Browsing by Author "Artur de la Villarmois, Elizabeth"

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    A chemical survey of the proto-stellar system IRAS 16253-2429
    (2023) Castillo Lara, Jaime; Guzmán Veloso, Viviana; Artur de la Villarmois, Elizabeth; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
    Presentamos un estudio químico de IRAS 16253-2429 (de aquí en adelante IRAS 16253), una proto-estrella de Clase 0 y de baja masa clasificada como un very low luminosity object (VeLLO) y localizada en el complejo de formación estelar ρ Ophiucus. Las moléculas CN, c-C3H2, y H2CO son detectadas por primera vez en IRAS 16253. H2CO se muestra compacta y simétrica en la región central, que incluye el disco y el envoltorio interior. c-C3H2 y CN también se presentan en la región central, pero con una emisión asimétrica y más extendida. También presentamos observaciones previas de 13CO, C17O, C18O, SO, CO, C2H y N2H+, con detecciones tentativas de DCO+ y N2D+. C2H se presenta en las paredes de la cavidad, en ambas direcciones de la ejección de gas, pero principalmente en la dirección norte. 13CO está presente en la región central y en la cavidad sur, C18O muestra una emisión compacta y simétrica, CO traza ambas direcciones de la ejección de gas, SO y C17O están centradas pero extendidas y asimétricas, y N2H+ está presente en el envoltorio exterior. A través de un diagrama rotacional para H2CO, estimamos una temperatura rotacional de ∼ 9.3K para la molecula. Esta baja temperatura rotacional sugiere un régimen sub-termal para H2CO, lo que a su vez implica que H2CO está presente sólo en el envoltorio interno, y no en el disco. A través de un ajuste de estructura hiperfina para N2H+, se estima una temperatura de excitación de ∼ 4 K para la molécula, esta baja temperatura de excitación también sugiere un régimen sub-termal, consistente con las bajas densidades del envoltorio exterior. Comparamos nuestros resultados con otros estudios de otras fuentes de Clase 0, pero más masivas. Encontramos que, en contra de nuestras expectativas, los trazadores de gas frío DCO+, N2H+ y N2D+ no son más abundantes en este VeLLO en comparación a otras proto-estrellas más masivas. Nuestros resultados sugieren que la química de IRAS 16253 es una versión a menor escala de la química encontrada en fuentes de Clase 0 más masivas.
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    Radial and Vertical Constraints on the Icy Origin of H2CO in the HD 163296 Protoplanetary Disk
    (2024) Hernandez-Vera, Claudio; Guzman, Viviana V.; Artur de la Villarmois, Elizabeth; OEberg, Karin I.; Cleeves, L. Ilsedore; Hogerheijde, Michiel R.; Qi, Chunhua; Carpenter, John; Fayolle, Edith C.
    H2CO is a small organic molecule widely detected in protoplanetary disks. As a precursor to grain-surface formation of CH3OH, H2CO is considered an important precursor of O-bearing organic molecules that are locked in ices. Still, since gas-phase reactions can also form H2CO, there remains an open question on the channels by which organics form in disks, and how much the grain versus the gas pathways impact the overall organic reservoir. We present spectrally and spatially resolved Atacama Large Millimeter/submillimeter Array observations of several ortho- and para-H2CO transitions toward the bright protoplanetary disk around the Herbig Ae star HD 163296. We derive column density, excitation temperature, and ortho-to-para ratio (OPR) radial profiles for H2CO, as well as disk-averaged values of N-T similar to 4 x 10(12) cm(-2), T-ex similar to 20 K, and OPR similar to 2.7, respectively. We empirically determine the vertical structure of the emission, finding vertical heights of z/r similar to 0.1. From the profiles, we find a relatively constant OPR similar to 2.7 with radius, but still consistent with 3.0 among the uncertainties, a secondary increase of N-T in the outer disk, and low T-ex values that decrease with disk radius. Our resulting radial, vertical, and OPR constraints suggest an increased UV penetration beyond the dust millimeter edge, consistent with an icy origin but also with cold gas-phase chemistry. This Herbig disk contrasts previous results for the T Tauri disk, TW Hya, which had a larger contribution from cold gas-phase chemistry. More observations of other sources are needed to disentangle the dominant formation pathway of H2CO in protoplanetary disks.
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    The Perseus ALMA Chemical Survey (PEACHES) III. Sulfur-bearing species tracing accretion and ejection processes in young protostars
    (EDP Sciences S A, 2023) Artur de la Villarmois, Elizabeth; Guzmán Veloso, Viviana; Yang, Y. -l.; Zhang, Y.; Sakai, N.
    Context. Sulfur chemistry is poorly understood in the process of low-mass star and planet formation, where the main carriers of sulfur in both the gas and the dust phase are still unknown. Furthermore, the chemical evolution of sulfur-bearing species is not fully understood given that simple S-bearing molecules, such as SO and SO2, are commonly seen in embedded Class 0/I sources but hardly detected in more evolved Class II disks. Despite the fact that simple S-bearing molecules are usually detected toward embedded sources, large surveys of S-bearing molecules with high angular resolution and sensitive observations are currently lacking., Aims. The goal of this work is to present an unbiased survey of simple sulfur-bearing species in protostars and provide new statistics on detection rates, emitting regions, and molecular column densities. In addition, we investigate the role of S-bearing molecules in accretion processes and the connection between (non-)detection of complex organic molecules (COMs) and S-related species., Methods. We present the observations of sulfur-bearing species (CS, SO,(SO)-S-34, and SO2) that are part of the Perseus ALMA Chemical Survey (PEACHES). We analyzed a total of 50 Class 0/I sources with observations that have an average angular resolution of about 0.'' 6 (similar to 180 au) in ALMA band 6., Results. Class 0 sources show detection rates of 97% for CS, 86% for SO, 31% for(34)SO, and 44% for SO2, while Class I sources present detection rates of 71% for CS, 57% for SO, 36% for (SO)-S-34, and 43% for SO2. When (SO)-S-34 is detected, the SO/(SO)-S-34 ratio is lower than the canonical value of 22, suggesting optically thick emission, and the lowest values are found for those sources that are rich in COMs. When SO2 is detected, those sources that show CS and SO emission parallel to the outflow direction are usually very rich in COMs, while for sources where the CS and SO emission is perpendicular to the outflow direction, only a few or no COMs are detected. When CH3OH and SO2 are detected, the comparison between CH3OH and SO2 abundances shows a positive trend and CH3OH is between 10 and 100 times more abundant than SO2. The SO2 abundances toward the PEACHES sample are, on average, two orders of magnitude lower than values from the Ophiuchus star-forming region and comparable with sources in Taurus., Conclusions. The SO/(SO)-S-34 ratio seems to be a good tracer of the inner high-density envelope and it could be used in the future to infer the presence of multiple COMs. The detection of multiple COMs seems to be related to the presence of collimated outflows (seen in CS and SO emission), where a high column density of warm material is expected close to the protostar, and SO2 emission seems to trace the warm gas in those sources where CH3OH is also detected. The difference in SO2 abundances between different star-forming regions might indicate that the sulfur depletion in the gas-phase could depend on the external UV radiation toward the molecular cloud. Finally, the SO2 emission detected in different evolutionary stages seems to arise from different physical mechanisms: high column density of warm material in Class 0 sources, shocks in Class I/II, and exposure to UV radiation from the protostar in more evolved Class II disks.
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    Water masers in the ALMA era: an excellent tool to study star formation at sub-arcsecond spatial scales
    (2023) de Gregorio-Monsalvo, Itziar; Gil Toriello, Santiago; Santamaría Miranda, Alejandro; Gómez, José Francisco; Pérez Sánchez, Andrés Felipe; Plunkett, Adele; Artur de la Villarmois, Elizabeth; Guzmán Veloso, Viviana Gabriela; Schreiber, Matthias R.
    The water molecule is one of the most common compounds in the Universe and it exhibits several maser transitions at submillimeter wavelengths, which can be observed at ALMA. Previous studies have primarily focused on water masers at 22 GHz, which are excited in regions of high density and high temperature. These masers are typically very bright, spectrally narrow, and originate from very compact regions. Consequently, they have been invaluable for studying circumstellar structure and dynamics at sub-arcsecond spatial scales. Different water maser transitions can be pumped over a range of astrophysical conditions. The submillimeter transitions at 321 GHz and 325 GHz, in particular, trace respectively warmer and lower density regions than the 22 GHz transition. They have been identified as tracers of mass-loss phenomena in a limited number of star-forming regions. Conversely, transitions such as the one at 183 GHz, which primarily undergo collisional pumping, can provide valuable insights on the physical conditions of the region where powerful molecular outflows interact with the material from the parental cloud. Observations of different water maser lines need to be used to constrain the physical conditions in the masing region and they constitute excellent tools to study common phenomena associated with the star formation process at sub-arcsecond resolution, if observed with interferometers like ALMA. In this poster we present the results of a survey searching for submillimeter water maser transitions at 321 and 325 GHz complemented with ALMA data at 183 GHz on a sample of young stellar objects spanning a wide range of masses, from high to low-mass.