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Results for "Ewine F. van Dishoeck"

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Astrochemistry of dust, ice and gas: introduction and overviewNov 19 2014A brief introduction and overview of the astrochemistry of dust, ice and gas and their interplay is presented, aimed at non-specialists. The importance of basic chemical physics studies of critical reactions is illustrated through a number of recent examples. ... More
Chemical changes during star formation: high- versus low-mass YSOsJan 25 2003Recent observational studies of high- and low-mass YSOs at (sub)millimeter and infrared wavelengths are reviewed, and chemical diagnostics of the different physical components are summarized. Methods for determining the temperature, density and abundance ... More
ISO spectroscopy of gas and dust: from molecular clouds to protoplanetary disksMar 02 2004Observations of interstellar gas-phase and solid-state species in the 2.4-200 micron range obtained with the spectrometers on board the Infrared Space Observatory are reviewed. Lines and bands due to ices, polycyclic aromatic hydrocarbons, silicates and ... More
Star and Planet Formation with ALMA: an OverviewAug 22 2007Submillimeter observations with ALMA will be the essential next step in our understanding of how stars and planets form. Key projects range from detailed imaging of the collapse of pre-stellar cores and measuring the accretion rate of matter onto deeply ... More
Models and Observations of the Chemistry near Young Stellar ObjectsJun 07 1999The study of the chemical evolution of gas and dust from pre-stellar dense cores to circumstellar disks around young stars forms an essential part of understanding star- and planet formation. Throughout the collapse- and protostellar phases, simple and ... More
Molecular photodissociationJun 20 2011Feb 09 2015Photodissociation is the dominant removal process of molecules in any region exposed to intense ultraviolet (UV) radiation. This includes diffuse and translucent interstellar clouds, dense photon-dominated regions, high velocity shocks, the surface layers ... More
Water Vapor in the Inner 25 AU of a Young Disk around a Low-Mass ProtostarJan 10 2010Water is one of the key molecules in the physical and chemical evolution of star- and planet-forming regions. We here report the first spatially resolved observation of thermal emission of (an isotopologue of) water with the Plateau de Bure Interferometer ... More
Water in Star and Planet Forming RegionsOct 19 2011In this paper we discuss the astronomical search for water vapor in order to understand the disposition of water in all its phases throughout the process of star and planet formation. Our ability to detect and study water vapor has recently received a ... More
The HDO/H2O ratio in gas in the inner regions of a low-mass protostarNov 12 2010The HDO/H2O abundance ratio is thought to be a key diagnostic on the evolution of water during the star- and planet-formation process and thus on its origin on Earth. We here present millimeter-wavelength high angular resolution observations of the deeply ... More
Limits on the cosmic-ray ionization rate toward massive young starsJun 19 2000Recent models of the envelopes of seven massive protostars are used to analyze observations of H3+ infrared absorption and H13CO+ submillimeter emission lines toward these stars, and to constrain the cosmic-ray ionization rate zeta. The H13CO+ gives best-fit ... More
Chemistry in the Envelopes around Massive Young StarsFeb 04 2000Recent observational studies of intermediate- and high-mass star-forming regions at submillimeter and infrared wavelengths are reviewed, and chemical diagnostics of the different physical components associated with young stellar objects are summarized. ... More
Sun-bathing around low-mass protostars: APEX-CHAMP+ observations of high-J COSep 19 2009We present the first maps of high-excitation CO J=6-5 and 7-6 and isotopologue lines over 2'-5' regions at 10" resolution toward low-mass protostars to probe the origin of the warm gas in their surroundings. The data were obtained using the CHAMP+ 650/850 ... More
Photodissociation of water in crystalline ice: a molecular dynamics studyMay 31 2005Ultraviolet irradiation of ice is of great interest for understanding the chemistry in both atmospheric and astrophysical environments. In interstellar space, photodissociation of H2O molecules can be a driving force behind the chemistry on icy dust grains ... More
Chemical history of molecules in circumstellar disksJul 11 2011The chemical composition of a protoplanetary disk is determined not only by in situ chemical processes during the disk phase, but also by the history of the gas and dust before it accreted from the natal envelope. In order to understand the disk's chemical ... More
Astrochemistry of Sub-Millimeter Sources in Orion: Studying the Variations of Molecular Tracers with Changing Physical ConditionsOct 06 2003Cornerstone molecules (CO, H_2CO, CH_3OH, HCN, HNC, CN, CS, SO) were observed toward seven sub-millimeter bright sources in the Orion molecular cloud in order to quantify the range of conditions for which individual molecular line tracers provide physical ... More
Protoplanetary disk masses from CO isotopologues line emissionOct 08 2014One of the methods for deriving disk masses relies on direct observations of the gas, whose bulk mass is in the outer cold ($T\lesssim30$K) regions. This zone can be well traced by rotational lines of less abundant CO isotopologues, that probe the gas ... More
A primordial origin for molecular oxygen in comets: A chemical kinetics study of the formation and survival of O$_2$ ice from clouds to disksAug 25 2016Molecular oxygen has been confirmed as the fourth most abundant molecule in cometary material O$_2$/H$_2$O $\sim 4$ %) and is thought to have a primordial nature, i.e., coming from the interstellar cloud from which our solar system was formed. However, ... More
Subarcsecond resolution observations of warm water towards three deeply embedded low-mass protostarsMar 22 2012Water is present during all stages of star formation: as ice in the cold outer parts of protostellar envelopes and dense inner regions of circumstellar disks, and as gas in the envelopes close to the protostars, in the upper layers of circumstellar disks ... More
Molecular abundances in low-mass protostellar envelopesNov 24 2002A study of the chemical structure of the envelopes around a sample protostars is introduced. Physical models for the envelopes derived using 1D radiative transfer modeling of their dust continuum emission are used as input for Monte Carlo modeling of ... More
Determining protoplanetary disk gas masses from CO isotopologues line observationsMay 25 2016Despite intensive studies of protoplanetary disks, there is still no reliable way to determine their total mass and their surface density distribution, quantities that are crucial for describing both the structure and the evolution of disks up to the ... More
Ro-vibrational excitation of an organic molecule (HCN) in protoplanetary disksDec 04 2014(Abridged) Organic molecules are important constituents of protoplanetary disks. Their ro-vibrational lines observed in the near- and mid-infrared are commonly detected toward T Tauri disks. These lines are the only way to probe the chemistry in the inner ... More
Photodesorption of ices I: CO, N2 and CO2Sep 08 2008Jan 23 2009A longstanding problem in astrochemistry is how molecules can be maintained in the gas phase in dense inter- and circumstellar regions. Photodesorption is a non-thermal desorption mechanism, which may explain the small amounts of observed cold gas in ... More
Spectroscopic properties of Young Stellar Objects in the Lupus Molecular CloudsAug 04 2011The results of an optical spectroscopic survey of a sample of young stellar objects (YSOs) and pre-main sequence (PMS) stars in the Lupus Clouds are presented. 92 objects were observed with VLT/FLAMES. All of those objects show IR excess as discovered ... More
The molecular composition of the planet-forming regions of protoplanetary disks across the luminosity regimeJul 30 2015Sep 02 2015(Abridged) Near- to mid-IR observations of protoplanetary disks show that the inner regions (<10AU) are rich in small organic volatiles (e.g., C2H2 and HCN). Trends in the data suggest that disks around cooler stars (~3000K) are potentially more carbon- ... More
Setting the volatile composition of (exo)planet-building material. Does chemical evolution in disk midplanes matter?Jul 22 2016[Abridged] Chemical evolution in the protoplanetary disk midplane can modify the composition of ices and gases. We have investigated if and how chemical evolution affects the abundances and distributions of key volatile species in the midplane of a protoplanetary ... More
Cold gas as an ice diagnostic toward low mass protostarsJan 08 2009Up to 90% of the chemical reactions during star formation occurs on ice surfaces, probably including the formation of complex organics. Only the most abundant ice species are however observed directly by infrared spectroscopy. This study aims to develop ... More
Warm water deuterium fractionation in IRAS 16293-2422 - The high-resolution ALMA and SMA viewNov 28 2012Measuring the water deuterium fractionation in the inner warm regions of low-mass protostars has so far been hampered by poor angular resolution obtainable with single-dish ground- and space-based telescopes. Observations of water isotopologues using ... More
Physical structure and CO abundance of low-mass protostellar envelopesMay 05 2002We present 1D radiative transfer modelling of the envelopes of a sample of 18 low-mass protostars and pre-stellar cores with the aim of setting up realistic physical models, for use in a chemical description of the sources. The density and temperature ... More
CO2 infrared emission as a diagnostic of planet-forming regions of disksJan 27 2017[Abridged] The infrared ro-vibrational emission lines from organic molecules in the inner regions of protoplanetary disks are unique probes of the physical and chemical structure of planet forming regions and the processes that shape them. The non-LTE ... More
Lines of Circumstellar C2, CN, and CH+ in the Optical Spectra of Post-Agb StarsSep 04 1996Recent optical spectra of post-AGB stars show the presence of C2, CN, and CH+ originating in the circumstellar shell. We present here new, higher resolution spectra which provide constraints on the physical parameters and information on the line profiles. ... More
Molecular Oxygen in Oort Cloud Comet 1P/HalleyDec 05 2015Recently the ROSINA mass spectrometer suite on board the European Space Agency's Rosetta spacecraft discovered an abundant amount of molecular oxygen, O2, in the coma of Jupiter family comet 67P/Churyumov-Gerasimenko of O2/H2O = 3.80+/-0.85%. It could ... More
Interstellar water chemistry: from laboratory to observationsDec 17 2013Water is observed throughout the universe, from diffuse interstellar clouds to protoplanetary disks around young stars, and from comets in our own solar system and exoplanetary atmospheres to galaxies at high redshifts. This review summarizes the spectroscopy ... More
Different dust and gas radial extents in protoplanetary disks: consistent models of grain growth and CO emissionMay 17 2017Jun 01 2017ALMA observations of protoplanetary disks confirm earlier indications that there is a clear difference between the dust and gas radial extents. The origin of this difference is still debated, with both radial drift of the dust and optical depth effects ... More
The Abundance and Emission of H2O and O2 in Clumpy Molecular CloudsNov 23 2000Recent observations with the Submillimeter Wave Astronomy Satellite indicate abundances of gaseous H2O and O2 in dense molecular clouds which are significantly lower than found in standard homogeneous chemistry models. We present here results for the ... More
Gas structure inside dust cavities of transition disks: Oph IRS 48 observed by ALMADec 10 2013(Abridged) Transition disks are recognized by the absence of emission of small dust grains inside a radius of up to several 10s of AUs. Due to the lack of angular resolution and sensitivity, the gas content of such dust holes has not yet been determined, ... More
Detection of interstellar H_2D^+ emissionJun 12 1999We report the detection of the 1_{10}-1_{11} ground state transition of ortho-H_2D^+ at 372.421 GHz in emission from the young stellar object NGC 1333 IRAS 4A. Detailed excitation models with a power-law temperature and density structure yield a beam-averaged ... More
Warm formaldehyde in the Oph IRS 48 transitional diskFeb 03 2014Feb 07 2014Simple molecules like H2CO and CH3OH in protoplanetary disks are the starting point for the production of more complex organic molecules. So far, the observed chemical complexity in disks has been limited due to freeze out of molecules onto grains in ... More
Structure and Evolution of the Envelopes of Deeply Embedded Massive Young StarsJan 31 2000Feb 01 2000The physical structure of the envelopes around a sample of fourteen massive (1000-100,000 solar L) young stars is investigated on 100- 100,000 AU scales using maps and spectra in submillimeter continuum and lines of C17O, CS and H2CO. The total column ... More
Abundance profiles of CH3OH and H2CO toward massive young stars as evolutionary tracersAug 01 2000The chemical evolution of thirteen regions of massive star formation is studied through single-dish and interferometer line observations at submillimeter wavelengths. The wealth of CH3OH and H2CO lines covering a large range of excitation conditions allows ... More
Volatile snowlines in embedded disks around low-mass protostarsJul 27 2015(Abridged*) Models of the young solar nebula assume a hot initial disk with most volatiles are in the gas phase. The question remains whether an actively accreting disk is warm enough to have gas-phase water up to 50 AU radius. No detailed studies have ... More
Chemistry of massive young stellar objects with a disk-like structureApr 15 2013Our goal is to take an inventory of complex molecules in three well-known high-mass protostars for which disks or toroids have been claimed and to study the similarities and differences with a sample of massive YSOs without evidence of such flattened ... More
Robustness of N2H+ as tracer of the CO snowlineOct 21 2016[Abridged] Snowlines in protoplanetary disks play an important role in planet formation and composition. Since the CO snowline is difficult to observe directly with CO emission, its location has been inferred in several disks from spatially resolved ALMA ... More
Effects of Reagent Rotation and Vibration on H + OH (v,j) $\to$ O + H2Feb 25 2014The dynamics of the reaction H + OH $\to$ O (3P) + H2 have been studied in a series of quasi-classical trajectory (QCT) calculations and transition state theory (TST) methods using high quality 3A' and 3A'' potential energy surfaces (PESs). Accurate OH ... More
Submillimeter lines from circumstellar disks around pre-main sequence starsAug 23 2001Observations of submillimeter lines of CO (up to J=6-5), HCO+, HCN (up to J=4-3) and their isotopes from circumstellar disks around low mass pre-main sequence stars are presented. The different line ratios and optical depths indicate that most of the ... More
Tracing the envelopes around embedded low-mass young stellar objects with HCO+ and millimeter-continuum observationsJun 09 1997Interferometer observations of millimeter-continuum (OVRO) and single-dish observations of HCO+ and H13CO+ J=1-0, 3-2, and 4-3 (JCMT, IRAM 30m) are presented of nine embedded low-mass young stellar objects (YSOs) in Taurus. All nine objects are detected ... More
Axi-symmetric models of ultraviolet radiative transfer with applications to circumstellar disk chemistryNov 01 2002A new two-dimensional axi-symmetric ultraviolet radiative transfer code is presented, which is used to calculate photodissociation and ionization rates for use in chemistry models of flaring circumstellar disks. Scattering and absorption of photons from ... More
Evidence for Hco+ Infall toward T Tauri?Feb 22 1994High spectral and spatial resolution observations of the HCO+ molecule toward the T Tau binary system obtained with the Owens Valley Millimeter Array reveal a broad emission line profile (V_LSR = 7.2 km/s, width = 2.0 km/s) upon which a narrow, redshifted ... More
Molecular Dynamics Simulations of CO2 Formation in Interstellar IcesOct 11 2013CO2 ice is one of the most abundant components in ice-coated interstellar ices besides H2O and CO, but the most favorable path to CO2 ice is still unclear. Molecular dynamics calculations on the ultraviolet photodissociation of different kinds of CO-H2O ... More
Organic molecules in protoplanetary disks around TTauri and HerbigAe starsJun 25 2004The results of single-dish observations of low- and high-J transitions of selected molecules from protoplanetary disks around two TTauri stars (LkCa15 and TWHya) and two HerbigAe stars (HD163296 and MWC480) are reported. Simple molecules such as CO, 13CO, ... More
Complex molecules toward low-mass protostars: the Serpens coreJul 28 2011Gas-phase complex organic molecules are commonly detected toward high-mass protostellar hot cores. Detections toward low-mass protostars and outflows are comparatively rare, and a larger sample is key to investigate how the chemistry responds to its environment. ... More
Neutral and Ionized Hydrides in Star-forming Regions -- Observations with Herschel/HIFIAug 26 2013The cosmic abundance of hydrides depends critically on high-energy UV, X-ray, and particle irradiation. Here we study hydrides in star-forming regions where irradiation by the young stellar object can be substantial, and density and temperature can be ... More
Circumstellar C2, CN, and CH+ in the optical spectra of post-AGB starsOct 09 1996We present optical high-resolution spectra of a sample of sixteen post-AGB stars and IRC +10216. Of the post-AGB stars, ten show C2 Phillips and Swan and CN Red System absorption, one CH+ emission, one CH+ absorption, and four without any molecules. We ... More
ISO-LWS detection of the 112 micron HD J=1-0 line toward the Orion BarJan 28 1999We report the first detection outside of the solar system of the lowest pure rotational J=1-0 transition of the HD molecule at 112 microns. The detection was made toward the Orion Bar using the Fabry-Perot of the Long Wavelength Spectrometer (LWS) on ... More
Tracing FUV Radiation in the Embedded Phase of Star FormationJan 10 2011Molecules containing one or a few hydrogen atoms and a heavier atom (hydrides) have been predicted to trace FUV radiation. In some chemical models, FUV emission by the central object or protostar of a star forming region greatly enhances some of the hydride ... More
Photodesorption of Ices II: H2O and D2ODec 10 2008Gaseous H2O has been detected in several cold astrophysical environments, where the observed abundances cannot be explained by thermal desorption of H2O ice or by H2O gas phase formation. These observations hence suggest an efficient non-thermal ice desorption ... More
Hydrides in Young Stellar Objects: Radiation tracers in a protostar-disk-outflow systemJul 20 2010Context: Hydrides of the most abundant heavier elements are fundamental molecules in cosmic chemistry. Some of them trace gas irradiated by UV or X-rays. Aims: We explore the abundances of major hydrides in W3 IRS5, a prototypical region of high-mass ... More
Do siblings always form and evolve simultaneously? Testing the coevality of multiple protostellar systems through SEDsApr 20 2016Multiplicity is common in field stars and among protostellar systems. Models suggest two paths of formation: turbulent fragmentation and protostellar disk fragmentation. We attempt to find whether or not the coevality frequency of multiple protostellar ... More
Photodissociation and chemistry of N$_2$ in the circumstellar envelope of carbon-rich AGB starsJun 28 2014The envelopes of AGB stars are irradiated externally by ultraviolet photons; hence, the chemistry is sensitive to the photodissociation of N$_2$ and CO, which are major reservoirs of nitrogen and carbon, respectively. The photodissociation of N$_2$ has ... More
A 30 AU radius CO gas hole in the disk around the Herbig Ae star Oph IRS 48Oct 10 2011The physical processes leading to the disappearance of disks around young stars are not well understood. A subclass of transitional disks, the so-called cold disks with large inner dust holes, provide a crucial laboratory for studying disk dissipation ... More
High-precision C17O, C18O and C16O measurements in young stellar objects: analogues for CO self-shielding in the early solar systemJun 05 2009Using very high resolution (lambda / Dlambda ~ 95000) 4.7 micron fundamental and 2.3 micron overtone ro-vibrational CO absorption spectra obtained with the CRIRES infrared spectrometer on the Very Large Telescope (VLT), we report detections of four CO ... More
The Physical Structure of Protoplanetary Disks: the Serpens Cluster Compared with Other RegionsDec 13 2012Spectral energy distributions are presented for 94 young stars surrounded by disks in the Serpens Molecular Cloud, based on photometry and Spitzer IRS spectra. Taking a distance to the cloud of 415 pc rather than 259 pc, the distribution of ages is shifted ... More
Evolution of CO lines in time-dependent models of protostellar disk formationApr 18 2013(Abridged) Star and planet formation theories predict an evolution in the density, temperature, and velocity structure as the envelope collapses and forms an accretion disk. The aim of this work is to model the evolution of the molecular excitation, line ... More
Hot water in the inner 100 AU of the Class 0 protostar NGC1333 IRAS2AMar 25 2013Evaporation of water ice above 100 K in the inner few 100 AU of low-mass embedded protostars (the so-called hot core) should produce quiescent water vapor abundances of ~10^-4 relative to H2. Observational evidence so far points at abundances of only ... More
On the Evolution of Dust Mineralogy, From Protoplanetary Disks to Planetary SystemsApr 18 2011Mineralogical studies of silicate features emitted by dust grains in protoplanetary disks and Solar System bodies can shed light on the progress of planet formation. The significant fraction of crystalline material in comets, chondritic meteorites and ... More
The chemical connection between 67P/C-G and IRAS 16293-2422Feb 08 2018The chemical evolution of a star- and planet-forming system begins in the prestellar phase and proceeds across the subsequent evolutionary phases. The chemical trail from cores to protoplanetary disks to planetary embryos can be studied by comparing distant ... More
Nitrogen isotope fractionation in protoplanetary disksFeb 08 2018Aims: The two stable isotopes of nitrogen, 14N and 15N, exhibit a range of abundance ratios both inside and outside the solar system. The elemental ratio in the solar neighborhood is 440. Recent ALMA observations showed HCN/HC15N ratios from 83 to 156 ... More
The Infrared Band Strengths of H2o, Co and Co2 in Laboratory Simulations of Astrophysical Ice MixturesSep 28 1994Mar 14 1995Infrared spectroscopic observations toward objects obscured by dense cloud material show that H$_2$O, CO and, likely, CO$_2$ are important constituents of interstellar ice mantles. In order to accurately calculate the column densities of these molecules, ... More
VLT/X-shooter Spectroscopy of a Dusty Planetary Nebula Discovered with Spitzer/IRSDec 06 2010As part of a mid-infrared spectroscopic survey of young stars with the Spitzer Space Telescope, an unclassified red emission line object was discovered. Based on its high ionization state indicated by the Spitzer spectrum, this object could either be ... More
Quantification of segregation dynamics in ice mixturesJul 22 2009(Abridged) The observed presence of pure CO2 ice in protostellar envelopes is attributed to thermally induced ice segregation, but a lack of quantitative experimental data has prevented its use as a temperature probe. Quantitative segregation studies ... More
Multidimensional chemical modelling, II. Irradiated outflow wallsJun 03 2009Observations of the high-mass star forming region AFGL 2591 reveal a large abundance of CO+, a molecule known to be enhanced by far UV (FUV) and X-ray irradiation. In chemical models assuming a spherically symmetric envelope, the volume of gas irradiated ... More
Water: from clouds to planetsJan 31 2014Feb 25 2014Results from recent space missions, in particular Spitzer and Herschel, have lead to significant progress in our understanding of the formation and transport of water from clouds to disks, planetesimals, and planets. In this review, we provide the underpinnings ... More
The warm gas atmosphere of the HD 100546 disk seen by Herschel (Evidence of a gas-rich, carbon-poor atmosphere?)Jan 23 2012(Abridged) Context. With the Herschel Space Observatory, lines of simple molecules (C+, O, and CO) have been observed in the atmosphere of protoplanetary disks. When combined with ground-based [CI], all principle forms of carbon can be studied. The absence ... More
Deep Spitzer spectroscopy of the `Flying Saucer' edge-on disk: Large grains beyond 50 AUFeb 14 2007We present deep Spitzer-IRS low-resolution (lambda/Delta lambda ~ 100) 5-35 micron spectroscopy of the edge-on disk ``the Flying Saucer'' (2MASS J16281370-2431391) in the Ophiuchus molecular cloud. The spectral energy distribution exhibits the characteristic ... More
Water and methanol in low-mass protostellar outflows: gas-phase synthesis, ice sputtering and destructionFeb 28 2014Water in outflows from protostars originates either as a result of gas-phase synthesis from atomic oxygen at T > 200 K, or from sputtered ice mantles containing water ice. We aim to quantify the contribution of the two mechanisms that lead to water in ... More
HD far infrared emission as a measure of protoplanetary disk massMay 22 2017Protoplanetary disks around young stars are the sites of planet formation. While the dust mass can be estimated using standard methods, determining the gas mass - and thus the amount of material available to form giant planets - has proven to be very ... More
Photon Dominated Regions in Low UV Fields: A Study of The Peripheral Region of L1204/S140Dec 11 2001We have carried out an in-depth study of the peripheral region of the molecular cloud L1204/S140, where the far ultraviolet radiation and the density are relatively low. Our observations test theories of photon-dominated regions (PDRs) in a regime that ... More
The complex chemistry of outflow cavity walls exposed: the case of low-mass protostarsMay 21 2015Complex organic molecules are ubiquitous companions of young low-mass protostars. Recent observations suggest that their emission stems, not only from the traditional hot corino, but also from offset positions. In this work, 2D physicochemical modelling ... More
c2d Spitzer IRS spectra of embedded low-mass young stars: gas-phase emission linesMay 17 2010A survey of mid-IR gas-phase emission lines of H2, H2O and various atoms toward a sample of 43 embedded low-mass young stars in nearby star-forming regions is presented. The sources are selected from the Spitzer "Cores to Disks" (c2d) legacy program. ... More
The effect of a strong external radiation field on protostellar envelopes in OrionDec 12 2005We discuss the effects of an enhanced interstellar radiation field (ISRF) on the observables of protostellar cores in the Orion cloud region. Dust radiative transfer is used to constrain the envelope physical structure by reproducing SCUBA 850 micron ... More
Molecular dynamics study of photodissociation of water in crystalline and amorphous iceDec 23 2005We present results of classical dynamics calculations, performed to study the photodissociation of water in crystalline and amorphous ice surfaces at a surface temperature of 10 K. Dissociation in the top six monolayers is considered. Desorption of H2O ... More
The effect of H2O on ice photochemistryJun 11 2010UV irradiation of simple ices is proposed to efficiently produce complex organic species during star- and planet-formation. Through a series of laboratory experiments, we investigate the effects of the H2O concentration, the dominant ice constituent in ... More
Complex organic molecules in organic-poor massive young stellar objectsJan 13 2015Massive young stellar objects (MYSOs) with hot cores are classic sources of complex organic molecules. The origins of these molecules in such sources, as well as the small- and large-scale differentiation between nitrogen- and oxygen-bearing complex species, ... More
Methanol Along the Path from Envelope to Protoplanetary DiscSep 08 2014Interstellar methanol is considered to be a parent species of larger, more complex organic molecules. A physicochemical simulation of infalling parcels of matter is performed for a low-mass star-forming system to trace the chemical evolution from cloud ... More
Exploring organic chemistry in planet-forming zonesDec 13 2012Dec 14 2012Over the last few years, the chemistry of molecules other than CO in the planet-forming zones of disks is starting to be explored with Spitzer and high-resolution ground-based data. However, these studies have focused only on a few simple molecules. The ... More
A cold complex chemistry toward the low-mass protostar B1-b: evidence for complex molecule production in icesMay 04 2010Gas-phase complex organic molecules have been detected toward a range of high- and low-mass star-forming regions at abundances which cannot be explained by any known gas-phase chemistry. Recent laboratory experiments show that UV irradiation of CH3OH-rich ... More
A Keplerian disk around a Class 0 source: ALMA observations of VLA1623AOct 31 2013Context: Rotationally supported disks are critical in the star formation process. The questions of when do they form and what factors influence or hinder their formation have been studied but are largely unanswered. Observations of early stage YSOs are ... More
Disks and Outflows in CO Rovibrational Emission from Embedded, Low-Mass Young Stellar ObjectsJun 27 2011Young circumstellar disks that are still embedded in dense molecular envelopes may differ from their older counterparts, but are historically difficult to study because emission from a disk can be confused with envelope or outflow emission. CO fundamental ... More
Matryoshka Holes: Nested Emission Rings in the Transitional Disk Oph IRS 48Sep 07 2012The processes that form transition disks - disks with depleted inner regions - are not well understood; possible scenarios include planet formation, grain growth and photoevaporation. Disks with spatially resolved dust holes are rare, but, in general, ... More
Molecular Cloud Structure in the Magellanic Clouds: Effect of MetallicityDec 11 1997Jan 12 1998The chemical structure of neutral clouds in low metallicity environments is examined with particular emphasis on the H to H_2 and C+ to CO transitions. We observed near-IR H_2 lines and the CO J=1-0 line from 30 Doradus and N159/N160 in the Large Magellanic ... More
Photodesorption of H2O, HDO, and D2O ice and its impact on fractionationMar 02 2015The HDO/H2O ratio in interstellar gas is often used to draw conclusions on the origin of water in star-forming regions and on Earth. In cold cores and in the outer regions of protoplanetary disks, gas-phase water comes from photodesorption of water ice. ... More
The Impact of the Massive Young Star GL 2591 on its Circumstellar Material: Temperature, Density and Velocity StructureMay 05 1999The temperature, density and kinematics of the gas and dust surrounding the luminous young stellar object GL~2591 are investigated on scales as small as 100 AU, probed by 4.7 micron absorption spectroscopy, to over 60,000 AU, probed by single-dish submillimeter ... More
Interferometric Observations of Formaldehyde in the Protoplanetary Disk around LkCa15Nov 20 2002Jan 10 2003Emission from the $2_{12}-1_{11}$ line of H$_2$CO has been detected and marginally resolved toward LkCa15 by the Nobeyama Millimeter Array. The column density of H$_2$CO is higher than that observed in DM Tau and than predicted by theoretical models of ... More
Detection of H2 pure rotational line emission from the GG~Tau binary systemJun 14 1999We present the first detection of the low-lying pure rotational emission lines of H2 from circumstellar disks around T~Tauri stars, using the Short Wavelength Spectrometer on the Infrared Space Observatory. These lines provide a direct measure of the ... More
Outflow forces of low mass embedded objects in Ophiuchus: a quantitative comparison of analysis methodsMay 28 2013The outflow force of molecular bipolar outflows is a key parameter in theories of young stellar feedback on their surroundings. The focus of many outflow studies is the correlation between the outflow force, bolometric luminosity and envelope mass. However, ... More
Photodissociation of interstellar N2May 08 2013Molecular nitrogen is one of the key species in the chemistry of interstellar clouds and protoplanetary disks and the partitioning of nitrogen between N and N2 controls the formation of more complex prebiotic nitrogen-containing species. The aim of this ... More
Probing the Surfaces of Interstellar Dust Grains: The Adsorption of CO at Bare Grain SurfacesOct 25 2004A solid-state feature was detected at around 2175 cm-1 towards 30 embedded young stellar objects in spectra obtained using the ESO VLT-ISAAC. We present results from laboratory studies of CO adsorbed at the surface of Zeolite wafers, where absorption ... More
Isotope selective photodissociation of N2 by the interstellar radiation field and cosmic raysJan 08 2014Photodissociation of 14N2 and 14N15N occurs in interstellar clouds, circumstellar envelopes, protoplanetary discs, and other environments due to UV radiation from stellar sources and the presence of cosmic rays. This source of N atoms initiates the formation ... More
Far-Infrared and Sub-Millimeter Observations and Physical Models of the Reflection Nebula Ced 201Nov 16 1998ISO [C II] 158 micron, [O I] 63 micron, and H_2 9 and 17 micron observations are presented of the reflection nebula Ced 201, which is a photon-dominated region illuminated by a B9.5 star with a color temperature of 10,000 K (a cool PDR). In combination ... More
c2d Spitzer IRS Spectra of Disks around T Tauri Stars. III. [Ne II], [Fe I], and H_2 gas-phase linesApr 18 2007Apr 20 2007We present a survey of mid-infrared gas-phase lines toward a sample of 76 circumstellar disks around low mass pre-main sequence stars from the Spitzer "Cores to Disks" legacy program. We report the first detections of [Ne II] and [Fe I] toward classical ... More
Rotationally-supported disks around Class I sources in Taurus: disk formation constraintsDec 19 2013(Abridged) Disks are observed around pre-main sequence stars, but how and when they form is still heavily debated. While disks around young stellar objects have been identified through thermal dust emission, spatially and spectrally resolved molecular ... More