times scales

Disks are accreting Excess energy over photospheric flux which cannot be accounted for by stellar energy Potential energy of matter accreting onto star Accretion from disk (where most of the mass of the molecular cloud core was deposited)

Disks are accreting Inner disk is truncated by stellar magnetic field (~ KG, Valenti & Johns-Krull papers) at ~ 3-5 R*. Matter flows onto star following field lines – magnetospheric accretion flow Hartmann 1998

Evidence for magnetospheric accretion Broad emission lines Muzerolle et al. 1998, 2001 v ~ 0 km/s v ~ 250 km/s Excess emission/veiling velocity

Evidence for magnetospheric accretion Broad emission lines Muzerolle et al. 1998, 2001 Redshifted absorption if right inclination v ~ 0 km/s v ~ 250 km/s Excess emission/veiling Calvet & Gullbring 1998

Accretion luminosity and mass accretion rate Gullbring et al. (1998) Excess emission over photosphere ~ L acc = G M (dM/dt) / R Link to disk properties Ingleby et al 2007 STIS data

Present picture of inner disk Near-IR emission mostly from wall at dust destruction radius

Emission from Wall at dust destruction radius Emission ~ Black-body at T ~ 1400K, ~ vertical wall frontally illuminated Increases with accretion luminosity, T ~ 1400K at larger radius R d  (L * + L acc ) 1/2 Consistent with L acc determinations Muzerolle et al 2003

Accretion luminosity and mass accretion rate Measure dM/dt for populations ~ Myr UV excess or excess at U (calibrated to L acc ) Intrinsic chromospheric emission prevents measurement of low accretion luminosity Model H  line profiles to get mass accretion rate (Muzerolle papers) Basis of all calibrations to obtain mass accretion rates for weak accretors (ie, brown dwarfs, “weak” TTS) Uncertainties: temperature structure, geometry, effects of winds (Alencar et al. 2006; Kurosawa et al 2006)

Mass accretion rate decreases with time Hartmann et al. (1998), Muzerolle et al. (2001), Calvet et al. (2005) Viscous evolution - Gas

Viscous evolution Hartmann et al. (1998)  (R) decreases with time Disk expands Region of dM/dt ~ const,  ~ 1/R Models for steady disks Irradiated accretion disks (D’Alessio models) using dM/dt onto star (from UV)  (R) given dM/dt determined from UV for each object (not a free parameter)

Irradiated steady accretion disks Irradiated (steady) accretion disks (D’Alessio models)  (R) given observed dM/dt  ~ (dM/dt) /  Uncertainty in  M disk ~  x size,  “calibrated” by measurement of disk mass Uncertainty in mass determination – dust opacity, multiwavelength observations to constrain dust mixture If MRI, then layered accretion (Gammie 1996), dead zone Photoevaporation (Clarke et al 2001)

High accretors: FU Ori  Zhu et al 2007 Flared outer disk irradiated by inner disk Inner disk: standard accretion disk dM/dt ~ M sun /yr Instability region ~ 0.6 AU, >> Bell & Lin 1994

High accretors: DR Tau  Silicate emission and high far-IR flux because of irradiation by high energy radiation from accretion shock dM/dt = 2 e-7 M sol /yr D’Alessio et al 2007 wall viscous

High accretors at 5 Myr  Orion OB1b sample (Hernandez e al 2007)

Mass accretion rate decreases with time Hartmann et al. (1998), Muzerolle et al. (2001), Calvet et al. (2005) Fraction of accreting objects decreases with time: not explained by viscous evolution: dust evolution?

Dust properties from SED: Grain growth Median SED of Taurus a max =0.3  m, ISM a max = 1mm D’Alessio et al 2001 a max increases,  1  decreases, less heating, less IR emission  mm increases, higher fluxes

Evolution of grains in disks As disk ages, dust growths and settles toward midplane Weidenschilling 1997 Dullemond and Dominik 2004 Upper layers get depleted t = 0 Population of big grains at midplane

Settling of solids: TW Hya 3.5 cm flux ~ constant => Dust emission Wilner et al Jet/wind? Nonthermal emission?

Settling: bimodal grain size distribution Weidenschilling 1997 Wilner et al Small + 5-7mm  ~ 1/R

Dust evolution effects on SED Decrease of dust/gas in upper layers Weidenschilling 1997 Lower opacity, less heating, less IR emission, but silicate emission D’Alessio et al Dullemond & Dominik 2004; Lada et al 2006  Increasing depletion of upper layers

Spitzer/IRS data of Taurus (1-2 Myr) Furlan et al Large range of properties at one age

Settling of dust toward midplane Median of Taurus from IRAC fluxes for 60 stars (Hartmann et al 2005) and IRS spectra of ~75 objects (Furlan et al 2005) Upper laters depleted by 10 to 1% of standard dust-to-gas ratio Furlan et al 2006 Depletion of upper layers:  upp /  st D’Alessio et al 2006

Settling of dust toward midplane: small grains in upper layers Sargent et al 2006 Silicate emission feature formed in hot upper inner disk layers Small grains in upper layers, consistent with settling Crystalline components

SED evolution:comparison at different ages IRAC data for a number of clusters and associations with ages 1 – 10 Myr: Gradual decrease of excess emission Data from Hartmann et al 2005 Sicilia-Aguilar et al 2005 Lada et al 2006 Hernandez et al 2007b Taurus Hernandez et al 2007 [3.6] – [4.5]

SED evolution: inner disk Decrease of median slope with age: consistent with decrease of dM/dt and dust settling in inner disk Hernandez et al 2007b Photosphere

SED evolution Slope becomes stepper - less excess as Degree of settling increases Accretion rate decreases wall disk log dM/dt= -10, -9, -8, -7  decreases Art by Luis Belerique & Rui Azevedo

SED evolution Taurus 1-2 Myr Tr 37 3 Myr NGC Myr Evolution of the median SED from IRAC and MIPS 24 measurements: Faster evolution of inner disk Sicilia-Aguilar et al 2005

SED evolution Present evidence: As a given population ages, the fraction of remaining disks tend to have lower accretion rates and their dust more settled toward the midplane But fraction of remaining disks decreases with time. What happened to the other disks?

Transition disks Transition disks? Lack of significant excess flux below 10  m But flux comparable to the median of Taurus at longer wavelengths Model: Clearing of the innermost, hotter disk regions Truncated outer optically thick disk Wall at truncation radius illuminated frontally by star

Transition disks Calvet et al 2002 TW Hya 10 Myr old Taurus median Near to mid-IR flux deficit Sharp rise Flux at longer consistent with optically thick emission

Inner disk clearing Uchida et al Spectra from IRS on board SPITZER TW Hya, ~ 4 AU ~ 10 Myr Inner disk Wall Optically thin region with lunar mass amount of micron size dust + gas (accreting star) Optically thick outer disk

Inner disk clearing Forrest et al. 2004; D’Alessio et al CoKu Tau 4, ~ 10 AU ~ 2 Myr No inner disk, silicate from wall atmosphere Non-accreting star 4 AU T= K dd

More disks in transition in Taurus Calvet et al 2005 R w ~ 24AU outer disk + inner disk with little dust + gap (~ 5-24AU) R w ~ 3 AU only external disk but accreting star Inner disk

Transition Disk in a Brown Dwarf Muzerolle et al 2006 R w = 1AU

Evolving transition disks: grain growth Espaillat et al 2007 R w = 47AU Micron-size grains in optically thin inner disk and wall ISM Ne II line, enhanced penetration of X-rays

Inner disk Substantial mass accretion rates and high mm fluxes in GM Aur, DM Tau, TW Hya CO emission in inner disk of TW Hya (Rettig et al 2004) H 2 emission from inner disk of GM Aur, DM Tau, TW Hya in FUV spectra (Bergin et al 2004) Ne II, X-ray induced ionization (Espaillat et al 2007, following ionization model Glassgold et el 2007)

Inner disk clearing: photoevaporation of outer disk? UV radiation photoevaporates outer disk When mass accretion rate (decreasing by viscous evolution) ~ mass loss rate, no mass reaches inner disk R g ~ G M * / c s 2 (10000K) ~ 10 AU (M * /M sol ) Evolution with photoeva poration Evolution without photoeva poration RgRg Clarke et al 2001

Inner disk clearing:photoevaporation of outer disk? Prediction: low mass accretion rate and mm flux in transitional disks But average mass accretion rates and high mm fluxes in GM Aur, DM Tau, TW Hya Clarke et al 2001

Inner disk clearing: photoevaporation of outer disk? Increasing hole sizes with mass High disk masses and accretion rates Transition disks in brown dwarfs (Muzerolle et al 2006)  No significant UV flux Inner disk

Inner disk clearing: planet(s)? Wall of optically thick disk = outer edge of gap at a few AU Bryden et al 1999 Giant planet forms in disk opening a gap Inner gas disk with minute amount of small dust – silicate feature but little near IR excess, bigger bodies may be present

Inner disk clearing: planets? Tidal truncation by planet Hydrodynamical simulations+Montecarlo transfer – SED consistent with hole created and maintained by planet – GM Aur: ~ 2M J at ~ 2.5 AU – Rice et al SED depends on mass of planet (and Reynolds number) M J 1.7 M J 21 M J 43 M J

Inner disk clearing: planets? D’Alessio et al CoKu Tau 4, wall at ~ 10 AU No inner disk Planet-disk system with planet mass of 0.1 M jup for CoKu Tau 4 Quillen et al Long term duration of system?

Inner disk clearing: planets? Planet formation can explain: SEDs of transition disks short timescale for transition phase ~ run-away gas accretion/gap opening rapid disappearance of inner disk, viscous time scale at gap, increased efficiency of MRI in low opacity inner disk Problems: outer disk may make planet migrate inwards in viscous timescale, small  ? Recurrent events? High accretors at advanced ages?

Summary Space data crucial for progress in understanding disk evolution Disks gradually evolve accreting mass at decreasing rates onto star while dust grows and settles toward midplane At some point, disk enters into transition phase, eventually turning off accretion and clearing up inner disk Alternative models for clearing are planet formation and photoevaporation of outer disks. Present evidence may favor planet formation Need characterization of properties of transitional disks in large samples of different ages plus theoretical efforts