Molecular Surveys of the Disks Encircling T Tauri/Herbig Ae Stars

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Molecular Surveys of the Disks Encircling T
Tauri/Herbig Ae Stars
Geoffrey A. Blake CalTech
Chemistry as a Diagnostic of Star Formation
Waterloo, Canada 23Aug2002
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People Really Doing the Work!
Caltech -Jacqueline Kessler, Chunhua Qi (now
at the SMA/CfA) -Adwin Boogert Leiden
w/Ewine van Dishoeck -Klaus Pontoppidan,
Gerd Jan van Zadelhoff, Wing-Fai Thi (now
at UCL) Arizona -Michiel Hogerheijde

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Study Isolated Disks (Weak/No Outflow)

Beckwith Sargent 1996
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Spectroscopy of Disk Atmospheres
G.J. van Zadelhoff 2002

IR disk surface within several tens of
AU (sub)mm disk surface at large radii,
disk interior
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MM-Wave CO Traces Dynamics, Others?
M. Simon et al. 2001, PdBI
Measure R_disk M_star Inclination w/resolved ima
ges.

Dutrey et al. 1997, IRAM 30m Kastner et al.
1997, TW Hya, JCMT
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OVROCSO/JCMT MM-Wave Disk Survey
The Sample (drawn from larger single dish survey)
MWC 480
Mannings, Koerner Sargent 1997
Koerner Sargent 1995
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See also poster 67 (SMA maps)
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OVROCSO/JCMT MM-Wave Disk Survey II
van Zadelhoff et al. 2001
Combine 3/1.3 mm array images w/higher J spectra
to constrain OUTER disk properties, chemical
networks.
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Disk Ionization Structure CO and Ions
Disk properties vary widely with radius, height
and depend on accretion rate, etc. (Aikawa et al.
2002, w/ DAlessio et al. disk models, poster
21).
Currently sensitive only to Rgt100 AU in gas
tracers, Rlt100 AU dust. CO clearly optically
thick, other species likely to be as
well. Model via 2D Monte Carlo using disk
structure and chemical models as input, vary
to fit observations (Kessler talk).
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UV Fields HCN and CN
CN/HCN traces enhanced UV fields
(Fuente et al. 1993, Chiang et al. 2001)
LkCa 15
Molecular distribution ring-like? Photochemistr
y or desorption?
Qi et al., in prep
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Sulfur Species
NT(CS) 1013-1014 cm-2 Upper limits only for
H2S,SO,SO2 CS dominant
Reminiscent of early time chemistry.
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Grain chemistry CH3OH, SiO, H2CO
CH3OH, H2CO - grain surface production SiO -
grain sputtering gas phase rxn
Si O2 ? SiO O
h?
h?
Si
H2CO
H2CO
CH3OH
CH3OH
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Are Even Larger Molecules Present?

• Observations can test gas/grain models, HIFI and
  arrays can uniquely access small, dense cores
  disks.
• Laboratory spectra urgently needed, work underway
  (posters 11,84).

Grain Chemistry Model (Charnley 2001)

Glycine
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Are these large disks unusual?
CO, HCO (and NNH) chemistry well predicted by
disk models. Other species, esp. CS, CN, HCN,
much more intense, with unusual emission patterns
in some cases (LkCa 15).
MM-continuum surveys do not reveal such large,
massive disks in similarly aged clusters (IC348)
and clouds (NGC 2024, MBM12).
Environment? Need better (sub)mm-wave imaging
capabilities.
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Future of the U.S. University Arrays CARMA
CARMA BIMA (9 6.1m) OVRO (6 10.4m) SZ Array
(8 3.5m) telescopes.
SUP submitted 2003 SZA on site 2004 move
OVRO 2004 move BIMA 2005 full operations
Juniper Flat
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How can we probe the planet-forming region?
(pre-ALMA) The size scales are too small even for
the largest current near-IR arrays Spectroscopy
to the rescue!
Theory
Jupiter (5 AU) V_doppler 13 m/s V_orbit 20
km/s
Simulation G. Bryden
Observation?
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High Resolution IR Spectroscopy Disks
R10,000-100,000 (30-3 km/s) echelle
spectrographs (ISAAC,MICHELLE, NIRSPEC,
PHOENIX,TEXES) on 8-10m telescopes can now
probe typical T Tauri/Herbig Ae stars
Keck
CO M-band fundamental

NIRSPEC R25000
VLT
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Orientation is Pivotal in the IR!
Edge-on absorption.
L1489 Gas/Ice10/1, accretion. CRBR2422.8 Gas
/Ice1/1, velocity field? Elias
18 Gas/Icelt1/10 (Shuping et al.)
Poster 79
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H3 in absorption?
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Edge-on Disks Comets?
N7538 W33A Hale-Bopp Water 100
100 100 CO 10 1
23 CO2 16 3
6 CH4 1 0.7 0.6 H2CO
3 2 1 CH3OH
9 10 2 HCOOH 2 0.5
0.1 NH3 10 4
0.7 OCS 0.1 0.05 0.4
IR studies of edge on disks could map out both
gas phase grain mantle composition, compare
to that found in massive YSOs, comets.
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More typically, emission is seen in M-band
GSS30 Class I T Tauri star, accretion shock
emission?
(NIRSPEC, R25000)
Pontoppidan et al. 2002 (ISAAC, R5000, poster
66)
Broad H I from accretion/outflow, narrow CO from
disk. Gap tracer (Carr et al. 2001, DQ Tau)?
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How is the CO excited in these disks?
CO and 13CO rotation diagrams show two
components, but even the hot component is
lt500 K. Very small amounts of gas.
Collisional excitation unimportant at these
temperatures, Resonant scattering! Need
detailed radiative transfer models (similar
effects seen in massive YSOs, Mitchell et
al., van der Tak et al.).
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Where does the CO emission come from?
Flared disk models often possess 2-5 micron
deficiency in model SEDs, where a bump is
often observed for Herbig Ae stars.
Dullemond et al. 2002
Explanation Dust sublimation near the star
exposes the inner disk to direct stellar
radiation, heating the dust and puffing up
the disk.
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SED Fits versus IR Interferometry
Fits to AB Aur SED yield an inner radius of 0.5
AU (and 0.06 AU for T Tau).
(Monnier Millan-Gabet 2002, astro-ph/0207292)
Dullemond et al. 2002
This model can now be directly tested via YSO
size determinations with K-band
interferometry. Intense dust emission pumps
CO, rim shadowing can produce moderate T_rot.
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Future Near-IR (1-5 um) Spectroscopy
Brittain Rettig 2002, poster 10
Many other species and disk types
(transitional, debris, etc.) should be examined
in both absorption (edge on disks) and
emission
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H3, CH4, H2O, OCS...
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Mid-IR Spectroscopy Unique access to warm H2
Rotational H2 lines potentially provide
direct measure of gas mass w/o need for
abundance calibrations.
Thi et al. 2001
Additional studies/confirmation in optically
thick, transitional pivotal. Difficult, but
doable, from the ground.
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SIRTF

• - IRAC (mid-IR cameras, 3.6
• 4.5, 5.8, 8.0 mm)
• - MIPS (far-IR cameras, 24, 70
• 160 mm, R20 SED mode)
• - IRS (5-40 mm long slit,R150,
• 10-38 mm echelle, R600)
• 09 Jan 2003 launch

- GTO observations - Legacy program -
General observations
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SIRTF Spectroscopy of Dust and Ice
ISO SWS data on A stars, SIRTF can do sun-like
stars, high spectral resolution needed
for gas phase features. Evans et al.,
c2d 170 sources first look follow up of
mapping (poster 46). Meyer et
al. Photometry350 sources, IRS follow up
(Class III).
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Disk Spectroscopy - Conclusions
(Sub)mm-wave instruments can only study the
outer reaches of large disks at
present. Expanded arrays (CARMA, eSMA, ALMA)
will provide access to much smaller scales. HIFI
will enable first assault on water in the cold
regions of disks, and may provide a new window
on molecular complexity. High resolution IR
spectroscopy just starting, is immensely
powerful, and will provide unique access to
the 1-10 AU region until the advent of ALMA,
large IR interferometers. SIRTF will provide
many new targets!
SFCHEM 2002 23Aug02