J.C. Mottram1, E.F. van Dishoeck1,2, M.Schmalzl1, L.E. Kristensen3, R. Visser4, M.R. Hogerheijde1, S. Bruderer2

1Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, the Netherlands – 2Max-Planck-Institut fur Extraterresterische Physik, Giessenbachstrasse 1, 85748 Garching, Germany – 3Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA – 4Department of Astronomy, University of Michigan, MI, USA

References:[1] van Dishoeck et al., 2011, PASP, 123, 138[2] Kristensen et al., 2010, A&A, 521, L30[3] Kristensen et al., 2012, A&A, 542, A8 [4] Schmalzl et al., in prep.[5] Shen et al., 2004, A&A, 415, 203[6] Hollenbach et al., 2009, ApJ, 690, 1497

Water is uniquely sensitive to motion of any kind within the protostellar environment due to its large Einstein A coefficient. As part of the ‘Water in star-forming regions with Herschel’ (WISH,[1]) survey, infall signatures were detected in the HIFI water spectra observed towards 5 Class 0/I protostars observed [2,3].

The combination of observations of multiple water transitions and full 1-D non-LTE radiative transfer models of protostellar envelopes provides a self-consistent way to probe the physics and chemistry of infalling envelope material.

ScanforPNG mottram @ strw.leidenuniv.nl

We use SWaN (Simplified Water Network) to model the gas-phase water abundance profile of our sources based on their temperature and density profile (see [4], Poster 1B071 for details). A comparison with a drop abundance profile is shown in Fig. 1. The main free-parameter which affects the water line profiles is the cosmic-ray induced UV flux (Gcr). For

comparison the interstellar radiation flux is of order 108 photons cm-2 s-1 [6].

Assumptions of the physical structure in our RATRAN models:

• Density n = n0(r/r0)p and temperature from

1-D continuum fits to SCUBA dust intensity profile and the SED [3] • Infalling material in free-fall i.e. v = v0(r/r0)

-0.5

• Constant turbulence with radius, parameterised using the Doppler b-parameter • Ortho:para ratio of 3 for H2O, thermal for H2 limited to 10-3

• Absorption against outflow included during synthetic-image creation

Fig. 1: Comparison of model H2O line profiles using a drop (blue) or SWaN (red) abundance profile (top) with WISH observations (black).The drop profile fails to correctly reproduce the 211-202 and 202-111 lines.

Fig. 2:Comparison of model line profiles for IRAS4A with infall stopped at various radii (see top plot) with observations (black). Models where infall stops outside 1000 AU do not reproduce the 202-111

and 202-101

lines.

We constrain the infall velocity, turbulence and Gcr, then the

minimum radius of infall (rmdi, see Fig. 2). This allows us to calculate the gravitational mass (Mg) and mass infall rate at rmdi.

Mottram et al., 2013, A&A, submitted

Physics:

• Infall must take place on 3-10×103 AU scales in the protostars studied.

• The Mass infall rate in IRAS4A is so high that any central structure cannot be stable long term. This could lead to episodic accretion or rotational fragmentation.

Chemistry:

• Simple chemical networks such as SWaN [4] reproduce the observed water line profiles well, while drop abundance profiles do not.

• Most sources require a cosmic-ray induced UV field of (0.2-1)×104 photons cm-2 s-1, consistent with estimates [5].

Cartoon of infall in a protostellar envelope

Source v(103AU) b log10(Gcr) rmdi Mg Minf

(kms−1) (kms−1) (ph.cm−2s−1) (103AU) (M⊙) (10−5M⊙yr−1)

IRAS4A 1.10 0.4 4.00 1 0.68 15.4L1527 0.37 0.9 3.75 5 0.08 1.6BHR71 1.26 0.2 3.50 3 0.90 3.7IRAS15398 0.94 0.7 3.75 3 0.50 3.4L1157 1.44 0.4 3.25 3 1.17 5.3

▶Physical Model

▶Water Abundance

▶Take-Home Message

▶Results