Transcript No Slide Title

Disk Evolution Timescales
2 March, 1999
Glenn Schneider
Steward Observatory
HUBBLE SPACE TELESCOPE
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: ~ 10 4
Sun
109
yrs
Current
age of
the Sun:
5x109 yrs .
Clearing of
inner solar
system,
formation of a
Kuiper
cometary
belt?
HUBBLE SPACE TELESCOPE
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
G
.
K
S
O
I
L
D O
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 TELESCOPE
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 60m
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 TELESCOPE
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 TELESCOPE
file:/starsrus.as.arizona.edu/YSNE/YSNE_TODAY.CANV
G. Schneider, 03/36/2001
TW Hydrae
Glenn Schneider
Steward Observatory
HUBB LE S PA CE TELE SCOP 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 PA CE TELE SCOP E
Flared Disk
+
Hole
1.1m
1.6 m
-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
F1.6m(rau) = (78/rau)2.6 mJy arcsec -2
F1.1m(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 PA CE TELE SCOPE
HR 4796A RING MAJOR AXIS FLUX
Glenn Schneider
F160W - 15 MAR 1998 (0.375" WIDTH STRIP)
NICMOS Project
Steward Observatory
SW
P
S
F
NE
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 1.1m image
z=0.5AU, R=5AU,
NIR=0.25
e0 = 10-3
m0 = 10MMSN
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—100 m 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 PA CE TELE SCOPE
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 TELESCOPE
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 PA CE TELE SCOPE
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 PA CE TELE SCOPE
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 PA CE TELE SCOPE
(Koerner, et al, 2000)
Glenn Schneider
NICMOS Project
Steward Observatory
What Next?
2 March, 1999
Glenn Schneider
Steward Observatory
HUBBLE SPACE TELESCOPE
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