Home > ALMA Jセミナー | 太陽系小天体セミナー | 科学研究部コロキウム > 2022.1.10-2022.1.17


JAN 11 Tue 10:00~11:30  太陽系小天体セミナー / Solar System Minor Body Seminar zoom

JAN 12 Wed 14:30~15:30  ALMA-J seminar   zoom

JAN 12 Wed 15:30~17:00  NAOJ Science Colloquium    zoom






Campus: Mitaka
Seminar: ALMA-J seminar
Regularly Scheduled/Sporadic: Every Wednesday

Date and Time: 2022 January 12 14:30-15:30
Place: Zoom
Speaker:Ajeddig Hamza (CEA Paris Saclay)
Title: Probing the role of magnetic fields in star-forming filaments and protostellar cores: Observations with NIKA2-Pol and SOFIA/HAWC+
Abstract: Herschel findings support a filament paradigm for star formation (SF) in which: (1) Large-scale magnetohydrodynamic (MHD) supersonic turbulence compresses interstellar material to form a cobweb of filamentary structures with a common inner width of about ∼ 0.1 pc; (2) The densest filaments fragment to form prestellar cores due to gravitational instability when M_line is close to or exceeds the critical mass per unit length M^crit_line. However, the detailed process of how filaments fragment into cores remains actively debated. There are hints that the magnetic field may be a key ingredient toward a better understanding of SF. Planck results suggest that the B-field lines tend to be parallel to low density filaments and perpendicular to the high-density filaments. Due to the low angular resolution of Planck polarization data (10 arcmin), these observations are, however, unable to probe the magnetic field inside filaments on scales at which fragmentation occurs. The detailed knowledge of the role of magnetic fields in the SF process has therefore not yet been achieved. Constraining the B-field geometry/strength at different wavelengths and high angular resolution will help understand how magnetic fields may regulate the SF in the cold interstellar medium (ISM). The B-FUN large program with the NIKA2-Pol polarimeter on the IRAM 30m telescope will provide high angular resolution (11.7 arcsec) and sensitive polarization data toward nearby star-forming filaments. I will present my results on the commissioning of NIKA2-Pol. Especially, the instrumental polarization (IP) or intensity-to-polarization “leakage” effect. The characterization of the leakage effect with several parameters (elevation, focus position, and observing conditions). I will show a possible origin of the IP, and present an analytical model for the IP leakage. I will show how the NIKA2-Pol IP can be corrected for, leading to reliable exploitable data in a structured, extended field such as the OMC-1 filament in the Orion A molecular cloud. I will present a statistical comparison between NIKA2-Pol and SCUBA2-Pol2 results in the OMC-1 region. These results help to demonstrate the ability of NIKA2-Pol to provide high-quality polarization data. I will also present preliminary results on the geometry/strength of the magnetic field toward the OMC-1 filament using NIKA2-Pol commissioning data. I confirm the presence of a previously-detected large-scale hourglass pattern in the magnetic field distribution, and I report evidence of a possible new local hourglass centered at the position of Orion-KL detected thanks to the high angular resolution of NIKA2-Pol data. I will discuss estimates of the magnetic field strength in this region using the Davis-Chandrasekhar-Fermi method. I will also present briefly our results from SOFIA/HAWC+ polarization observations which prove new insights into the magnetic field geometry/strength in the B211/B213 filament of the Taurus molecular cloud.

Facilitator: Patricio A. Sanhueza Nunez, Satoko Sorahana


Seminar:NAOJ Science Colloquium
Regularly Scheduled/Sporadic:Every Wednesday
Date and time:2022 January 12, 15:30-17:00
Speaker:Bing Zhang
Title:The Physics of Fast Radio Bursts
Abstract:Fast radio bursts (FRBs) are mysterious cosmological millisecond-duration bursts in the radio band. In this talk, I will review the latest observational status in the field including the identification of a Galactic magnetar as the source of FRBs. I will also review our current understanding of the physical mechanisms of FRBs in reference to two related astrophysical phenomena, namely, radio pulsars and gamma-ray bursts. I will discuss the observational evidence in favor of FRB emission involving neutron star magnetospheres. Some ideas and issues of various radiation mechanisms for FRBs will be critically discussed. Several open questions in the field regarding repeaters vs. non-repeaters and whether there are engines other than magnetars will be presented.

-Name:Akimasa Kataoka

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