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