The chemical history of molecules in circumstellar disks - I. Ices

Context. Many chemical changes occur during the collapse of a molecular cloud to form a low-mass star and the surrounding disk. One-dimensional models have been used so far to analyse these chemical processes, but they cannot properly describe the incorporation of material into disks. Aims. The goal of this work is to understand how material changes chemically as it is transported from the cloud to the star and the disk. Of special interest is the chemical history of the material in the disk at the end of the collapse. Methods. A two-dimensional, semi-analytical model is presented that, for the first time, follows the chemical evolution from the pre-stellar core to the protostar and circumstellar disk. The model computes infall trajectories from any point in the cloud and tracks the radial and vertical motion of material in the viscously evolving disk. It includes a full time-dependent radiative transfer treatment of the dust temperature, which controls much of the chemistry. A small parameter grid is explored to understand the effects of the sound speed and the mass and rotation of the cloud. The freeze-out and evaporation of carbon monoxide (CO) and water (H 2 O), as well as the potential for forming complex organic molecules in ices, are considered as important first steps towards illustrating the full chemistry. Results. Both species freeze out towards the centre before the collapse begins. Pure CO ice evaporates during the infall phase and re-adsorbs in those parts of the disk that cool below the CO desorption temperature of ∼ 18 K. Water remains solid almost everywhere during the infall and disk formation phases and evaporates within ∼10 AU of the star. Mixed CO-H 2 O ices are important in keeping some solid CO above 18 K and in explaining the presence of CO in comets. Material that ends up in the planet- and comet-forming zones of the disk (∼5-30 AU from the star) is predicted to spend enough time in a warm zone (several 104 yr at a dust temperature of 20-40 K) during the collapse to form first-generation complex organic species on the grains. The dynamical timescales in the hot inner envelope (hot core or hot corino) are too short for abundant formation of second-generation molecules by high-temperature gas-phase chemistry.

[1]  U. Michigan,et al.  The chemical history of molecules in circumstellar disks - II. Gas-phase species , 2011, 1109.1741.

[2]  C. Brinch,et al.  Time-dependent CO depletion during the formation of protoplanetary disks , 2008, 0807.1057.

[3]  E. Rosolowsky,et al.  The Mass Distribution and Lifetime of Prestellar Cores in Perseus, Serpens, and Ophiuchus , 2008, 0805.1075.

[4]  R. Garrod,et al.  Complex Chemistry in Star-forming Regions: An Expanded Gas-Grain Warm-up Chemical Model , 2008, 0803.1214.

[5]  R. Garrod,et al.  Molecular Evolution and Star Formation: From Prestellar Cores to Protostellar Cores , 2007, 0710.0712.

[6]  T. Fuse,et al.  Organic Volatiles in Comet 73P-B/Schwassmann-Wachmann 3 Observed during Its Outburst: A Clue to the Formation Region of the Jupiter-Family Comets , 2007 .

[7]  Jonathan P. Williams,et al.  A Submillimeter View of Circumstellar Dust Disks in ρ Ophiuchi , 2007, 0708.4185.

[8]  E. Bergin,et al.  Cold Dark Clouds: The Initial Conditions for Star Formation , 2007, 0705.3765.

[9]  S. Schlemmer,et al.  Photodesorption of CO Ice , 2007, 0705.0260.

[10]  Y. Aikawa.  Cold CO Gas in Protoplanetary Disks , 2007, astro-ph/0701366.

[11]  Qizhou Zhang,et al.  PROSAC: A Submillimeter Array Survey of Low-Mass Protostars. I. Overview of Program: Envelopes, Disks, Outflows, and Hot Cores , 2007, astro-ph/0701115.

[12]  Jonathan P. Williams,et al.  Hot corinos in NGC 1333-IRAS4B and IRAS2A , 2006, astro-ph/0611480.

[13]  Jonathan P. Williams,et al.  High-Resolution Submillimeter Constraints on Circumstellar Disk Structure , 2006, astro-ph/0610813.

[14]  R. Garrod,et al.  Formation of methyl formate and other organic species in the warm-up phase of hot molecular cores , 2006, astro-ph/0607560.

[15]  T. Henning,et al.  Gas-Phase CO in Protoplanetary Disks: A Challenge for Turbulent Mixing , 2006, astro-ph/0607010.

[16]  L. Hartmann,et al.  Why Do T Tauri Disks Accrete? , 2006, astro-ph/0605294.

[17]  A. Sargent,et al.  The Evolution of Outflow-Envelope Interactions in Low-Mass Protostars , 2006, astro-ph/0605139.

[18]  D. Sasselov,et al.  On the Location of the Snow Line in a Protoplanetary Disk , 2006, astro-ph/0602217.

[19]  D. Apai,et al.  Crystalline Silicates as a Probe of Disk Formation History , 2006, astro-ph/0602154.

[20]  S. Schlemmer,et al.  Desorption rates and sticking coefficients for CO and N2 interstellar ices , 2006, astro-ph/0601082.

[21]  T. Guillot,et al.  Evolution of protoplanetary disks: Constraints from DM Tauri and GM Aurigae , 2005, astro-ph/0506496.

[22]  N. Evans,et al.  EVOLUTIONARY SIGNATURES IN THE FORMATION OF LOW-MASS PROTOSTARS. II. TOWARD RECONCILING MODELS AND OBSERVATIONS , 2005, 0912.5229.

[23]  J. Silk,et al.  Towards simulating star formation in the interstellar medium , 2004, astro-ph/0411383.

[24]  A. Koratkar,et al.  Chandra X-Ray Observations of the Inner Optical Filaments in Centaurus A , 2004 .

[25]  Mark R. Anderson,et al.  A laboratory survey of the thermal desorption of astrophysically relevant molecules , 2004 .

[26]  E. Bergin,et al.  Evolution of Chemistry and Molecular Line Profiles during Protostellar Collapse , 2004, astro-ph/0408091.

[27]  Institute for Astronomy,et al.  Complex Molecules in the Hot Core of the Low-Mass Protostar NGC 1333 IRAS 4A , 2004, astro-ph/0407154.

[28]  S. Viti,et al.  Evaporation of ices near massive stars: models based on laboratory temperature programmed desorption data , 2004, astro-ph/0406054.

[29]  E. Dishoeck,et al.  Physical-chemical modeling of the low-mass protostar IRAS 16293-2422 , 2004, astro-ph/0402610.

[30]  J. Greenberg,et al.  Cosmic ray induced explosive chemical desorption in dense clouds , 2004 .

[31]  C. Dominik,et al.  Flaring vs. self-shadowed disks: The SEDs of Herbig Ae/Be stars , 2004, astro-ph/0401495.

[32]  M. Wolff,et al.  Two-dimensional Radiative Transfer in Protostellar Envelopes. I. Effects of Geometry on Class I Sources , 2003, astro-ph/0303479.

[33]  S. Charnley,et al.  Chemical Evolution in Protostellar Envelopes: Cocoon Chemistry , 2003 .

[34]  G. V. Zadelhoff,et al.  Axi-symmetric models of ultraviolet radiative transfer with applications to circumstellar disk chemistry , 2002, astro-ph/0211014.

[35]  E. F. Dishoeck,et al.  Does IRAS 16293–2422 have a hot core? Chemical inventory and abundance changes in its protostellar environment , 2002, astro-ph/0205457.

[36]  A. Kouchi,et al.  Efficient Formation of Formaldehyde and Methanol by the Addition of Hydrogen Atoms to CO in H2O-CO Ice at 10 K , 2002 .

[37]  P. Ehrenfreund,et al.  Gas-grain chemical models of star-forming molecular clouds as constrained by ISO and SWAS observations , 2001 .

[38]  David A. Williams,et al.  Thermal desorption of water ice in the interstellar medium , 2001, astro-ph/0107487.

[39]  P. Gerakines,et al.  Interstellar Extinction and Polarization in the Taurus Dark Clouds: The Optical Properties of Dust near the Diffuse/Dense Cloud Interface , 2001 .

[40]  L. Hartmann,et al.  Accretion Disks around Young Objects. III. Grain Growth , 2001, astro-ph/0101443.

[41]  W. Langer,et al.  The Importance of Photoprocessing in Protoplanetary Disks , 2000 .

[42]  P. Bodenheimer,et al.  The Formation of Protostellar Disks. III. The Influence of Gravitationally Induced Angular Momentum Transport on Disk Structure and Appearance , 1999 .

[43]  L. Hartmann,et al.  Accretion Disks around Young Objects. II. Tests of Well-mixed Models with ISM Dust , 1999, astro-ph/9907330.

[44]  David Koerner,et al.  HUBBLE SPACE TELESCOPE/NICMOS Imaging of Disks and Envelopes around Very Young Stars , 1999, astro-ph/9902101.

[45]  N. Calvet,et al.  Accretion Disks around Young Objects. I. The Detailed Vertical Structure , 1998, astro-ph/9806060.

[46]  Hirohiko Masunaga,et al.  A Radiation Hydrodynamic Model for Protostellar Collapse. I. The First Collapse , 1998 .

[47]  F. Adams,et al.  Evolution of the Bolometric Temperature and Luminosity of Young Stellar Objects , 1998 .

[48]  E. Bergin,et al.  Chemical Evolution in Preprotostellar and Protostellar Cores , 1997 .

[49]  S. Miyama,et al.  Evolution of Molecular Abundance in Protoplanetary Disks , 1997, astro-ph/9706204.

[50]  D. Simonelli,et al.  Radiative heating of interstellar grains falling toward the solar nebula: 1-D diffusion calculations. , 1997, Icarus.

[51]  A. Tielens,et al.  Far-Infrared Line Emission from Collapsing Protostellar Envelopes , 1996 .

[52]  L. Hartmann,et al.  Pre-Main-Sequence Evolution in the Taurus-Auriga Molecular Cloud , 1995 .

[53]  A. Boss,et al.  Spectral energy of first protostellar cores: Detecting 'class -I' protostars with ISO and SIRTF , 1995 .

[54]  A. Tielens,et al.  Grain destruction in shocks in the interstellar medium , 1994 .

[55]  Alexander G. G. M. Tielens,et al.  The physics of grain-grain collisions and gas-grain sputtering in interstellar shocks , 1994 .

[56]  David A. Neufeld,et al.  Dense molecular shocks and accretion onto protostellar disks , 1994 .

[57]  Italo Mazzitelli,et al.  New pre-main-sequence tracks for M less than or equal to 2.5 solar mass as tests of opacities and convecti on model , 1994 .

[58]  F. Shu,et al.  Collapse of magnetized molecular cloud cores. I: Semianalytical solution , 1993 .

[59]  Alyssa A. Goodman,et al.  Dense cores in dark clouds. VIII - Velocity gradients , 1993 .

[60]  T. Owen,et al.  Noble gases in atmospheres , 1993, Nature.

[61]  A. Tielens,et al.  On the molecular complexity of the hot cores in Orion A - Grain surface chemistry as 'The last refuge of the scoundrel' , 1992 .

[62]  Tobias Owen,et al.  Possible cometary origin of heavy noble gases in the atmospheres of Venus, Earth and Mars , 1992, Nature.

[63]  F. Palla,et al.  The evolution of intermediate-mass protostars. I, Basic results , 1991 .

[64]  F. Adams,et al.  Star Formation in Molecular Clouds: Observation and Theory , 1987 .

[65]  F. Adams,et al.  Infrared Spectra of Rotating Protostars , 1986 .

[66]  P. Cassen,et al.  The collapse of the cores of slowly rotating isothermal clouds , 1984 .

[67]  P. Cassen,et al.  On the formation of protostellar disks , 1981 .

[68]  J. Bohdansky,et al.  An analytical formula and important parameters for low‐energy ion sputtering , 1980 .

[69]  F. Shu.  Self-similar collapse of isothermal spheres and star formation. , 1977 .

[70]  D. Lynden-Bell,et al.  The Evolution of viscous discs and the origin of the nebular variables. , 1974 .