| 1. |
- André, Ph., et al.
(författare)
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Probing the cold magnetised Universe with SPICA-POL (B-BOP)
- 2019
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Ingår i: Publications Astronomical Society of Australia. - : Cambridge University Press (CUP). - 1323-3580 .- 1448-6083. ; 36
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Forskningsöversikt (refereegranskat)abstract
- Space Infrared Telescope for Cosmology and Astrophysics (SPICA), the cryogenic infrared space telescope recently pre-selected for a 'Phase A' concept study as one of the three remaining candidates for European Space Agency (ESA's) fifth medium class (M5) mission, is foreseen to include a far-infrared polarimetric imager [SPICA-POL, now called B-fields with BOlometers and Polarizers (B-BOP)], which would offer a unique opportunity to resolve major issues in our understanding of the nearby, cold magnetised Universe. This paper presents an overview of the main science drivers for B-BOP, including high dynamic range polarimetric imaging of the cold interstellar medium (ISM) in both our Milky Way and nearby galaxies. Thanks to a cooled telescope, B-BOP will deliver wide-field 100-350 mu m images of linearly polarised dust emission in Stokes Q and U with a resolution, signal-to-noise ratio, and both intensity and spatial dynamic ranges comparable to those achieved by Herschel images of the cold ISM in total intensity (Stokes I). The B-BOP 200 mu m images will also have a factor similar to 30 higher resolution than Planck polarisation data. This will make B-BOP a unique tool for characterising the statistical properties of the magnetised ISM and probing the role of magnetic fields in the formation and evolution of the interstellar web of dusty molecular filaments giving birth to most stars in our Galaxy. B-BOP will also be a powerful instrument for studying the magnetism of nearby galaxies and testing Galactic dynamo models, constraining the physics of dust grain alignment, informing the problem of the interaction of cosmic rays with molecular clouds, tracing magnetic fields in the inner layers of protoplanetary disks, and monitoring accretion bursts in embedded protostars.
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| 2. |
- Heald, G., et al.
(författare)
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Magnetism science with the square kilometre array
- 2020
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Ingår i: Galaxies. - : MDPI AG. - 2075-4434. ; 8:8
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Tidskriftsartikel (refereegranskat)abstract
- The Square Kilometre Array (SKA) will answer fundamental questions about the origin, evolution, properties, and influence of magnetic fields throughout the Universe. Magnetic fields can illuminate and influence phenomena as diverse as star formation, galactic dynamics, fast radio bursts, active galactic nuclei, large-scale structure, and dark matter annihilation. Preparations for the SKA are swiftly continuing worldwide, and the community is making tremendous observational progress in the field of cosmic magnetism using data from a powerful international suite of SKA pathfinder and precursor telescopes. In this contribution, we revisit community plans for magnetism research using the SKA, in light of these recent rapid developments. We focus in particular on the impact that new radio telescope instrumentation is generating, thus advancing our understanding of key SKA magnetism science areas, as well as the new techniques that are required for processing and interpreting the data. We discuss these recent developments in the context of the ultimate scientific goals for the SKA era.
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| 3. |
- Gomez, J. F., et al.
(författare)
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An SiO Toroid and Wide-angle Outflow Associated with the Massive Protostar W75N(B)-VLA2
- 2023
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Ingår i: Astrophysical Journal Letters. - 2041-8213 .- 2041-8205. ; 956:2
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Tidskriftsartikel (refereegranskat)abstract
- We have carried out Atacama Large Millimeter/submillimeter Array observations of the massive star-forming region W75N(B), which contains the massive protostars VLA1, VLA2, and VLA3. Particularly, VLA2 is an enigmatic protostar associated with a wind-driven H2O maser shell, which has evolved from an almost isotropic outflow to a collimated one in just 20 yr. The shell expansion seemed to be halted by an obstacle located to the northeast of VLA2. Here we present our findings from observing the 1.3 mm continuum and H2CO and SiO emission lines. Within a region of ∼30″ (∼39,000 au) diameter, we have detected 40 compact millimeter continuum sources, three of them coinciding with VLA1, VLA2, and VLA3. While the H2CO emission is mainly distributed in a fragmented structure around the three massive protostars, but without any of the main H2CO clumps spatially coinciding with them, the SiO is highly concentrated on VLA2, indicating the presence of very strong shocks generated near this protostar. The SiO emission is clearly resolved into an elongated structure (∼0.″6 × 0.″3; ∼780 au×390 au) perpendicular to the major axis of the wind-driven maser shell. The structure and kinematics of the SiO emission are consistent with a toroid and a wide-angle outflow surrounding a central mass of ∼10 M ⊙, thus supporting previous theoretical predictions regarding the evolution of the outflow. Additionally, we have identified the expected location and estimated the gas density of the obstacle that is hindering the expansion of the maser shell.
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| 4. |
- Dall` Olio, Daria, 1981, et al.
(författare)
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ALMA reveals the magnetic field evolution in the high-mass star forming complex G9.62+0.19
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 626
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Tidskriftsartikel (refereegranskat)abstract
- Context. The role of magnetic fields during the formation of high-mass stars is not yet fully understood, and the processes related to the early fragmentation and collapse are as yet largely unexplored. The high-mass star forming region G9.62+0.19 is a well known source, presenting several cores at different evolutionary stages. Aims. We seek to investigate the magnetic field properties at the initial stages of massive star formation. We aim to determine the magnetic field morphology and strength in the high-mass star forming region G9.62+0.19 to investigate its relation to the evolutionary sequence of the cores. Methods. We made use of Atacama Large Millimeter Array (ALMA) observations in full polarisation mode at 1 mm wavelength (Band 7) and we analysed the polarised dust emission. We estimated the magnetic field strength via the Davis-Chandrasekhar-Fermi and structure function methods. Results. We resolve several protostellar cores embedded in a bright and dusty filamentary structure. The polarised emission is clearly detected in six regions: two in the northern field and four in the southern field. Moreover the magnetic field is orientated along the filament and appears perpendicular to the direction of the outflows. The polarisation vectors present ordered patterns and the cores showing polarised emission are less fragmented. We suggest an evolutionary sequence of the magnetic field, and the less evolved hot core exhibits a stronger magnetic field than the more evolved hot core. An average magnetic field strength of the order of 11 mG was derived, from which we obtain a low turbulent-to-magnetic energy ratio, indicating that turbulence does not significantly contribute to the stability of the clump. We report a detection of linear polarisation from thermal line emission, probably from methanol or carbon dioxide, and we tentatively compared linear polarisation vectors from our observations with previous linearly polarised OH masers observations. We also compute the spectral index, column density, and mass for some of the cores. Conclusions. The high magnetic field strength and smooth polarised emission indicate that the magnetic field could play an important role in the fragmentation and the collapse process in the star forming region G9.62+019 and that the evolution of the cores can be magnetically regulated. One core shows a very peculiar pattern in the polarisation vectors, which can indicate a compressed magnetic field. On average, the magnetic field derived by the linear polarised emission from dust, thermal lines, and masers is pointing in the same direction and has consistent strength.
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| 5. |
- Padovani, M., et al.
(författare)
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Adaptable radiative transfer innovations for submillimetre telescopes (ARTIST) Dust polarisation module (DustPol)
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 543, s. Article Number: A16 -
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Tidskriftsartikel (refereegranskat)abstract
- We present a new publicly available tool (DustPol) aimed to model the polarised thermal dust emission. The module DustPol, which is publicly available, is part of the ARTIST (Adaptable Radiative Transfer Innovations for Submillimetre Telescopes) package, which also offers tools for modelling the polarisation of line emission together with a model library and a Python-based user interface. DustPol can easily manage analytical as well as pre-gridded models to generate synthetic maps of the Stokes I, Q, and U parameters. These maps are stored in FITS format which is straightforwardly read by the data reduction software used, e. g., by the Atacama Large Millimeter Array (ALMA). This turns DustPol into a powerful engine for the prediction of the expected polarisation features of a source observed with ALMA or the Planck satellite as well as for the interpretation of existing submillimetre observations obtained with other telescopes. DustPol allows the parameterisation of the maximum degree of polarisation and we find that, in a prestellar core, if there is depolarisation, this effect should happen at densities of 10(6) cm(-3) or larger. We compare a model generated by DustPol with the observational polarisation data of the low-mass Class 0 object NGC 1333 IRAS 4A, finding that the total and the polarised emission are consistent.
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| 6. |
- Alves, F. O., et al.
(författare)
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The magnetic field of IRAS 16293-2422 as traced by shock-induced H2O masers
- 2012
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Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 8:5287, s. 74-78
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Konferensbidrag (refereegranskat)abstract
- H2O masers are important magnetic field tracers in very high density gas. We show one of the first magnetic field determinations at such high density in a low-mass protostar: IRAS 16293-2422. We used the Very Large Array (VLA) to carry out spectro-polarimetric observations of the 22 GHz Zeeman emission of H2O masers. A blend of at least three maser features can be inferred from our data. They are excited in zones of compressed gas produced by shocks between the outflows ejected by this source and the ambient gas. The post-shock particle density is in the range 1 - 3 × 109 cmt−3, and the line-of-sight component of the magnetic field is estimated as ~ 113 mG. The outflow dynamics is likely magnetically dominated.
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| 7. |
- Alves, F. O., et al.
(författare)
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The magnetic field of IRAS 16293-2422 as traced by shock-induced H2O masers
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 542
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Tidskriftsartikel (refereegranskat)abstract
- Context. Shock-induced H2O masers are important magnetic field tracers of very high density gas. Water masers are found in both high-and low-mass star-forming regions, and are a powerful tool for comparing magnetic field morphologies in both mass regimes. Aims. We present one of the first magnetic field determinations for the low-mass protostellar core IRAS 16293-2422 at volume densities as high as 10(8-10) cm(-3). Our goal is to determine wether the collapsing regime of this source is controlled by magnetic fields or other factors such as turbulence. Methods. We used the Very Large Array (VLA) to carry out spectropolarimetric observations of the 22 GHz Zeeman emission from H2O masers. From the Stokes V line profile, we are then able to estimate the magnetic field strength in the dense regions around the protostar. Results. A blend of at least three maser features can be inferred from our relatively high spatial resolution data set (similar to 0.1 ''), which is reproduced as a clear non-Gaussian line profile. The emission is very stable in terms of polarization fraction and position angle across the channels. The maser spots are aligned with some components of the complex outflow configuration of IRAS 16293-2422, and are excited in zones of compressed gas produced by shocks. The post-shock particle density is in the range of 1-3 x 10(9) cm(-3), consistent with typical water-maser pumping densities. Zeeman emission is produced by a very strong line-of-sight magnetic field (B similar to 113 mG). Conclusions. The magnetic field pressure derived from our data is comparable to the ram pressure of the outflow dynamics. This indicates that the magnetic field is energetically important to the dynamical evolution of IRAS 16293-2422.
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| 8. |
- Alves, F. O., et al.
(författare)
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Magnetic field in a young circumbinary disk
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 616
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Tidskriftsartikel (refereegranskat)abstract
- Context. Polarized continuum emission at millimeter-to-submillimeter wavelengths is usually attributed to thermal emission from dust grains aligned through radiative torques with the magnetic field. However, recent theoretical work has shown that under specific conditions polarization may arise from self-scattering of thermal emission and by radiation fields from a nearby stellar object. Aims. We use multi-frequency polarization observations of a circumbinary disk to investigate how the polarization properties change at distinct frequency bands. Our goal is to discern the main mechanism responsible for the polarization through comparison between our observations and model predictions for each of the proposed mechanisms. Methods. We used the Atacama Large Millimeter/submillimeter Array to perform full polarization observations at 97.5 GHz (Band 3), 233 GHz (Band 6) and 343.5 GHz (Band 7). The ALMA data have a mean spatial resolution of 28 AU. The target is the Class I object BHB07-11, which is the youngest object in the Barnard 59 protocluster. Complementary Karl G. Jansky Very Large Array observations at 34.5 GHz were also performed and revealed a binary system at centimetric continuum emission within the disk. Results. We detect an extended and structured polarization pattern that is remarkably consistent between the three bands. The distribution of polarized intensity resembles a horseshoe shape with polarization angles following this morphology. From the spectral index between Bands 3 and 7, we derived a dust opacity index β ~ 1 consistent with maximum grain sizes larger than expected to produce self-scattering polarization in each band. The polarization morphology and the polarization levels do not match predictions from self-scattering. On the other hand, marginal correspondence is seen between our maps and predictions from a radiation field model assuming the brightest binary component as main radiation source. Previous molecular line data from BHB07-11 indicates disk rotation. We used the DustPol module of the ARTIST radiative transfer tool to produce synthetic polarization maps from a rotating magnetized disk model assuming combined poloidal and toroidal magnetic field components. The magnetic field vectors (i.e., the polarization vectors rotated by 90°) are better represented by a model with poloidal magnetic field strength about three times the toroidal one. Conclusions. The similarity of our polarization patterns among the three bands provides a strong evidence against self-scattering and radiation fields. On the other hand, our data are reasonably well reproduced by a model of disk with toroidal magnetic field components slightly smaller than poloidal ones. The residual is likely to be due to the internal twisting of the magnetic field due to the binary system dynamics, which is not considered in our model.
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| 9. |
- Alves, F. O., et al.
(författare)
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Molecular outflow launched beyond the disk edge
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 603, s. Article no L3 -
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Tidskriftsartikel (refereegranskat)abstract
- One of the long-standing problems of star formation is the excess of angular momentum of the parent molecular cloud. In the classical picture, a fraction of angular momentum of the circumstellar material is removed by the magneto-centrifugally driven disk wind that is launched from a wide region throughout the disk. In this work, we investigate the kinematics in the envelope-disk transition zone of the Class I object BHB07-11, in the B59 core. For this purpose, we used the Atacama Large Millimeter/submillimeter Array in extended configuration to observe the thermal dust continuum emission (lambda(0) similar to 1.3 mm) and molecular lines (CO, (CO)-O-18 and H2CO), which are suitable tracers of disk, envelope, and outflow dynamics at a spatial resolution of similar to 30 AU. We report a bipolar outflow that was launched at symmetric positions with respect to the disk (similar to 80 AU in radius), but was concentrated at a distance of 90-130 AU from the disk center. The two outflow lobes had a conical shape and the gas inside was accelerating. The large off set of the launching position coincided with the landing site of the infall materials from the extended spiral structure (seen in dust) onto the disk. This indicates that bipolar outflows are efficiently launched within a narrow region outside the disk edge. We also identify a sharp transition in the gas kinematics across the tip of the spiral structure, which pinpoints the location of the so-called centrifugal barrier.
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| 10. |
- Girart, J. M., et al.
(författare)
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MAPPING THE LINEARLY POLARIZED SPECTRAL LINE EMISSION AROUND THE EVOLVED STAR IRC+10216
- 2012
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 751:1
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Tidskriftsartikel (refereegranskat)abstract
- We present spectro-polarimetric observations of several molecular lines obtained with the Submillimeter Array toward the carbon-rich asymptotic giant branch star IRC+10216. We have detected and mapped the linear polarization of the CO 3-2, SiS 19-18, and CS 7-6 lines. The polarization arises at a distance of similar or equal to 450 AU from the star and is blueshifted with respect to the Stokes I. The SiS 19-18 polarization pattern appears to be consistent with a locally radial magnetic field configuration. However, the CO 3-2 and CS 7-6 line polarization suggests an overall complex magnetic field morphology within the envelope. This work demonstrates the feasibility of using spectro-polarimetric observations to carry out tomographic imaging of the magnetic field in circumstellar envelopes.
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