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School of Physics and AstronomyFACULTY OF MATHEMATICS & PHYSICAL SCIENCES
Chemical Diagnostics of Star Forming RegionsPaola Caselli
Wilking, Gagne & Allen 2008, Handbook of Star Forming Regions, Vol. II
N2H+(1-0)
Di Francesco et al. 2004
N2H+(3-2) Bourke et al. in prep
Collaborators
• Low-mass: Belloche (Bonn), Bourke (CfA), Ceccarelli(Grenoble), Crapsi (Leiden), Di Francesco (Victoria), Emprechtinger(Caltech), Foster (BU), Friesen (NRAO), Goodman (Harvard),Jørgensen (Bonn), Keto (CfA), Mitchell (Leeds), Myers (CfA), Pineda(Harvard), Rushton (Leeds), Schnee (Victoria), Tafalla (Madrid),Vastel (Toulouse), van der Tak (Groningen), Walmsley (Arcetri)
• Intermediate-mass: Alonso-Albi (Madrid), Ceccarelli(Grenoble), Fuente (Madrid), McCoey (Victoria), Johnstone (Victoria),Plume (Calgary)
• Massive: Bourke (CfA), Butler (Florida), Fontani (IRAM),Hernandez (Florida), Jimenez-Serra (Leeds), Pillai (Caltech), Tan(Florida), Zhang (CfA)
Outline
• Chemical/physical structure of pre-stellar cores (PSCs)• Environmental effects• PSCs in isolated and clustered star forming regions• Summary/open questions• Future directions (PSCs as astrophysical laboratories)
Complex chemical structure in thesimplest physical units
N2
N2H+
Suzuki et al. 1992
• N2 takes longer than CO to form(Herbst & Klemperer 1973)
•CO freeze-out & D-fractionation (Lepp & Dalgarno 1984)
H3+ + HD ⇒ H2D+ + H2 + 230 K
H2D+ / H3+ increases if the abundance of gas phase neutral
species (in particular CO) decreases (Dalgarno & Lepp 1984; Roberts & Millar 2000).
Deuterium Fractionation at T < 20 K
N2 → N2D+ + H2H2D+ + CO → DCO+ + H2
Watson 1974Millar et al. 1989
Evidences of freeze-out: deuterium fractionation ortho-H2D+ in pre-stellar cores
o-H2D+
CSO
N2D+(2-1)IRAM
N2H+(1-0)IRAM
Vastel et al. 2006
Caselli et al. 2003, 2008; van der Tak et al. 2005
The o-H2D+ line is strong and its emission is extended 5000 AU Only models includingall multiply deuterated
forms of H3+ can
reproduce these data(Roberts et al. 2003;Walmsley et al. 2004;Aikawa et al. 2005)
Evidences of freeze-out: deuterium fractionation
Crapsi, Caselli, Walmsley & Tafalla 2007
• On size scale of ~800 AU:no NH3 (and N2) freeze-out (see alsoHily-Blant et al. 2010 arXiv:1001.3930)
• The gas temperature drops to ~6 Kin the central 1000 AU
• The deuterium fractionation is ~0.4in the central 3000 AU
• Loss of specific angularmomentum towards the small scales
N(NH3) @ VLA
N(NH2D) @ PdBI
L1544 interferometric observations
700 AU
1400 AU
Evidences of freeze-out: deuterium fractionation Radiative transfer Analysis
Keto & Caselli 2008, 2010
• Static and contractingBonnor-Ebert sphere
• Simple CO chemistry (freeze-out + photodissociation)
• Radiative energy balance(+photoelectric heating)
• Radiative transfer
ζ ~ 1x10-17 s-1, fluffy grains,nc~2×107 cm-3 within 500 AU
N2H+(1-0)
Environmental effects
Foster et al.2009
NH3 and CCS inPerseus cores:
CCS almost absentin clustered proto-
and pre-stellarcores
Chemical evolutiondepends on the
environment.
Pineda et al., in prep.
Protostellarfeedback affectsthe physicalconditions of thesurrounding cloud(especially incluster formingregions).
Quiscence is soonlost…
Velocity Dispersion
Velocity DispersionProtostellar feedback
Evidences of freeze-out: deuterium fractionation Environmental effects
C17O(1-0) emission(Caselli et al. 1999)
CO hole
dust peak
Dust emission in L1544 (Ward-Thompson et al. 1999)
0.01 pc
0.03 pc
Image: dust emission in ρ Oph A(Di Francesco et al. 2004)Contours: CO depletion factor(Rushton et al., in prep.)See also Friesen et al. 2009 !
Evidences of freeze-out: deuterium fractionation N6: starless core in ρ Oph A, the nearest cluster-forming region
SMA + JCMT
BOURKE et al., in prep.
0.050.2M (M)Within N2H+(3-2)
0.230.25ΔvNT/ΔvN2H+(3-2)
0.180.25Δv (km/s)N2H+(3-2)
714Tc (K)
0.200.06N(N2D+)/N(N2H+)
~80003000x1500Size (AU)N2H+(3-2)
L1544N6
Evidences of freeze-out: deuterium fractionation D-fractionation in Infrared Dark CloudsCaselli et al., in prep.
Jimenez-Serra, Caselli, Tan +, in prep.
N2D+/N2H+
~ 0.03
3’
Water traces ‘hot spots’ where shocks dump energy into cloud
L1157-mm outflowD = 440 pc, Lbol = 8.3 Lo
B2
B1
R
H2OCH3OH SiO
Only H2O is detected on-source!
Summary • Astrochemical/radiative transfer modeling +observations are needed to identify the righttracer to study the initial conditions of starformation.
• Environment, protostellar feedback, gas-dustinteractions affect chemical/physical evolutiondifficult to gauge ages and initial conditions.
• Still puzzling:• presence of (N-bearing) gas phasemolecules at nH > 106 cm-3 (N2 vs CO)• different behavior of NH2D and N2D+
• desorption processes
Dense and cold material in IRDCs isprobably concentrated in smallregions (<6″), filling ~3% of the volume.
Evidences of freeze-out: deuterium fractionation Future directions
Metalabundance
H2 ortho-to-para ratio
Oxygenabundance
Cosmic-rayionization rate
Grain sizedistribution
Ice mantle
Evidences of freeze-out: deuterium fractionation Future directions
van Loo, Hartquist, Falle Cazaux, Cuppen
Keto, Broderick, Spaans
Pineda + Boley, Spaans,Hartquist