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Search Results: 1 - 10 of 400750 matches for " Tafalla M. "
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Dense core formation by fragmentation of velocity-coherent filaments in L1517
A. Hacar,M. Tafalla
Physics , 2011, DOI: 10.1051/0004-6361/201117039
Abstract: Context. Low-mass star-forming cores differ from their surrounding molecular cloud in turbulence, shape, and density structure. Aims. We aim to understand how dense cores form out of the less dense cloud material by studying the connection between these two regimes. Methods. We observed the L1517 dark cloud in C18O(1-0), N2H+(1-0), and SO(JN=32-21) with the FCRAO 14m telescope, and in the 1.2mm dust continuum with the IRAM 30m telescope. Results. Most of the gas in the cloud lies in four filaments that have typical lengths of 0.5 pc. Five starless cores are embedded in these filaments and have chemical compositions indicative of different evolutionary stages. The filaments have radial profiles of C18O(1-0) emission with a central flattened region and a power-law tail, and can be fitted approximately as isothermal, pressure-supported cylinders. The filaments, in addition, are extremely quiescent. They have subsonic internal motions and are coherent in velocity over their whole length. The large-scale motions in the filaments can be used to predict the velocity inside the cores, indicating that core formation has not decoupled the dense gas kinematically from its parental material. In two filaments, these large-scale motions consist of oscillations in the velocity centroid, and a simple kinematic model suggests that they may be related to core-forming flows. Conclusions. Core formation in L1517 seems to have occurred in two steps. First, the subsonic, velocity-coherent filaments have condensed out of the more turbulent ambient cloud. Then, the cores fragmented quasi-statically and inherited the kinematics of the filaments. Turbulence dissipation has therefore occurred mostly on scales on the order of 0.5 pc or larger, and seems to have played a small role in the formation of the individual cores.
Chains of dense cores in the Taurus L1495/B213 complex
M. Tafalla,A. Hacar
Physics , 2014, DOI: 10.1051/0004-6361/201424576
Abstract: (Abridged) We study the kinematics of the dense gas in the Taurus L1495/B213 filamentary region to investigate the mechanism of core formation. We use observations of N2H+(1-0) and C18O(2-1) carried out with the IRAM 30m telescope. We find that the dense cores in L1495/B213 are significantly clustered in linear chain-like groups about 0.5pc long. The internal motions in these chains are mostly subsonic and the velocity is continuous, indicating that turbulence dissipation in the cloud has occurred at the scale of the chains and not at the smaller scale of the individual cores. The chains also present an approximately constant abundance of N2H+ and radial intensity profiles that can be modeled with a density law that follows a softened power law. A simple analysis of the spacing between the cores using an isothermal cylinder model indicates that the cores have likely formed by gravitational fragmentation of velocity-coherent filaments. Combining our analysis of the cores with our previous study of the large-scale C18O emission from the cloud, we propose a two-step scenario of core formation in L1495/B213. In this scenario, named "fray and fragment," L1495/B213 originated from the supersonic collision of two flows. The collision produced a network of intertwined subsonic filaments or fibers ("fray" step). Some of these fibers accumulated enough mass to become gravitationally unstable and fragment into chains of closely-spaced cores. This scenario may also apply to other regions of star formation.
HH 114 MMS: a new chemically active outflow
M. Tafalla,A. Hacar
Physics , 2013, DOI: 10.1051/0004-6361/201321303
Abstract: Context. A small group of bipolar protostellar outflows display strong emission from shock-tracer molecules such as SiO and CH3OH, and are generally referred to as "chemically active." The best-studied outflow from this group is the one in L 1157. Aims. We study the molecular emission from the bipolar outflow powered by the very young stellar object HH 114 MMS and compare its chemical composition with that of the L1157 outflow. Methods. We have used the IRAM 30m radio telescope to observe a number of transitions from CO, SiO, CH3OH, SO, CS, HCN, and HCO+ toward the HH 114 MMS outflow. The observations consist of maps and a two-position molecular survey. Results. The HH 114 MMS outflow presents strong emission from a number of shock-tracer molecules that dominate the appearance of the maps around the central source. The abundance of these molecules is comparable to the abundance in L 1157. Conclusions. The outflow from HH 114 MMS is a spectacular new case of a chemically active outflow.
Dust emission from young outflows: the case of L1157
F. Gueth,R. Bachiller,M. Tafalla
Physics , 2003, DOI: 10.1051/0004-6361:20030259
Abstract: We present new high-sensitivity 1.3 mm bolometer observations of the young outflow L1157. These data show that the continuum emission arises from four distinct components: a circumstellar disk, a protostellar envelope, an extended flattened envelope --the dense remnant of the molecular cloud in which the protostar was formed--, and the outflow itself, which represents ~20% of the total flux. The outflow emission exhibits two peaks that are coincident with the two strong shocks in the southern lobe of L1157. We show that the mm continuum is dominated by thermal dust emission arising in the high velocity material. The spectral index derived from the new 1.3 mm data and 850 mu observations from Shirley et al. (2000), is ~5 in the outflow, significantly higher than in the protostellar envelope (~3.5). This can be explained by an important line contamination of the 850 mu map, and/or by different dust characteristics in the two regions, possibly smaller grains in the post-shocks regions of the outflow. Our observations show that bipolar outflows can present compact emission peaks which must not be misinterpreted as protostellar condensations when mapping star forming regions.
Chemical modeling of the L1498 and L1517B prestellar cores: CO and HCO+ depletion
S. Maret,E. A Bergin,M. Tafalla
Physics , 2013, DOI: 10.1051/0004-6361/201322089
Abstract: Prestellar cores exhibit a strong chemical differentiation, which is mainly caused by the freeze-out of molecules onto the grain surfaces. Understanding this chemical structure is important, because molecular lines are often used as probes to constrain the core physical properties. Here we present new observations and analysis of the C18O (1-0) and H13CO+ (1-0) line emission in the L1498 and L1517B prestellar cores, located in the Taurus-Auriga molecular complex. We model these observations with a detailed chemistry network coupled to a radiative transfer code. Our model successfully reproduces the observed C18O (1-0) emission for a chemical age of a few 10^5 years. On the other hand, the observed H13CO+ (1-0) is reproduced only if cosmic-ray desorption by secondary photons is included, and if the grains have grown to a bigger size than average ISM grains in the core interior. This grain growth is consistent with the infrared scattered light ("coreshine") detected in these two objects, and is found to increase the CO abundance in the core interior by about a factor four. According to our model, CO is depleted by about 2-3 orders of magnitude in the core center.
El coste de la diabetes tipo 2 en Espa?a: El estudio CODE-2
Mata,M.; Anto?anzas,F.; Tafalla,M.; Sanz,P.;
Gaceta Sanitaria , 2002, DOI: 10.1590/S0213-91112002000600009
Abstract: objective: to estimate the cost of providing health care to patients with type 2 diabetes, by differentiating costs of the disease, costs of complications, and other unrelated health costs. methods: data on resource use were retrospectively collected from medical records and personal interviews in 29 primary health care centers in spain. patients were randomly selected from each center's diabetes registry. results: we evaluated 1004 patients (561 women) with a mean age of 67.42 years and a mean disease duration of 10.07 years. a total of 50.9% had no complications, 17.7% had macrovascular complications only, 19.5% had microvascular complications only and 11.9% presented both types of complication. the annual health cost per patient was 1305.15 euros. of this cost, 28.6% (373.27 euros) was directly related to diabetes control, 30.51% (398.20 euros) was related to complications of the disease, and 40.89% (533.68 euros) was unrelated. the mean cost of patients with no complications was 883 euros compared with 1403 euros for those with microvascular complications, 2022 euros for those with macrovascular complications and 2133 euros for patients with both types of complication. conclusions: because of the high cost of treating type 2 diabetes and its complications, preventive measures should be implemented and control of the disease should be improved to reduce the costs associated with chronic complications.
El coste de la diabetes tipo 2 en Espa a: El estudio CODE-2
Mata M.,Anto?anzas F.,Tafalla M.,Sanz P.
Gaceta Sanitaria , 2002,
Abstract: Objetivo: Estimar el coste de la atención sanitaria al paciente diabético tipo 2, diferenciando el gasto derivado del control de la enfermedad, de la atención de sus complicaciones y de otros costes directos asociados. Métodos: Recogida retrospectiva del consumo de recursos a partir de la historia clínica y la entrevista personal en 29 centros de atención primaria de todo el territorio nacional de una muestra de pacientes seleccionados de forma aleatoria a partir del registro de diabéticos de cada centro. Resultados: Se evaluó a 1.004 pacientes (561 mujeres) con una media de edad de 67,42 a os y una media de evolución de la enfermedad de 10,07 a os. El 50,9% no presentaba complicaciones, el 17,7% sólo macrovasculares, el 19,5% sólo microvasculares y el 11,9% ambas. El coste anual sanitario por paciente fue de 1.305,15 euros. De este coste el 28,6% (373,27 euros) estaba relacionado directamente con el control de la diabetes, el 30,51% (398,20 euros) con sus complicaciones y el 40,89% (533,68 euros) no estaba relacionado. El coste medio de un paciente sin complicaciones fue de 883 euros frente a 1.403 de un paciente con complicaciones microvasculares, 2.022 cuando existían complicaciones macrovasculares y 2.133 cuando coexistían ambos tipos de complicaciones. Conclusiones: El elevado coste del tratamiento de la diabetes tipo 2 y sus complicaciones, sugiere la posibilidad de que la mejora del control de la enfermedad pueda no sólo mejorar la supervivencia y la calidad de vida, sino reducir los costes asociados con las complicaciones crónicas.
L483: A Protostar In Transition From Class 0 to Class I
M. Tafalla,P. C. Myers,D. Mardones,R. Bachiller
Physics , 2000,
Abstract: We present molecular-line observations toward the dense core in L483 and its bipolar outflow powered by the Class 0 object IRAS 18148-0440. CO (carbon monoxide) maps show that the outflow is well collimated and asymmetric, and that its gas is warmer than the surrounding cloud by at least a factor of 2. H2CO (formaldehyde) lines toward the outflow show prominent high-velocity wings and evidence for an H2CO abundance enhancement of a factor of 20. At ambient velocities, these lines show strong self-absorption and a brighter blue peak, a characteristic signature of inward motions. Finally, and in contrast with the outflows from other Class 0 objects, the CH3OH (methanol) lines in L483 do not show high velocity wings, and no evidence for abundance enhancement is found in this molecule or in SiO (silicon monoxide). Comparing the physical and chemical properties of the outflow in L483 with those of other outflows from Class 0 and Class I sources, we find that the L483 outflow is somewhat intermediate between these types. This suggests that the L483 central source has already started its transition between Class 0 and Class I, and that its mixed properties illustrate how this transition occurs.
The origin of the HH7-11 outflow
R. Bachiller,F. Gueth,S. Guilloteau,M. Tafalla,A. Dutrey
Physics , 2000,
Abstract: New, high-sensitivity interferometric CO J=2-1 observations of the HH 7-11 outflow show that despite previous doubts, this system is powered by the Class I source SVS 13. The molecular outflow from SVS 13 is formed by a shell with a large opening angle at the base, which is typical of outflows from Class I sources, but it also contains an extremely-high-velocity jet composed of ``molecular bullets'', which is more typical of Class 0 outflows. This suggests that SVS 13 could be a very young Class I, which still keeps some features of the previous evolutionary stage. We briefly discuss the nature of some sources in the SVS 13 vicinity which are emitters of cm-wave continuum, but have no counterpart at mm wavelengths.
A molecular survey of outflow gas: velocity-dependent shock chemistry and the peculiar composition of the EHV gas
M. Tafalla,J. Santiago-Garcia,A. Hacar,R. Bachiller
Physics , 2010, DOI: 10.1051/0004-6361/201015158
Abstract: (Abridged) We present a molecular survey of the outflows powered by L1448-mm and IRAS 04166+2706, two sources with prominent wing and extremely high velocity (EHV) components in their CO spectra. The molecular composition of the two outflows presents systematic changes with velocity that we analyze by dividing the outflow in three chemical regimes, two of them associated with the wing component and the other the EHV gas. The analysis of the two wing regimes shows that species like H2CO and CH3OH favor the low-velocity gas, while SiO and HCN are more abundant in the fastest gas. We also find that the EHV regime is relatively rich in O-bearing species, as is not only detected in CO and SiO (already reported elsewhere), but also in SO, CH3OH, and H2CO (newly reported here), with a tentative detection in HCO+. At the same time, the EHV regime is relatively poor in C-bearing molecules like CS and HCN. We suggest that this difference in composition arises from a lower C/O ratio in the EHV gas. The different chemical compositions of the wing and EHV regimes suggest that these two outflow components have different physical origins. The wing component is better explained by shocked ambient gas, although none of the existing shock models explains all observed features. The peculiar composition of the EHV gas may reflect its origin as a dense wind from the protostar or its surrounding disk.
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