Chemical Evolution During Star Formation Half a Decade of ALMA: Cosmic Dawns Transformed, Sep. 20-23, 2016 Chemical Evolution During Star Formation Jeong-Eun Lee Kyung Hee University

Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee Outline Low mass star formation process Chemical evolution during star formation ALMA observations of protostars Episodic accretion and chemical vestige Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Low mass star formation Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Chemical characteristics Prestellar stage: Freeze-out of carbon-bearing molecules (e.g. CO & CS) on to grains surfaces due to the cold (<10 K) and dense (> 105 cm-3) condition Abundant nitrogen-bearing molecules (e.g. N2H+ and NH3) because of the long formation timescale of N2 and depletion of their destroyers (e.g. CO) from gas High D/H ratios in molecular species (high abundances of DCO+, N2D+, etc.) since the lower ground energy levels of deuterated molecules are favored by the cold condition Complex molecules forming on grain surfaces Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Chemical characteristics Prostellar stage: Evaporation of molecules close to protostars, depending on the binding energies of molecular species (e.g. Teva(CO)=25 K, Teva(H2O)=100 K) Depletion of ionic species such as N2H+ and HCO+ because of their reactions with evaporated CO and H2O, respectively Hot corinos with complex organic molecules (e.g. CH3OH, CHOOCH3) formed by the hot core chemistry at the region hot enough to evaporate water ice (e.g. IRAS 16293-2422) Carbon-chain molecules (e.g. c-C3H2) formed by Warm Carbon Chain Chemistry (WCCC), which is induced by the evaporation of CH4 from grain surfaces (e.g. L1527) Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Chemical characteristics Protoplanetary disk stage: Three layers of chemistry Hot atomic layer (PDR) Warm molecular layer (Hot Core chemistry) Cold icy layer (cold prestellar core chemistry) From Henning & Semenov 2013 One of major questions in astrochemistry is whether the disk material are basically inherited from the ISM, or they are significantly altered within the disk. To answer this question, we need to observe disks of embedded protostars. !!! ALMA !!! Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Chemical evolution during star formation Lee et al. (2004) combined dynamics, dust continuum radiative transfer, gas energetics, chemistry, and line radiative transfer self-consistently in 1-D. Dynamics from prestellar to protostellar: Bonner-Ebert spheres + Shu’s inside-out collapse model Dust continuum: DUSTY with an assumed luminosity evolution considering accretion, disk, and protostar Gas energetics: photoelectric heating, cosmic-ray heating, grain-gas collision, cooling by various emission lines Chemistry: gas chemistry, gas-grain interactions, no surface chemistry except for H2 formation Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Chemo-Dynamical Model Evolution Model of Luminosity n(r,t), v(r,t) B.-E. spheres + Shu’s collapse model TD(r,t) Continuum Radiative Transfer Tk(r,t) Gas Energetics Simulated line profile (r,t) Line Radiative Tansfer X(r’,t)  X(r,t) Chemical evolution along infalling gas Lee et al. (2004) Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Chemo-Dynamical Model Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Chemo-Dynamical Model SiO2 mantle Av,e=0.5 mag Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

2-D Chemodynamical models Visser et al. (2011) combined a 2-D semi-analytic dynamical model with chemistry to follow parcels’ trajectories in the 2-D space until the parcels accrete to disk to map the distributions of species in the disk. H2O with different evolution histories NH3 with different evolution histories Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

2-D chemodynamical models Hincelin et al. (2016) combined a 2-D radiative MHD simulation with chemistry to study the chemical evolution in envelope, pseudo-disk, disk, and outflow up to the formation of FHSC. Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

A protostellar system revealed by ALMA L1527 IRS Sakai et al. 2014 Rotating infalling envelope: CCH, c-C3H2, CS, and H2CO Centrifugal barrier: SO Disk: CH3OH Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee 13

Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee New Data Part of a Cycle 1 program, “Star Formation via Infall: A Definitive Test by ALMA (PI: Neal Evans)” Observed in 14 June, 2014 Beam size: 0".54 x 0".36 (PA= -3.1 deg) Velocity resolution: ~0.05 km/s Sensitivity: 1.1 mJy/beam (cont), ~30 mJy/beam (lines) Continuum, HCO+ J=4-3, HCN J=4-3, CS J=7-6, H13CN J=4-3 Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Rotating infalling envelope, outflow, disk |v|<2 km/s High velocity shocked gas Colors: HCO+ Contours: HCN IRAC 3.6 ㎛ |v|>7 km/s shock chemistry model: n =105 cm-3 Tgas=1000 K during shock (100 yrs) Tgas=30 K before (105 yrs) and after (107 yrs) shock Lee et al. in prep. Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee Modeling of L1527 Density Temperature Disk: Tobin et al. (2013) Envelope: Kristensen et al. (2012) RADMC-3D using dust properties from Tobin et al. (2013) Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

CASA simulation of C18O J=2-1 for L1527 ΔDEC (arcsec) South North X(C18O) colors: observation contours: model Rdisk=100 AU Mstar=0.4 M Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee Luminosity problem Shu’s continuous accretion model, Lacc ~ GMṀ/R R ~ 3 R M ~ 0.08 M (Protostar/Brown dwarf boundary) Ṁ ~ 2×10-6 M yr-1 (Shu 1977) Lacc ~ GMṀ/R ~ 1.6 L Spitzer Space Telescope discovered 59% of the embedded protostars have luminosity lower than 1.6 L (c2d survey; Evans et al. 2009). 1.6 L Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Episodic Accretion Model Mass accretion occurs in episodic bursts. Material piles up on a disk until gravitational instabilities drive mass inward in short lived bursts (Vorobyov & Basu 2005). Most of the mass accretes in a small fraction of the lifetime. Protostars stay at low luminosities except accretion bursts. Dunham & Vorobyov (2012) Luminosity is not a proxy for protostellar mass. Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Chemical fingerprint of Episodic Accretion Episodic accretion process heats up the surrounding material during a burst accretion, but it cools down spontaneously right after the bust accretion stops. Chemistry changes responding to the variation of physical conditions with a much longer timescale, keeping the memory of the hot moment even long after the burst accretion ends. Therefore, chemical distribution can be used as a fingerprint of episodic accretion. Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Chemical fingerprint of Episodic Accretion A toy model by Lee et al. (2007): Use Chemo-dynamical model (Lee et al. 2004)‏ Chemical distribution at the timescale when fits the SED of IRAM04191 assumptions: constant accretion from envelope to disk episodic accretion from disk to star (accretion event every 104 yrs for 103 yrs)‏ Model prameters: Mcore = 1 M⊙ Rcore = 6200 AU normal accretion rate = 4.8 x 10-6 M⊙/yr accretion rate (accretion phase) = 10 x normal rate accretion rate (quiet phase) = 0.01 x normal rate Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Chemical fingerprint of episodic accretion 3000 yrs after a burst accretion (quiescent phase) Jorgensen et al. (2015) SMA C18O J=2-1 observations of 16 embedded protostars indicate that the radii of CO emission regions are bigger than what expected from their current luminosities. Evidence for burst accretions!!! ~1” resolution, d=140 pc C18O J=2-1 Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

ALMA for Episodic accretion X(CH3OH) X(HCO+) X(H2O) IRAS 15398 CH3OH at <1” (red) H13CO+ at 1–2” (blue) Surface chemistry included Only gas chemistry considered Episodic accretion Continuous accretion Jorgensen et al. (2013), ALMA Cycle 0 program Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

ALMA for Episodic accretion 5 AU Effective grain coagulation Low opacity V883 Ori 42 AU Cieza et al. (2016) ALMA Cycle 2 & 3 programs with 0.03” resolution at 218 GHz & 232.6 GHz Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

ALMA for Episodic accretion A disk model: Aikawa et al. (2015) Ṁ =10-4 M yr-1 H2O snow line=125 AU (following Min et al. 2011) Keplerian rotation around 0.5 M D=500 pc ALMA Cycle 4 programs for FUors disks to study fresh sublimates, which is a unique and direct probe for the ice composition in the pre-eruption 2016.01302.S – FUors in different evolutionary stages and environment 2016.01304.T – when a new FUor detected by various transient surveys Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Environmental and dynamical effects X(HCN) Short prestellar phase X(CH4) X(CH3OH) warmer prestellar phase Standard model with prestellar timescale of 106 yrs model with prestellar timescale of 105 yrs model with prestellar core temperature of 18 K Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee Summary Star formation is associated with energetic activities such as infall, accretion, jets, and outflows. These dynamical processes produce energy to affect the physical and chemical conditions of associated material. In particular, the accretion mechanism has a prime impact on the temperature structures of the inner envelope and disk, which set the initial conditions of planet formation, resulting in inevitable alterations of their chemical distribution. The high sensitivity and high resolution of ALMA are critical to study the chemical evolution of disks and inner envelopes around protostars. Half a Decade of ALMA, Sep. 20, 2016, J.-E. Lee

2014-2 SSTF Grant Proposal, J.-E. Lee Thank you 2014-2 SSTF Grant Proposal, J.-E. Lee

Tracing the Chemical Vestige with ALMA CASA simulation of the ALMA observation with: Compact configuration with 50 antenna 1 hour integration Synthesized beam of 1.9”x 1.7”

Tracing the Chemical Vestige with ALMA Episodic Accretion Continuous Accretion Simulation of observations in C18O J=2-1 → rms nosie ~0.003 Jy/beam cf. SMA-extended configuration: 4hr-integration with 0.1 km/s → rms nosie ~0.2 Jy/beam

2014-2 SSTF Grant Proposal, J.-E. Lee surface chemistry explicitly using rate equations Willacy et al. (2006), Garrod and Herbst (2006), Dodson-Robinson et al. (2009) 2014-2 SSTF Grant Proposal, J.-E. Lee

For exothermic reaction without an activation energy : P =1 With an activation energy (Ea) b = 1 Å , μr = reduced mass 2014-2 SSTF Grant Proposal, J.-E. Lee