国立天文台　セミナー情報　/　Seminar Information

Sep　11　Mon　 　15:00-16:30　　Solar and Space Plasma Seminar
　　　　　　　　　　　　　　　　hybrid; Central Building (North) / 310 or Zoom

Sep　13　Wed　　　　14:30-15:30 　　 ALMA-J seminar 　
　　　　　　　　　　　　　　　　　　　ALMA building #102 / Zoom (hybrid)　　　　　　　　　　　　　　

詳細は下記からご覧ください。

=============== Sep　11　Mon===============

Campus： Mitaka
Seminar： Solar and Space Plasma Seminar
Regularly Scheduled/Sporadic： Scheduled
Date and time：Sep 11th (Sep), 15:00-16:30
Place： hybrid; Central Building (North) / 310 or Zoom
Speaker：Teodora Mihailescu
Affiliation：Mullard Space Science Laboratory, University College London
Title：Intriguing Plasma Composition Pattern in a Solar Active Region: a Result of Non-Resonant Alfvén Waves?

Abstract：The plasma composition of the solar corona is different from that of the solar photosphere. Elements that have a low first ionisation potential (FIP) are preferentially transported to the corona and, therefore, show enhanced abundances in the corona compared to the photosphere. The level of enhancement is measured using the FIP bias parameter. The highest FIP bias values are typically observed in active regions, but they also vary at sub-active region level. In this work, we use data from the EUV Imaging Spectrometer (EIS) on Hinode to study the plasma composition in an active region following an episode of significant new flux emergence into the pre-existing magnetic environment of the active region. We use two FIP bias diagnostics: Si X 258.375 Å/S X 264.233 Å (formation temperature of 1.5 MK) and Ca XIV 193.874 Å /Ar XIV 194.396 Å (formation temperature of 4 MK). We observe different plasma composition patterns in the newly emerging loops and the preexisting loops (those that had been formed before the flux emergence). This result can be interpreted in the context of the ponderomotive force model, which proposes that the enhancement of low-FIP elements in the corona is generally driven by Alfvén waves. We suggest that the low-FIP elements enhancement pattern observed in the emerging loops could be driven by resonant waves originating in the active region core loops. Conversely, we suggest that the pattern observed in preexisting loops could be driven by non-resonant waves and we discuss potential sources of these waves. This different type of wave activity is what could explain the different patterns of low-FIP elements enhancement in these two sets of loops.

Facilitator
Name：Takayoshi oba
Comment：in English

=============== Sep 13　Wed==============

Campus: Mitaka
Seminar: ALMA-J seminar
Regularly Scheduled/Sporadic: Every Wednesday
Date and time: September 13, 2023 (Wed), 14:30-15:30
Place: ALMA building #102 / Zoom (hybrid)
Speaker: Kaho Morii
Affiliation: The University of Tokyo/NAOJ
Title: Unveiling Early Stages of High-Mass Star Formation: Insights from Infrared Dark Clouds

Abstract:
Physical properties in infrared dark clouds (IRDCs) provide insights into the initial conditions of high-mass star and stellar cluster formation. We have conducted the ALMA Survey of 70 µm Dark High-mass Clumps in Early Stages (ASHES) on thirty-nine high-mass clumps, which are the dense parts of IRDCs. These targets are dark at 24 µm and 70 µm and have low temperatures, high masses, and high density, best candidates to investigate the earliest stages of high-mass star formation. Our ALMA observations reveal their internal structure and have identified an unprecedented number of 839 cores from dust continuum emission.  We find that less than 1% (7/839) of the cores possess masses exceeding 27 Msun. All of these cores are gravitationally bound and associated with molecular outflows. No high-mass prestellar core has been observed. Furthermore, among our sample, 90%  (35 out of 39) only host low- to intermediate-mass cores, indicating the necessity of additional mass input for high-mass star formation. Observed core properties generally follow the thermal Jeans fragmentation of the clumps. In this talk, I will present the first results of the statistical study of the 839 cores as well as a summary of the pilot survey, and discuss the characteristics of the initial stages of high-mass star formation.

Facilitator: Bunyo Hatsukade and Kouichiro Nakanishi

August　30　Wed　 　13:30-15:00　　Solar and Space Plasma Seminar
　　　　　　　　　　　　　　　　　　　　 hybrid; Central Building (North)310 or Zoom

August　30　Wed　　　14:30-15:30 　　 ALMA-J seminar 　
　　　　　　　　　　　　　　　　　　　　 Zoom / ALMA building #102 (hybrid)　　　　　　　　　　　　　　　

詳細は下記からご覧ください。

=============== August　30　Wed===============

Campus： Mitaka
Seminar： Solar and Space Plasma Seminar
Regularly Scheduled/Sporadic： Scheduled
Date and time：Aug 30th (Wed), 13:30-15:00
Place： hybrid; Central Building (North) / 310 or Zoom
Speaker：Dr. Masahito Kubo
Affiliation：NAOJ
Title：Comparison of polar magnetic fields derived from MILOS and MERLIN inversions for Hinode/SOT-SP data

Abstract：The detailed investigation of the polar magnetic field and its time evolution is one of the major achievements of Hinode. Precise measurements of the polar magnetic field are essential for understanding the solar cycle, and they provide important constraints for identifying the source regions of the solar wind. The Spectropolarimeter (SP) of the Solar Optical Telescope (SOT) on board Hinode has been the instrument best suited to make such measurements. In this study, we compare SOT-SP data for the polar regions as processed using two representative Milne-Eddington inversion codes, MILOS and MERLIN. These codes are applied to the same level-1 SOT/SP data, and the same disambiguation algorithm is used on the maps that go through the two inversions. We find that the MERLIN inversion tends to give the radial magnetic flux density (the magnetic flux density with respect to the local vertical) that is about 20% larger than the MILOS inversion. The somewhat higher radial magnetic flux density from MERLIN appears to be common to the polar magnetic fields observed at different phases of the solar cycle. We attribute the difference in the radial magnetic flux density to different filling factors adopted by the two inversions, based on different assumptions of the scattered light profiles. The relationship between the radial magnetic flux density and the magnetic filling factor could be more complex in the polar (limb) observations due to the possible contributions of the transverse magnetic field component that may affect the estimated radial magnetic flux density.

Facilitator
-Name：Takayoshi oba
-Comment：in English

=============== August 　30　Wed==============

Campus: Mitaka
Seminar: ALMA-J seminar
Regularly Scheduled/Sporadic: Every Wednesday
Date and time: August 30, 2023 (Wed), 14:30-15:30
Place: ALMA building #102 / Zoom (hybrid)
Speaker: Jan-Willem Steeb
Affiliation: National Radio Astronomy Observatory
Title: AstroHACK: Holography Antenna Commissioning Kit

Abstract: Correcting the surface of a dish antenna by adjusting the panels can significantly improve the dish’s performance. For instance, the VLA panel adjustments completed in 2000 more than doubled the high-frequency sensitivity of the VLA dishes. The software presently utilized by ALMA and VLA is written in Fortran and is becoming challenging to maintain. Consequently, the CASA team is developing AstroHACK, which generates antenna aperture images and calculates antenna panel adjustment corrections from calibrated holography measurement sets. AstroHACK is the first non-prototype software package developed using the Python-based VIPER (Visibility and Image Parallel Execution Reduction) Framework, previously known as the CASA Next Generation Infrastructure Software Framework. This framework was designed to meet the requirements of the ngVLA and the ALMA Wideband Sensitivity upgrade. In this seminar, I will provide an overview of the VIPER Framework and the functionalities of AstroHACK, followed by a live demonstration.