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تسجيل مستخدم جديدThe young protostellar disk in IRAS16293-2422 B is hot and shows signatures of gravitational instability
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Deeply embedded protostars are actively fed from their surrounding envelopes through their protostellar disk. The physical structure of such early disks might be different from that of more evolved sources due to the active accretion. We present 1.3 and 3,mm ALMA continuum observations at resolutions of 6.5,au and 12,au respectively, towards the Class 0 source IRAS 16293-2422 B. The resolved brightness temperatures appear remarkably high, with $T_{rm b} >$ 100,K within $sim$30,au and $T_{rm b}$ peak over 400,K at 3,mm. Both wavelengths show a lopsided emission with a spectral index reaching values less than 2 in the central $sim$ 20,au region. We compare these observations with a series of radiative transfer calculations and synthetic observations of magnetohydrodynamic and radiation hydrodynamic protostellar disk models formed after the collapse of a dense core. Based on our results, we argue that the gas kinematics within the disk may play a more significant role in heating the disk than the protostellar radiation. In particular, our radiation hydrodynamic simulation of disk formation, including heating sources associated with gravitational instabilities, is able to generate the temperatures necessary to explain the high fluxes observed in IRAS 16293B. Besides, the low spectral index values are naturally reproduced by the high optical depth and high inner temperatures of the protostellar disk models. The high temperatures in IRAS 16293B imply that volatile species are mostly in the gas phase, suggesting that a self-gravitating disk could be at the origin of a hot corino.
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While recent studies of the solar-mass protostar IRAS16293-2422 have focused on its inner arcsecond, the wealth of Herschel/HIFI data has shown that the structure of the outer envelope and of the transition region to the more diffuse ISM is not clear
ly constrained. We use rotational ground-state transitions of CH (methylidyne), as a tracer of the lower-density envelope. Assuming LTE, we perform a $chi^2$ minimization of the high spectral resolution HIFI observations of the CH transitions at ~532 and ~536 GHz in order to derive column densities in the envelope and in the foreground cloud. We obtain column densities of (7.7$pm$0.2)$times10^{13}$ cm$^{-2}$ and (1.5$pm$0.3)$times10^{13}$ cm$^{-2}$, respectively. The chemical modeling predicts column densities of (0.5-2)$times10^{13}$ cm$^{-2}$ in the envelope (depending on the cosmic-ray ionization rate), and 5$times10^{11}$ to 2.5$times10^{14}$ cm$^{-2}$ in the foreground cloud (depending on time). Both observed abundances are reproduced by the model at a satisfactory level. The constraints set by these observations on the physical conditions in the foreground cloud are however weak. Furthermore, the CH abundance in the envelope is strongly affected by the rate coefficient of the reaction H+CH$rightarrow$C+H$_2$ ; further investigation of its value at low temperature would be necessary to facilitate the comparison between the model and the observations.
We have observed the Class 0 protostellar source IRAS 16293-2422 A in the C17O and H2CS lines as well as the 1.3 mm dust continuum with the Atacama Large Millimeter/submillimeter Array at an angular resolution of ~0.1 (14 au). The continuum emission
of the binary component, Source A, reveals the substructure consisting of 5 intensity peaks within 100 au from the protostar. The C17O emission mainly traces the circummultiple structure on a 300 au scale centered at the intensity centroid of the continuum, while it is very weak within the radius of 50 au from the centroid. The H2CS emission, in contrast, traces the rotating disk structure around one of the continuum peaks (A1). Thus, it seems that the rotation centroid of the circummultiple structure is slightly different from that of the disk around A1. We derive the rotation temperature by using the multiple lines of H2CS. As approaching to the protostar A1, the rotation temperature steeply rises up to 300 K or higher at the radius of 50 au from the protostar. It is likely due to a local accretion shock and/or the preferential protostellar heating of the transition zone from the circummultiple structure to the disk around A1. This position corresponds to the place where the organic molecular lines are reported to be enhanced. Since the rise of the rotation temperature of H2CS most likely represents the rise of the gas and dust temperatures, it would be related to the chemical characteristics of this prototypical hot corino.
We present ALMA observations of organic molecules towards five low-mass Class 0/I protostellar disk candidates in the Serpens cluster. Three sources (Ser-emb 1, Ser-emb 8, and Ser-emb 17) present emission of CH3OH as well as CH3OCH3, CH3OCHO, and CH2
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We present 3 mm ALMA continuum and line observations at resolutions of 6.5 au and 13 au respectively, toward the Class 0 system IRAS 16293-2422 A. The continuum observations reveal two compact sources towards IRAS 16293-2422 A, coinciding with compac
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