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J/ApJ/842/L9  ALMA obs. of polarized dust emission from Ser-emb 8  (Hull+, 2017)

Unveiling the role of the magnetic field at the smallest scales of star formation. Hull C.L.H., Mocz P., Burkhart B., Goodman A.A., Girart J.M., Cortes P.C., Hernquist L., Springel V., Li Z.-Y., Lai S.-P. <Astrophys. J., 842, L9 (2017)> =2017ApJ...842L...9H
ADC_Keywords: Polarization ; YSOs ; Interstellar medium ; Magnetic fields ; Millimetric/submm sources Keywords: ISM: magnetic fields; magnetic fields; magnetohydrodynamics (MHD); polarization ; stars: formation ; turbulence Abstract: We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of polarized dust emission from the protostellar source Ser-emb 8 at a linear resolution of 140au. Assuming models of dust-grain alignment hold, the observed polarization pattern gives a projected view of the magnetic field structure in this source. Contrary to expectations based on models of strongly magnetized star formation, the magnetic field in Ser-emb 8 does not exhibit an hourglass morphology. Combining the new ALMA data with previous observational studies, we can connect magnetic field structure from protostellar core (∼80000au) to disk (∼100au) scales. We compare our observations with four magnetohydrodynamic gravo-turbulence simulations made with the AREPO code that have initial conditions ranging from super-Alfvenic (weakly magnetized) to sub-Alfvenic (strongly magnetized). These simulations achieve the spatial dynamic range necessary to resolve the collapse of protostars from the parsec scale of star-forming clouds down to the ∼100au scale probed by ALMA. Only in the very strongly magnetized simulation do we see both the preservation of the field direction from cloud to disk scales and an hourglass-shaped field at <1000au scales. We conduct an analysis of the relative orientation of the magnetic field and the density structure in both the Ser-emb 8 ALMA observations and the synthetic observations of the four AREPO simulations. We conclude that the Ser-emb 8 data are most similar to the weakly magnetized simulations, which exhibit random alignment, in contrast to the strongly magnetized simulation, where the magnetic field plays a role in shaping the density structure in the source. In the weak-field case, it is turbulence-not the magnetic field-that shapes the material that forms the protostar, highlighting the dominant role that turbulence can play across many orders of magnitude in spatial scale. Description: The 870um (Band 7) ALMA dust polarization observations of Ser-emb 8 were taken on 2015 June 3 and 7 and have ∼0.3" angular resolution. Objects: ------------------------------------------------------------- RA (ICRS) DE Designation(s) ------------------------------------------------------------- 18 29 48.09 +01 16 45.0 Ser-emb 8 = [EES2009] Ser-emb 8 ------------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 40 191 870um (Band 7) ALMA data img/* 0 6 The five maps in FITS format which served to create Figure 1
Description of file: The subdirectory img/ (in the FTP section) contains the 3 cleaned maps of total intensity (Stokes I), Stokes Q and Stokes U dust emission. A map of the position angle of the true dust polarization. And a map of total debiased polarized dust emission. The five files are in FITS format. See also: J/ApJ/603/584 : Polarimetry toward Musca dark cloud (Pereyra+, 2004) J/ApJ/692/973 : Protostars in Perseus, Serpens and Ophiuchus (Enoch+, 2009) J/ApJS/182/143 : SCUPOL Legacy polarimetry of SCUBA (Matthews+, 2009) J/ApJS/186/406 : 350um polarimetry from CSO (Dotson+, 2010) J/A+A/569/L1 : Polarization hole in a starless core (Alves+, 2014) J/ApJS/213/13 : Polarization maps of star-forming cores & SFRs (Hull+, 2014) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 9 F9.5 deg RAdeg Right ascension in decimal degrees (J2000) 11- 17 F7.5 deg DEdeg Declination in decimal degrees (J2000) 19- 23 F5.1 deg chi [0.4/178] Orientation of the magnetic field, measured counterclockwise from north 25- 27 F3.1 deg e_chi [1.2/9.5] Uncertainty in chi 29- 33 F5.3 mJy/beam PInt [0.07/0.6] Polarized intensity 35- 40 F6.3 mJy/beam Int ? Total Intensity (1)
Note (1): Int is the total intensity, reported where I>3σ. Due to differences in dynamic range between the images of Stokes I and polarized intensity, there are cases where PInt is detectable but Int is not.
History: From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 02-Feb-2018
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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