4,685 research outputs found

    A Mid-Infrared Study of the Class 0 Cluster in LDN 1448

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    We present ground-based mid-infrared observations of Class 0 protostars in LDN 1448. Of the five known protostars in this cloud, we detected two, L1448N:A and L1448C, at 12.5, 17.9, 20.8, and 24.5 microns, and a third, L1448 IRS 2, at 24.5 microns. We present high-resolution images of the detected sources, and photometry or upper limits for all five Class 0 sources in this cloud. With these data, we are able to augment existing spectral energy distributions (SEDs) for all five objects and place them on an evolutionary status diagram.Comment: Accepted by the Astronomical Journal; 26 pages, 9 figure

    Two Bipolar Outflows and Magnetic Fields in a Multiple Protostar System, L1448 IRS 3

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    We performed spectral line observations of CO J=2-1, 13CO J=1-0, and C18O J=1-0 and polarimetric observations in the 1.3 mm continuum and CO J=2-1 toward a multiple protostar system, L1448 IRS 3, in the Perseus molecular complex at a distance of ~250 pc, using the BIMA array. In the 1.3 mm continuum, two sources (IRS 3A and 3B) were clearly detected with estimated envelope masses of 0.21 and 1.15 solar masses, and one source (IRS 3C) was marginally detected with an upper mass limit of 0.03 solar masses. In CO J=2-1, we revealed two outflows originating from IRS 3A and 3B. The masses, mean number densities, momentums, and kinetic energies of outflow lobes were estimated. Based on those estimates and outflow features, we concluded that the two outflows are interacting and that the IRS 3A outflow is nearly perpendicular to the line of sight. In addition, we estimated the velocity, inclination, and opening of the IRS 3B outflow using Bayesian statistics. When the opening angle is ~20 arcdeg, we constrain the velocity to ~45 km/s and the inclination angle to ~57 arcdeg. Linear polarization was detected in both the 1.3 mm continuum and CO J=2-1. The linear polarization in the continuum shows a magnetic field at the central source (IRS 3B) perpendicular to the outflow direction, and the linear polarization in the CO J=2-1 was detected in the outflow regions, parallel or perpendicular to the outflow direction. Moreover, we comprehensively discuss whether the binary system of IRS 3A and 3B is gravitationally bound, based on the velocity differences detected in 13CO J=1-0 and C18O J=1-0 observations and on the outflow features. The specific angular momentum of the system was estimated as ~3e20 cm^2/s, comparable to the values obtained from previous studies on binaries and molecular clouds in Taurus.Comment: ApJ accepted, 20 pages, 2 tables, 10 figure

    Molecules in Bipolar Outflows

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    Bipolar outflows constitute some of the best laboratories to study shock chemistry in the interstellar medium. A number of molecular species have their abundance enhanced by several orders of magnitude in the outflow gas, likely as a combined result of dust mantle disruption and high temperature gas chemistry, and therefore become sensitive indicators of the physical changes taking place in the shock. Identifying these species and understanding their chemical behavior is therefore of high interest both to chemical studies and to our understanding of the star-formation process. Here we review some of the recent progress in the study of the molecular composition of bipolar outflows, with emphasis in the tracers most relevant for shock chemistry. As we discuss, there has been rapid progress both in characterizing the molecular composition of certain outflows as well as in modeling the chemical processes likely involved. However, a number of limitations still affect our understanding of outflow chemistry. These include a very limited statistical approach in the observations and a dependence of the models on plane-parallel shocks, which cannot reproduce the observed wing morphology of the lines. We finish our contribution by discussing the chemistry of the so-called extremely high velocity component, which seems different from the rest of the outflow and may originate in the wind from the very vicinity of the protostar.Comment: 15 pages, 7 figures. Contribution to the IAU Conference "The Molecular Universe" held in Toledo in June 201

    The radio continuum spectrum of Mira A and Mira B up to submillimeter wavelengths

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    We present new measurements of the flux densities at submillimeter wavelengths based on ALMA band 7 (338 GHz) and band 9 (679 GHz) observations to better constrain the origin of the continuum emission of the Mira AB binary system and to check its orbit. We have measured the Mira A and Mira B continuum in ALMA band 7, with a resolution of ~0"31, and for the first time in ALMA band 9, with a resolution of ~0"18. We resolved the binary system at both bands, and derived the continuum spectral index of the stars and their relative position. We also analyzed ALMA SciVer data obtained in bands 6 and 3. Measurements at centimeter wavelengths obtained by other authors have been included in our study of the spectral energy distribution of the Mira components. The Mira A continuum emission has a spectral index of 1.98+-0.04 extending from submillimeter down to centimeter wavelengths. The spectral index of the Mira B continuum emission is 1.93+-0.06 at wavelengths ranging from submillimeter to ~3.1 mm, and a shallower spectral index of 1.22+-0.09 at longer wavelengths. The Mira A continuum emission up to submillimeter wavelengths is consistent with that of a radio photosphere surrounding the evolved star for which models predict a spectral index close to 2. The Mira B continuum emission cannot be described with a single ionized component. An extremely compact and dense region around the star can produce the nearly thermal continuum measured in the 0.4-3.1 mm wavelength range, and an inhomogeneous, less dense, and slightly larger ionized envelope could be responsible for the emission at longer wavelengths. Our results illustrate the potential of ALMA for high precision astrometry of binary systems. We have found a significant discrepancy of ~14 milliarcsec between the ALMA measurements and the predicted orbit positions.Comment: 6 pages, 3 figures, 2 tables, accepted for publication in Astronomy and Astrophysic

    The origin of complex organic molecules in prestellar cores

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    Complex organic molecules (COMs) have been detected in a variety of environments, including cold prestellar cores. Given the low temperature of these objects, these last detections challenge existing models. We report here new observations towards the prestellar core L1544. They are based on an unbiased spectral survey of the 3mm band at the IRAM-30m telescope, as part of the Large Program ASAI. The observations allow us to provide the full census of the oxygen bearing COMs in this source. We detected tricarbon monoxide, methanol, acetaldehyde, formic acid, ketene, and propyne with abundances varying from 5e-11 to 6e-9. The non-LTE analysis of the methanol lines shows that they are likely emitted at the border of the core, at a radius of ~8000 AU where T~10 K and nH2~2e4 cm-3. Previous works have shown that water vapour is enhanced in the same region because of the photodesorption of water ices. We propose that a non-thermal desorption mechanism is also responsible for the observed emission of methanol and COMs from the same layer. The desorbed oxygen and a tiny amount of desorbed methanol and ethene are enough to reproduce the abundances of tricarbon monoxide, methanol, acetaldehyde and ketene measured in L1544. These new findings open the possibility that COMs in prestellar cores originate in a similar outer layer rather than in the dense inner cores, as previously assumed, and that their formation is driven by the non-thermally desorbed species.Comment: Accepted in ApJ

    Star formation in the vicinity of the IC 348 cluster

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    Aims. We present molecular line observations of the southwestern part of the IC 348 young cluster, and we use them together with NIR and mm continuum data to determine the distribution of dense gas, search for molecular outflows, and analyze the ongoing star formation activity in the region. Methods. Our molecular line data consists of C18O(1--0) and N2H+(1--0) maps obtained with the FCRAO telescope at a resolution of about 50'' and CO(2--1) data obtained with the IRAM 30m telescope at a resolution of 11''. Results. The dense gas southwest of IC 348 is concentrated in two groups of dense cores, each of them with a few solar masses of material and indications of CO depletion at high density. One of the core groups is actively forming stars, while the other seems starless. There is evidence for at least three bipolar molecular outflows in the region, two of them powered by previously identified Class 0 sources, while the other one is powered by a still not well characterized low-luminosity object. The ongoing star formation activity is producing a small stellar subgroup in the cluster. Using the observed core characteristics and the star formation rate in the cluster we propose that that similar episodes of stellar birth may have produced the subclustering observed in the halo of IC 348.Comment: 10 pages, 6 figures, A&A accepte

    First evidence for molecular interfaces between outflows and ambient clouds in high-mass star-forming regions?

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    We present new observations of the Cep A East region of massive star formation and describe an extended and dynamically distinct feature not previously recognized. This feature is present in emission from H2CS, OCS, CH3OH, and HDO at −5.5 km s−1 but is not traced by the conventional tracers of star-forming regions, H2S, SO2, SO, and CS. The feature is extended up to at least 0.1 pc. We show that the feature is neither a hot core nor a shocked outflow. However, the chemistry of the feature is consistent with predictions from a model of an eroding interface between a fast wind and a dense core; mixing between the two media occurs in the interface on a timescale of 10–50 yr. If these observations are confirmed by detailed maps and by detections in species also predicted to be abundant (e.g., HCO+, H2CO, and NH3), this feature would be the first detection of such an interface in regions of massive star formation. An important implication of the model is that a significant reservoir of sulfur in grain mantles is required to be in the form of OCS
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