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Submm Survey of Low-mass Submm Survey of Low-mass Protostars:Protostars:Tracing the physical and chemical structure Tracing the physical and chemical structure and evolutionand evolution
Jes Jørgensen (Leiden), Sebastien Maret (CESR,Grenoble)E. van Dishoeck, E. Caux, C. Ceccarelli, F. Schöier, M.Hogerheijde, A. Tielens
DUSTY 2004 meeting, Paris, Oct. 28 2004
Other surveys being carried out in Texas, Manchester, ….
Relation between physical and chemical properties?
Diagnostics of different protostellar components?
Can chemistry be used to trace the protostellar evolution?
This studyThis studyEstablish the physical and chemical structure of a sample of ~ 20 low-mass protostars (class 0/I); using single-dish obs. (JCMT, IRAM, Onsala), mm interferometry and detailed radiative transfer modeling.
ApproachApproach
Dust continuum emission
Physical structure
Molecular excitationChemical structure
Interferometry:small scale structure
Detailed chemical model
SCUBA obs. + Rad. transfer model.SCUBA obs. + Rad. transfer model.
Single-dish obs. + Monte Carlo model.Single-dish obs. + Monte Carlo model.
• CO• CS, SO
• HCO+, N2H+
• HCN, HNC, CN• DCN, DCO+
• H2CO, CH3OH
• SO2, SiO, H2S, CH3CN
(~ 16 species, 40 lines)
Physical structure from dust emission
Joergensen et al. 2002
Ice evaporation
Freeze-out
Outer envelope: CO freeze-out Outer envelope: CO freeze-out
Example: modeling of CO lines toward L723
- Adopt n(r) and T(r) from continuum: constrain abundances
- Overall philosophy: use simplest possible abundance models (constant, jump, drop) and add complexities only if needed (‘retrieval’ method)
- ‘Forward’ modeling also being pursued; consistent picture
CO freezes out at low temp. ( 35 K)
Objects with high envelope masses (younger?) show significantly higher degree of CO depletion
CO depletion: constant CO depletion: constant abundanceabundance
“Canonical” CO abundance (Lacy et al. 1994)
“Drop” abundance model
nde
Tev
Constant
Drop
Constant abundance model
“Drop” abundance model
L723:
- Drop abundance much better fit to J=1-0 to 3-2
Pre-stellar core:
•Low temperature
•Depletion toward center
•...but not edge
Protostellar core:
•Central heating ~ temperature gradient
•Thermal desorption toward center
•...outside (low T): depletion/no depletion regions as in pre-stellar stages
Abundance
- Is this an evolutionary sequence?- Can chemistry constrain timescales? ~105 yr?
HCOHCO++ and N and N22HH++ abundances abundances
Jørgensen et al. 2004
Correlation HCO+ with CO
Anticorrelation N2H+ with CO
- Empirical chemical network- Freeze-out of CO leads to very high deuteration ratios
Jørgensen 2004
L483:L483:
450 m cont.
N2H+
C18O
Chemical structure confirmed by interferometry
Inner envelope: Ice evaporation Inner envelope: Ice evaporation
JCMTTex~80 K
Inner envelope chemistry
Hot CH3OH gas
Evaporated ices and complex organics around solar-mass star
Ceccarelli et al. 2000, Schöier et al. 2002, Maret et al. 2004
IRAS 16293-2422
- CH3OH data can only be fitted if abundance jumps by factor of 20-100 in inner region at T=90 K radius
Evaporation of ices other than CO
Freeze-out
Jump
XJ
Example: CH3OH jump abundance structure
Chemical richness low-mass YSOsChemical richness low-mass YSOs
- Line density similar to that in high-mass YSOs- Which molecules are first generation evaporated ices, and which are second generation produced in gas-phase?- How are molecules liberated? Passive heating or shocks?
IRAS 16293JCMT survey
Cazaux et al.2003Caux et al.,In prep
Starting to image the hot coresStarting to image the hot cores
Kuan et al. 2004, SMASchöier et al. 2004, OVRO
Bottinelli et al. 2004, PdB
Chemical differentiation found on small scales
CH3CN
HCOOCH3
ConclusionsConclusions
A A quantitativequantitative framework for the interpretation of framework for the interpretation of the physical and chemical structure of protostars the physical and chemical structure of protostars has been established on scales of 300-10000 AU has been established on scales of 300-10000 AU
Outer envelope: chemistry controlled by CO freeze-out - Depletion related to thermal/dynamical evolution=> t?
- Effect on other key species, e.g., HCO+ and N2H+
Inner envelope: chemistry controlled by evaporation ices
- Ices released by passive heating and/or shocks
- Small-scale structure (<1000 AU) important (disks, holes,..)
Future: Herschel and ALMAFuture: Herschel and ALMA
Water observations Main ice freezing-out and evaporating Herschel HIFI, PACS => key program
Submilimeter interferometry Direct imaging radial structure chemistry and physics SMA, PdB, CARMA, ALMA: need multi-line
Deep mid-infrared studies Warm dust inner envelope, outflow cavities Spitzer, ground-based 8-m class
Detailed modeling Chemical structure (forward modeling) Coupling with dynamics (Lee et al. 2004)
HH22O and HDO O and HDO
H2O 557 GHz SWASHDO 464 GHz JCMT
-H2O abundance jumps by factor of ~10?-HDO abundance jumps by factor of >100?
Stark et al. 2004Parise et a. 2004
IRAS 16293
ISO water observationsISO water observations
Nisini et al. 1999Ceccarelli et al. 1998
-Herschel will improve on ISO by orders of magnitude in spatial and spectral resolution and sensitivity