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Disk Evolution Timescales 2 March, 1999 Glenn Schneider Steward Observatory HUBBLE SPACE T ELESCOPE Current theories of circumstellar disk evolution suggest that the presumed epochs of planet-building via the formation and agglomerative growth of embryotic b o d i e s and the subsequent a c c r e t i o n o f g a s e o u s atmospheres onto hot giant planets is attendant with a significant decline in the gas-to-dust ratios in the remnant protostellar environments. In this critical evolutionary phase of newly-formed (or still forming) extra-solar planetary systems, from a few megayears to a few tens of megayears, the circumstellar environments become dominated by a secondgeneration, non-primordial, population containing larger grains through collisional erosion of planetesimals. Planet-Building Timeline HUBBLE SPACE TELESCOPE Taurus, Ophiuchus star forming regions Steward Observatory Tucanae Hyades TW Hydrae Assoc Pleiades Persei Assoc 106 yrs Collapsing protostar forms protoplanetary disk Glenn Schneider 107 yrs 108 yrs Giant planets accrete gaseous atmospheres Rocky cores of giant planets form Era of heavy bombarment by comets Terrestrial planets form Primary Dust (Š m) Secondary Dust (•m) Locked to Gas Collisional erosion Clearing Timescales: P-R drag few 10 6 Rad. Pressure: ~ 104 Sun 109 yrs Current age of the Sun: 5x109 yrs . Clearing of inner solar system, formation of a Kuiper cometary belt? HUBBLE SPACE T ELESCOPE Observational Evidence Getting the Whole Picture Glenn Schneider Steward Observatory Sub-mm: Emission from Cold Dust Mid-IR: Emission from Hot Dust Vis/Near-IR: Scattered Light from Dust Y K G S O I D OL H P R O . Scattered light Disk:Star contrast ratios are very low -> need A/O*, space-based, and coronagraphic systems Resolved imaging -> spatial distribution of dust Asymmetries (radial & azimuthal): • Scattering properties (phase functions) • Inference of Perturbers (planets) from: Rings, Gaps, Clumps, Central Hole, Pericenter Glow... M * but, still VERY Challenging HUBBLE SPACE T ELESCOPE Hot dust around young stars had been inferred from thermal (IR) Glenn Schneider excesses since IRAS, though until recently the expected cold dust Steward Observatory component had been imaged only about Pictoris. 1984 - B.A. Smith & R.J. Terrile 6" radius coronagraphic mask, Las Campanas (discovery image) 1992 - 40 AUto 200 AU, ESO 2.2 m (BDL antibloom CCD) IRAS 60m 1996 - Beuzit et al, J-band, ADONIS/coronagraph, ESO 3.6m, La Silla 1995 - Kalas & Jewitt, r-band, coronagraph 6.5" radius mask (10" obscuration), U. Hawaii, 2.2m, Mauna Kea. 13.1"x13.1" HUBBLE SPACE T ELESCOPE HST/NICMOS Search for Dusty Circumstellar Debris Disks Glenn Schneider NICMOS Project Steward Observatory Using the Near Infrared Camera and Multi-Object Spectrometer on the Hubble Space Telescope we have carried out a coronagraphic imaging survey of 22 young (< ~ 100My) unembedded (i.e., largely unobscured by primordial material) stars with known for-IR excesses, imaging and resolving other examples of dusty or dust-dominated debris disks. file:/starsrus.as.arizona.edu/DATA1/HILO/ORBITS.CANV G. Schneider, 1/31/2001 Today We Discuss the Properties Glenn Schneider 2 March, 1999 Steward Observatory Three TWA Debris Disk Systems 1) The pole-on optically thick disk of the classical T-Tauri star TW Hya which, while dusty, posesses a significant amount of remnant primordial gas. 2) The dust-dominated and possibly Kuiper-belt like circumstellar ring about the young main-sequence star HR 4796A exhibiting morphological structures and anisotropies which may suggest recent or on-going planet formation. 3) The debris disk about HD 98800B, undetected in scattered light, a likely analog to the zodiacal bands in our own solar system. The properties of these disks (and others imaged by HST) show structures that suggest reprocessing of the dust, indicative of the likely evolution of collisionally induced grain populations, possibly as a result of planet formation. HUBBLE SPACE T ELESCOPE file:/starsrus.as.arizona.edu/YSNE/YSNE_TODAY.CANV G. Schneider, 03/36/2001 TW Hydrae Glenn Schneider Steward Observatory HUBB LE S P A CE TE LE S COP E TW Hydrae, a classical T-Tauri star, is the archetypal member of the young stellar association which bears its name. TW Hya was found to harbor an optically thick face-on disk (r - 190 AU) seen in NICMOS F110W and F160W coronagraphic images, and also by Krist et al. (2000) with WFPC-2, which is fit very well at both wavelengths with an r-2.6 power law. Areal scattering profiles, in both colors, corrected for the color of the star reveal a break in the surface density of scatterers at R - 100 AU which may be indicative of sculpting of the disk grains. • K7Ve (Rucinski & Krautter, 1983) • Distance: 56±7 pc (Hipparchus) • Age: 6 Myr • Ha and UV Excesses Isolated T-Tauri Star • Member TW Hya Association (TWA ~ 10 Myr, 60 pc) • Long Wavelength Excesses t ~ Ldisk /Lstar ~ 0.3 (IRAS) CO emission (Zuckerman et al. 1995) • Submm Continuum (Weintraub et al. 1989) TW Hydrae Glenn Schneider (NICMOS F110W & F160W) Steward Observatory HUBB LE S P A CE TE LE S COP E Flared Disk + Hole 1.1m 1.6m -2) ln Surface Brightness (mJy arcsec • Radial Profile: R-2.6 power law to 135 AU radius • Gray scattering: F110W - F160W = 0.96 mag (same as star) Thin Disk HUBBLE SPACE TELESCOPE TW Hydrae NIR Surface Brightness Profiles Glenn Schneider Steward Observatory F1.6m(rau) = (78/rau)2.6 mJy arcsec -2 F1.1m(rau) = (67/rau)2.6 mJy arcsec -2 file:/starsrus.as.arizona.edu/DATA1/HILO_1/TWHYA_SURF.CANV G. Schneider, 1/31/2001 WFPC-2 data courtesy of J. Krist. 12 Zone 1 2 14 3 4 NICMOS - Weinberger et al. 1999 WFPC-2 - Krist et al. 2000 16 18 F160W F110W F814W F606W 50CCD (uncalibrated) 20 22 0.6 0.8 1 2 Radius (Arc Seconds) 3 4 HUBB LE S P A CE TE LE S COP E HR 4796A RING MAJOR AXIS FLUX F160W - 15 MAR 1998 (0.375" WIDTH STRIP) SW P S F NE Glenn Schneider NICMOS Project Steward Observatory Modeling the HR 4796A Disk Kenyon & Wood (2000, ApJ, 524, L119) Glenn Schneider Steward Observatory HUBBLE SPACE TELESCOPE Planetesimal Accretion Calculations Monte Carlo runs constrain geometry & dust Produce observed dust distibution in 10 Myr Minitial: 10-20x minimum-mass solar nebula Assume: isotropic scattering and, = 0.3 (Augereau et al, 1999) Adust to obtain ~ 1.5x10-3 Coagulation code: "particle in a box method" Kenyon & Luu (1999, ApJ, 526, 465) e0 = 10 -3 NICMOS 1.1m image z=0.5AU, R=5AU, NIR=0.25 e0 = 10 -3 m0 = 10 MMSN a CONCLUSIONS: • Planet formation @ 70 AU in 10 Myr possible with initial disk mass =10—20MMMSN. • Dust production associated with planet formation is then confined to a ring with a = 7—15 AU. • Optical depth in ring satisfies constraints on scattered light at 1—2 m and on thermal emission at 10—100m if the -q dust size distribution is N ~ ri with q • 3 for r i Š 1 m. z=5AU, R=10AU, NIR=0.2 z=1AU, R=20AU, NIR=0.1 • Models with disk masses smaller than 10MMSN fail to produce planets and an observable dusty ring in 10 Myr. HD 98800 HUBB LE S P A CE TE LE S COP E A Remarkable Quadruple with a PDS Glenn Schneider Steward Observatory • Found by IRAS to contain one of the brightest debris systems in the sky. • Quadruple with two "similar" PMS K dwarfs. • Each K star has a low mass spectroscopic companion with periods of: (Aa+Ab) = 262 days, (Ba+Bb) = 315 days (Torres et al., 1995) and separations of ~ 1AU. • Distance = 46.7±6pc, and current AB separation = 0.8", so is easily resolved at all HST 's. • Member of the TW Hydrae Association (Kastner et al. 1997; Webb et al. 1999). • Soderbloom et al. (1998) estimates age ~ 10 Myr (as for TWA), and AB masses M ~ 1 solar. • Gehrz et al. (1999) showed PDS is centered on B form 4.7 and 9.8 m observations. • 20% of luminosity of B is emitted in a 164±5K SED from mid-IR to submm. • High-precision NIR photometry straddling peak of stellar SEDs by Low et al. (1999) find Teff(A) = 3831±55K, Teff(B) = 3459±37K, no NIR excess. They suggest scattered:total light from B < 6% -> PDS < 0.3. Suggest a PDS with an "equivalent" radius = 2AU, an actual rinner ~ 4.5AU, subtending no more than 20% of the sky seen from the stars, possibly similar to the debris system around our Sun as it may have appeared a few million years after formation. • Koerner et al (1999) confirm circumbinary disk about B, and is the only source of the large IR excess upon which a silicate feature is imposed. From mid-IR imaging they suggest a disk: rinner = 5.0±2AU, r = 13±8AU, effective grain size = 2 (+4, -1.5)m, = 0±2.5, and total cross-section of grains = 16±3AU 2, with a total disk mass of 0.001—0.1 lunar masses. file:/starsrus.as.arizona.edu/DATA1/IAU_1/HD198800_INTRO.CANV G. Schneider, 7/31/2000 HUBBLE SPACE T ELESCOPE HD 98800 A/B 2 March, 1999 NICMOS Coronagraphic Imaging Glenn Schneider Steward Observatory LEFT: Direct (not PSF subtracted) NICMOS F110W coronagraphic images of the HD 98800AB system (A/B separation = 0.814"). Left panels stretched 0-25000 ADU/sec/pixel to show first Airy rings around PSF cores. Right panels to stretched 0-500 ADU/sec/pixel to show diffraction spikes to r ~ 2.5". the location of the 0.3" radius coronagraphic hole is indicated by the red circle. Top panels: Both equal-brightness components of the system unocculted with the northern (upper right) component 0.814" from the center of the coronagraph. Middle panels: Northern component in the coronagraph. Bottom panels: Southern component in the coronagraph. RIGHT: Replicate template PSF-subtraction of above coronagraphic images of HD 98800, alternately using A as a template for B, and B as a template for A. HD 98800 SEDs of A, B, and PDS Glenn Schneider NICMOS Project Steward Observatory (Low, Hines & Schneider, 1999) HUBB LE S P A CE TE LE S COP E 0.4 0.5 0.6 0.7 0.8 0.9 1 Wavelength ( m) 2 (a) A T(A) = 3831 (55) K T(B) = 3459 (37) K T(PDS) = 164 (5) K B PDS Flux Density (Jy) 1 10 1 0.1 0.1 0.01 1 file:/starsrus.as.arizona.edu/DATA1/IAU_1/HD98800_SED1.CANV 10 100 1000 G. Schneider, 8/01/2000 HD 98800 HUBB LE S P A CE TE LE S COP E A Remarkable Quadruple with a PDS Glenn Schneider Steward Observatory Koerner et al, 2000, ApJ, 533, L37 "Keck/MIRLIN imaging of the thermal infrared emission from the HD 98800 quadruple system oriented with up axis aligned due north. The spectroscopic binaries HD 98800A and HD 98800B are clearly resolved from each other and are identified, respectively, with northern and southern point sources separated by 0.8" (38 AU). Emission from HD 98800A steadily decreases with wavelength as -2 and is no longer detected in the 20 m images. In contrast, radiation from the optical secondary, HD 98800B, increases dramatically out to 24.5 m." HD 98800 SEDs of A, B, and PDS HUBB LE S P A CE TE LE S COP E (Koerner, et al, 2000) Glenn Schneider NICMOS Project Steward Observatory What Next? 2 March, 1999 Glenn Schneider Steward Observatory HUBBLE SPACE T ELESCOPE Can we build a morphological "evolutionary" sequence? Dependencies on: • AGE DETERMINATIONS • Stellar spectral types (masses) • Composition/density of parent molecular cloud • Interactions with stellar/sub-stellar companions Many more observations are, obviously, needed. file:/starsrus.as.arizona.edu/HILO_01/WHAT_NEXT.CANV G. Schneider, 01/31/2001