R. T. Garrod

Cornell University, Ithaca, New York, United States

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Publications (39)180.57 Total impact

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    ABSTRACT: Both grain surface and gas phase chemistry have been invoked to explain the disparate relative abundances of methyl formate and its structural isomers acetic acid and glycolaldehyde in the Sgr B2(N) star-forming region. While a network of grain surface chemistry involving radical–radical reactions during the warm-up phase of a hot core is the most chemically viable option proposed to date, neither qualitative nor quantitative agreement between modeling and observation has yet been obtained. In this study, we seek to test additional grain surface and gas phase processes to further investigate methyl formate-related chemistry by implementing several modifications to the Ohio State University gas/grain chemical network. We added two new gas phase chemical pathways leading to methyl formate, one involving an exothermic, barrierless reaction of protonated methanol with neutral formic acid; and one involving the reaction of protonated formic acid with neutral methanol to form both the cis and trans forms of protonated methyl formate. In addition to these gas phase processes, we have also investigated whether the relative product branching ratios for methanol photodissociation on grains influence the relative abundances of methyl formate and its structural isomers. We find that while the new gas phase formation pathways do not alter the relative abundances of methyl formate and its structural isomers, changes in the photodissociation branching ratios and adjustment of the overall timescale for warm-up can be used to explain their relative ratios in Sgr B2(N).
    The Astrophysical Journal 09/2015; 728:71-9. · 6.73 Impact Factor
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    ABSTRACT: The Chamaeleon clouds are excellent targets for low-mass star formation studies. Cha I and II are actively forming stars while Cha III shows no sign of ongoing star formation. We aim to determine the driving factors that have led to the very different levels of star formation activity in Cha I and III and examine the dynamical state and possible evolution of the starless cores within them. Observations were performed in various molecular transitions with APEX and Mopra. Five cores are gravitationally bound in Cha I and one in Cha III. The infall signature is seen toward 8-17 cores in Cha I and 2-5 cores in Cha III, which leads to a range of 13-28% of the cores in Cha I and 10-25% of the cores in Cha III that are contracting and may become prestellar. Future dynamical interactions between the cores will not be dynamically significant in either Cha I or III, but the subregion Cha I North may experience collisions between cores within ~0.7 Myr. Turbulence dissipation in the cores of both clouds is seen in the high-density tracers N2H+ 1-0 and HC3N 10-9. Evidence of depletion in the Cha I core interiors is seen in the abundance distributions of C17O, C18O, and C34S. Both contraction and static chemical models indicate that the HC3N to N2H+ abundance ratio is a good evolutionary indicator in the prestellar phase for both gravitationally bound and unbound cores. In the framework of these models, we find that the cores in Cha III and the southern part of Cha I are in a similar evolutionary stage and are less chemically evolved than the central region of Cha I. The measured HC3N/N2H+ abundance ratio and the evidence for contraction motions seen towards the Cha III starless cores suggest that Cha III is younger than Cha I Centre and that some of its cores may form stars in the future. The cores in Cha I South may on the other hand be transient structures. (abridged)
    11/2014;
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    ABSTRACT: The largest noncyclic molecules detected in the interstellar medium (ISM) are organic with a straight-chain carbon backbone. We report an interstellar detection of a branched alkyl molecule, iso-propyl cyanide (i-C3H7CN), with an abundance 0.4 times that of its straight-chain structural isomer. This detection suggests that branched carbon-chain molecules may be generally abundant in the ISM. Our astrochemical model indicates that both isomers are produced within or upon dust grain ice mantles through the addition of molecular radicals, albeit via differing reaction pathways. The production of iso-propyl cyanide appears to require the addition of a functional group to a nonterminal carbon in the chain. Its detection therefore bodes well for the presence in the ISM of amino acids, for which such side-chain structure is a key characteristic.
    Science (New York, N.Y.). 09/2014; 345(6204):1584-7.
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    Robin T. Garrod
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    ABSTRACT: The first off-lattice Monte Carlo kinetics model of interstellar dust-grain surface chemistry is presented. The positions of all surface particles are determined explicitly, according to the local potential minima resulting from the pair-wise interactions of contiguous atoms and molecules, rather than by a pre-defined lattice structure. The model is capable of simulating chemical kinetics on any arbitrary dust-grain morphology, as determined by the user-defined positions of each individual dust-grain atom. A simple method is devised for the determination of the most likely diffusion pathways and their associated energy barriers for surface species. The model is applied to a small, idealized dust grain, adopting various gas densities and using a small chemical network. Hydrogen and oxygen atoms accrete onto the grain, to produce H2O, H2, O2 and H2O2. The off-lattice method allows the ice structure to evolve freely; ice mantle porosity is found to be dependent on the gas density, which controls the accretion rate. A gas density of 2 x 10^{4} cm^{-3}, appropriate to dark interstellar clouds, is found to produce a fairly smooth and non-porous ice mantle. At all densities, H2 molecules formed on the grains collect within the crevices that divide nodules of ice, and within micropores (whose extreme inward curvature produces strong local potential minima). The larger pores produced in the high-density models are not typically filled with H2. Direct deposition of water molecules onto the grain indicates that amorphous ices formed in this way may be significantly more porous than interstellar ices that are formed by surface chemistry.
    The Astrophysical Journal 10/2013; 778(2). · 6.73 Impact Factor
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    Robin T Garrod, Susanna L Widicus Weaver
    Chemical Reviews 09/2013; · 41.30 Impact Factor
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    ABSTRACT: Based on astrochemical theory, the complex molecular composition around high-mass YSOs should evolve from the outer envelope in toward the central hot region as a sequence of temperature dependent chemical pathways are activated in ices and in the gas-phase. The resulting complex molecules have been broadly classified into three generations dependent on the temperature (<25, >25, and >100 K) required for formation. We combine IRAM 30m and Submillimeter Array observations to explore the spatial distribution of organic molecules around the high-mass young stellar object NGC 7538 IRS9, whose weak complex molecule emission previously escaped detection, quantifying the emission and abundance profiles of key organic molecules as a function of distance from the central protostar. We find that emission from N-bearing organics and saturated O-bearing organics present large increases in emission around 8000 AU and R<3000 AU, while O-bearing molecules and hydrocarbons do not. The increase in flux from some complex molecules in the envelope, around 8000 AU or 25 K, is consistent with recent model predictions of an onset of complex ice chemistry at 20-30 K. The emission increase for some molecules at R<3000 AU suggests the presence of a weak hot core, where thermal ice evaporation and hot gas-phase chemistry drives the chemistry. Complex organics thus form at all radii and temperatures around this protostar, but the composition changes dramatically as the temperature increases, which is used to constrain the chemical generation(s) to which different classes of molecule belong.
    The Astrophysical Journal 05/2013; 771(2). · 6.73 Impact Factor
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    Robin T. Garrod
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    ABSTRACT: A new chemical model is presented that simulates fully-coupled gas-phase, grain-surface and bulk-ice chemistry in hot cores. Glycine (NH2CH2COOH), the simplest amino acid, and related molecules such as glycinal, propionic acid and propanal, are included in the chemical network. Glycine is found to form in moderate abundance within and upon dust-grain ices via three radical-addition mechanisms, with no single mechanism strongly dominant. Glycine production in the ice occurs over temperatures ~40-120 K. Peak gas-phase glycine fractional abundances lie in the range 8 x 10^{-11} - 8 x 10^{-9}, occuring at ~200 K, the evaporation temperature of glycine. A gas-phase mechanism for glycine production is tested and found insignificant, even under optimal conditions. A new spectroscopic radiative-transfer model is used, allowing the translation and comparison of the chemical-model results with observations of specific sources. Comparison with the nearby hot-core source NGC 6334 IRS1 shows excellent agreement with integrated line intensities of observed species, including methyl formate. The results for glycine are consistent with the current lack of a detection of this molecule toward other sources; the high evaporation temperature of glycine renders the emission region extremely compact. Glycine detection with ALMA is predicted to be highly plausible, for bright, nearby sources with narrow emission lines. Photodissociation of water and subsequent hydrogen-abstraction from organic molecules by OH, and NH2, are crucial to the build-up of complex organic species in the ice. The inclusion of alternative branches within the network of radical-addition reactions appears important to the abundances of hot-core molecules; less favorable branching ratios may remedy the anomalously high abundance of glycolaldehyde predicted by this and previous models.
    The Astrophysical Journal 02/2013; 765(1). · 6.73 Impact Factor
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    ABSTRACT: We investigate the molecular evolution and D/H abundance ratios that develop as star formation proceeds from a dense-cloud core to a protostellar core, by solving a gas-grain reaction network applied to a 1-D radiative hydrodynamic model with infalling fluid parcels. Spatial distributions of gas and ice-mantle species are calculated at the first-core stage, and at times after the birth of a protostar. Gas-phase methanol and methane are more abundant than CO at radii $r\lesssim 100$ AU in the first-core stage, but gradually decrease with time, while abundances of larger organic species increase. The warm-up phase, when complex organic molecules are efficiently formed, is longer-lived for those fluid parcels in-falling at later stages. The formation of unsaturated carbon chains (warm carbon-chain chemistry) is also more effective in later stages; C$^+$, which reacts with CH$_4$ to form carbon chains, increases in abundance as the envelope density decreases. The large organic molecules and carbon chains are strongly deuterated, mainly due to high D/H ratios in the parent molecules, determined in the cold phase. We also extend our model to simulate simply the chemistry in circumstellar disks, by suspending the 1-D infall of a fluid parcel at constant disk radii. The species CH$_3$OCH$_3$ and HCOOCH$_3$ increase in abundance in $10^4-10^5$ yr at the fixed warm temperature; both also have high D/H ratios.
    The Astrophysical Journal 10/2012; 760(1). · 6.73 Impact Factor
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    ABSTRACT: We investigate the molecular evolution and D/H abundance ratios that develop as star formation proceeds from dense cloud cores to protostellar cores. We solve a gas-grain reaction network, which is extended to include multi-deuterated species, using a 1-D radiative hydrodynamic model with infalling fluid parcels to derive molecular distribution in assorted evolutionary stages. We find that the abundances of large organic species in the central region increase with time. The duration of the warm-up phase, in which large organic species are efficiently formed, is longer in infalling fluid parcels at later stages. Formation of unsaturated carbon chains in the CH4 sublimation zone (warm carbon chain chemistry) is more effective in later stage. The carbon ion, which reacts with CH4 to form carbon chains, increases in abundance as the envelope density decreases. The large organic molecules and carbon chains are both heavily deuterated, mainly because their mother molecules have high D/H ratios, which are set in the cold phase. The observed CH2DOH/CH3OH ratio towards protostars is reproduced if we assume that the grain-surface exchange and abstraction reactions of CH3OH + D occurs efficiently. In our 1-D collapse model, the fluid parcels directly fall into the protostar, and the warm-up phase in the fluid parcels is rather short. But, in reality, a circumstellar disk is formed, and fluid parcels will stay there for a longer timescale than a free-fall time. We investigate the molecular evolution in such a disk by assuming that a fluid parcel stays at a constant temperature (i.e. a fixed disk radius) after the infall. The species CH3OCH3 and HCOOCH3 become more abundant in the disk than in the envelope. Both have high D/H abundance ratios as well.
    07/2012;
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    ABSTRACT: High-angular resolution observations of dense molecular cores show that these cores can be clumpier at smaller scales, and that some of these clumps can also be unbound or transient. The use of chemical models of the evolution of the molecular gas provides a way to probe the physical properties of the clouds. We study the properties of the clump and inter-clump medium in the starless CS core in LDN 673 by carrying out a molecular line survey with the IRAM 30-m telescope toward two clumps and two inter-clump positions. We also observed the 1.2-mm continuum with the MAMBO-II bolometer at IRAM. The dust continuum map shows four condensations, three of them centrally peaked, coinciding with previously identified sub-millimetre sources. We confirm that the denser clump of the region, $n\sim3.6 \times10^5$\cmt, is also the more chemically evolved, and it could still undergo further fragmentation. The inter-clump medium positions are denser than previously expected, likely $n\sim1\times10^3$--1$\times10^4$\cmt\ due to contamination, and are chemically young, similar to the gas in the lower density clump position. We argue that the density contrast between these positions and their general young chemical age would support the existence of transient clumps in the lower density material of the core. We were also able to find reasonable fits of the observationally derived chemical abundances to models of the chemistry of transient clumps.
    Monthly Notices of the Royal Astronomical Society 06/2012; 425(3). · 5.52 Impact Factor
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    R T Garrod, T Pauly
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    ABSTRACT: We investigate the formation and evolution of interstellar dust-grain ices under dark-cloud con-ditions, with a particular emphasis on CO 2 . We use a three-phase model (gas/surface/mantle) to simulate the coupled gas–grain chemistry, allowing the distinction of the chemically-active surface from the ice layers preserved in the mantle beneath. The model includes a treatment of the compe-tition between barrier-mediated surface reactions and thermal-hopping processes. The results show excellent agreement with the observed behavior of CO 2 , CO and water ice in the interstellar medium. The reaction of the OH radical with CO is found to be efficient enough to account for CO 2 ice pro-duction in dark clouds. At low visual extinctions, with dust temperatures >∼12 K, CO 2 is formed by direct diffusion and reaction of CO with OH; we associate the resultant CO 2 -rich ice with the obser-vational polar CO 2 signature. CH 4 ice is well correlated with this component. At higher extinctions, with lower dust temperatures, CO is relatively immobile and thus abundant; however, the reaction of H and O atop a CO molecule allows OH and CO to meet rapidly enough to produce a CO:CO 2 ratio in the range ∼2–4, which we associate with apolar signatures. We suggest that the observational apolar CO 2 /CO ice signatures in dark clouds result from a strongly segregated CO:H 2 O ice, in which CO 2 resides almost exclusively within the CO component. Observed visual-extinction thresholds for CO 2 , CO and H 2 O are well reproduced by depth-dependent models. Methanol formation is found to be strongly sensitive to dynamical timescales and dust temperatures.
    The Astrophysical Journal 06/2011; 735. · 6.73 Impact Factor
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    ABSTRACT: Recent models of hot cores have incorporated previously-uninvestigated chemical pathways that lead to the formation of complex organic molecules (COMs; i.e. species containing six or more atoms). In addition to the gas-phase ion-molecule reactions long thought to dominate the organic chemistry in these regions, these models now include photodissociation-driven grain surface reaction pathways that can also lead to COMs. Here, simple grain surface ice species photodissociate to form small radicals such as OH, CH3, CH2OH, CH3O, HCO, and NH2. These species become mobile at temperatures above 30 K during the warm-up phase of star formation. Radical-radical addition reactions on grain surfaces can then form an array of COMs that are ejected into the gas phase at higher temperatures. Photodissociation experiments on pure and mixed ices also show that these complex molecules can indeed form from simple species. The molecules predicted to form from this type of chemistry reasonably match the organic inventory observed in high mass hot cores such as Sgr B2(N) and Orion-KL. However, the relative abundances of the observed molecules differ from the predicted values, and also differ between sources. Given this disparity, it remains unclear whether grain surface chemistry governed by photodissociation is the dominant mechanism for the formation of COMs, or whether other unexplored gas-phase reaction pathways could also contribute significantly to their formation. The influence that the physical conditions of the source have on the chemical inventory also remains unclear. Here we overview the chemical pathways for COM formation in hot cores. We also present new modeling results that begin to narrow down the possible routes for production of COMs based on the observed relative abundances of methyl formate (HCOOCH3) and its C2H4O2 structural isomers.
    Proceedings of the International Astronomical Union 05/2011; 7:79 - 87.
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    ABSTRACT: We investigate the molecular evolution in star forming cores from dense cloud cores (nH ~ 104 cm−3, T ~ 10 K) to protostellar cores. A detailed gas-grain reaction network is solved in infalling fluid parcels in 1-D radiation hydrodynamic model. Large organic molecules are mainly formed via grain-surface reaction at T ~ several 10 K and sublimated to the gas-phase at ~ 100 K, while carbon-chain species are formed at a few 10 K after the sublimation of CH4 ice. The former accounts for the high abundance of large organic molecules in hot corinos such as IRAS16293, and the latter accounts for the carbon chain species observed toward L1527. The relative abundance of carbon chain species and large organic species would depend on the collapse time scale and/or temperature in the dense core stage. The large organic molecules and carbon chains in the protostellar cores are heavily deuterated; although they are formed in the warm temperatures, their ingredients have high D/H ratios, which are set in the cold core phase and isothermal collapse phase. HCOOH is formed by the gas-phase reaction of OH with the sublimated H2CO, and is further enriched in Deuterium due to the exothermic exchange reaction of OH + D → OD + H.In the fluid parcels of the 1-D collapse model, warm temperature T. ~ several 10 K lasts for only ~ 104 yr, and the fluid parcels fall to the central star in ~ 100 yr after the temperature of the parcel rises to T ≥ 100 K. These timescales are determined by the size of the warm region and infall (~ free-fall) velocity: rwarm/tff. In reality, circum stellar disk is formed, in which fluid parcels stay for a longer timescale than the infall timescale. We investigate the molecular evolution in the disk by simply assuming that a fluid parcel stays at a constant temperature and density (i.e. a fixed disk radius) for 104 − 105 yrs. We found that some organic species which are underestimated in our 1-D collapse model, such as CH3OCH3 and HCOOCH3, become abundant in the disk. We also found that these disk species have very high D/H ratio as well, since their ingredients are highly deuterated.Finally we investigate molecular evolution in a 3D hydrodynamic simulation of star forming core. We found CH3OH are abundant in the vicinity of the first core. The abundances of large organic species are determined mainly by the local temperature (sublimation), because of the short lifetime of the first core and the efficient mass accretion via angular momentum transfer.
    Proceedings of the International Astronomical Union 05/2011; 7:33 - 42.
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    ABSTRACT: Complex organic molecules have been detected with space- and ground-based telescopes toward low- and high-mass star-forming regions, demonstrating the existence of efficient astrophysical pathways to chemical complexity. Understanding the origins of these species are crucial to use them as tracers of physical environments, to predict the prebiotic evolution during star- and planet-formation, and to plan future observations with e.g. JWST. Many complex organics form on interstellar grains, in ices that evolve with their environment and finally evaporate as the grains are heated by new-born stars or by shocks. This ice evolution has been explored through a combination of Spitzer spectra of ices, laboratory simulations of UV induced ice photochemistry, and millimeter observations tracing complex ice evaporation. The experiments show that UV irradiation of protostellar ices is efficient enough to explain the complex molecule observations in so called protostellar 'hot cores'. Moreover, the experiments predict that before the onset of thermal evaporation close to the protostar, small fractions of the complex ice will continuously evaporate non-thermally due to photodesorption, resulting in gas-phase fingerprints of the ice composition as it evolves. Some of the proposed chemical scenarios can be tested by current facilities, while others require more detailed experiments as well as access to upcoming NASA missions.
    05/2011;
  • Tyler Pauly, R. T. Garrod
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    ABSTRACT: We investigate the formation and evolution of interstellar dust-grain ices under cold cloud conditions, with a particular emphasis on CO2. We use a three-phase model (gas/surface/mantle) to simulate the coupled gas--grain chemistry, allowing the distinction of the chemically-active surface from the ice layers preserved in the mantle beneath. We undertake to treat more accurately the quantum-tunneling rates of barrier-mediated surface reactions, and we explicitly consider competition between such reaction rates and thermal hopping processes. These models show excellent agreement with the observed behavior of CO and CO2 ice in the interstellar medium. The observed threshold between regimes in which CO2 or CO is the dominant ice constituent after H2O is found to be caused ultimately by the near-complete gas-phase conversion of atomic carbon to CO, which is itself determined by CO and H2 self-shielding. The change in the availability of gas-phase carbon alters the balance of the grain-surface chemistry, leading to a sharp change-over in the dominance of CO2/CO. The most probable grain-surface production mechanism for CO2 is the formation of a loosely-bound O...CO complex, whose oxygen atom is easily hydrogenated, leaving a highly excited complex which quickly overcomes an activation energy barrier to form CO2 + H.
    01/2011;
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    H. M. Cuppen, R. T. Garrod
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    ABSTRACT: Context. Many interstellar molecules are formed through grain surface reactions. These reactions are usually modelled using rate equations, while considering a homogeneous grain with only one type of binding site for each species. However, amorphicity and the irregular character of interstellar dust grains make inhomogeneous grain surfaces much more likely. Aims: The aim of this study is to investigate the effect of surface inhomogeneity on surface reaction rates. The formation of molecular hydrogen is here taken as an example. Methods: The continuous-time random-walk Monte Carlo method is used to study the dependence of the H2 formation rate on surface size, fraction of strong binding sites and the distribution of these sites for different temperatures and bond strengths. Classical rate equations and modified rate equations are applied to try to reproduce these results. Results: The H2 formation efficiency is strongly affected by the introduction of a second type of binding site. This effect depends on the strength of the binding energy and the fraction of strong binding sites. The way in which the sites are distributed can change the formation rate by as much as four orders of magnitude. Classical rate equations fail to reproduce the formation rate for all tested situations. Modified rate equations are able to obtain a reasonable agreement with the Monte Carlo results for inhomogeneous surfaces with randomly distributed sites consisting of less than 30% strong sites. Conclusions: Since the different types of binding sites on interstellar grains are probably randomly distributed, we recommend the use of modified rate equations in gas grain models to include the effect of surface inhomogeneity. This method reproduces the most important features while being computationally inexpensive.
    Astronomy and Astrophysics 01/2011; 529. · 5.08 Impact Factor
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    ABSTRACT: Methanol is the most abundant organic molecule in interstellar ices, and its photodissociation is the dominant source of organic radicals in these ices. These organic radicals become mobile and react in warm (>30 K) environments. Such combination reactions lead to a variety of complex organic molecules with differing structural arrangements of organic functional groups. It is plausible, then, that methanol photodissociation branching ratios directly impact the relative abundances of structural isomers observed in interstellar environments. Previous laboratory investigations of the methanol photodissociation process yielded disparate results, and few of these experiments were conducted under conditions that can be directly applied to interstellar chemistry. We are therefore undertaking a combined laboratory spectroscopy and astrochemical modeling investigation of the methanol photodissociation reaction mechanism. In this talk, we will present our progress towards developing a submillimeter spectrometer designed to probe the gas-phase photodissociation branching ratios of methanol. We will also report on the results of an astrochemical modeling study that tests the influence of methanol photodissociation branching ratios on complex interstellar chemistry.
    06/2010;
  • Robin Garrod, A. Vasyunin
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    ABSTRACT: Grain-surface processes are crucial to the behavior of interstellar chemistry; a number of key molecules (including methanol, CH3OH, and methyl formate, HCOOCH3) have been found to have no viable gas-phase formation mechanisms, and many complex organic molecules detected in star-forming regions are believed to originate on dust-grain surfaces. Fully-coupled gas-phase and grain-surface interstellar chemistry is often simulated using rate equations; however, this method fails in cases where the grain chemistry behaves stochastically. So-called "exact" methods, such as Monte Carlo and/or master-equation techniques, are capable of accurately treating this behavior, but the exact methods are computationally highly expensive - prohibitively so, when considering large chemical networks and variable physical conditions. We present a new rate-modification scheme, in which the surface chemical rates are adjusted to take account of stochastic behavior. The scheme shows excellent agreement with Monte Carlo results for a full dark-cloud chemical reaction network over a large physical parameter space. The method is also easily incorporated into existing gas-phase models, and run-times are similar to those of standard rate-equation methods. Minor inaccuracies result from the use of incomplete chemical networks, as is also the case with standard rate-equation simulations. The use of the new modified-rate method with self-consistent chemical networks provides near-perfect agreement with the exact Monte Carlo method. The new method will allow fast, accurate chemical simulations of the most physically- and chemically-complex sources in the ISM, currently impossible using other methods.
    05/2010;
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    ABSTRACT: We compare the results of the unified Monte Carlo chemical model with the new modified-rate equation (MRE) method under a wide range of interstellar conditions, using a full gas-grain chemical network. In most of the explored parameter space, the new MRE method reproduces very well the results of the exact approach. Small disagreements between the methods may be remedied by the use of a more complete surface chemistry network, appropriate to the full range of temperatures employed here.
    The Astrophysical Journal 07/2009; · 6.73 Impact Factor
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    ABSTRACT: Sensitive and high angular resolution ($\sim$ 0.4\arcsec) SO$_2$[22$_{2,20}$ $\to$ 22$_{1,21}$] and SiO[5$\to$4] line and 1.3 and 7 mm continuum observations made with the Submillimeter Array (SMA) and the Very Large Array (VLA) towards the young massive cluster W51 IRS2 are presented. We report the presence of a large (of about 3000 AU) and massive (40 M$_\odot$) dusty circumstellar disk and a hot gas molecular ring around a high-mass protostar or a compact small stellar system associated with W51 North. The simultaneous observations of the silicon monoxide molecule, an outflow gas tracer, further revealed a massive (200 M$_\odot$) and collimated ($\sim14^\circ$) outflow nearly perpendicular to the dusty and molecular structures suggesting thus the presence of a single very massive protostar with a bolometric luminosity of more than 10$^5$ L$_\odot$. A molecular hybrid LTE model of a Keplerian and infalling ring with an inner cavity and a central stellar mass of more than 60 M$_\odot$ agrees well with the SO$_2$[22$_{2,20}$ $\to$ 22$_{1,21}$] line observations. Finally, these results suggest that mechanisms, such as mergers of low- and intermediate- mass stars, might be not necessary for forming very massive stars.
    The Astrophysical Journal 04/2009; 698(2). · 6.73 Impact Factor

Publication Stats

444 Citations
180.57 Total Impact Points

Institutions

  • 2009–2014
    • Cornell University
      • • Center for Radiophysics and Space Research (CRSR)
      • • Department of Astronomy
      Ithaca, New York, United States
  • 2007–2008
    • Max Planck Institute for Radio Astronomy
      Bonn, North Rhine-Westphalia, Germany
  • 2005–2006
    • The Ohio State University
      • Department of Physics
      Columbus, OH, United States
  • 2003–2004
    • University College London
      • Department of Physics and Astronomy
      London, ENG, United Kingdom