21 research outputs found
DiskMINT: A Tool to Estimate Disk Masses with CO Isotopologues
No full textCO is one of the most abundant molecules in protoplanetary disks, and
optically thin emission from its isotopologues has been detected in many of
them. However, several past works have argued that reproducing the relatively
low emission of CO isotopologues requires a very low disk mass or significant
CO depletion. Here, we present a Python code, DiskMINT, which includes gas
density and temperature structures that are both consistent with the thermal
pressure gradient, isotope-selective chemistry, and conversion of CO into
ice on grain-surfaces. The code generates a self-consistent
disk structure, where the gas disk distribution is obtained from a Spectral
Energy Distribution (SED)-derived dust disk structure with multiple grain
sizes. We use DiskMINT to study the disk of RU~Lup, a high-accreting star whose
disk was previously inferred to have a gas mass of only and gas-to-dust mass ratio of . Our best-fit
model to the long-wavelength continuum emission can explain the total
luminosity as well as the velocity and
radial intensity profiles, and obtains a gas mass of , an order of magnitude higher than previous results.
A disk model with parametric Gaussian vertical distribution that better matches
the IR-SED can also explain the observables above with a similarly high gas
mass . We confirm the conclusions of Ruaud et
al. (2022) that optically thin rotational lines provide
reasonable estimates of the disk mass and can therefore be used as gas disk
tracers.Comment: 15 pages, 7 figures, accepted for publication in the ApJ. Associated
code is released, see http://github.com/DingshanDeng/DiskMINT. v2 has updated
the reference and included a correction to Fig
Chemistry of the interstellar medium : from diffuse to dense
No full textL’évolution chimique des phases les plus diffuses aux plus denses du milieu interstellaireest un processus continu : la composition chimique du milieu interstellairedans une phase dépend de sa composition dans sa phase antérieure.Les études, qui s’intéressent à la chimie du milieu dense et froid ainsi qu’à l’évolutionde sa composition au cours du temps, font de fortes hypothèses sur son évolutiondepuis le milieu diffus.L’objectif de ma thèse a donc été de suivre l’évolution de la chimie de la matièreinterstellaire du milieu diffus jusqu’à la formation des nuages denses.J’ai pour cela utilisé un modèle de chimie gaz-grain dépendant du temps que j’aisignificativement contribué à améliorer pour la partie chimie de surface. J’ai dansun premier temps suivi une approche "classique" (c.-à-d. : semblable aux études préexistantes)de la modélisation des régions froides. Cela m’a permis d’étudier en détailles processus physiques et chimiques à l’origine de la complexité moléculaire dans lesnuages denses et froids et de comparer les prédictions du modèle avec les études existantes.Dans une deuxième partie, j’ai appliqué ce modèle pour suivre l’évolution de lacomposition chimique du milieu interstellaire au cours du processus de formation desnuages moléculaires à partir du milieu diffus. Pour cette étude, j’ai utilisé les résultatsd’une simulation hydrodynamique à l’échelle galactique. Cela m’a permis de montrerque l’histoire de l’évolution des conditions physiques dans les phases antérieures à laformation des nuages moléculaires peut avoir un impact significatif sur la compositionchimique de ces derniers.The chemical evolution from the most diffuse parts of the interstellar medium tothe formation of dense clouds is a continuous process : the chemical composition inone phase depends on the chemical composition in the previous one.However, most studies of the time dependent chemistry in the cold and dense interstellarmedium make strong assumptions on the transition between diffuse and densemedium.The goal of my thesis was to study the chemical evolution of the interstellar mediumfrom the most diffuse parts to the formation of dense clouds in a continuousway.To do so, I used a time dependent gas-grain model that I significantly contributedto improve for the treatment of the surface chemistry. In a first part, I followed a "classical"approach (i.e. : similar to most of the pre-existing studies) to model cold denseclouds. This allowed me to study in details the physical and the chemical mechanismsresponsible for the chemical complexity of dense clouds and to compare the modelpredictions with the existing literature. In a second part, I applied this model to followthe evolution of the chemical composition during the formation process of denseclouds from the diffuse medium. I used results from an hydrodynamical simulation ofthe interstellar medium at galactic scales. This study allowed me to show that the pastphysical history of each particles that form the dense clouds have a significant impacton their chemical composition
DiskMINT: A Tool to Estimate Disk Masses with CO Isotopologues
No full textCO is one of the most abundant molecules in protoplanetary disks, and optically thin emission from its isotopologues has been detected in many of them. However, several past works have argued that reproducing the relatively low emission of CO isotopologues requires a very low disk mass or significant CO depletion. Here, we present a Python code, DiskMINT , which includes gas density and temperature structures that are both consistent with the thermal pressure gradient, isotope-selective chemistry, and conversion of CO into CO _2 ice on grain surfaces. The code generates a self-consistent disk structure, where the gas disk distribution is obtained from a spectral energy distribution (SED)–derived dust disk structure with multiple grain sizes. We use DiskMINT to study the disk of RU Lup, a high-accreting star whose disk was previously inferred to have a gas mass of only ∼1.5 × 10 ^−3 M _⊙ and gas-to-dust mass ratio of ∼4. Our best-fit model to the long-wavelength continuum emission can explain the total C ^18 O luminosity as well as the C ^18 O velocity and radial intensity profiles, and it obtains a gas mass of ∼1.2 × 10 ^−2 M _⊙ , an order of magnitude higher than previous results. A disk model with parametric Gaussian vertical distribution that better matches the IR SED can also explain the observables above with a similarly high gas mass ∼2.1 × 10 ^−2 M _⊙ . We confirm the conclusions of Ruaud et al. that optically thin C ^18 O rotational lines provide reasonable estimates of the disk mass and can therefore be used as gas disk tracers
Chimie du milieu interstellaire : du diffus au dense
No full textThe chemical evolution from the most diffuse parts of the interstellar medium tothe formation of dense clouds is a continuous process : the chemical composition inone phase depends on the chemical composition in the previous one.However, most studies of the time dependent chemistry in the cold and dense interstellarmedium make strong assumptions on the transition between diffuse and densemedium.The goal of my thesis was to study the chemical evolution of the interstellar mediumfrom the most diffuse parts to the formation of dense clouds in a continuousway.To do so, I used a time dependent gas-grain model that I significantly contributedto improve for the treatment of the surface chemistry. In a first part, I followed a "classical"approach (i.e. : similar to most of the pre-existing studies) to model cold denseclouds. This allowed me to study in details the physical and the chemical mechanismsresponsible for the chemical complexity of dense clouds and to compare the modelpredictions with the existing literature. In a second part, I applied this model to followthe evolution of the chemical composition during the formation process of denseclouds from the diffuse medium. I used results from an hydrodynamical simulation ofthe interstellar medium at galactic scales. This study allowed me to show that the pastphysical history of each particles that form the dense clouds have a significant impacton their chemical composition.L’évolution chimique des phases les plus diffuses aux plus denses du milieu interstellaireest un processus continu : la composition chimique du milieu interstellairedans une phase dépend de sa composition dans sa phase antérieure.Les études, qui s’intéressent à la chimie du milieu dense et froid ainsi qu’à l’évolutionde sa composition au cours du temps, font de fortes hypothèses sur son évolutiondepuis le milieu diffus.L’objectif de ma thèse a donc été de suivre l’évolution de la chimie de la matièreinterstellaire du milieu diffus jusqu’à la formation des nuages denses.J’ai pour cela utilisé un modèle de chimie gaz-grain dépendant du temps que j’aisignificativement contribué à améliorer pour la partie chimie de surface. J’ai dansun premier temps suivi une approche "classique" (c.-à-d. : semblable aux études préexistantes)de la modélisation des régions froides. Cela m’a permis d’étudier en détailles processus physiques et chimiques à l’origine de la complexité moléculaire dans lesnuages denses et froids et de comparer les prédictions du modèle avec les études existantes.Dans une deuxième partie, j’ai appliqué ce modèle pour suivre l’évolution de lacomposition chimique du milieu interstellaire au cours du processus de formation desnuages moléculaires à partir du milieu diffus. Pour cette étude, j’ai utilisé les résultatsd’une simulation hydrodynamique à l’échelle galactique. Cela m’a permis de montrerque l’histoire de l’évolution des conditions physiques dans les phases antérieures à laformation des nuages moléculaires peut avoir un impact significatif sur la compositionchimique de ces derniers
Chemistry of the interstellar medium : from diffuse to dense
No full textL’évolution chimique des phases les plus diffuses aux plus denses du milieu interstellaireest un processus continu : la composition chimique du milieu interstellairedans une phase dépend de sa composition dans sa phase antérieure.Les études, qui s’intéressent à la chimie du milieu dense et froid ainsi qu’à l’évolutionde sa composition au cours du temps, font de fortes hypothèses sur son évolutiondepuis le milieu diffus.L’objectif de ma thèse a donc été de suivre l’évolution de la chimie de la matièreinterstellaire du milieu diffus jusqu’à la formation des nuages denses.J’ai pour cela utilisé un modèle de chimie gaz-grain dépendant du temps que j’aisignificativement contribué à améliorer pour la partie chimie de surface. J’ai dansun premier temps suivi une approche "classique" (c.-à-d. : semblable aux études préexistantes)de la modélisation des régions froides. Cela m’a permis d’étudier en détailles processus physiques et chimiques à l’origine de la complexité moléculaire dans lesnuages denses et froids et de comparer les prédictions du modèle avec les études existantes.Dans une deuxième partie, j’ai appliqué ce modèle pour suivre l’évolution de lacomposition chimique du milieu interstellaire au cours du processus de formation desnuages moléculaires à partir du milieu diffus. Pour cette étude, j’ai utilisé les résultatsd’une simulation hydrodynamique à l’échelle galactique. Cela m’a permis de montrerque l’histoire de l’évolution des conditions physiques dans les phases antérieures à laformation des nuages moléculaires peut avoir un impact significatif sur la compositionchimique de ces derniers.The chemical evolution from the most diffuse parts of the interstellar medium tothe formation of dense clouds is a continuous process : the chemical composition inone phase depends on the chemical composition in the previous one.However, most studies of the time dependent chemistry in the cold and dense interstellarmedium make strong assumptions on the transition between diffuse and densemedium.The goal of my thesis was to study the chemical evolution of the interstellar mediumfrom the most diffuse parts to the formation of dense clouds in a continuousway.To do so, I used a time dependent gas-grain model that I significantly contributedto improve for the treatment of the surface chemistry. In a first part, I followed a "classical"approach (i.e. : similar to most of the pre-existing studies) to model cold denseclouds. This allowed me to study in details the physical and the chemical mechanismsresponsible for the chemical complexity of dense clouds and to compare the modelpredictions with the existing literature. In a second part, I applied this model to followthe evolution of the chemical composition during the formation process of denseclouds from the diffuse medium. I used results from an hydrodynamical simulation ofthe interstellar medium at galactic scales. This study allowed me to show that the pastphysical history of each particles that form the dense clouds have a significant impacton their chemical composition
Cold Water Emission Cannot Be Used to Infer Depletion of Bulk Elemental Oxygen [O/H] in Disks
No full textWe reexamine the constraints provided by Herschel Space Observatory data regarding cold water emission from protoplanetary disks. Previous disk models that were used to interpret observed water emission concluded that oxygen (O/H) is depleted by at least 2 orders of magnitude if a standard, interstellar gas/dust mass ratio is assumed in the disk. In this work, we use model results from a recent disk parameter survey and show that most of the Herschel constraints obtained for cold water (i.e., for transitions with an upper energy level E _up < 200 K, where the bulk of the disk water lies) can be explained with disk models adopting interstellar medium-like oxygen elemental abundance (i.e., O/H = 3.2 × 10 ^−4 ) and the canonical gas/dust mass ratio of 100. We show that cold water vapor is mainly formed by photodesorption of water ice at the interface between the molecular layer and the midplane, and that its emission is relatively independent of the main disk properties like the disk gas mass and gas/dust mass ratio. We find that the abundance of water vapor in the outer disk is set by photoprocesses and depends on the (constant) vertical column density of water ice needed to attenuate the far-ultraviolet photon flux, resulting in roughly constant emission for the parameters (gas mass, dust mass, disk radius) varied in our survey. Importantly, water line emission is found to be optically thick and hence sensitive to temperature more than abundance, possibly driving previous inferences of large-scale oxygen depletion
Cold water emission cannot be used to infer depletion of bulk elemental oxygen [O/H] in disks
No full textWe re-examine the constraints provided by Herschel Space Observatory data
regarding cold water emission from protoplanetary disks. Previous disk models
that were used to interpret observed water emission concluded that oxygen (O/H)
is depleted by at least 2 orders of magnitude if a standard, interstellar
gas/dust mass ratio is assumed in the disk. In this work, we use model results
from a recent disk parameter survey and show that most of the \textit{Herschel}
constraints obtained for cold water (i.e. for transitions with an upper energy
level K, where the bulk of the disk water lies) can be
explained with disk models adopting ISM-like oxygen elemental abundance (i.e.
O/H=) and the canonical gas/dust mass ratio of 100. We show
that cold water vapor is mainly formed by photodesorption of water ice at the
interface between the molecular layer and the midplane, and that its emission
is relatively independent of the main disk properties like the disk gas mass
and gas/dust mass ratio. We find that the abundance of water vapor in the outer
disk is set by photoprocesses and depends on the (constant) vertical column
density of water ice needed to attenuate the FUV photon flux, resulting in
roughly constant emission for the parameters (gas mass, dust mass, disk radius)
varied in our survey. Importantly, water line emission is found to be optically
thick and hence sensitive to temperature more than abundance, possibly driving
previous inferences of large scale oxygen depletion.Comment: 17 pages, 9 figures, 1 tabl
Large Myr-old Disks Are Not Severely Depleted of Gas-phase CO or Carbon
No full textWe present an ACA search for [C i] 1-0 emission at 492 GHz toward large T Tauri disks (gas radii ≳ 200 au) in the ∼1-3 Myr-old Lupus star-forming region. Combined with Atacama Large Millimeter/submillimeter Array 12 m archival data for IM Lup, we report [C i] 1-0 detections in six out of 10 sources, thus doubling the known detections toward T Tauri disks. We also identify four Keplerian double-peaked profiles and demonstrate that the [C i] 1-0 fluxes correlate with 13CO, C18O, and 12CO(2-1) fluxes, as well as with the gas disk outer radius measured from the latter transition. These findings are in line with the expectation that atomic carbon traces the disk surface. In addition, we compare the carbon and carbon monoxide (CO) line luminosities of a Lupus and literature sample with [C i] 1-0 detections with predictions from the self-consistent disk thermo-chemical models of Ruaud et al. These models adopt interstellar medium carbon and oxygen elemental abundances as input parameters. With the exception of the disk around Sz 98, we find that these models reproduce all the available line luminosities and upper limits, with gas masses comparable to or higher than the minimum-mass solar nebula and gas-to-dust mass ratios ≥10. Thus, we conclude that the majority of large Myr-old disks conform to the simple expectation that they are not significantly depleted in gas, CO, or carbon. © 2023. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Relationship Marketing in Emerging Economies: Some Lessons for the Future
No full textInternational audienceRelationship marketing as a philosophy and a set of practices is now widely accepted by both academics and practitioners. At the centre of the relationship marketing paradigm is the notion that making the most out of existing clients is essential for long term profitability. Retaining clients by developing relationships with them is crucial to establishing and maintaining a competitive advantage in the market. But, moving away from an analysis of needs to an analysis of the customer, from management of the transaction to management of the relationship, marks a fundamental shift which positions relationship marketing as a double innovation: conceptual innovation (it has evolved into an entirely new and separate concept) and organizational innovation (it imposes transformation on organizations that are not limited to the marketing function but require the participation of all components of the firm). But, perceptions on what exactly constitutes relationship marketing may differ in various cultural settings.Indeed, the theoretical domains that relationship marketing has traditionally drawn upon have been Western theories developed in economics, psychology, and management. Having largely exhausted these sources, it is now perhaps time to look more widely and consider less traditional paradigms from a broader range of cultures. The author suggests looking at Eastern cultures where relationships have provided the foundations for business activity for thousands of years.This article is an initial attempt to bridge the gap in existing literature as no adequate conceptual framework exists as yet. It aims to contribute to the knowledge of the reasons for the emergence of relationship marketing in Western economies and makes a brief comparison of the study of relationships in Western and Eastern literature so as to identify how culturally based relationships are formed. In particular, the focus is on the Chinese complex concept of guanxi (loosely translated as ‘connections’ though ‘relationships’ might be better) and its importance in relationship development. This framework is the starting point for a set of criteria to be taken into account before transferring relationship marketing in emerging economies.In conclusion, this exploratory paper highlights the following: -Theory transgresses economies whether they are emerging or not. -Marketing has always studied relationships between institutions (B2B) and between institutions and customers (B2C). The basic rules of marketing, therefore, remain the same whatever the economy. What changes is the context. -The environment is and remains multi-cultural. In that sense, the dangers of ethnocentrism must be avoided and, on the contrary, the phenomena of acculturation and local appropriation must be embraced. -To be successfully implemented, relationship marketing should reflect the value system of the population to which it is targete
The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO). III. Dust and Gas Disk Properties in the Lupus Star-forming Region
No full textWe present Band 6 and Band 7 observations of 10 Lupus disks around M3-K6 stars from the Atacama Large Millimeter/submillimeter Array survey of Gas Evolution in PROtoplanetary disks (AGE-PRO) Large Program. In addition to continuum emission in both bands, our Band 6 setup covers the 12CO, 13CO, and C18O J = 2–1 lines, while our Band 7 setup covers the N2H+ J = 3–2 line. All of our sources are detected in 12CO and 13CO; seven out of ten are detected in C18O; and three are detected in N2H+. We find strong correlations between the CO isotopologue line fluxes and the continuum flux densities. With the exception of one disk, we also identify a strong correlation between the C18O J = 2–1 and N2H+ J = 3–2 fluxes, indicating similar CO abundances across this sample. For the two sources with well-resolved continuum and 12CO J = 2–1 images, we find that their gas-to-dust size ratio is consistent with the median value of ∼2 inferred from a larger sample of Lupus disks. We derive dust disk masses from continuum flux densities. We estimate gas disk masses by comparing C18O J = 2–1 line fluxes with those predicted by the limited grid of self-consistent disk models of M. Ruaud et al. A comparison of these mass estimates with those derived by L. Trapman et al., using a combination of CO isotopologue and N2H+ line emission, shows that the masses are consistent with each other. Some discrepancies appear for small and faint disks, but they are still within the uncertainties. Both methods find gas disk masses increase with dust disk masses, and gas-to-dust mass ratios are between 10 and 100 in the AGE-PRO Lupus sample
